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Theoretical Chemistry Accounts

Current research reports and chronological list of recent articles..




TCA publishes papers in all fields of theoretical chemistry, computational chemistry, and modeling. Fundamental studies as well as applications are included in the scope.

The publisher is Springer. The copyright and publishing rights of specialized products listed below are in this publishing house. This is also responsible for the content shown.

To search this web page for specific words type "Ctrl" + "F" on your keyboard (Command + "F" on a Mac). Then: type the word you are searching for in the window that pops up!

Additional research articles see Current Chemistry Research Articles. Magazines with similar content (theoretical chemistry):

 - International Journal of Quantum Chemistry,

 - Journal of Mathematical Chemistry.



Theoretical Chemistry Accounts - Abstracts



Theoretical studies of $${{\mathrm{{CN} + {H}}_{2}({\mathrm{D}}_{2})}}$$ CN + H 2 ( D 2 ) reactions: competition between H(D)-abstractions in $${\mathrm{H(D) + HCN(DCN)/HNC(DNC)}} $$ H ( D ) + HCN ( DCN ) / HNC ( DNC ) channels

Abstract

The \(\hbox {CN} + \hbox {H}_{2}\) reaction was investigated by considering the two possible channels, \(\hbox {H} + \hbox {HCN}\) and \(\hbox {H} + \hbox {HNC}\) , taking into account the isotopic effects and with the vibrationally excited states. The frequencies and structures for all species of the \(\hbox {CN} + \hbox {H}_{2}/\hbox {D}_{2}\) reaction were calculated using G3 method for further kinetics calculation. The thermal rate constants were calculated using the conventional transition-state theory (TST) and canonical variational transition-state theory (CVT) by APUAMA code, over the temperature range from 200 to 4000 K. In addition, rate coefficients for vibrationally excited reactants CN (v = 1) or \(\hbox {H}_{2}\) (v = 1) or \(\hbox {D}_{2}\) (v = 1) are presented. The branching ratio for the partitioning into H/D + HCN/DCN or H/D + HNC/DNC has, also, been determined. The results showed that the \(\hbox {CN} (v=0) + \hbox {H}_{2} (v=0) \rightarrow \hbox {H} + \hbox {HCN} \) channel is dominant at all range of temperature, while \(\hbox {CN } (v=1) + \hbox {H}_{2} (v=0) \rightarrow \hbox {H} + \hbox {HNC}\) channel is dominant at T \(\ge \) 1900 K. The isotopic effects are the same behavior that \(\hbox {CN}(v=0,1) + \hbox {H}_{2}(v=0,1) \rightarrow \hbox {H} + \hbox {HCN/HNC}\) reactions. Reasonable agreement was found between the experimental results and the rate constants predicted by conventional transition-state theory, with tunneling correction, using the theoretical transition-state properties.


Datum: 19.06.2019


Understanding structure of small $${\hbox {TiO}}_2$$ TiO 2 nanoparticles and adsorption mechanisms of PbS quantum dots for solid-state applications: a combined theoretical and experimental study

Abstract

A combined theoretical and experimental study on a series of \({\hbox {TiO}}_{2}\) , lead sulfide (PbS) and PbS@TiO \(_{2}\) nanocomposites was performed. \({\hbox {TiO}}_{2}\) structures were stabilized with simulated annealing using molecular dynamics at the ReaxFF level. A density functional theory study elucidated relevant electronic structure properties. We performed the study for a series of \({\hbox {TiO}}_2\) ) \(_{n}\) , where \(n =18\) , 28, 38, 76 and 114. Band gaps ranging from 1.2 to 2.2 eV were found. This range was attributed to the size of the \({\hbox {TiO}}_2\) cluster models used in the calculations, and some models became metallic at smaller sizes. We synthesized \({\hbox {TiO}}_2\) nanoparticles of anatase (101) facet, which were characterized with pair distribution functions, in excellent agreement with the theoretical results. We explored the possibility to anchor a PbS quantum dot with a \({\hbox {TiO}}_2\) model system. This intermolecular interaction was relevant, since the composite material could be used in solid-state devices' applications, in which stability in the formation of the \({\hbox {PbS}}/{\hbox {TiO}}_{2}\) interface plays an important role for the device performance. The possibility to form a PbS@TiO \(_{2}\) composite material was evidenced, via a covalent interaction, with contributions of the van der Waals type.


