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European Journal of Inorganic Chemistry - Current Research Articles



Current research articles: Inorganic Chemistry

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European Journal of Inorganic Chemistry - published by Wiley-VCH

EurJIC is the fastest growing journal in inorganic chemistry. It publishes Full Papers, Short Communications, and Microreviews from the entire spectrum of inorganic, organometallic, bioinorganic, and solid-state chemistry.




Current articles of the journal:



S–S Bond Activation in Multi-Copper ­Aggregates Containing Perthiocarboxylato Ligands

The direct reaction between [Cu(OAc)2·(H2O)]2 and n-butyldithiocarboxylic acid affords two copper(I) aggregates with dithiocarboxylato, [Cu(S2C-n-butyl)]4 (1), and perthiocarboxylato ligands, [Cu(S3C-n-butyl)]4 (2), in which the oxidation of dithiocarboxylato ligand is triggered by the CuII centers. The activation of the S–S bond in 2 by two reducing agents, PPh3 and NaBH4, has been investigated both experimentally and by DFT calculations. The successive S–S activation in 2 by reaction with 4 equiv. of PPh3 is a cooperative process, which implies that the intermediate species remain elusive. Such intermediates have been analyzed by DFT calculations, which established that the reactivity of the multi-copper structures depends on the balance between the interactions in the different coordination spheres imposed on the copper centers and the Cu···Cu distances. Furthermore, weak cuprophilic interactions are conditioned by the orbital orientation imposed by the structure. This implies that these metal–metal interactions are not always found between the pairs of Cu atoms with the shortest distances. Although different products have been isolated depending on the reducing agent, the overall theoretical data indicate that the reagent always attacks the terminal sulfur atom of the perthio group. As a consequence of S–S activation in [Cu4(?-S3C-n-butyl)4], a complex reactivity is triggered in which both Cu–S coordination versatility and subtle Cu···Cu interactions play distinct key roles.

Posted on 3 August 2015 | 11:50 am


Photoluminescence Modulation in Lan­thanide(III)/Pyrazine-2,5-dicarboxylato/Nitrato Frameworks

The solvent-free melt reactions between lanthanide(III) nitrates and pyrazine-2,5-dicarboxylic acid (H2pzdc) gave rise to four families of 3D compounds that differ from those accessible from conventional solvothermal synthesis, namely, {[Ln(?4-pzdc)(NO3)(H2O)2]·2.33H2O}n (1-Ln; Ln = La, Ce), {[Ln9(?4-pzdc)9(NO3)2(H2O)25](NO3)7·8H2O}n (2-Ln; Ln = Pr, Nd), {[Ln6(?4-pzdc)5(?3-pzdc)2(?-pzdc)(H2O)10](NO3)2·2H2O}n (3-Ln; Ln = Nd, Sm), and [Ln(?4-pzdc)(NO3)(H2O)]n (4-Ln; Ln = Eu, Gd, Tb). This synthetic approach promotes the incorporation of nitrate anions into the final crystal structure as terminal ligands or counterions, which replace water molecules in the coordination sphere and enhance the photoluminescence properties of these compounds. The neodymium, samarium, europium, and terbium compounds exhibit their characteristic emissions in the infrared and visible regions. The pzdc ligand shows the highest sensitization towards TbIII ions, and the photoluminescence intensity can be modulated by immersing the sample into different solvents and also by dehydrating it. Compounds 3-Ln have a topology named as jcr5, which has not been reported previously. Four types of 3D LnIII/pyrazine-2,5-dicarboxylato/nitrato frameworks are synthesized through a solvent-free approach. Their structural diversity is rationalized according to the lanthanide contraction effect and the role played by the nitrate ion (ligand or counterion). The photoluminescence of the complexes can be tuned in response to thermal dehydration.

Posted on 3 August 2015 | 11:50 am


Carrageenan–Silica Hybrid Nanoparticles Prepared by a Non-Emulsion Method

Spherical and monodispersed sub-micrometer sized particles of organic–inorganic hybrids were prepared by means of a sol–gel non-emulsion method using the biopolymer ?-carrageenan and the alkoxysilane 3-isocyanatopropyltriethoxysilane (ICPTES). The structural characterization of the carrageenan–silica hybrid particles was performed by using FTIR spectroscopy and solid-state 29Si and 13C NMR spectroscopy and confirmed that ?-carrageenan was covalently linked to the siliceous network via urethane bonds. Zeta-potential measurements indicate the hybrids were functionalized on the surface with sulfonate groups from the polysaccharide. These hybrids display thermal sensitivity, which is of great relevance for biomedical applications such as drug encapsulation and thermally controlled drug-delivery systems. Nanoparticles of ?-carrageenan–silica hybrids with narrow size distribution were prepared by using a sol–gel non-emulsion method. Unlike silica particles, these hybrids display thermal sensitivity, which is of great relevance for biomedical applications such as drug encapsulation and thermally controlled drug-delivery systems.

Posted on 3 August 2015 | 11:50 am


Photoinduced DNA Crosslink Formation by Dichloridooxidovanadium(IV) Complexes of Polypyridyl Bases

Oxidovanadium(IV) complexes [VO(pyphen)Cl2] (1) and [VO(pydppz)Cl2] (2), where pyphen is 2-(2?-pyridyl)-1,10-phenanthroline and pydppz is 3-(pyridin-2-yl)dipyrido[3,2-a:2?,3?-c]phenazine, show remarkable photoinduced DNA crosslinking ability and photocytotoxicity. The complexes are non-electrolytes in DMF, 1:1 electrolytes in 20?% aqueous DMF, and 1:2 electrolytes in 20?% aqueous DMF upon photoirradiation with visible light of 400–700 nm. The paramagnetic complexes, which have one unpaired electron, show a d–d band near 780 nm in aqueous DMF. The IR data suggest a V=O moiety trans to a V–N bond. Complex [VO(pydppz)Cl2] (2), as a novel photoinducible nuclear ds-DNA crosslinking agent, shows visible-light-induced cytotoxicity in HeLa and MCF-7 cancer cells by an apoptotic pathway, giving IC50 values of 0.87?±?0.07 and 1.4?±?0.2 ?M, respectively, while being essentially nontoxic (IC50 > 40 ?M) in the dark and less toxic in normal MCF-10A cells. Oxidovanadium(IV) complexes of polypyridyl bases having two dissociable chloride ligands show DNA crosslink formation involving nuclear DNA in a buffer medium upon photoirradiation with visible light of 400–700 nm. The complexes are remarkably photocytotoxic in cancer cells while being essentially nontoxic in the dark.

Posted on 30 July 2015 | 11:20 am


Trimetallic PEPPSI-Type Palladium N-Heterocyclic Carbene Complexes – Improved Catalyst Lifetime in the Mizoroki–Heck Coupling Reaction

A series of mono- and dendritic trimetallic PEPPSI-type (pyridine-enhanced precatalyst preparation stabilization and initiation) complexes bearing N-heterocyclic carbene (NHC) ligands containing a protected amine in the form of an ethylphthalimido group have been synthesized. These discrete prototypes of complexes covalently bound to suitable supports have been studied in the Mizoroki–Heck coupling of aryl iodides under mild conditions, including sets of experiments to assess the lifetime of the active species. The palladated dendrons are more efficient and robust catalysts than their monometallic counterparts. Dendritic trimetallic PEPPSI-type (pyridine-enhanced precatalyst preparation stabilization and initiation) complexes are more efficient and robust catalysts than their monometallic counterparts in the Mizoroki–Heck coupling of aryl iodides under mild conditions.

Posted on 30 July 2015 | 11:20 am


Borosulfates Cs2B2S3O13, Rb4B2S4O17, and A3HB4S2O14 (A = Rb, Cs) – Crystalline Approximants for Vitreous B2O3?

New borosulfates were obtained by reaction of B2O3 in oleum or concentrated H2SO4 at temperatures between 300 and 360 °C. They are the first examples of borosulfates with directly connected boron polyhedra, that is, ditetrahedral B2O7 or layers of trigonal-planar BO3 units. Cs2B2S3O13 [P21/c, Z = 4, a = 14.765(3), b = 6.710(1), c = 12.528(3) Å, ? = 104.60(3)°] contains layers of corner-sharing BO4 and SO4 tetrahedra. The BO4 tetrahedra form dimers. SO4 tetrahedra connect four B2O7 dimers to rings containing 10 tetrahedra, which are condensed to a layer. A third SO4 tetrahedron connects two BO4 tetrahedra of the B2O7 unit. The layers are stacked in the [100] direction. One Cs+ cation is located within the layer of tetrahedra, the second one between the layers. In Rb4B2S4O17 or Rb4[B2O(SO4)4] [Pnna, Z = 4, a = 8.0415(9), b = 10.6466(11), c = 20.425(2) Å], there are isolated [B2O(SO4)4] units which consist of a central B2O7 unit. Besides one B–O–B bridge, two SO4 tetrahedra connect the BO4 tetrahedra. Additionally, each BO4 tetrahedron has a terminal SO4 unit. In the structure of A3HB4S2O14 or A3H(SO4)2(B2O3)2 [P63/m, Z = 2, A = Cs: a = 6.5648(2), c = 19.5669(5) Å; A = Rb: a = 6.502(6), c = 19.023(14) Å], the SO4 tetrahedra are isolated. Boron forms planar layers of corner-sharing trigonal-planar BO3 units. There are two different types of BO3 units in a ratio of 3:1. The first type forms six-membered boroxol rings, B3O3, which are connected to the layers by the second type of BO3 units. The layers are separated by isolated SO42– tetrahedra and Cs+ cations. The “missing” proton could not be localized but was assumed to achieve electroneutrality and was confirmed by IR spectroscopy. Planar layers of B2O3 with trigonal-planar BO3 units and boroxol rings are supposed to exist as structure elements in vitreous boron oxide. Cs2B2S3O13 and Rb4B2S4O17 are the first examples of borosulfates with directly connected BO4 tetrahedra. Similar motifs are known for borates and borosulfates. In A3HB4S2O14 (A = Rb, Cs) there are planar layers of B2O3 with trigonal BO3 units and boroxol rings B3O3. These are the characteristic features of vitreous B2O3.

Posted on 30 July 2015 | 11:20 am


Graphical Abstract: Eur. J. Inorg. Chem. 21/2015

Posted on 28 July 2015 | 2:48 pm


Artificial Diiron Enzymes with a De Novo Designed Four-Helix Bundle Structure

Invited for the cover of this issue is the group of Angela Lombardi at the University of Napoli “Federico II”, Italy. The cover image shows a construction site where workers are building up a four-helix bundle scaffold. Fine-tuning of the metal binding site, which is the heart of the construction, enables a specific function, such as oxidative chemistry. This approach has been successfully employed to develop diiron–oxo protein models. The road to construct molecules that function as environmentally safe catalysts and biosensing devices is now open...Read more about the story behind the cover in the Cover Profile and about the research itself on p. 3371 ff.

Posted on 28 July 2015 | 2:48 pm


Biological Oxidation Reactions

EurJIC, with Guest Editors Ebbe Nordlander and Wesley Browne, offers a collection of high-quality papers clustered around the theme Biological Oxidation Reactions – Mechanisms and Design of New Catalysts. This cluster issue is based on the COST Action CM1003 with the same name and presents the advances in designing new biological, biomimetic and bioinspired catalysts. EurJIC, with Guest Editors Ebbe Nordlander and Wesley Browne, offers a collection of high-quality papers clustered around the theme Biological Oxidation Reactions – Mechanisms and Design of New Catalysts. This cluster issue is based on the COST Action CM1003 with the same name and presents the advances in designing new biological, biomimetic and bioinspired catalysts.

Posted on 28 July 2015 | 2:48 pm


Masthead: Eur. J. Inorg. Chem. 21/2015

Posted on 28 July 2015 | 2:48 pm


Modelling Binuclear Metallobiosites: Insights from Pyrazole-Supported Biomimetic and Bioinspired Complexes (Eur. J. Inorg. Chem. 21/2015)

The back cover picture shows the overlap between natural metallobiosites and synthetic pyrazolato-based model complexes with respect to their ability to activate ubiquitous small molecules, such as dioxygen and water. The crystal structures illustrate this activation, depicting the peroxide-bound form of hemocyanin and the hydroxide-bridged configuration of phosphotriesterase, as well as the central coordination motifs in the two corresponding pyrazole-supported biomimetic complexes. Insights derived from studying such models of these and related binuclear metalloproteins are relevant in fields ranging from biological to inorganic and medicinal chemistry, and in catalysis research. Details are presented in the Microreview by K. E. Dalle and F. Meyer on p. 3391 ff.

Posted on 28 July 2015 | 2:48 pm


Biological Oxidation Reactions – Mechanisms and Design of New Catalysts

An overview of the papers in this cluster issue is presented. “Biological oxidation reactions utilising dioxygen, superoxide or hydrogen peroxide as oxidants are amongst the most ubiquitous of metal-catalysed reactions in biology. Over the last four years, the COST action CM1003 ‘Biological Oxidation Reactions – Mechanisms and Design of New Catalysts’ has brought together over 150 researchers from over 18 European countries to exchange ideas and collaborate on answering key questions facing the field.” An overview of the papers in this cluster issue is presented. “Biological oxidation reactions utilising dioxygen, superoxide or hydrogen peroxide as oxidants are amongst the most ubiquitous of metal-catalysed reactions in biology. Over the last four years, the COST action CM1003 ‘Biological Oxidation Reactions – Mechanisms and Design of New Catalysts’ has brought together over 150 researchers from over 18 European countries to exchange ideas and collaborate on answering key questions facing the field.”

Posted on 28 July 2015 | 2:48 pm


Artificial Diiron Enzymes with a De Novo Designed Four-Helix Bundle Structure (Eur. J. Inorg. Chem. 21/2015)

The front cover picture shows a construction site where workers are building up a four-helix bundle scaffold. A protein designer, working like an architect, has to adjust each minimal structural element in order to build up a stable and functional model. The metal site in the helical bundle scaffold represents the heart of the construction. Fine-tuning of the metal binding site enables a specific function, such as oxidative chemistry. This approach has been successfully employed to develop diiron–oxo protein models. Details are presented in the Microreview by A. Lombardi et al. on p. 3371 ff. For more on the story behind the cover research, see the Cover Profile.

Posted on 28 July 2015 | 2:48 pm


Copper(II) Cyclam Complexes with N-­Propionic Acid Pendant Arms

Four cyclam (1,4,8,11-tetraazacyclotetradecane) ligands with different numbers of N-substituted propionic acid groups lead to pentacoordinate copper(II) complexes that adopt trans-I configurations (4+1 geometry), that is, the complexes have a d?x?2–y?2 ground state with significant rhombic distortion. From the structural data (X-ray diffraction analysis and electron paramagnetic resonance, UV/Vis and IR spectroscopy), as the number of secondary amine groups of the macrocyclic ring substituted with propionic acid groups increases, the distortion from square pyramidal to trigonal bipyramidal increases, and this is expected to lead to relatively low complex stabilities. This is confirmed by in vitro studies with superoxide dismutase (SOD) and human serum challenge experiments as well as by biodistribution data with the 64Cu-labelled complexes. The 64Cu-labelled complexes with cyclam monopropionic and dipropionic acid show high in vitro and in vivo stabilities, and the latter provides a comparable biodistribution profile to that of 64Cu–TETA (TETA = 1,4,8,11-tetraazacyclotetradecane-1,4,8,11-tetraacetic acid). Four cyclam ligands with different numbers of N-propionic acid pendant arms were screened as potential bifunctional chelators for CuII radioisotopes. The pendant arms of the ligands strongly influence the stability of the CuII complexes formed. In this series, the cyclam ligands with one (HL1) and two N-propionic acid arms (H2L2) are promising ligands for radiopharmaceutical applications.

Posted on 27 July 2015 | 8:50 am


Experimental and Theoretical Investigations of CO2 Sorption by a 3D In-MOF with Multiple 1D Channels

The CO2 sorption capacity of the 3D In-MOF (Et2NH2)[In(2,6-NDC)2]·2H2O·DEF (I) (where 2,6-NDC is 2,6-naphthalenedicarboxylate and DEF is N,N-diethylformamide) was investigated. The solvent-free I contains three distinct types of 1D micropores with different shapes and pore dimensions. The evacuated I sorbed 297.2 cm3?g–1 (13.3 mmol?g–1) of CO2 at 196 K, 72.2 cm3?g–1 (3.22 mmol?g–1) at 273 K, and 39.8 cm3?g–1 (1.78 mmol?g–1) at 298 K. The difference between the uptake at 196 K and those at 273 and 298 K is relatively large. The shapes of the sorption isotherms are also dramatically different. At 196 K, the adsorption–desorption isotherms are S-shaped without significant hysteretic behavior between the adsorption and desorption branches. On the contrary, the adsorption isotherms measured at 273 and 298 K fit well with the Langmuir–Freundlich equation. The low-surface-coverage isosteric heat (Qst) of CO2 adsorption by I is 19.6 kJ?mol–1. Detailed estimations of the adsorption sites for CO2 were then performed by DFT calculations. The calculated binding energies were typically dependent on the dimension of the micropores when nonbonding (van der Waals) interactions were considered; the larger the micropore dimensions, the smaller the calculated binding energy. In addition, not only the framework CH···OCO contacts for Ch3 but also the counter-cation CH···OCO contacts for Ch1 and Ch2 were found to be important. The low-pressure CO2 sorption capacity of the 3D In-MOF (Et2NH2)[In(2,6-NDC)2]·2H2O·DEF (I) (where 2,6-NDC is 2,6-naphthalenedicarboxylate and DEF is N,N-diethylformamide) was investigated at various temperatures.

Posted on 24 July 2015 | 3:30 pm


Mechanisms of Oxygen Atom Transfer between Main-Group Elements

Oxygen atom transfer (OAT) between main-group elements is pivotal to a number of industrial processes such as the synthesis of thionyl chloride (SO3 + SCl2??SO2 + SOCl2) and sodium chlorate (3 NaOCl??NaClO3 + 2 NaCl), as well as the historic method of CO detection in mines via its reaction with I2O5 (I2O5 + 5 CO??I2 + 5 CO2). Surprisingly, little is known about the mechanisms of these and other OAT reactions involving main-group elements. Even the basic question as to whether such reactions are one-step, SN2-like displacements or multistep, involving oxo-bridged intermediates, remains largely unanswered. Extensive density functional theory calculations reported herein indicate a direct, SN2-like pathway as the norm for such processes. In the major quantum chemical study of oxygen atom transfer between main-group element centers, DFT calculations unequivocally indicate a one-step, SN2-like pathway as the normative mechanism, as opposed to a two-step associative-dissociative sequence that is common for transition metals.

Posted on 24 July 2015 | 3:30 pm


Orthogonal Functionalization of Ferritin via Supramolecular Re-Assembly

To investigate if the degree of functionalization of ferritin could be controlled using a supramolecular self-assembly process, two photophysical separable batches of ferritin were created by functionalizing ferritin capsids with either Cy3- or Cy5-dye (loading rate of about 50?%). After dis-assembly, Cy3-, Cy5- as well as non-functionalized ferritin subunits were mixed in variable ratios. Photophysical measurements revealed that the ratio in which the subunits were mixed was indeed indicative for the ratios in which the functionalized subunits were observed in the re-assembled capsids. During re-assembly, however, a slight preference for the inclusion of non-functionalized subunits was observed, indicating the reactivity decreased following functionalization. The iron biomineralization properties of ferritin were retained by the multi-functionalized capsids as FeII diffused rapidly inside making it visible by transmission electron microscopy (TEM). These combined data indicate that it is possible to functionalize ferritin in an orthogonal manner using the supramolecular interaction between ferritin subunits. To investigate the control on ferritin functionalization by supramolecular re-assembly, ferritin with modular functionality and still capable of iron mineralization was created. The ratio in which Cy3-, Cy5-, and non-functionalized subunits were mixed, was indicative for the ratio in which the variable subunits were observed in the re-assembled capsids.

Posted on 24 July 2015 | 3:20 pm


Synthesis and Characterization of GaIII, InIII and LuIII Complexes of a Set of dtpa Bis-Amide Ligands

The synthesis and characterization of five new diethylenetriaminepentaacetic acid (dtpa) ligands, (dtpa)-N,N?-bis(alkoxyphenylamide), and their complexation with GaIII, InIII and LuIII are reported. The procedures for the synthesis of all complexes in aqueous media are described as well as a synthetic pathway for the preparation of GaIII complexes in chloroform. All substances were characterized by NMR spectroscopy, mass spectrometry, elemental analysis and HPLC. Single-crystal structure analysis was performed where applicable, which revealed the presence of hepta- and octa-coordinated isomers for InIII complexes and a nine-fold coordination of LuIII ions in the solid state. Additional NMR experiments suggested a hepta-coordinated InIII species in solution, whereas the GaIII complexes appear to be hexa-coordinated and the LuIII complexes to be octa-coordinated. Both NMR and HPLC studies indicated the presence of a single isomer in every complex. The synthesis and characterization of new GaIII, InIII and LuIII complexes of five dtpa bis-amides are described. As determined by single-crystal structure analysis, the InIII complexes are hepta- or octa-coordinated, whereas the LuIII are nona-coordinated in the solid state. NMR studies were undertaken to characterize the coordination behaviour of the complexes in solution.

Posted on 23 July 2015 | 2:20 pm


Cytocompatible Fluorescent Quantum Dot/PEG-Chitosan Bioconjugates for Nanomedicine Applications

In this study, novel nanobioconjugates based on quantum dots and a PEGylated chitosan derivative (PEG-CHI) have been designed and synthesised by a single-step aqueous route at room temperature. Chitosan was chemically modified by PEGylation aiming to significantly improve its water solubility and used as the capping ligand in the preparation of CdS quantum dot (QD) colloidal systems. UV/Vis and photoluminescence spectroscopy, transmission electron microscopy, dynamic light scattering, and the zeta potential were used to characterise the biopolymer-capped semi-conductor nanocrystals and their relative stability. The results clearly demonstrated that the PEG-CHI derivative is remarkably effective in nucleating and stabilising ultra-small colloidal CdS QDs in aqueous suspensions under acidic, neutral and alkaline media with an average size of approximately 2.0–3.0 nm and simultaneously showing luminescent activity in the visible range. In addition, the results of cell viability analysis in vitro using two cell cultures based on MTT bioassays demonstrated no cytotoxicity of the CdS QD/PEG-chitosan bioconjugates. Thus, based on these findings, it can be envisioned that these bioconjugates have potential use as biocompatible fluorescent biomarkers for nanomedicine applications. Novel nanobioconjugates based on Cd-based quantum dots and a PEGylated chitosan derivative as capping ligand have been designed and synthesised by a single-step aqueous route at room temperature. These nanohybrids are luminescent and cytocompatible towards two cell lines tested in vitro, therefore showing potential as biomarkers in nanomedicine applications.

Posted on 23 July 2015 | 2:20 pm


Recognition of Prochiral Sulfides in Five-Coordinate PtII Complexes

This article describes a stereochemical study on five-coordinate complexes of PtII containing a prochiral alkene (E-R1O2CCH=CHCO2R1) and a prochiral sulfide R2SR3, of general formula [PtMe(R2SR3)(dmphen) (E-R1O2CCH=CHCO2R1)]BF4. Through mono- and two-dimensional NMR spectroscopy, it was demonstrated that there is mutual recognition between the prochiral ligands in the presence of aryl sulfides R2SAr, whose origin was also explained. The equilibrium constants of sulfide exchange were also evaluated, which are in full agreement with the ?-donor properties of the ligands. A stereochemical study on five-coordinate complexes of PtII containing a prochiral alkene (E-R1O2CCH=CHCO2R1) and a prochiral sulfide R2SR3, of general formula [PtMe(R2SR3)(dmphen) (E-R1O2CCH=CHCO2R1)]BF4, has been described. It has been demonstrated that there is mutual recognition between the prochiral ligands in the presence of aryl sulfides R2SAr, whose origin has also been explained.

Posted on 23 July 2015 | 2:20 pm


One-Pot Synthesis of an Oxalato-Bridged CuII Coordination Polymer Containing an In Situ Produced Pyrazole Moiety: A Precursor for the Preparation of CuO Nano­structures

The synthesis, characterization, and thermal decomposition behaviour of the oxalato-bridged copper(II) coordination polymer [Cu2(C2O4)(L)2Cl2(MeOH)2]n (1) (L = 3,5-dimethyl-1H-pyrazole) is reported. Complex 1 is prepared in a straightforward fashion by a one-pot reaction of acetylacetone, thiosemicarbazide, oxalic acid and copper(II) chloride in a molar ratio of 2:2:1:2. Complex 1 was characterized by means of FT-IR spectroscopy, mass spectrometry and elemental analysis as well as single-crystal X-ray diffraction. Furthermore, the electrochemical behavior of 1 was investigated in DMSO by cyclic voltammetry. The thermal stability of complex 1 was studied by thermal gravimetric (TG) and differential thermal analyses (DTA). Solventless thermolysis of complex 1 at 550 °C and 1000 °C under air afforded copper oxide nanoparticles and nanosheets, respectively. The CuO nanostructures were characterized by using a series of techniques including FT-IR, UV/Vis, XRD, XPS, EDAX, and SEM. The one-pot reaction of acetylacetone, thiosemicarbazide, oxalic acid and copper(II) chloride in a molar ratio of 2:2:1:2 affords coordination polymer [Cu2(C2O4)(L)2Cl2(MeOH)2]n (1) (L = 3,5-dimethyl-1H-pyrazole generated in situ). Thermolysis of complex 1 under neat conditions in air at 550 °C and 1000 °C generates CuO nanoparticles and nanosheets, respectively.

Posted on 23 July 2015 | 2:20 pm


Towards Selective Light-Activated RuII-Based Prodrug Candidates

Photoactivated chemotherapy (PACT) relies on the use of a drug and light to cause cell death. Unlike photodynamic therapy (PDT), its mechanism of action is independent of the presence of oxygen in tissues. This approach is therefore also effective for tumours characterized by hypoxic conditions. Herein we present the use of three novel RuII–polypyridyl complexes derivatized with a light-sensitive cage and targeting peptides as selective PACT agents. Light irradiation allowed the selective release of the cytotoxic compounds from the molecular cages in living cells. Further selectivity was conferred on the system by a peptide carrier (i.e., bombesin), which targets receptors overexpressed on the membranes of HeLa cells. As expected, this peptide was found to provide an increased uptake of the systems in HeLa cells compared with normal MRC-5 cells. As a result, for two of the compounds presented in this study, no cyto- or phototoxicity was observed in MRC-5 cells, whereas in HeLa cells, upon light irradiation, IC50 values of 42.2 and 60.0 ?M were obtained, which correspond to a two-fold increase in toxicity. Three novel RuII–polypyridyls have been synthesized and derivatized with a photolabile protecting group and two peptides. The targeting moieties allow a higher uptake in cancer cells compared with normal cells. The release of the metal component upon irradiation provided complete control of the cytotoxicity with a mechanism of action that is independent of the presence of oxygen in the tissues.

Posted on 22 July 2015 | 9:10 am


Dioxygen Activation by an in situ Reduced CuII Hydrazone Complex

A CuII hydrazone complex has been synthesized that can be reduced in situ in boiling methanol to give the corresponding CuI complex. The latter complex readily activates dioxygen under ambient conditions, as was unambiguously shown by isotopic labeling studies. As a consequence of the dioxygen activation, the thienyl moiety appended to the hydrazone ligand is easily oxidized in ? position (C–H??C–O), finally leading to a change in the coordination environment of the central metal ion. All relevant complexes have been structurally characterized by single-crystal X-ray diffraction analyses. The hydrazone ligand applied in this study does not mimic a biologically relevant coordination motif in copper-containing oxygenases. Nonetheless, the reactivity of the CuI complex resembles that found in many oxygenases, indicating that hydrazone ligands may be well-suited for the generation of novel bioinspired oxidation catalysts. A CuII complex of a hydrazone ligand with N,N,S-donor functionality is reported that, after in situ reduction, is able to activate dioxygen, leading to a hydroxylation of the ligand and finally resulting in the formation of a CuII complex of a hydrazone ligand acting as an N,N,O-donor.

Posted on 20 July 2015 | 2:50 pm


Easily Vaporizable Ionic Liquids – No Contradiction!

It was a big surprise to see crystals of an ionic liquid (IL) forming by sublimation at room temperature. ILs are generally accepted to have negligible vapour pressures at elevated temperatures, making their sublimation or distillation very difficult. ILs that sublime easily contain silylimidazolium-based cations. In order to establish the details of the unusual behaviour of this subclass of ILs, a combined spectroscopic, X-ray crystallographic, physicochemical and theoretical characterization was performed. The results are compared with those of other easily vaporizable compounds, like ammonium chloride and naphthalene. The single-crystal X-ray structure analysis of one of these compounds, N-methyl-N?-dimethyl(phenyl)silylimidazolium chloride (monoclinic, C2/c), clearly shows the existence of isolated ions, demonstrating that the compound is an ionic liquid. Ionic liquids (ILs) are commonly known as compounds with negligible vapour pressure, which makes them difficult to boil/distil or sublime. Surprisingly, ILs with imidazolium-based cations with the specialty of N-bonded silylorganic groups sublime very easily. The process of sublimation has been investigated thoroughly with physicochemical methods and theoretical calculations.

Posted on 20 July 2015 | 2:50 pm


Selective Oxidation of Sulfides Catalyzed by the Nanocluster Polyoxomolybdate (NH4)12[Mo36(NO)4O108(H2O)16]

The (NH4)12[Mo36(NO)4O108(H2O)16]·30.84H2O ({Mo36}) catalyst has been synthesized and successfully employed in the selective oxidation of various sulfides to sulfoxides with urea hydrogen peroxide as oxidant under mild reaction conditions with 84–99?% conversion and 58–99?% selectivity, with active functional groups such as the hydroxy group and C=C bonds tolerated in the oxidation. The {Mo36} catalyst showed high catalytic activity for a high substrate/catalyst ratio (up to 30000:1) and is recyclable. A polyoxomolybdate, (NH4)12[Mo36(NO)4O108(H2O)16]·30.84H2O ({Mo36}), has been synthesized and successfully used in the oxidation of sulfides with urea hydrogen peroxide as oxidant.