Datum: 14.06.2019


Theoretical investigation on the structures, electronic and magnetic properties of new 2D/1D composite nanosystems by adsorbing superhalogen MnCl 3 on the BN monolayer/nanoribbons

Abstract

Hexagonal boron nitride (h-BN), an inorganic analogue of graphene, possesses the remarkable physical and chemical properties and can be viewed as the powerful building block to construct novel composite nanomaterials. In this study, based on the first-principles calculations, we design a new class of hybrid nanosystems by depositing superhalogen MnCl3 on the surface of low-dimensional BN monolayer or nanoribbons (BNML/BNNRs). The large adsorption energies indicate that the MnCl3 can be stably adsorbed on the surface of the BN materials. Regardless of dimension, chirality, ribbon width as well as the adsorption site and coverage of MnCl3, adsorbing MnCl3 can endow these hybrid BN nanomaterials with a large magnetic moment and significantly reduce the robust wide band gap of BN materials to the range of 0.098–0.948 eV. Overall, these new MnCl3–BN composite nanostructures can display the large magnetism and an appropriate band gap, which is very promising to make them an application in the field of multifunctional nanodevices and magnetic materials in the near future.


Datum: 13.06.2019


The mechanism of electrophilic addition of singlet oxygen to pyrrolic ring

Abstract

Pyrrolic compounds assume an important role in the chemistry of living organisms, coal surrogates and novel drugs. However, literature reports a few studies on their reactivity towards prominent oxidising agents. This contribution presents a comprehensive mechanistic study of the oxidation of unsubstituted pyrrole with singlet oxygen (O21g) by deploying a quantum chemical framework leading to the production of succinimide, as the major products, through a Diels–Alder addition of O21g to the aromatic ring. Other products such as maleimide, hydroperoxide, formamide and epoxide adducts appear to form via insignificant channels. The primary Diels–Alder channel encompasses a barrier of 41 kJ/mol with a fitted rate constant of k(T) = 1.87 × 10−13 exp(− 48,000/RT) cm3 mol−1 s−1. Furthermore, a kinetic study has been undertaken to investigate the influence of substituents on reaction rate of the Diels–Alder addition of singlet oxygen to a pyrrolic ring. The results clarify that electropositive substituents such as BeH and BH2 operate as π-acceptors and thus deactivate the ring towards electrophilic attack of singlet oxygen. However, substituents comprising of strong π-donors, e.g., NH2 and OH, destabilise the ring structure, increasing its oxidation reactivity.


Datum: 11.06.2019


Performance of the NOF-MP2 method in hydrogen abstraction reactions

Abstract

The recently proposed natural orbital functional second-order Møller–Plesset (NOF-MP2) method is capable of achieving both dynamic and static correlations even for those systems with a significant multiconfigurational character. We test its reliability to describe the electron correlation in radical formation reactions, namely in the homolytic X–H bond cleavage of LiH, BH, \({\hbox {CH}}_{4}, {\hbox {NH}}_{3}, {\hbox {H}}_{2}{\hbox {O}}\) and HF molecules. Our results are compared with CASSCF and CASPT2 wavefunction calculations and the experimental data. For a dataset of 20 organic molecules, the thermodynamics of C–H homolytic bond cleavage, in which the C–H bond is broken in the presence of different chemical environments, is presented. The radical stabilization energies obtained for such general dataset are compared with the experimental data. It is observed that NOF-MP2 is able to give a quantitative agreement for dissociation energies, with a performance comparable to that of the accurate CASPT2 method.


Datum: 10.06.2019


Electronic structure and adsorption geometry of Pt and Pd metal complexes with 1,3-dithiole-2-thione-4,5-dithiolate ligand on TiO 2 (101) surface from first-principles calculations