Posted on 17 July 2015 | 11:20 am


?-Excess ?2P=C–N–Heterocycles: Catalytic P-Arylation and Alkylation of N-Alkyl-1,3-benzazaphospholes and Isolation of P,N-Disubstituted Dihydrobenzaza­phosphole P-Oxides

2-Unsubstituted N-alkyl-1,3-benzazaphospholes, diagonally P–C related to 2,3-unsubstituted indoles, were successfully arylated by aryl iodides and bromides or alkylated by neopentyl iodide by heating in DMF in the presence of a catalytic amount of PdCl2 or H2PtCl6 and a suitable base. In contrast to the known 2-arylations of indoles under these conditions, the reactions led to arylation in the 3-position and proceeded via highly moisture-sensitive intermediates to P-substituted 1,3-benzazaphosphole P-oxides. Thus, we present a novel route for the direct P-substitution of aromatic ?2P-heterocycles with electrophilic aryl/alkyl halides. Characteristic NMR spectroscopic data of the intermediates are consistent with –P(aryl)–C(Br/Cl)–N– species formed by metal-mediated addition of the aryl halides at the P=C bond rather than by oxidative addition to ylidic intermediates. Benzazaphospholium salts, accessible by using triethyloxonium tetrafluoroborate at room temperature and also very sensitive to hydrolysis, display distinct NMR spectroscopic data. The structures of the products were elucidated by conclusive NMR spectroscopy and HRMS data and crystal-structure analysis. Minor amounts of a bis(arylation) product could likewise be identified by crystal-structure analysis. Aromatic ?2P-heterocycles are unreactive to aryl/alkyl halides. Heating in the presence of Pd or Pt catalysts and a suitable base, however, allows direct P-arylation or P-alkylation. The intermediate products are extremely moisture-sensitive and are transformed into phosphine oxides. Et3OBF4 provides benzazaphospholium salts without a catalyst, but these also tend to hydrolyze to phosphine oxides.

Posted on 17 July 2015 | 11:20 am


Water-Soluble Palladium(II) Sulfonated Thiosemicarbazone Complexes: Facile Synthesis and Preliminary Catalytic Studies in the Suzuki–Miyaura Cross-Coupling Reaction in Water

A series of mono- and binuclear sulfonated thiosemicarbazone PdII complexes have been synthesised and characterised using nuclear magnetic resonance spectroscopy, infrared spectroscopy, electrospray ionisation mass spectrometry and elemental analysis. The complexes display excellent water-solubility at room temperature and in addition, 1H and 31P{1H} NMR spectroscopic experiments reveal that the mononuclear complex 4 is very stable in water at 70 °C. Consequently, preliminary catalytic experiments show the water-soluble complexes to be efficient catalyst precursors in the Suzuki–Miyaura cross-coupling reaction in water. No evidence of homo-coupling was observed and the water-soluble complexes demonstrated versatility in coupling substrates containing various functional groups. Mono- and binuclear thiosemicarbazone complexes were synthesized and characterized. The mononuclear complexes are very stable in water and all the catalysts are active for the Suzuki–Miyaura cross-coupling reaction of various substrates. The mononuclear catalysts were more active than their binuclear analogues. Catalyst 4 could be recycled efficiently twice.

Posted on 17 July 2015 | 11:20 am


Key Considerations for Sensing FeII and FeIII in Aqueous Media

Recently Ghosh et al. reported on the fluorescent response of commercially available N-(2-aminoethyl)naphthalen-1-amine toward FeII, FeIII, and HgII (K. Ghosh, S. Rathi, P. Gupta, P. Vashisth, V. Pruthi, Eur. J. Inorg. Chem. 2015, 311). The authors conclude that metal binding to the diamine chelator leads to chelation-induced quenching; however, the experimental protocols are incompatible with the aqueous chemistry of FeIII, which precludes this interpretation of the data. Recently, Ghosh et al. reported on the fluorescent response of N-(2-aminoethyl)naphthalen-1-amine toward FeII, FeIII, and HgII (K. Ghosh, S. Rathi, P. Gupta, P. Vashisth, V. Pruthi, Eur. J. Inorg. Chem. 2015, 311), concluding that metal binding to the diamine chelator leads to chelation-induced quenching; however, the experimental protocols are incompatible with the aqueous chemistry of FeIII.

Posted on 17 July 2015 | 11:20 am


Trinuclear CuII Structural Isomers: Coordination, Magnetism, Electrochemistry and Catalytic Activity towards the Oxidation of Alkanes

The reaction of the Schiff base (3,5-di-tert-butyl-2-hydroxybenzylidene)-2-hydroxybenzohydrazide (H3L) with copper(II) nitrate, acetate or metaborate has led to the isomeric complexes [Cu3(L)2(MeOH)4] (1), [Cu3(L)2(MeOH)2]·2MeOH (2) and [Cu3(L)2(MeOH)4] (3), respectively, in which the ligand L exhibits dianionic (HL2–, in 1) or trianionic (L3–, in 2 and 3) pentadentate 1?O,O?,N:2?N?,O? chelation modes. Complexes 1–3 were characterized by elemental analysis, IR spectroscopy, single-crystal X-ray crystallography, electrochemical methods and variable-temperature magnetic susceptibility measurements, which indicated that the intratrimer antiferromagnetic coupling is strong in the three complexes and that there exists very weak ferromagnetic intermolecular interactions in 1 but weak antiferromagnetic intermolecular interactions in both 2 and 3. Electrochemical experiments showed that in complexes 1–3 the CuII ions can be reduced, in distinct steps, to CuI and Cu0. All the complexes act as efficient catalyst precursors under mild conditions for the peroxidative oxidation of cyclohexane to cyclohexyl hydroperoxide, cyclohexanol and cyclohexanone, leading to overall yields (based on the alkane) of up to 31?% (TON = 1.55?×?103) after 6 h in the presence of pyrazinecarboxylic acid. Three isomeric CuII complexes derived from Schiff base (3,5-di-tert-butyl-2-hydroxybenzylidene)-2-hydroxybenzohydrazide and three different CuII sources are reported. Their structural, electrochemical and magnetic properties as well as catalytic activity toward the peroxidative oxidation of cyclohexane to cyclohexyl hydroperoxide, cyclohexanol and cyclohexanone under mild conditions are described.

Posted on 17 July 2015 | 10:40 am


Studies on the Reaction of Reduced Vitamin B12 Derivatives with the Nitrosyl ­Hydride (HNO) Donor Angeli's Salt: HNO Oxidizes the Transition-Metal Center of Cob(I)alamin

Although it is well established that nitrosyl hydride (nitroxyl, HNO) reduces transition metals including transition-metal centers of porphyrins and metalloproteins, oxidation of a metal center by HNO has yet to be reported. Kinetic and mechanistic studies on the CoII vitamin B12 form, cob(II)alamin [Cbl(II)], with the widely used HNO donor Angeli's salt (AS) have been carried out. The stoichiometry of the reaction is Cbl(II)/AS = 1:2, and AS decomposition to give HNO and nitrite is the rate-determining step. Separate studies on the reaction between cob(I)alamin [Cbl(I)–] and AS and experiments in the presence of excess nitrite or the efficient cob(III)alamin trapping agent cyanide support a mechanism in which HNO reduces Cbl(II) to Cbl(I)–, being itself oxidized to NO·. A second molecule of HNO then oxidizes Cbl(I)– back to Cbl(II), which reacts rapidly with NO· to form nitroxylcobalamin [nitrosylcobalamin, NO––Cbl(III), NOCbl]. Kinetic studies on the reaction between cob(II)alamin [Cbl(II)] and Angeli's salt (AS) show that AS decomposition to give HNO is the rate-determining step. A mechanism is proposed involving a cob(I)alamin [Cbl(I)–] intermediate that is oxidized back to Cbl(II) by a second HNO molecule. Separate studies on the reaction of Cbl(I)– with AS support this mechanism.

Posted on 17 July 2015 | 10:40 am


Controlled SBU Approaches to Isoreticular Metal-Organic Framework Ruthenium-Analogues of HKUST-1

A controlled secondary building unit approach (CSA) was employed to obtain a series of ruthenium metal-organic frameworks (MOFs) of the general formula [Ru3(BTC)2Xx]·Gg (BTC = 1,3,5-benzenetricarboxylate; X = counter-anion, G = guest molecules) which are structural analogues of [M3(BTC)2] (M = Cu, Zn, Ni, Cr, Mo). The compounds [Ru2(OOCR)4X] and [Ru2(OOCCH3)4]Y were varied as Ru sources for CSA; namely strong coordinating X (Cl–) and weakly coordinating Y ([BF4]– or [BPh4]–) as well as the alkyl groups at the carboxylate ligand [R = CH3 or C(CH3)3] were utilized. Four phase-pure Ru-MOFs were obtained: [Ru3(BTC)2Cl0.5(OH)]·(AcOH)1.5 (1), [Ru3(BTC)2Cl1.2(OH)0.3]·(H3BTC)0.15(AcOH)2.4(PivOH)0.45 (2), [Ru3(BTC)2F0.5(OH)]·(AcOH)1.0 (3) and [Ru3(BTC)2(OH)1.5]·(H3BTC)0.5·(AcOH)1.4 (4) {AcOH = CH3COOH, PivOH = (CH3)3CCOOH}. The series of characterization data support the analytical composition and isostructural nature of 1–4, i.e. powder X-ray diffraction (PXRD), IR- and 1H-NMR spectroscopy, thermal gravimetric analysis (TGA) and N2 sorption were employed. The valence state of the Ru-sites were studied by X-ray absorption spectroscopy (XAS). The chosen precursors for CSA and optimized synthesis, work-up and activation protocols allowed improvement of the overall crystallinity, purity (i.e., residual solvent molecules) and surface area of the Ru-MOF materials. A controlled secondary building unit approach (CSA) was employed to obtain a series of isostructural ruthenium metal-organic frameworks (MOFs) of the general formula [Ru3(BTC)2Xx]·Gg (BTC = 1,3,5-benzenetricarboxylate; X = counter anion, G = guest molecules) which are analogues of [Cu3(BTC)2] (HKUST-1).

Posted on 17 July 2015 | 10:40 am


Catalytic Oxidation of Alkanes and Alkenes by H2O2 with a ?-Oxido Diiron(III) Complex as Catalyst/Catalyst Precursor

A new ?-oxo diiron(III) complex of the lithium salt of the pyridine-based unsymmetrical ligand 3-[(3-{[bis(pyridin-2-ylmethyl)amino]methyl}-2-hydroxy-5-methylbenzyl)(pyridin-2-ylmethyl)amino]propanoate (LiDPCPMPP), [Fe2(?-O)(LiDPCPMPP)2](ClO4)2, has been synthesized and characterized. The ability of the complex to catalyze oxidation of several alkanes and alkenes has been investigated by using CH3COOH/H2O2 (1:1) as an oxidative system. Moderate activity in cyclohexane oxidation (TOF = 33 h–1) and good activity in cyclohexene oxidation (TOF = 72 h–1) were detected. Partial retention of configuration (RC = 53?%) in cis- and trans-1,2-dimethylcyclohexane oxidation, moderate 3°/2° selectivity (4.1) in adamantane oxidation, and the observation of a relatively high kinetic isotope effect for cyclohexane oxidation (KIE = 3.27) suggest partial metal-based oxidation, probably in tandem with free-radical oxidation. Low-temperature UV/Vis spectroscopy and mass spectrometric studies in the rapid positive detection mode indicate the formation of a transient peroxido species, [Fe2(O)(O2)(LiDPCPMPP)2]2+, which might be an intermediate in the metal-based component of the oxidation process. A ?-oxido diiron(III) complex, [Fe2(?-O)(LiDPCPMPP)2](ClO4)2, was synthesized and characterized. This complex was used as catalyst in C–H bond oxidation with CH3COOH–H2O2 as chemical oxidant. Reactivity studies indicate that the oxidation process goes through a metal-based mechanism concomitant with a radical process.

Posted on 17 July 2015 | 10:40 am


Mechanisms and Factors Controlling Photoisomerization Equilibria, Ligand Exchange, and Water Oxidation Catalysis Capabilities of Mononuclear Ruthen­ium(II) Complexes

The photoisomerization equilibrium between distal- and proximal-[Ru(tpy)(pyqu)OH2]2+ [d- and p-RuH2O, tpy = 2,2?;6?,2?-terpyridine, pyqu = 2-(2?-pyridyl)quinoline] is characterized. The kinetic analysis of the pD-dependent photoisomerization reactions (monitored by 1H NMR) of d-RuH2O and p-RuH2O shows (1) that both hydroxo isomers, distal- and proximal-[Ru(tpy)(pyqu)OH]+, are inert to photoisomerization, and (2) that the back reaction (distal to proximal) is 3.0 times faster than the forward reaction (proximal to distal). Isolation of distal- and proximal-[Ru(tpy)(pyqu)Cl]+ (d- and p-RuCl) as well as d- and p-RuH2O isomers enabled comprehensive studies on geometric structures, ligand exchange and redox reactions, and water oxidation catalysis for these isomers. The observed aquation rate constant (9.2?×?10–2?s–1 at 40 ?M) of p-RuCl to form p-RuH2O is 1700 times higher than that (5.4?×?10–5?s–1 at 63 ?M) of d-RuCl at 298 K owing to the steric repulsion between a chloro ligand and the 8-proton of the quinoline moiety. The turnover frequency (TOF = 1.7?×?10–3?s–1) of p-RuH2O for catalytic water oxidation is 1.7 times greater than that (1.0?×?10–3?s–1) for d-RuH2O, in contrast to the [Ru(tpy)(pynp)OH2]2+ isomer system, in which the TOF of the distal isomer is higher than that of the proximal one by one order of magnitude. The mechanisms and factors controlling the photoisomerization equilibria and water oxidation catalysis of the d- and p-RuH2O isomers are discussed on the basis of experimental and theoretical investigations. The photoisomerization equilibrium between distal- and proximal-[Ru(tpy)(pyqu)OH2]2+ [d- and p-RuH2O, tpy = 2,2?,6?,2?-terpyridine, pyqu = 2-(2-pyridyl)quinoline] is illustrated. Isolation of distal- and proximal-[Ru(tpy)(pyqu)Cl]+ and d- and p-RuH2O isomers enabled comprehensive studies on geometric structures, ligand exchange and redox reactions, and water oxidation catalysis for these isomers.

Posted on 17 July 2015 | 10:40 am


Biomimetic Autocatalytic Synthesis of Organized Silica Hybrids

Biogenic formation of silica is a fundamental process occurring under mild conditions. Here we report autocatalytic generation of silica hybrid materials. Self-organized siloxanes containing imidazole self-catalytic groups can be transformed to hybrid silica by using mild biomimetic conditions similar to those under which primitive organisms make silica. Biomimetic formation of self-organized silica hybrids can be achieved by self-catalytic processes. Active imidazole moieties catalyze hydrolysis/condensation reactions in the absence of conventional sol–gel catalysts. Siloxane–imidazole proxy interactions are beneficial for the synthesis. As in natural systems, highly organized hybrid silica can be obtained with a very high degree of control.

Posted on 17 July 2015 | 10:40 am


Pd@UiO-66-Type MOFs Prepared by Chemical Vapor Infiltration as Shape-Selective Hydrogenation Catalysts

Host-guest inclusion properties of UiO-66 and UiO-67 metal-organic frameworks have been studied using ferrocene (FeCp2) as probe molecule. According to variable-temperature solid-state 1H and 13C CP-MAS-NMR, two different environments exist for adsorbed FeCp2 inside UiO-66 and UiO-67, which have been assigned to octahedral and tetrahedral cavities. At room temperature, a rapid exchange between these two adsorption sites occurs in UiO-67, while at –80 °C the intracrystalline traffic of FeCp2 through the triangular windows is largely hindered. In UiO-66, FeCp2 diffusion is already impeded at room temperature, in agreement with the smaller pore windows. Palladium nanoparticles (Pd NPs) encapsulated inside UiO-66 and UiO-67 have been prepared by chemical vapor infiltration of (allyl)Pd(Cp) followed by UV light irradiation. Infiltration must be carried out at low temperature (–10 °C) to avoid uncontrolled decomposition of the organometallic precursor and formation of Pd NPs at the external surface of the MOF. The resulting Pd-MOFs are shape selective catalysts, as shown for the hydrogenation of carbonyl compounds with different steric hindrance. Encapsulation of Pd nanoparticles inside the pores of UiO-66 and UiO-67 by chemical vapor infiltration leads to shape-selective catalysts, as shown for the hydrogenation of carbonyl compounds of different steric hindrance.

Posted on 17 July 2015 | 10:30 am


Structural, Magnetic, DFT, and Biological Studies of Mononuclear and Dinuclear CuII Complexes with Bidentate N-Heteroaromatic Schiff Base Ligands

Copper(II) complexes with the condensation derivative of methyl hydrazinoacetate and 2-acetylpyridine were synthesized. The X-ray crystal structures for both complexes revealed that they are polymerized isomers. A common feature of both complexes is the bidentate coordination of the ligand by one hydrazone and one pyridine nitrogen atom. In the monomeric complex, the copper(II) center is tetracoordinate, whereas dimerization through chlorido bridges results in a pentacoordinate arrangement about the metal ions in the dimer. The electronic and magnetic properties of both complexes are discussed on the basis of their X-ray structures, electron paramagnetic resonance (EPR) spectroscopy studies, and superconducting quantum interference device (SQUID) magnetization measurements combined with DFT calculations. Magnetostructural comparisons with structurally similar copper(II) complexes are also provided, and a possible correlation has been established. The antitumor activities of the CuII complexes were investigated against six different cancer cell lines, and the results suggest that the antiglioma action of the dimeric species is based on oxidative-stress-mediated phosphatidylserine externalization and caspase activation, which indicate apoptosis. We report the synthesis and XRD structures of monomeric and dimeric CuII complexes 1 and 2. The magnetic properties of 1, 2, and three similar CuII complexes are discussed on the basis of electron paramagnetic resonance (EPR) spectroscopy studies combined with DFT calculations. The antitumor action of the CuII complexes against six different cancer cell lines is investigated.

Posted on 17 July 2015 | 10:30 am


Mononuclear, Tetranuclear and 1D Polymeric Copper(I) Complexes of Large Bite Bisphosphines Containing Nitrogen and Oxygen Donor Atoms

The syntheses of new bisphosphines containing nitrogen and oxygen donor atoms, N,N-bis(diphenylphosphinobenzyl)-N-phenylamine (PNP) (1), bis(2-diphenylphosphinobenzyl) ether (POP) (2) and their coordination chemistry with copper(I) halides have been explored. The ligand structure plays a major role in controlling the coordination sphere and the structural features of copper(I) complexes. The reaction of 1 with CuX (X = Cl, Br, I) in 1:2 molar ratio yielded tetranuclear cuboid complexes [Cu4(?-X)4{C6H5N(CH2-2-C6H4PPh2)2}2-P,P] (3–5), whereas the similar reactions of 2 afforded tetranuclear stair-step type complexes [Cu4(?2-X)2(?3-X)2{O(CH2-2-C6H4PPh2)2}2-P,P] (9–11). The reactions of 1 with CuX in 1:1 molar ratio afforded 1D coordination polymers [CuX{C6H5N(CH2-2-C6H4PPh2)2}-P,P]n, (6–8). The reaction of CuI with 2 in a 1:1 molar ratio also yielded a tetranuclear stair-step complex [Cu4(?2-I)2(?3-I)2{O(CH2-2-C6H4PPh2)2}2-P,O,P] (12) but with tridentate P,O,P coordination along with 11, whereas the similar reaction with CuCl gave a simple mononuclear complex [CuCl{O(CH2-2-C6H4PPh2)2}-P,O,P] (13). In both the complexes, the ligand 2 exhibits a tridentate mode of coordination. Many of these complexes have been structurally characterized. This paper describes the synthesis of new bisphosphines containing nitrogen and oxygen donor atoms, N,N-bis(diphenylphosphinobenzyl)-N-phenylamine (PNP) (1), bis(2-diphenylphosphinobenzyl) ether (POP) (2) and their coordination chemistry with copper(I) halides.

Posted on 17 July 2015 | 10:30 am


Tunable Blue–Red Emission and Energy-Transfer Properties of Mg3(PO4)2:­Eu2+,­Mn2+ Phosphors

A series of Eu2+-doped and Eu2+/Mn2+-codoped Mg3(PO4)2 phosphors were synthesized by the combustion-assisted synthesis method. Under UV excitation, Mg3(PO4)2:Eu2+ presents a broad emission band, which can be decomposed into two symmetrical bands centered at ? = 427 and 467 nm, owing to the substitution of two kinds of Mg2+ sites by Eu2+ ions. In Mg3(PO4)2:Eu2+,Mn2+ phosphors, the excitation spectra monitored at the red emission of the Mn2+ ions is similar to that monitored at the blue emission of the Eu2+ ions, which illustrates the possibility of energy transfer from the Eu2+ ions to the Mn2+ ions. The variations of the emission spectra and decay lifetimes further demonstrate the existence of energy transfer from the Eu2+ ions to the Mn2+ ions under UV excitation. The energy-transfer mechanism is dominated by electric dipole–dipole interactions, which can be validated by the agreement of the critical distances obtained from the concentration-quenching (9.69 Å) and spectrum-overlap methods (8.04 Å). The 4T1??6A1 emission band of the Mn2+ ions in Mg3(PO4)2:0.04Eu2+,yMn2+ shows a redshift as a function of the Mn2+ concentration (y), which has been discussed in relation to the exchange interactions between Mn2+–Mn2+ pairs. Mg3(PO4)2:Eu2+,Mn2+ phosphors with blue and red emission bands are synthesized. Mg3(PO4)2 has two Mg2+ sites for the Eu2+ ions to occupy; therefore, they form two emission centers. Energy transfer from Eu2+ to Mn2+ ions occurs, and the transfer mechanism is determined. The Mn2+ 4T1??6A1 emission band of Mg3(PO4)2:Eu2+,Mn2+ shows a redshift owing to exchange interactions between the Mn2+ ions.

Posted on 17 July 2015 | 10:30 am


Dye-Sensitized Solar-Cell Performance of a Cobalt(III/II) Redox Mediator with the 2,6-Bis(8-quinolinyl)pyridine Ligand

Optical and electrochemical properties of the homoleptic cobalt(III/II) complexes mer,mer-[Co(tpy-?3N,N?,N?)]n+ and mer,mer-[Co(bqp-?3N,N?,N?)]n+ (n = 3+ or 2+) are presented [tpy = 2,2?:6?,2?-terpyridine; bqp = 2,6-bis(8?-quinolinyl)pyridine]. Both [Co(tpy)2]3+/2+ and [Co(bqp)2]3+/2+ systems have been used to formulate redox-mediator electrolytes for application in dye-sensitized solar-cell (DSSC) devices with the MK-2 dye TiO2 sensitizer. The [Co(tpy)2]3+/2+-based electrolyte shows a slightly higher percentage power-conversion efficiency (? = 4.47?%) in a DSSC device relative to the [Co(bqp)2]3+/2+-based electrolyte (? = 3.73?%). Although the [Co(bqp)2]3+/2+ electrolyte shows a slightly higher open-circuit potential (VOC = 0.79 V), it suffers from a reduced short-circuit current (JSC = 6.21 mA?cm–2) relative to that of the [Co(tpy)2]3+/2+ system (JSC = 10.84 mA?cm–2). Tafel and electrochemical impedance analysis (EIS) of symmetric FTO/Pt||Pt/FTO cells, as well as EIS and chronocoulometry of the functional DSSC device are presented. Collectively, this data points toward a decreased turnover of the CoIII/II redox couple at the Pt counter electrode for the [Co(bqp)2]3+/2+ system concomitant with an increased resistance to mass-transfer diffusion. Electrochemical properties of the [Co(bqp)2]3+/2+ redox mediator is evaluated in a dye-sensitized solar-cell (DSSC) device with the MK-2 dye photosensitizer. A comparable photovoltaic efficiency is observed for [Co(bqp)2]3+/2+ (? = 3.73?%) vs. the established [Co(tpy)2]3+/2+ mediator (? = 4.47?%).

Posted on 14 July 2015 | 5:52 pm


Ruthenium Imidazophenanthrolinium Complexes with Prolonged Excited-State Lifetimes

A series of ruthenium polypyridyl complexes [Ru(tbbpy)3][PF6]2 (0, tbbpy = 4,4?-di-tert-butyl-2,2?-bipyridine), [Ru(tbbpy)2(bbip)][PF6]3 {1, (bbip)Br = 1,3-(bisbenzyl)-1H-imidazo[4,5-f][1,10]phenanthrolinium bromide}, [Ru(tbbpy)(bbip)2][PF6]4 (2), and [Ru(bbip)3][PF6]5 (3) were synthesized. The new complexes 2 and 3 were fully characterized, and their X-ray crystal structures, absorption and emission spectra, quantum yields of emission, and cyclic voltammograms were determined. Within this series, a trend towards increased lifetime and quantum yields of emission can be observed, especially in the presence of oxygen. The location of the first excited state on the imidazophenanthrolinium ligands has been elucidated by resonance Raman spectroscopy of 1 and 3, which revealed that the energy of the ?* orbitals of the bbip ligands is lower than that of the ?* orbitals of the tbbpy ligand. A series of ruthenium polypyridyl complexes containing an imidazolium-functionalized phenanthroline ligand are presented. The complexes are fully characterized, and their solid-state structures are determined. The influence of the new ligand is investigated through absorption and emission spectroscopy, cyclic voltammetry, and resonance Raman spectroscopy investigations.

Posted on 14 July 2015 | 5:52 pm


The Reaction of Terminal Phosphinidene Complexes [RP–W(CO)5] with Vinylbor­onic Acids: Cycloaddition vs. P–C Bond Formation

The reaction of terminal phosphinidene complexes [RP–W(CO)5] with vinylboronic acids is very sensitive to the presence or absence of solid K3PO4 in suspension in the reaction medium. The products are phosphirane complexes without the salt and secondary vinylphosphine complexes in the presence of the salt. This shift of the reaction pathway is explained by the formation of vinyborates in the presence of potassium phosphate. Terminal phosphinidene complexes react with vinylboronic acid to give the expected phosphirane complexes, but the addition of K3PO4 changes the course of the reaction, and secondary vinylphosphine complexes are obtained instead.

Posted on 14 July 2015 | 5:52 pm


Si(OCH2Fc)4: Synthesis, Electrochemical Behavior, and Twin Polymerization

The preparation and twin polymerization of the twin monomer Si(OCH2Fc)4 [Fc = Fe(?5-C5H4)(?5-C5H5)] (2) by the reaction of FcCH2OH (1) with SiCl4 in the presence of pyridine was explored. The electronic properties of 2 were investigated by cyclic voltammetry, square-wave voltammetry, and UV/Vis/near-IR spectroelectrochemistry, which showed a redox separation caused by electrostatic repulsion. Thermally induced condensation of 2 is characteristic, as evidenced by differential scanning calorimetry (DSC) and thermogravimetry coupled mass spectrometry (TG–MS). Upon heating 2 to 210 °C, twin polymerization occurred and a hybrid material was formed that showed similarities with known systems derived from 2,2?-spirobi[4H-1,3,2-benzodioxasiline] (SBS), such as the nanopatterning of the formed silicon dioxide, which is characteristic for twin polymerization. Electron microscopy of this material revealed the absence of typical microstructuring found for other twin polymers, and hence, the herein presented system can be characterized as a borderline system if compared to known twin monomers such as SBS. The copolymerization of 2 and SBS afforded a hybrid material from which porous carbon or silica materials containing iron oxide nanoparticles could be obtained. The oxidation state of the incorporated particles was examined by Mössbauer experiments, which confirmed that only FeIII was incorporated within the porous carbon and silica materials, respectively. The preparation of iron oxide containing porous carbon capsules was achieved by applying a mixture of 2 and SBS to silicon dioxide spheres (d = 200 nm). After twin polymerization and carbonization, porous carbon capsules with incorporated iron oxide nanostructures were obtained. The straightforward preparation of iron-rich porous carbon and silica materials by twin polymerization of Si(OCH2Fc)4 [Fc = Fe(?5-C5H4)(?5-C5H5)] and 2,2?-spirobi[4H-1,3,2-benzodioxasiline] is reported; the electrochemical properties of Si(OCH2Fc)4 are discussed.

Posted on 14 July 2015 | 5:52 pm


Cobalt(I) and Nickel(II) Complexes of Bis(1,3-diphosphacyclobutadiene) Sandwich Anions

Complexes [(C4Me4)Co(CO)2{Co(P2C2tBu2)2}] (1, C4Me4 = tetramethylcyclobutadiene) and [CpNi{Co(P2C2tBu2)2}(PPh3)] (2, Cp = cyclopentadienyl) were synthesized by transmetalating [Tl(thf)2{Co(P2C2tBu2)2}] with [(C4Me4)Co(CO)2I] and [CpNiBr(PPh3)]. Compounds 1 and 2 were fully characterized by X-ray crystallography, multinuclear NMR, UV/Vis, and IR spectroscopy, and elemental analysis. Their molecular structures show ?-coordination of one phosphorus atom of the [Co(P2C2tBu2)2]– anion to the second metal atom (cobalt or nickel). Time-dependent density functional theory (TD-DFT) calculations were applied to gain insight into the electronic structures and the nature of the electronic transitions observed in the UV/Vis spectra. Cyclic voltammetry studies revealed the similar redox behavior of 1 and 2, which are reversibly oxidized to the corresponding monocations 1+ and 2+ with retention of the dinuclear structures. The cyclic voltammograms furthermore show that 1 and 2 decompose upon reduction with cleavage of the dinuclear structures into the free [Co(P2C2tBu2)2]– anion and further uncharacterized products. Dinuclear diphosphacyclobutadiene complexes have been synthesized by transmetalating the thallium(I) salt [Tl(thf)2{Co(P2C2tBu2)2}] with organometallic cobalt(I) and nickel(II) halides. The structural, spectroscopic, and redox properties of two new bimetallic complexes are presented, and their electronic structures are analyzed by DFT calculations.

Posted on 14 July 2015 | 5:52 pm


An Efficient Approach to Octabromophenylethyl-Functionalized Cage Silsesquioxane and Its Use in Constructing Hybrid Porous Materials

Octabromophenylethyl-functionalized silsesquioxane (BrPh-SQ) was synthesized by the Friedel–Crafts alkylation of octavinylsilsesquioxane (OVS) with bromobenzene, which acted as both the solvent and reactant and, furthermore, could be recycled after the reaction. The approach possesses the advantages of being mild, economic, and highly efficient. Further, BrPh-SQ was used as a building block in Heck reactions with OVS and tetrakis(4-vinylphenyl)silane to form two hybrid network polymers, that is, cage polymers 1 and 2, respectively. Cage polymer 1 showed moderate porosity with a Brunauer–Emmett–Teller specific surface area of 334 m2?g–1 and a total pore volume of 0.208 cm3?g–1. For gas-sorption applications, the CO2 uptake of cage polymer 1 was 2.44 wt.-% (0.55 mmol?g–1) at 273 K and 101 kPa. Octabromophenylethyl-functionalized cage silsesquioxane (BrPh-SQ) is successfully prepared through a green and efficient approach involving the Friedel–Crafts alkylation of octavinylsilsesquioxane (OVS) with bromobenzene. BrPh-SQ can be utilized as a building block to construct a hybrid porous material with OVS by the Heck reaction.