Abstract

Metal complexes based on 1,3-dithiole-2-thione-4,5-dithiolate (dmit) ligand have been intensively studied for more than 40 years due to their unusual chemical and physical properties. Besides, the highly delocalized frontier orbitals, that allow direct electron transfer through the ligand π orbitals, make these class of complexes promising candidates for photochemical devices as well as sensitizer for dye-sensitized solar cells. In this work, we investigated the electronic and geometric properties of Pd and Pt (CH3)2[M(dmit)2] complexes isolated on TiO2(101) surface by means of first-principles calculations using plane-wave basis sets and DFT calculation. Adsorption energies of metal complexes supported on a TiO2(101) surface are calculated for three different configurations, linked by the sulfur atom of Sthione, Sthiole–Sthiolate, and planar. The studies found that the most stable adsorption molecular configuration mode for the palladium(II) and platinum(II) complexes is the planar mode. TD-DFT molecular calculations revealed that the lowest energy transition in the ultraviolet visible near-infrared range mainly corresponds to the HOMO–LUMO excitation for the (CH3)2[M(dmit)2] complexes. Theoretical calculations of optical absorption spectra of (CH3)2[M(dmit)2] complexes adsorbed on the anatase (101) surface show that the interaction induces a slightly redshift of electronic absorption bands. Density of states for the metal complexes/TiO2(101) system revealed that the LUMO of the metal complexes lies at below the edge of the TiO2 conduction band. The adsorption of the (CH3)2[Pd(dmit)2] complex on the anatase (101) surface results in the emergence of new transitions below 1 eV that can be ascribed to the presence of a favorable overlap between the LUMO of the complex and the conduction band of the TiO2 semiconductor.


Datum: 08.06.2019


Photophysical properties of bichromophoric Fe(II) complexes bearing an aromatic electron acceptor

Abstract

The replacement of heavy metals used by industry to produce optical devices would considerably reduce the environmental and economic cost of man-made technology. A possible strategy relies on the employment of lighter and more abundant metals like iron. The exploitability of the photophysics of Fe(II) complexes is, however, generally limited by their short excited-state lifetimes and poor emission properties. The present work studies the impact of appending an electron acceptor (anthracene) to N-heterocyclic carbene (NHC) iron complexes with the aim to trap the excited-state energy and, therefore, delay the excited-state decay of the considered iron compounds. Hence, the photophysical properties of six prototypes (built with different spacers between the NHC ligand and the anthracene moieties) have been studied by using time-dependent density functional theory and by determining the natural transition orbitals of the excited states. The computational results suggest that ethynyl bridges induce dual absorption properties, covering red and infrared wavelengths in addition to the violet–blue absorption of the metal-to-ligand charge transfer band, already reported for the parent compound. The nature of the lowest lying triplet states indicates that, for all the considered prototypes, the excitation involves π* orbitals localized over anthracene, confirming its electron acceptor capabilities and suggesting a possible equilibrium between different excited states that might lead to enhanced excited-state lifetimes and/or boosted luminescence properties.


Datum: 06.06.2019


A density functional theory study on the [3 + 2] cycloaddition of N -( p -methylphenacyl)benzothiazolium ylide and 1-nitro-2-( p -methoxyphenyl) ethene: the formation of two diastereomeric adducts via two different mechanisms

Abstract

The [3 + 2] cycloaddition reaction of N-(p-methylphenacyl)benzothiazolium ylide (NBY) and 1-nitro-2-(p-methoxyphenyl) ethane (NME), experimentally investigated by Yan et al., was studied theoretically. They reported that the reaction proceeds via a stepwise mechanism and produces two diastereomeric adducts in a 4:1 ratio. For the study of the reaction, two regioselective attacks were considered between the reagents and their theoretical parameters were calculated. In excellent agreement with the experimental outcomes, the Fukui and Parr functions reactivity indices analysis as well as the energetic results indicated that among the two studied regioselective attacks, one which leads to the formation of two experimentally reported adducts, is more favorable than the other. The molecular mechanism of the studied reactions was characterized using the IRC, QTAIM and Wiberg bond indices analyses and the results suggested that two diastereomeric adducts are generated via two different mechanisms. The major adduct is produced via a two-stage one-step mechanism without the formation of any stable intermediate, whereas the minor one is generated through a stepwise mechanism along with the formation of a stable zwitterionic intermediate. The analysis of global electron density transfer showed that the reactions are polar and electron density fluxes from NBY toward NME. It was found from molecular electrostatic potential map that at the more favorable transition state, approach of reactants locates the oppositely charged regions over each other resulting in attractive forces between the two fragments. Analysis of the frontier molecular orbitals indicated that the HOMO orbital of NBY is also a frontier effective-for-reaction molecular orbital.