Posted on 14 July 2015 | 5:52 pm


Understanding and Tuning Bioinorganic Interfaces for the Design of Bionanocomposites

Interactions between biological molecules and inorganic species are of tremendous importance in nature. Attempts to create bionanocomposites associating nanoscale inorganic objects with biomolecules face major challenges with regard to controlling their mutual reactivity and preserving their intrinsic properties. This review describes the interactions arising between polyoxometallates or silica particles and biomolecules – including proteins, polysaccharides, lipids and nucleic acids – that depend on physicochemical conditions. It shows that chemical modification of the inorganic and/or bio-organic partner allows fine-tuning of their interface. The specific properties of these bionanocomposites are illustrated, with emphasis on their potential in biotechnology and biomedicine. This field contributes to a better understanding of the “biochemistry of solids” and offers an almost unlimited playground for the elaboration of new materials that combine molecular biodiversity with chemistry in its many facets. Understanding and controlling interfacial interactions between biological molecules – from lipids to proteins – and inorganic nano-objects, polyoxometallates and colloids allows the synthesis of bionanocomposites with applications in biotechnology and biomedicine.

Posted on 14 July 2015 | 5:52 pm


Synthesis and Reactivity of Ruthenium–Antimony Carbonyl Clusters

The reaction of Na[HRu3(CO)11] (2) with SbPh2Cl in dry tetrahydrofuran (THF) afforded the cluster Ru3(CO)10(?-H)(?-SbPh2) (3); in dry dichloromethane (DCM), the six-membered ring Ru6(CO)20(?-H)2(?-SbPh2)2 (4) was obtained instead. The trimethylamine N-oxide (TMNO) activated reaction of Ru3(CO)12 (1) with distibine Sb2Ph4 produced Ru3(CO)10(?-SbPh2)2 (6) through an Sb–Sb bond oxidative addition. Cluster 6 is fluxional through Ru–Ru bond isomerization. In contrast, its group 15 monosubstituted derivatives Ru3(CO)9(?-SbPh2)2(L) (7, L = phosphane, arsine or stibine) or the disubstituted derivatives Ru3(CO)8(?-SbPh2)2(L)2 (8) did not exhibit such fluxionality. Instead, isomerization through a turnstile mechanism involving the group 15 ligand occurred. The treatment of 6 with SbPh2Cl afforded the fused-ring clusters Ru3(CO)9(?-SbPh2)3(Cl) (9) and Ru3(CO)8(?-SbPh2)3(Cl)(SbPh2CH2Cl) (10). A series of ruthenium–antimony carbonyl clusters are prepared by the oxidative addition of Sb–Cl or Sb–Sb bonds to lightly stabilized ruthenium carbonyl clusters. Their solid- and solution-state structures are studied in detail by X-ray crystallography and variable-temperature multinuclear NMR experiments, respectively.

Posted on 14 July 2015 | 5:52 pm


Heterodi- (Fe, Pd/Pt) and Heterotrimetallic (Fe2, Pd) Complexes Derived from 4-(Ferrocenylmethyl)-N-(2-methoxyethyl)-3,5-­diphenylpyrazole as Potential Antitumoral Agents

The study of the reactivity of the pyrazole derivative 1-[MeO(CH2)2]-3,5-Ph2-4-(CH2Fc)–(C3N2) (1, Fc = ferrocenyl) with Na2[PdCl4], Pd(OAc)2, and [MCl2(dmso)2] (M = Pd or Pt, dmso = dimethyl sulfoxide) has allowed us to isolate trans-[Pd{?-N-(1-{MeO(CH2)2}-3,5-Ph2-4-{CH2Fc}–{C3N2})}2Cl2] (2), [Pd{?2-C,N(1-{MeO(CH2)2}-3-{C6H4}-5-Ph-{C3N2})}{?-N-(1-{MeO(CH2)2}-3,5-Ph2-4-{CH2Fc}–{C3N2})}Cl] (3), [Pd{?2-C,N(1-{MeO(CH2)2}-3-{C6H4}-4-{CH2Fc}-5-Ph-{C3N2})}Cl(PPh3)] (4), and the trans (5) and cis (6) isomers of [Pt{?-N-(1-{MeO(CH2)2}-3,5-Ph2-4-{CH2Fc}–{C3N2})}Cl2(dmso)]. Compound 1 acts as a N (in 2, 5, and 6) or (C,N)– donor ligand (in 4) and shows both binding modes in 3. The cytotoxic assessment of 1–6 against MCF7, MDA-MB231 (breast), and HCT-116 (colon) cancer cell lines reveal that (1) 1 is more potent than 1-[MeO(CH2)2]-3,5-Ph2-(C3HN2) (V), (2) 2–6 have cytotoxic activity, (3) 2 and 3 are less active than 4–6, and (4) 6 is the most potent compound against the three cancer cell lines. The bifunctional role of new ferrocene–pyrazole compound as a ligand for PdII or PtII complexes and as a potent antitumor agent is investigated.

Posted on 8 July 2015 | 11:10 am


Silylated Group 14 Ylenes: An Emerging Class of Reactive Compounds

Silyl-substituted heavy-element tetrylenes are very reactive entities and therefore prefer variously to dimerize to heavy olefin analogues, to oligomerize to cyclic products, or to undergo some type of rearrangement reaction. Our work on the synthesis of oligosilanyl-substituted plumbylenes, stannylenes, and germylenes has shown that trapping such tetrylenes as phosphine adducts is a good method for preventing dimerization or rearrangement and allows the chemistry of the free tetrylene to be studied either through phosphane abstraction or even through thermally induced dissociation. In addition to a number of typical reactions with these tetrylenes, which occur in such a way that the divalent element becomes tetravalent, it was found in the case of germylenes that addition of monosubstituted alkynes proceeds by insertion into a Ge–Si bond with preservation of the divalent state of the germylene. The obtained tetrylene phosphane adducts could also be used as precursors for the generation of transition-metal complexes with tetrylene ligands. Silyl-substituted heavy-element tetrylenes are reactive species that either dimerize or undergo rearrangement of some kind. Trapping them as phosphine adducts prevents dimerization and allows study of the reactivity of the free tetrylenes and their introduction as ligands into transition-metal complexes.

Posted on 8 July 2015 | 10:50 am


A Hierarchical MoO2/Au/MnO2 Hetero­structure with Enhanced Electrochemical Performance for Application as Supercapacitor

A hierarchical MoO2/Au/MnO2 heterostructure was prepared by a two-step electrodeposition method. The ion-diffusion and charge-collection capacity improved after spraying a Au layer. Electrochemical tests show that the areal specific capacitance for MoO2/Au/MnO2 is up to 112 mF?cm–2 at a scan rate of 5 mV?s–1. Furthermore, the obtained MoO2/Au/MnO2 heterostructure also displays an excellent rate capability and remarkable cycling stability. A hierarchical MoO2/Au/MnO2 heterostructure was fabricated by a two-step electrodeposition method. It displayed excellent long-term cycling stability and high rate capability for application as supercapacitor.

Posted on 8 July 2015 | 10:50 am


Silver-Based 4A Zeolite Composite Catalyst for Styrene Epoxidation by One-Pot Hydrothermal Synthesis

A silver-based 4A zeolite composite catalyst had been successfully synthesized by a facile one-pot hydrothermal method. Silver ions were fully mixed with the zeolite crystal nucleus and formed silver nanoparticles in the process of zeolite crystallization. The catalyst was characterized by FTIR spectroscopy, diffuse-reflectance UV/Vis spectroscopy, scanning electron microscopy (SEM), field-emission SEM (FESEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The distribution of the silver nanoparticles is relatively homogeneous inside and outside of the 4A zeolite. Furthermore, the catalytic performance for the epoxidation of styrene was tested, and the prepared catalyst showed excellent catalytic activity. The catalyst amount, reaction time, and different solvents were comprehensively investigated, and the catalytic activity of the silver-based 4A zeolite composite catalyst was displayed fully in acetonitrile. The conversion of styrene was 80.8?%, and the selectivity of styrene oxide (SO) reached 89.2?%. A one-pot hydrothermal method is used to synthesize a silver-based 4A zeolite composite catalyst for styrene epoxidation. A silver/ammonia solution is mixed with poly(ethylene glycol). Then, the mixture is added to the aging system, which contains the crystal nucleus of 4A zeolite, and absolute ethyl alcohol is added to the system. Finally, the composite catalyst is obtained by crystallization.

Posted on 8 July 2015 | 10:50 am


Synthesis and Characterization of ?-­NiMoO4 Nanorods for Supercapacitor ­Application

We report the synthesis of electrode materials based on one-dimensional ?-NiMoO4 nanorods for application as a supercapacitor. The structure and morphology of the electrodes were characterized by powder X-ray diffraction, Raman analysis, X-ray photoelectron spectroscopy, and scanning and transmission electron microscopy. The maximum specific capacitance obtained from electrochemical measurements on a standard three-electrode system was 730 F?g–1 at a scan rate of 5 mV?s–1. Furthermore, an asymmetric supercapacitor (ASC) was fabricated in which the NiMoO4 nanorods were used as the positive electrode and reduced graphene oxide was used as the negative electrode. The maximum specific energy obtained from the ASC study was 12.31 Wh?kg–1 at a specific current of 0.5 A?g–1 in an aqueous KOH electrolyte. This ASC cell showed good stability with 85?% capacitance retention up to 2000 cycles. These results reveal that our ASC shows a high performance and specific energy as well as good cycling stability. We report the synthesis of electrode materials based on 1D ?-NiMoO4 nanorods for application as a supercapacitor. The nanorod morphology can be easily controlled by optimizing the initial reaction conditions. Thus, this simple chemical approach to the synthesis of binary metal oxides could be extended to other metal oxides and lead to promising performances in energy storage applications.

Posted on 8 July 2015 | 10:50 am


Electro-Assisted Reduction of CO2 to CO and Formaldehyde by (TOA)6[?-SiW11O39Co(_)] Polyoxometalate

We report here on the multiproton-multielectron electrochemical reduction of CO2 in homogeneous solution by using (TOA)6[?-SiW11O39Co(_)] (TOA = tetraoctyl ammonium; _ = vacant position in the coordination sphere of Co) as an electrocatalyst. First, the electrochemical behavior of (TOA)6[?-SiW11O39Co(_)] was analyzed in detail by cyclic voltammetry in dichloromethane, studying the influence of the presence of protons and/or CO2. These preliminary results were further used to optimize the conditions of electrolysis in terms of reduction potentials. Analysis of the electrolysis products in the gas and liquid phases show the formation of CO and HCHO without formation of H2. Our results tend to show that the (TOA)6[?-SiW11O39Co(_)] polyoxometalate is a catalyst for CO2 electroreduction, with unique selectivity. The cobalt derivative of the silico-undecatungstate [?-SiW11O39Co(_)]6– is a catalyst for the multiproton-multielectron electrochemical reduction of CO2, with unique selectivity. Analysis of electrolysis products in the gas and liquid phases shows the formation of CO and HCHO without detection of H2.

Posted on 8 July 2015 | 10:50 am


Dinuclear Nitrato Coordination Compounds with Bis(3,5-tert-butylpyrazol-1-yl)­acetate

Two dinuclear centrosymmetric coordination compounds with the bis(3,5-di-tert-butylpyrazol-1-yl)acetic acid anion (L– = bdtbpza), namely, violet [Co(bdtbpza)(NO3)]2 (1) and turquoise [Cu(bdtbpza)(NO3)]2 (2), are reported. Around each metal(II) ion, the L– ligand is ?3-N,N,O coordinated, and the M–O bonds are significantly longer than both M–N bonds. The coordination sphere is completed by short nitrato and M–O bonds to a ligand that is already ?3-N,N,O coordinated to the adjacent intra-dinuclear metal center. Therefore, each L– ligand has a total coordination number of four but with different carboxylate modes, namely, ?4-N,N,O,O (1,1) in 1 and ?4-N,N,O,O? (1,3) in 2 for the C(1)–O–C(2) group. Thus, the coordination spheres are MO2N2O in both cases, though 1 is distorted trigonal bipyramidal, whereas 2 is square pyramidal. Antiferromagnetic (AFM) coupling (17 cm–1) is seen only in 1, though the best fit was obtained with consideration of spin–orbit coupling along with zero-field splitting owing to exchange anisotropy. The new dinuclear nitrato species might be alternatives to previously reported mimics of enzyme active sites. Two dinuclear compounds with the bis(3,5-tert-butylpyrazol-1-yl)acetic acid anion (bdtbpza), [Co(NO3)(bdtbpza)]2 (1) and [Cu(NO3)(bdtbpza)]2 (2), are reported. Nitrato coligands are present instead of the commonly observed chlorido anions in dinuclear species with MO2N2O chromophores; 1 is distorted trigonal bipyramidal, and 2 is square pyramidal. Antiferromagnetic coupling is seen only in 1.

Posted on 8 July 2015 | 10:50 am


Pt, Pd and Hg Complexes with Potentially Tridentate Telluroether Ligands

N-[3-(Phenyltellanyl)propyl]picolinamide (HL1) or N-[N?,N?-methyl(phenyl)aminothiocarbonyl]-N?-[3-(phenyltellanyl)propyl]benzamidine (HL2) react with equivalent amounts of PtCl2 or PdCl2 with formation of neutral [MCl(L1-?N,N?,Te)] or [MCl(L2-?S,N,Te)] chelates. A corresponding reaction of HL2 with HgCl2 results in the formation of [HgCl2(HL2-?S,Te)]. Treatment of [PtCl(L1-N,N?,Te)] with elemental iodine results in the exclusive oxidation of the metal ion and the platinum(IV) complex [PtI3(L1-?N,N?,Te)] could be isolated in reasonable amounts. A decomposition of the tellurium-containing ligand and the formation of [PdI2(PhTeI)2] was observed during a similar procedure with the corresponding palladium complex. The bonding situation inside the latter compound was analyzed through density functional theory calculations. Reactions between MCl2 (M = Pt, Pd, Hg) and potentially tridentate telluroether ligands with additional picolinamido or thiocarbamoylbenzamidinato units give neutral chelates. Long-range Te···M, Te···halide, or Te···S interactions assemble the obtained molecules to dimeric and/or polymeric arrangements in the solid state.

Posted on 8 July 2015 | 10:50 am


The Effects of Morphology and Linker Length on the Properties of Peptide–Lanthanide Upconversion Nanomaterials as G2 Phase Cell Cycle Inhibitors

In this work, the shape effect of our same-sized hybrid nanomaterials conjugated with two different Plk1-specific peptides had been investigated in terms of their photophysical properties, cellular uptake efficiencies, and selective inhibitory effects towards cancer and normal cells. The results clearly indicate that our spherical NaGdF4@SiO2-P1 nanoparticles achieve the best performance for in vitro imaging, G2 phase cell arrest, and, hence, cell cycle inhibition. Plk1-specific peptides are bioconjugated onto spherical and cubic NaGdF4@SiO2 nanoparticles, and the inhibitory effects of the hybrid materials towards normal cells and cancer cells are investigated.

Posted on 8 July 2015 | 10:50 am


Production and Photoelectric Activity of P and Al Co-Doped ZnO Nanomaterials

Materials that have both conductivity and photocatalytic activity are widely applied in electrical devices and as environmental pollution handles. Based on such requirements, phosphorus and aluminium co-doped conductive zinc oxide nanocrystals (PAZO NCs) with novel visible-light catalytic activities have been mass produced by the combustion method. The PAZO NCs have diameters of 30–100 nm and BET specific surface areas of 15.27–18.99?m2?g–1. These PAZO NCs exhibited novel photocatalytic activity and good conductivity [the powder conductivity was (0.98–1.76)?×10–4 S?cm–1], the reason being mainly attributed to the increase in carrier concentration and defects through P and Al co-doping. In addition, we found that the 3PAZO NCs, in which the molar ratio of Zn to P atoms is 100:3, had the best visible-light catalytic efficiency of the PAZO NCs, and the size of PAZO NCs decreased with increasing doping of phosphorus and aluminium. This study is useful as a reference for the mass production of modified ZnO NCs and its applications, such as in environmental management, photocatalysis, and anti-static electricity. Phosphorus and aluminium co-doped conductive zinc oxide nanocrystals (PAZO NCs) with novel visible-light catalytic activities have been mass produced by the combustion method. The size of PAZO NCs decreased with increasing doping of phosphorus and aluminium. The 3PAZO (molar ratio of Zn to P atoms is 100:3) NCs showed the best visible-light catalytic efficiency of the PAZO NCs.

Posted on 8 July 2015 | 10:50 am


Protonation-Dependent Luminescence of an Iridium(III) Bibenzimidazole Chromophore

We present the synthesis and a detailed structural and photophysical investigation of the bis(phenylpyridine)iridium(III) complex of 4,4?,5,5?-tetramethyl-2,2?-bibenzimidazole [Ir(tmBBI)-H2] and its homodinuclear complex [Ir(tmBBI)Ir]. Their structures were determined by single-crystal X-ray diffraction analysis and NMR spectroscopy, and detailed UV/Vis and emission spectroscopy studies were performed. Ir(tmBBI)-Hx shows strong protonation-state-dependent luminescence and is luminescent in all three of its protonation states, which allows for protonation-state-dependent color tuning from the green to blue spectral region. The diastereomeric meso and rac forms of the dinuclear Ir(tmBBI)Ir could be separated by fractional crystallization and both showed strong luminescence. A comparison with structurally related ruthenium complexes showed pronounced differences in their photophysical properties. The syntheses of the bis(phenylpyridine)iridium(III) complex of 4,4?,5,5?-tetraethyl-2,2?-bibenzimidazole [Ir(tmBBI)-Hx] and the homodinuclear complex [Ir(tmBBI)Ir] are described. The structures are determined by single-crystal X-ray diffraction analysis and NMR spectroscopy, and detailed UV/Vis and emission spectroscopy studies are performed.

Posted on 8 July 2015 | 10:50 am


Artificial Diiron Enzymes with a De Novo Designed Four-Helix Bundle Structure

A single polypeptide chain may provide an astronomical number of conformers. Nature selected only a trivial number of them through evolution, composing an alphabet of scaffolds, that can afford the complete set of chemical reactions needed to support life. These structural templates are so stable that they allow several mutations without disruption of the global folding, even having the ability to bind several exogenous cofactors. With this perspective, metal cofactors play a crucial role in the regulation and catalysis of several processes. Nature is able to modulate the chemistry of metals, adopting only a few ligands and slightly different geometries. Several scaffolds and metal-binding motifs are representing the focus of intense interest in the literature. This review discusses the widespread four-helix bundle fold, adopted as a scaffold for metal binding sites in the context of de novo protein design to obtain basic biochemical components for biosensing or catalysis. In particular, we describe the rational refinement of structure/function in diiron–oxo protein models from the due ferri (DF) family. The DF proteins were developed by us through an iterative process of design and rigorous characterization, which has allowed a shift from structural to functional models. The examples reported herein demonstrate the importance of the synergic application of de novo design methods as well as spectroscopic and structural characterization to optimize the catalytic performance of artificial enzymes. The de novo design of nature-inspired four-helix bundle metalloproteins is discussed. Special attention is given to the rational refinement of structure/function in diiron–oxo protein models from the due ferri family, which has allowed a shift from structural to functional models.

Posted on 6 July 2015 | 11:50 am


Probing Solid-State Breathing and Structural Transformations in a Series of Silver(I) Porous Coordination Polymers

Key observations of the role anions and solvents play in the solid-state flexibility of a series of isostructural silver(I) porous coordination polymers (PCPs) are reported. Building upon earlier results for the perchlorate salt, the structural transformations of two new analogues of a 3D PCP [Ag(dpzm)]X (1) (dpzm = 2,2?-dipyrazinylmethane; X = PF6, ClO4, BF4), which contain either PF6 (1a) or BF4 (1c) counterions, are investigated. These materials undergo a remarkable guest-induced single-crystal to single-crystal (SC-SC) solid-state contraction and expansion, which is accurately elucidated by X-ray crystallography. The extent of breathing for PCPs 1a–1c is shown to relate to the type of anion contained within their 3D structures and the nature of the solvent guest. Using X-ray diffraction, further light is shed on structural transformations that take place upon desolvation for this group of materials. These investigations reveal that, while the as-synthesised forms (containing DMSO) undergo a transformation (porous 3D to close-packed 3D; porous 3D to 2D) upon desolvation, the solvent-exchanged forms are more stable. Herein two new examples of an AgI porous coordination polymer that display solid-state breathing are reported. Additional transformations of these materials to non-porous 2D and 3D structures are investigated.

Posted on 2 July 2015 | 1:30 pm


Insight into CaMgSi2O6:Eu2+,Mn2+,Dy3+ Nanoprobes: Influence of Chemical Composition and Crystallinity on Persistent Red Luminescence

Optical imaging in which photons are the information source seems to be a very important technique, less expensive and less harmful than more conventional diagnostic methods and suitable, for instance, for sensitive diagnosis capable of detecting cancer at an early stage. We have recently developed inorganic persistent luminescent nanoparticles (PLNPs) as nanoprobes useful for in vivo imaging that can master the difficulties of the biological environment such as tissue autofluorescence, absorption, or photobleaching because they are excited before injection into the animal. In this work, we have focused on silicate materials, CaMgSi2O6, that emit in the red/near-infrared range for several hours. With the aim of improving their luminescent properties and nanoparticle size, we have explored a new method of synthesis that allows a suitable yield of particles and studied the influence of chemical composition and crystalline structure on luminescence intensity. Adjusting the molar ratio of Ca/Mg/Si and crystallization temperature, very fine nanoparticles of PLNPs have been obtained with an improved luminescence and the high production yield necessary to promote the emergence of these nanoprobes in the field of optical imaging. Nanoparticles of CaxMgySi2O6 doped with Eu2+, Mn2+, and Dy3+ have been prepared with a high production yield by a sol–gel method inspired by the Stöber process with the aim of improving the luminescent properties and decreasing the size of silicate-based nanoprobes. Such a study is essential to promote the emergence of these nanoprobes in the field of optical imaging.

Posted on 2 July 2015 | 1:20 pm


Synthesis of Stable Magnetic Polyaniline Nanohybrids with Pyrene as a Cross-Linker for Simultaneous Diagnosis by Magnetic Resonance Imaging and Photothermal Therapy

We have developed pyrene-modified magnetic polyaniline nanoparticles (MPANs), a hybridization of MnFe2O4 magnetic nanoparticles (MNPs) and polyaniline (PANI) with pyrene as a cross-linker, for diagnosis by simultaneous magnetic resonance (MR) imaging and photothermal therapy. In general, the strong affinity between PANI molecules, owing to interchain hydrogen bonding and the ?–? interactions mediated by their aromatic composition, hinders the successful synthesis of complexes of PANI with inorganic materials. To overcome this obstacle, we used pyrene as a cross-linker to synthesize a stable complex of PANI with MNPs. We first modified the hydrophobic MNPs with pyrene through a hydrophobic interaction and then formed a complex with PANI. The pyrene-induced ?–? interactions between the pyrene molecules on the MNPs and PANI reduced the affinity between the PANI molecules, and the strong affinity between the PANI molecules and MNPs rendered stable nanocomplexes of MPANs. Finally, Cetuximab-conjugated MPANs were fully tested for simultaneous diagnosis by magnetic resonance imaging (MRI) from superparamagnetic MnFe2O4 and photothermal ablation therapy from the near-infrared absorbing characteristics of PANI in epidermal growth factor receptor (EGFR) overexpressed cancer cells (A-431 cells) in vitro. Magnetic polyaniline nanoparticles (MPANs) are synthesized and show evenly mixed magnetic nanoparticles (MNPs) and polyaniline (PANI) with increased colloidal stability owing to the hydrophobic and ?–? interactions between the PANI and pyrene molecules.

Posted on 2 July 2015 | 1:20 pm


Mercury Complexes with Tripodal Pseudopeptides Derived from D-Penicillamine Favour a HgS3 Coordination

The pseudopeptides L4 and L5 are built on a nitrilotriacetic scaffold and functionalized with three D-penicillamine (D-Pen) units. D-Pen is an interesting building block and a bulkier analogue of cysteine with the ?-methylene hydrogen atoms replaced by larger methyl groups. The two sulfur ligands L4 and L5 are studied here with the toxic HgII ion. The formation of the two mononuclear complexes HgL4 and HgL5 is demonstrated by 1H NMR spectroscopy and mass spectrometry and the tristhiolato coordination is unambiguously evidenced by the UV absorption signatures. An important feature is the stabilization of the HgS3 coordination mode at the expense of the generally preferred HgS2 linear coordination. It appears that the hindered D-Pen pseudopeptide L5 is capable of stabilizing the unusual HgS3 coordination over a large pH range in water, pH?> 5.5. This water-soluble compound can therefore be considered as a promising chelating agent for mercury detoxification. Tripodal pseudopeptides anchored on a nitrilotriacetic chemical scaffold and extended with three D-penicillamine units stabilize the unusual HgS3 coordination over a large pH range in a hindered coordination environment.

Posted on 1 July 2015 | 11:20 am


Off–On, Ratiometric, and On–Off Fluorescence Responses of Thioether-Linked Bisquinolines toward Hg2+ and Fe3+ Ions

Fifteen bisquinoline derivatives with a thioether linker have been prepared, and their Hg2+- and Fe3+-specific fluorescence responses have been investigated. Upon the addition of Hg2+ ions, unsubstituted 2-quinolylmethyl derivatives 1a–1c exhibit a fluorescence enhancement (off–on) response. On the other hand, ratiometric and fluorescence quenching (on–off) responses are accomplished for derivatives with monomethoxy (2a–2c) and trimethoxy (3a–3c) substituents on the aromatic ring, respectively. The 8-quinolylmethyl derivatives 4a–4c and 5a–5c exhibit a similar response pattern to those of 1 and 2 with enhanced Hg2+ ion selectivity. Increasing the number of sulfur atoms through the extension of the linker chain also improves the Hg2+ ion selectivity. The selectivity of fluorescent bisquinoline derivatives with thioether linkers for Hg2+ ions is improved by 8-quinolylmethyl tethering and increasing the number of sulfur atoms through the extension of the linker.

Posted on 1 July 2015 | 11:20 am


Redox-State Dependent Ligand Exchange in Manganese-Based Oxidation Catalysis

Manganese-based oxidation catalysis plays a central role both in nature, in the oxidation of water in photosystem II (PSII) and the control of reactive oxygen species, as well as in chemical processes, in the oxidation of organic substrates and bleaching applications. The focus of this review is on efforts made to explore and elucidate the redox-dependent coordination chemistry of these manganese-based systems in solution and the mechanisms by which their catalytic redox reactions proceed. We also examine the behaviour and activity of complexes that have been developed and used as models for the active sites of the corresponding enzymes, or used as catalysts in the oxidation of organic substrates. Given the current concern over the environmental and economic impact of chemical processes, manganese catalysts that use H2O2 as oxidant are the primary focus of this review. The role played by Mn-based complexes in controlling reactive oxygen species and in the water oxidation complex of photosystem II has inspired the design of catalysts for chemical processes such as the oxidation of organic substrates and bleaching applications. Here, the redox and pH dependence of the coordination chemistry of Mn complexes applied in oxidations with H2O2 is reviewed.

Posted on 30 June 2015 | 12:10 pm


Synthesis and Characterisation of Various Diester and Triester Adducts of TiCl4

Titanium(IV) chloride and the triester glycerol tribenzoate (gtb) were reacted under moisture-free conditions in order to investigate the use of triester-containing oils in the purification of TiCl4 in industrial processes. This resulted in the isolation of a chloro-bridged dimeric complex containing four titanium centres [{(TiCl4)2(gtb)}2] (1). Further novel coordination compounds of TiCl4 and the diesters; diisopropyl malonate, dibenzyl malonate and diethyl succinate were synthesised by direct reaction under moisture-free conditions, yielding [TiCl4{CH2(COOiPr)2}] (2), [TiCl4{CH2(COOCH2Ph)2}] (3) and [TiCl4{C2H4(COOEt)2}] (4) respectively. The structures of compounds 1–4 were determined by single-crystal X-ray diffraction. All structures assumed an octahedral geometry consisting of the titanium bound to four chloride ligands and the diester molecule acting as a bidentate ligand, through its two carbonyl oxygen atoms. Exposure of the isopropyl malonate reaction to trace amounts of water during synthesis resulted in the formation of an oxo-bridged dimeric structure [Ti2(?-O)Cl3{CH2(COOiPr)2}2] (2b), the structure of which was also obtained via single-crystal X-ray diffraction. The synthesis of novel titanium complexes with triesters and diesters was achieved using Schlenk techniques for the purpose of ellucidating the previously unknown mechanisms at play during the industrially used Chloride Process.

Posted on 30 June 2015 | 12:10 pm


Aerosol-Assisted Chemical-Vapour Deposition of Zinc Oxide from Single-Source ?-Iminoesterate Precursors

Single-source zinc ?-iminoesterate precursors have been used for the first time in the aerosol-assisted chemical-vapour deposition (AACVD) of ZnO thin films. Depositions at 450 °C on silica-coated glass substrates produced strongly adherent films with excellent coverage of the substrate. The zinc ?-iminoesterates [Zn(L1)2] (1) and [Zn(L2)2] (2) were synthesised by the reaction between ZnEt2 and 2 equiv. of a synthesised ?-iminoester ligand CH3C[NHCH(CH3)2]CHC(O)OCH2CH3 (L1) and CH3C(NHCH3)CHC(O)OCH2CH3 (L2). The synthesised complexes were isolated and characterised by 1H and 13C NMR spectroscopy, mass spectrometry and thermal gravitational analysis (TGA). The structures of the compounds were determined by single-crystal X-ray diffraction. The ZnO films deposited from 1 and 2 were analyzed by glancing-angle X-ray powder diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and their optical properties determined by UV/Vis/NIR transmission spectroscopy. These results reveal that the organic ligand attached to the N moiety of the zinc complex has a significant effect on the level of carbon incorporated into the deposited thin film. Upon annealing, highly transparent hexagonal wurtzite ZnO thin films were produced. The synthesis, isolation and characterisation of zinc ?-iminoesterate precursors of the type [Zn(CH3C(NR)CHC(O)OCH2CH3)] are described, as well as their use for the first time in the aerosol-assisted chemical-vapour deposition (AACVD) of ZnO thin films at 450 °C. Results show that changing the R group on the N moiety of the precursors has a significant effect on carbon contamination in the films.

Posted on 30 June 2015 | 12:10 pm


Origin of Projected Excellent Thermoelectric Transport Properties in d0-Electron AMN2 (A = Sr or Ba; M = Ti, Zr, Hf) Layered Complex Metal Nitrides

Layered materials have several properties that make them suitable as high-performance thermoelectric materials. In this study, we elucidated the potential of d0-electron layered complex metal nitrides, AMN2 (A = Sr or Ba; M = Ti, Zr, Hf), with KCoO2-type and ?-NaFeO2-type crystal structures. The detailed electronic structures and electronic transport coefficients for AMN2 compounds were calculated by using density-functional theory and Boltzmann theory, respectively. The KCoO2-type AMN2 compounds show highly anisotropic thermoelectric properties. The effective masses at the lowest conduction bands in both KCoO2-type and ?-NaFeO2-type AMN2 compounds were significantly smaller than that in three-dimensional perovskite SrTiO3, a well-known compound with good thermoelectric properties. The results suggest that the excellent thermoelectric transport properties arise from appropriate electronic structures and small effective masses in AMN2 layered complex metal nitrides. d0-Electron layered complex metal nitrides (AMN2) are expected to exhibit excellent thermoelectric properties that arise from their electronic structures and small effective masses.

Posted on 30 June 2015 | 12:10 pm


Mo-V-Phosphoric Heteropoly Acids and Their Salts: Aqueous Solution Preparation – Challenges and Perspectives

Vanadium-containing heteropoly acids (HPAs) are effective acidic and oxidizing catalysts in various reactions. The existing wide application of such catalysts requires their safe, waste-free, and easy preparation on a large scale. Unfortunately, the so-called ether method, first suggested more than 100 years ago, is still mainly used for the purpose, producing a lot of harmful waste material. Nowadays environmental safety requirements necessitate revision of such preparation processes and searching for alternative methods of synthesis. At present, there exist a range of new methods for preparing HPAs, with a so-called peroxide method seeming to be the most generally applicable one. For this reason, the aim of this review is to discuss some recent progress in obtaining aqueous solutions of Keggin and Wells–Dawson Mo-V-P HPAs and their salts. These solutions can be used as individual homogeneous oxidation catalysts, bifunctional catalysts for one-pot acidic and oxidizing transformations, or precursors for preparing their heterogeneous analogues. Preliminary V2O5 activation by addition of hydrogen peroxide H2O2 allows one to obtain vanadium-containing heteropoly acid (HPA) solutions directly from V2O5, MoO3, and H3PO4 without extraneous components. Such a synthetic pathway, named a peroxide route, offers a promising ecological method for preparing valuable Mo-V-P HPAs in short reaction times on a large scale.

Posted on 29 June 2015 | 10:10 am


Dye-Sensitized Solar Cells with Biferrocenyl Antennae Having Quinoxaline Spacers

Four biferrocene-based dyes with quinoxaline spacers possessing functional groups [H (2), Cl (3), NO2 (4) and COOH (5)] were successfully synthesized and characterized by elemental analyses, IR spectroscopy, electronic absorption, 1H NMR and 13C NMR spectroscopy, and mass spectrometry. The synthesized dyes as well as the starting diketenone (1), from which quinoxalines 2–5 were synthesized, were exploited as photosensitizers in TiO2-based dye-sensitized solar cells. The spectral responses of dyes 2–5 were extended into the visible region up to ? = 550 nm. Amongst all the ferrocenyl dyes with a quinoxaline spacer, dyes having Cl (3), NO2 (4), and COOH (5) substituents showed photovoltaic performance that was superior to that of starting material 1 and that of quinoxaline derivative 2. The superior performances of 3, 4, and 5 are probably because of the abilities of these systems to accept high loadings of the dye on the TiO2 surface and the long lifetime of electrons in the TiO2 conduction band. Dye 5 showed better thermal stability than the state-of-art dye N719 and has a comparable lifetime of electrons in the conduction band. Four biferrocenyl quinoxaline derivatives are synthesized and their light-harvesting properties are explored. Dyes having Cl, NO2, and COOH substituents on the spacers show the best photovoltaic performance, and this may be attributed to their ability to accept high loadings of the dye on the TiO2 surface and the long lifetime of electrons in the TiO2 conduction band.

Posted on 29 June 2015 | 10:10 am


High Turnover Catalase Activity of a Mixed-Valence MnIIMnIII Complex with Terminal Carboxylate Donors

The neutral dimanganese(II,III) complex [Mn2(BCPMP)(OAc)2] [1; BCPMP3– = 2,6-bis({(carboxymethyl)[(1-pyridyl)methyl]amino}methyl)-4-methylphenolato] has been synthesized and characterized. The complex contains two terminal carboxylate donors. Complex 1 was found to be an effective catalyst for the disproportionation of H2O2 with high catalytic rate and a turnover number of 7500, the highest turnover reported to date for a catalase mimic. The rates and TON were significantly higher than recorded for a dicationic dimanganese(II,III) counterpart ([Mn2(BPBP)(OAc)2]·(ClO4)2, 2; BPBP– = 2,6-bis{[bis(2-pyridylmethyl)amino]methyl}-4-butylphenolato), which lacks the terminal carboxylate donors, suggesting that introduction of a terminal carboxylate donor improves activity. A well-resolved 16-line pattern obtained upon addition of H2O2 to complex 1 suggests involvement of an MnIIIMnIV species in the catalytic cycle. The neutral dimanganese(II,III) complex [Mn2(BCPMP)(OAc)2] (1) has been synthesized and characterized. Complex 1 was found to be an effective catalyst for the disproportionation of H2O2 with high catalytic rate and a turnover number of 7500, the highest turnover reported to date for a catalase mimic.

Posted on 29 June 2015 | 10:10 am


Azadipyrromethene-Based Near-Infrared Dyes: Effect of Thienylethynyl Substitution at the Distal and Proximal Phenyl Groups

Azadipyrromethene (ADP) ligands substituted with thienylethynyl substituents either at the distal phenyl groups H(CD1) or the proximal phenyl groups H(CD2) were synthesized and characterized. The thienyl groups have a hexyl group at the third position to improve solubility in organic solvents and prevent homocoupling of the ethynylthiophene reactants. To further tune the opto-electronic properties, the substituted ADPs were coordinated with BF2+ and ZnII. Absorption spectroscopy shows that the thienylethynyl substitutions redshift the absorption spectra of the dyes, with a larger shift when the substituents are added on the proximal phenyl groups. Cyclic voltammetry experiments show that the substitutions stabilize the anion and dianion. The reduction potentials for the modified ligands (or zinc chelates) were not affected by the placement of the thienylethynyl groups. Preliminary studies of blends of the new molecules with poly(3-hexylthiophene) (P3HT) suggest that the zinc(II) chelates have potential as electron acceptors for organic solar cells. Azadipyrromethene ligands substituted with thienylethynyl substituents at the distal or proximal phenyl groups were synthesized and coordinated with BF2+ and ZnII. Thienylethynyl substitutions redshift the absorption spectra of the dyes, with a larger shift for proximal substitution. Substitutions also stabilize the anions, and the placement of the thienylethynyl groups do not affect the reduction potentials.

Posted on 25 June 2015 | 1:24 pm


Latest Developments in Metalloenzyme Design and Repurposing

In the past decade, artificial metalloenzymes (AMEs) have emerged as attractive alternatives to more traditional homogeneous catalysts and enzymes. This microreview presents a selection of recent achievements in the design of such hybrid catalysts. These include artificial zinc hydrolases and metathesases, the heme-protein repurposing for C–H, N–H, and S–H insertion reactions, novel light-driven redox hybrid catalysts, novel scaffold proteins, and metallocofactor anchoring techniques and metalloenzyme models. Artificial metalloenzymes (AMEs) combine homogeneous catalysis with enzymatic catalysis. In this microreview the authors describe recent developments in this fascinating field, ranging from artificial zinc hydrolases, metathesases, new heme protein reactions to light-driven redox reactions and enzyme models.

Posted on 18 June 2015 | 12:20 pm


A Computational Comparison of Oxygen Atom Transfer Catalyzed by Dimethyl Sulf­oxide Reductase with Mo and W

A thorough computational study has been performed to investigate oxygen atom transfer (OAT) reactions catalyzed by dimethyl sulfoxide reductase (DMSOR) with a catalytic molybdenum or tungsten ion. Thirteen different density functional theory (DFT) methods have been employed to obtain structural parameters along the reaction pathway, and single-point energies were computed with local correlation coupled-cluster methods [LCCSD(T0)]. For both Mo and W, most DFT methods indicate that the enzyme follows a two-step mechanism with a stable intermediate in which a DMSO molecule coordinates to the metal ion in the +IV oxidation state, and this is also confirmed by the LCCSD(T0) energies. The W-substituted models have a 26–30 kJ/mol lower activation barrier for the OAT reaction, and the reaction is 63–70 kJ/mol more exothermic than that with Mo. Different DFT methods give widely different activation and reaction energies, which roughly depend on the amount of exact exchange in the method; these differences are also reflected in the structures, especially for the rate-limiting transition state. Consequently, there is quite a large variation in energies and various energy corrections (thermal, solvation, dispersion, and relativistic; up to 39 kJ/mol) depending on which DFT method is used to obtain the geometries. Therefore, a mechanism predicted by a single method should be viewed with caution. The dimethyl sulfoxide (DMSO) reductase reaction with Mo and W was studied by using 13 different DFT methods calibrated to accurate LCCSD(T0)/CBS energies. A two-step reaction was found, the second barrier being rate limiting. This barrier is about 28 kJ/mol lower for W than for Mo owing to a ca. 67 kJ/mol more exothermic reaction energy. The experimental activation enthalpy for Mo is reproduced within 5–9 kJ/mol.

Posted on 9 June 2015 | 10:20 am


Synthesis and Characterization of a Dinuclear Copper Complex Bearing a Hydrophobic Cavity as a Model for Copper-Containing Monooxygenases

The synthesis and characterization of a dinuclear copper complex as a model of mononuclear copper-containing monooxygenases [dopamine ?-monooxygenase (D?M), tyramine ?-monooxygenase (T?M), and peptidylglycine ?-hydroxylating monooxygenase (PHM)] are described. This model is based on a cyclophane moiety bearing two bis(picolylamine) ligands for the complexation of two copper atoms and exhibits macroscopic features equivalent to those of the enzymes: (1) the two copper centers are 11.5 Å apart (11 Å for the enzymes) and (2) there is a hydrophobic pocket consisting of a cyclophane moiety in which substrates can bind near the two copper centers. The synthesis and characterization of a dinuclear copper complex as a model of mononuclear Cu-containing monooxygenases are described. This model exhibits features equivalent to those of the enzymes: (1) the two Cu centers are 11.5 Å apart and (2) there is a hydrophobic pocket consisting of a cyclophane moiety in which substrates can bind near the two Cu centers.

Posted on 3 June 2015 | 12:40 pm


Modelling Binuclear Metallobiosites: Insights from Pyrazole-Supported Biomimetic and Bioinspired Complexes

Numerous enzymes use two closely spaced metal ions to activate and transform small molecules. This allows these biocatalysts to perform diverse physiological functions, achieving impressive chemistry under remarkably mild conditions. Model studies of these metalloenzymes contribute to furthering our understanding of the unusual mechanistic aspects and interplay of cooperative effects used by Nature, and help provide clues as to how such reactivity might be harnessed for applications outside of the natural systems. This microreview describes synthetic models of binuclear metalloenzymes, focusing on complexes which are bridged by pyrazole ligand scaffolds. Structural and functional models of iron, nickel, copper and zinc binuclear active sites are discussed, in addition to several cobalt complexes possessing biologically relevant features. Metal separation and secondary-coordination-sphere interactions are recurring themes which aid in highlighting aspects of common importance in the native enzymes. Metalloenzymes with binuclear active sites are widespread in Nature. Synthetic modelling of these active sites has helped to highlight important structural and functional aspects which can dictate reactivity, providing blueprints for the development of new bioinspired catalysts. This microreview focuses on biologically relevant insights provided by complexes of 3,5-disubstitued pyrazole ligands.

Posted on 2 June 2015 | 9:50 am


Too Many Cooks Spoil the Broth – Variable Potencies of Oxidizing Mn Complexes of a Hexadentate Carboxylato Ligand

Given the hexadenticity of the monoanionic ligand in the procatalyst [Mn(tpena)(H2O)](ClO4) {tpena– = N,N,N?-tris(2-pyridylmethyl)ethylenediamine-N?-acetate}, it is perhaps surprising that this complex can catalyze the epoxidation of alkenes. When peracetic acid is used as terminal oxidant, the selectivity and rates of reactions are comparable with those reported for the manganese complexes of the commonly employed neutral tetradentate N4 ligands under analogous conditions. Cyclooctene conversion rates are similar when tert-butyl hydroperoxide (TBHP) is used; however, the selectivity is greatly diminished. In the absence of organic substrates, [MnII(tpena)]+ catalyzes water oxidation by TBHP (initial rate ca. 23 mmol/h when [Mn] = 0.1 mM, at room temp.). To explain the variations in the selectivity of catalytic epoxidations and the observation of competing water oxidation, we propose that several metal-based oxidants (the “cooks”) can be generated from [MnII(tpena)]+. These embody different potencies. The most powerful, and hence least selective, is proposed to be the isobaric isomer of [MnIV2(O)2(tpena)2]2+, namely an oxylic radical complex, [(tpena)MnIII(?2-O)MnIV(O·)(tpena)]2+. The formation of this species depends on the catalyst concentration, and it is favoured when TBHP is used as the terminal oxidant. The generation of the less potent [MnIV(O)(tpena)]+, which we propose as the direct oxidant in epoxidation reactions, is favoured in non-aqueous solutions when peracetic acid is used as the terminal oxidant. A manganese(II) complex of a hexadentate ligand catalyzes epoxidation. However, reaction conditions are critical since several metal-based oxidants with varying potencies can be generated. This observation is probably general for related catalysts, and consequences include decreased selectivity and competing water oxidation.

Posted on 29 April 2015 | 3:10 pm


Regioselective Cleavage of Electron-Rich Double Bonds in Dienes to Carbonyl Compounds with [Fe(OTf)2(mix-BPBP)] and a Combination of H2O2 and NaIO4

A method for the regioselective transformation of dienes to carbonyl compounds has been developed. Electron-rich olefins react selectively to yield valuable aldehydes and ketones. The method is based on the catalyst [Fe(OTf)2(mix-BPBP)] with an oxidant combination of H2O2 (1.0 equiv.) and NaIO4 (1.5 equiv.); it uses mild conditions and short reaction times, and it outperforms other olefin cleavage methodologies. The combination of an Fe-based catalyst, [Fe(OTf)2(mix-BPBP)], and the oxidants H2O2 and NaIO4 can discriminate between electronically different double bonds and oxidatively cleave the electron-rich bond in dienes to yield aldehydes and ketones in a regioselective manner. The reaction requires mild conditions (0–50 °C) and short reaction times (70 min).

Posted on 27 April 2015 | 9:50 pm


Dioxomolybdenum(VI) and -tungsten(VI) Complexes with Multidentate Aminobisphenol Ligands as Catalysts for Olefin Epoxidation

The synthesis of four molybdenum and tungsten complexes bearing tetradentate tripodal amino bisphenolate ligands with either hydroxyethylene (1a) or hydroxyglycolene (1b) substituents is reported. The molybdenum dioxo complexes [MoO2L] (L = 2a, 2b) and tungsten complexes [WO2L] (3a, 3b) were synthesized using [MoO2(acac)2] and [W(eg)3] (eg = 1,2-ethanediolato, ethylene glycolate), respectively, as precursors. All complexes were characterized by spectroscopic means as well as by single-crystal X-ray diffraction analyses. The latter reveal, in all cases, hexacoordinate complexes in which the hydrogen atom of the hydroxy group is involved in hydrogen bonding with one of the metal oxo groups. In the case of the glycol substituent, the ether oxygen atom is coordinated to the metal whereas the hydroxy group remains uncoordinated. The complexes were tested as catalysts in the epoxidation of cyclooctene under eco-friendly conditions, using an aqueous solution of H2O2 as the oxidant and dimethyl carbonate (DMC) as solvent or neat conditions, as substitutes for chlorinated solvents. Molybdenum complexes 2a and 2b showed good catalytic activity using H2O2 without added solvent, and tungsten complexes 3a and 3b showed very high activity in the epoxidation of cyclooctene using H2O2 and DMC as solvents. Four new molybdenum and tungsten complexes bearing tetradentate tripodal amino bisphenolate ligands with either hydroxyethylene or hydroxyglycolene substituents were synthesized and found to catalyze olefin epoxidation reactions under eco-friendly conditions.

Posted on 27 April 2015 | 9:50 pm


Synthesis, Structure and Redox Properties of Asymmetric (Cyclopentadienyl)(ene-1,2-dithiolate)cobalt(III) Complexes Containing Phenyl, Pyridyl and Pyrazinyl Units

The compounds [(?5-C5H5)Co{SC(H)CRS}] [R = phenyl (1), pyridin-3-yl (2) or pyrazin-2-yl (3)] have been synthesized and characterized by elemental analysis, 1H NMR, mass spectrometry and X-ray crystallography. The variation in the UV/Vis and redox properties of these compounds alone and upon acidification has been investigated. In CH2Cl2 solution each compound undergoes a reversible one-electron reduction, and the EPR spectrum of each monoanion has been recorded. In the presence of a 5:1 excess of trifluoroacetic acid the one-electron reduction of both 2 and 3 occurs at a less negative potential. The information obtained has been interpreted with the aid of DFT calculations for [1]y, [2]y and [3]y (y = 0 or –1) and the monoprotonated forms [2H]z and [3H]z (z = +1 or 0), and this has provided insight into the nature of the redox-active orbitals in these complexes. The HOMOs and LUMOs of these species are delocalized and each involves contributions from cobalt, ene-1,2-dithiolate and R orbitals. The information from the experimental and theoretical investigations is used to suggest that, for the pyran ring-opened form of the molybdenum cofactor of oxygen-atom-transfer enzymes, the pterin may participate in the redox reactions involved in the catalytic cycle. Structural, electrochemical, spectroscopic and theoretical studies of [(?5-C5H5)Co(dithiolene)] complexes suggest that the pyran ring-opened form of the molybdenum cofactor of Mo- and W-containing oxygen-atom-transfer enzymes may participate in the redox reactions involved in the catalytic cycle.

Posted on 22 April 2015 | 12:50 pm


Viral Nanotemplates Armed with Oxygenic Polyoxometalates for Hydrogen Peroxide Detoxification

Layer-by-layer (LbL) assembly strategies were exploited to decorate wild-type TMV (tobacco mosaic virus) 1D nanoscaffolds with a totally inorganic, multiredox, tetraruthenate complex belonging to the class of polyoxometalate catalysts. The hybrid capsids give rise to an entangled network of fibrils and ribbon-like nanoassemblies, whose functional activity was probed towards H2O2 dismutation in neutral water. Combined solid-state and surface characterization evidence, including Z-potential, electronic microscopy, thermogravimetry and XPS, delineate a favorable tunability of the nanohybrid material as a function of the added cationic binder. A polyoxometalate with oxygenic activity was anchored on the TMV (tobacco mosaic virus). The rod-like biogenic template enables the formation of catalytic nanoarrays for H2O2 dismutation.

Posted on 22 April 2015 | 12:40 pm


Mechanistic Links in the in-situ Formation of Dinuclear Manganese Catalysts, H2O2 Disproportionation, and Alkene Oxidation

The oxidation of substrates, such as alkenes, with H2O2 and the catalyst [MnIV2(?-O)3(tmtacn)2]2+ (1; tmtacn = 1,4,7-trimethyl-1,4,7-triazacyclononane) is promoted by the addition of carboxylic acids through the in situ formation of bis(carboxylato) complexes of the type [MnIII2(?-O)(?-RCO2)2(tmtacn)2]2+. The conversion of 1 to these complexes requires a complex series of redox reactions coupled with the overall exchange of ?-oxido ligands for ?-carboxylato ligands. Here, we show that the mechanism by which this conversion occurs holds implications with regard to the species that is directly engaged in the catalytic oxidation of alkenes. Through a combination of UV/Vis absorption, Raman, resonance Raman and electron paramagnetic resonance (EPR) spectroscopy, it is shown that the conversion proceeds by an autocatalytic mechanism and that the species that engages in the oxidation of organic substrates also catalyses H2O2 decomposition, and the former process is faster. The in situ formation of catalytically active species through the reduction of a precatalyst, H2O2 disproportionation and alkene oxidation are linked to a common active species.

Posted on 21 April 2015 | 12:20 pm


A Bioinspired System for Light-Driven Water Oxidation with a Porphyrin Sensitizer and a Tetrametallic Molecular Catalyst

Inspired by natural photosynthesis, the aim of light-driven water splitting is to produce renewable fuels by exploiting solar radiation. Sustained hydrogen production is desirable in such systems, and the oxidation of water to oxygen is currently recognized as the bottleneck of the entire process. Therefore, solutions for this difficult task retain a fundamental interest. In this paper, we present a bioinspired, three-component system for water oxidation that comprises a tetracationic porphyrin ZnII complex as the photosensitizer, a tetraruthenium water-oxidation catalyst, and sodium persulfate as the electron acceptor. An in-depth photophysical study reveals the photogeneration of a pentacation radical of the porphyrin (quantum yield up to ? = 1.01) upon oxidative quenching of the triplet excited state by persulfate. Electron transfer from the water-oxidation catalyst to the pentacation radical (hole scavenging) is slow (bimolecular rate constant, k?<?4?×?107 M–1?s–1), and this is likely the main reason for the low efficiency of the system in photocatalytic tests for water oxidation. Perspectives for improvements of the system and for the development of a light-activated device for water splitting are discussed. The photoinduced events and the light-driven water-oxidation ability of a bioinspired, three-component catalyst/photosensitizer/acceptor molecular system are investigated.

Posted on 8 April 2015 | 12:30 pm


Controlling the Activities of the Diiron Centre in Bacterial Monooxygenases: Lessons from Mutagenesis and Biodiversity

The soluble diiron monooxygenases (SDIMOs) are a diverse group of bacterial enzymes that possess a deeply buried binuclear iron centre that forms an oxo-diferryl (FeIV) intermediate that is capable of oxygenating a wide range of unfunctionalised hydrocarbons and other hydrophobic organic molecules, ranging in size from methane to diaromatics such as naphthalene and substituted biphenyls. In the environment, these enzymes are important in bioremediation of hydrocarbons and chlorinated hydrocarbons and in mitigation of the greenhouse effect due to methane, and also have numerous potential applications in synthetic organic chemistry. In this review we consider how both natural variations among the enzymes and an increasing body of evidence from mutagenesis studies cast light on how the protein controls the size of substrates that can access the active site, the precision of regio- and stereoselectivity and the oxidising power of the active centre. The soluble diiron monooxygenases (SDIMOs) are a diverse group of enzymes that use a diiron active centre to add oxygen to a wide range of organic molecules. Here we review how natural biodiversity and laboratory mutagenesis studies have revealed how the protein scaffold of SDIMOs controls the activity of the enzymes and the presentation of substrates to the diiron site.

Posted on 2 April 2015 | 2:20 pm


Electronic Fine-Tuning of Oxygen Atom Transfer Reactivity of cis-Dioxomolybdenum(VI) Complexes with Thiosemicarbazone Ligands

A series of six cis-dioxomolybdenum(VI) complexes with thiosemicarbazone ligands was synthesized and characterized. The ligands were obtained by reacting ethyl thiosemicarbazide with salicylaldehydes substituted with a selection of electron-withdrawing and electron-donating groups. The crystal structures, IR, NMR spectroscopic data and oxygen atom transfer activities of the complexes revealed that the electronic effects of the substituents located in the para-position of the phenolate donor are transmitted through to the molybdenum center, as reflected by linear relationships between Hammett constants and key properties of the complexes, including the molybdenum–phenolate bond lengths and the coordination shift of the imine proton resonance. Compared with the unsubstituted catalyst, electron-withdrawing substituents increase the rate of oxygen atom transfer from dimethyl sulfoxide to triphenylphosphine, whereas electron-donating groups have the opposite effect. The highest rate enhancement was achieved through the introduction of a strongly electron-withdrawing NO2 substituent in the p-position of the phenolate donor. Thiosemicarbazone ligands (H2LR) derived from para-substituted salicylaldehydes allow the electronic properties and catalytic activities of cis-dioxo MoVI complexes of composition [MoO2(LR)MeOH] to be fine-tuned by electron-donating or electron-withdrawing groups R.

Posted on 2 April 2015 | 2:20 pm


Catalytic Models of Tyrosinase: Reactivity Differences between Systems Based on Mono- and Binucleating Ligands

A new tyrosinase model based on the binucleating ligand Lpy2 is synthesized and characterized. The ligand Lpy2 contains a combination of an imine and a pyridine function in the sidearms, which are bridged by a flexible alkyl spacer. As shown by UV/Vis and NMR spectroscopy, the Cu2Lpy2 complex catalyzed the conversion of the monophenol 2,4-di-tert-butylphenol (DTBP-H) into the o-quinone 3,5-di-tert-butylquinone (DTBQ) with a turnover number (TON) of 18. The dicopper complex of Lpy2 thus shows monophenolase activity that is comparable to that of the recently developed Lpy1 model of tyrosinase, which is based on a known mononucleating ligand (M. Rolff, J. Schottenheim, G. Peters, F. Tuczek, Angew. Chem. Int. Ed. 2010, 122, 6583). The electron-poor substrate 4-hydroxybenzoic acid methyl ester (MeBA-OH), in contrast, is converted by Cu2Lpy2 into the semiquinone. For both substrates, the oxygenation reactions were also conducted in a stoichiometric fashion to obtain information on the intermediates involved. For the substrate MeBA-OH, we detected a binuclear ?-catecholato copper(II) complex by high-resolution ESI mass spectrometry. These studies were complemented by investigations of deactivation mechanisms that could be invoked to explain the limitation of the TON. To this end, a bis-?-hydroxido Lpy2 dicopper(II) complex as well as a semiquinone Lpy2 complex were prepared. Both complexes may represent decay products of the catalyst. A tyrosinase model based on the binucleating ligand Lpy2 was developed and characterized. The ligand Lpy2 contains a combination of an imine and a pyridine function in the sidearms that are bridged by a flexible alkyl spacer. The Cu2Lpy2 complex catalyzes the conversion of monophenol DTBP-H into the o-quinone DTBQ (TON = 18). An electron-poor substrate is converted into the semiquinone.

Posted on 2 April 2015 | 2:20 pm


The Electrically Wired Molybdenum Domain of Human Sulfite Oxidase is Bioelectrocatalytically Active

We report electron transfer between the catalytic molybdenum cofactor (Moco) domain of human sulfite oxidase (hSO) and electrodes through a poly(vinylpyridine)-bound [osmium(N,N?-methyl-2,2?-biimidazole)3]2+/3+ complex as the electron-transfer mediator. The biocatalyst was immobilized in this low-potential redox polymer on a carbon electrode. Upon the addition of sulfite to the immobilized separate Moco domain, the generation of a significant catalytic current demonstrated that the catalytic center is effectively wired and active. The bioelectrocatalytic current of the wired separate catalytic domain reached 25?% of the signal of the wired full molybdoheme enzyme hSO, in which the heme b5 is involved in the electron-transfer pathway. This is the first report on a catalytically active wired molybdenum cofactor domain. The formal potential of this electrochemical mediator is between the potentials of the two cofactors of hSO, and as hSO can occupy several conformations in the polymer matrix, it is imaginable that electron transfer from the catalytic site to the electrode through the osmium center occurs for the hSO molecules in which the Moco domain is sufficiently accessible. The observation of catalytic oxidation currents at low potentials is favorable for applications in bioelectronic devices. Human sulfite oxidase and its catalytic molybdenum-cofactor-containing domain were wired to an electrode with poly(vinylpyridine)–[osmium(N,N?-methyl-2,2?-biimidazole)3]2+/3+, which mediated the electron transfer between either of the enzyme cofactors and the electrode, as demonstrated by electrocatalytic turnover currents.

Posted on 31 March 2015 | 10:10 am


Thymol Bromination – A Comparison between Enzymatic and Chemical Catalysis

The catalytic activity of the vanadium-dependent bromoperoxidase isolated from the brown alga Ascophyllum nodosum is compared with the activity of a cheap, commercially available V-catalyst precursor in the bromination of thymol. Organic solvents have been avoided to make the system appealing from a sustainable chemistry point of view. It is noteworthy that, notwithstanding the low solubility of the substrate, the thymol bromination reactions were performed in water, with a safe brominating source, under mild conditions, and with relatively inexpensive reagents. In this regard, the greenness of the systems was evaluated by the estimation of the E-factor value; the result is that the chemical reaction has a lower environmental impact than the enzymatic process, with an E-factor in the range of eco-friendly processes. Catalysis of thymol bromination by vanadium derivatives is directly compared to catalysis by a V-dependent bromoperoxidase. All reactions were performed under mild and sustainable conditions with relatively inexpensive reagents. Appealing results were obtained in terms of selectivity and sustainability.

Posted on 20 March 2015 | 12:10 pm


Synthesis, Characterization, and Stereoselective Oxidations of the Dinuclear Copper(II) Complex Derived from a Chiral Diamino-m-xylenetetra(benzimidazole) Ligand

Recent advances in dinuclear copper complexes as mimics of the catalytic centers of tyrosinase and catechol oxidase allowed the reproduction of the structural and mechanistic aspects of the enzymes. However, a challenging objective is the development of chiral complexes for bioinspired enantioselective oxidation reactions. Here, we report the synthesis and characterization of a dinuclear copper(II) complex with a new chiral diamino-m-xylenetetra(benzimidazole) ligand (L55Bu4), which has chiral centers at the four 2-methylbutyl substituents of the benzimidazole rings. The spectral characteristics, ligand binding properties, and reactivity of [CuII2L55Bu4]4+ in the catalytic oxidations of several biogenic catechols (L-/D-dopa, L-/D-DopaOMe, and L-/D-norepinephrine) and thioanisole are reported. The best discriminating properties are displayed towards the DopaOMe derivatives, for which the oxidation rate of the L enantiomer is approximately one order of magnitude larger than that of the opposite D isomer. A dinuclear copper(II) complex derived from a chiral hexadentate nitrogen ligand is reported as a new catalyst for asymmetric oxidations. For biogenic catechols as model substrates, the best enantioselectivity is obtained in the oxidation of the methyl esters of L-/D-Dopa, for which 70?%?ee is obtained in favor of the L enantiomer.

Posted on 9 March 2015 | 12:10 pm


Mononuclear Iron(III) Complexes as Functional Models of Catechol Oxidases and Catalases

Mononuclear amino triphenolate iron(III) complexes have been synthesized and characterized (UV/Vis spectroscopy, cyclic voltammetry, ESI-MS, 1H NMR spectroscopy, X-ray diffraction). These complexes act as biomimetic catalysts promoting the aerobic auto-oxidation of 3,5-di-tert-butylcatechol to the corresponding o-benzoquinone at room temperature and displaying catalase activity for the hydrogen peroxide dismutation with remarkable activity (TON up to 4000). Amino triphenolate iron(III) complexes promote effectively, at room temperature, the aerobic auto-oxidation of 3,5-di-tert-buthylcatechol to the corresponding o-benzoquinone (oxidase mimicking) and hydrogen peroxide dismutation (catalase mimicking).

Posted on 16 February 2015 | 4:50 pm





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