Datum: 06.06.2019


Molecular insights into the carbon dioxide–carboxylate anion interactions and implications for carbon capture

Abstract

In this work, we analyze the interaction of carbon dioxide with different carboxylate anion derivatives in the gas phase at the ab initio CCSD(T)//MP2 level using the aug-cc-pVTZ basis set. The systems considered here include the formate, acetate, propionate, bicarbonate, carbamate and glycinate anions. The study is relevant to get a better understanding of the interactions involved in novel carbon capture processes through either ionic liquids or amino acid salts. We describe the formation of covalent and non-covalent adducts and show that the formation energies are significantly larger than those previously reported for amines, which are used in conventional carbon capture processes. The nature of the interactions is analyzed using the natural bond orbitals methodology. The binding energy in the non-covalent processes does not depend much on the derivative, but covalent adducts display a rough correlation with nucleophilic/electrophilic indices provided distortion effects on the monomers are taken into account. In the case of glycinate, interactions with the amino and carboxylic moieties involve comparable energetics and the existence of several minima in the potential energy surface might be a factor contributing to the good CO2 capture capacity exhibited by this species in recent experimental studies.


Datum: 06.06.2019


Structures and relative stabilities of Na + Ne n ( n  = 1–16) clusters via pairwise and DFT calculations

Abstract

The structural properties and relative stabilities of the Na+Nen clusters, with n = 1–16, have been investigated by using pairwise and density functional theory (DFT) methods. The DFT calculations have been carried out using the M06-2X functional combined with the augmented aug-cc-pVTZ basis sets. For both methods, the high stability is obtained for Na+Ne12 cluster with an icosahedral structure, and the twelve Ne atoms complete the first solvation shell around the Na+ cation. Therefore, the icosahedral Na+Ne12 structure will be considered as the core for the larger sizes. The relative stabilities have been studied in terms of the binding energies, second-order difference of energies, fragmentation energies and HOMO–LUMO energy gaps. The Na–Ne interactions within the Na+Nen clusters in relation to the relative stabilities have been discussed through topological atom-in-molecules and reduced density gradient analyses. Finally, the relative stabilities of the Na+Nen clusters have been discussed topologically.


Datum: 05.06.2019


Ab initio investigation of cationic water cluster (H 2 O) 13 + via particle swarm optimization algorithm

Abstract

The configurations of cationic water cluster (H2O) 13+ have been explored through the particle swarm optimization algorithm conjunct with computational quantum chemistry approaches. Geometry optimization and vibrational analysis for the 15 possible low-lying clusters were calculated at the MPW1K/6–31++G** level as well as infrared spectrum calculation. Through various hybrid exchange–correlation functionals of density functional theory in combination with zero-point vibrational energies correction, we can definitely get the relative stable configurations and discuss the effect on the relative energy order of these clusters caused by different functionals in detail. Given the effect of temperature, it is found that as the temperature rises, the configuration with irregular shape will become more stable. By analyzing the infrared spectra, the structure and vibration analysis of these clusters are studied in detail. Based on topological analysis, we study the relationship between structural characteristics and the bonding strengths, and analyze the strength of hydrogen bonding at the bond critical points.


Datum: 01.06.2019


Unexpected molecular mechanism of trimethylsilyl bromide elimination from 2-(trimethylsilyloxy)-3-bromo-3-methyl-isoxazolidines

Abstract

The molecular mechanism of elimination of the trimethylsilyl bromide (2) from 2-(trimethylsilyloxy)-3-bromo-3-methyl-isoxazolidines (1a–d) has been analyzed within the molecular electron density theory using density functional theory calculations at the M06-2X(PCM)/6-31+G(d) computational level. These elimination reactions take place via a two-step mechanism involving an intermediate. Bonding evolution theory analysis allows to set apart seven phases along the reaction path. Elimination of trimethylsilyl bromide starts with rupture of the C1–Br2 bond of 2-(trimethylsilyloxy)-3-bromo-3-methyl-isoxazolidine (1a). Thereafter, we observed the formation of the N5–C1 double bond and the last step of this elimination is associated with formation of a new Br2–Si3 bond and breaking of the Si3–O4 bond.


Datum: 31.05.2019


A partition function for atoms and bonds in molecules

Abstract

A new weight function is proposed to work with the atoms and bonds in molecules theory. The molecular radial electron density ( \(\rho _{\mathrm{rad}}{({\mathbf {r}} )}\) ) and bond electron density ( \(\rho ^{A-B}{({\mathbf {r}} )}\) ) are visually illustrated using the proposed weight. The molecular properties including the total number of electrons, the electron–nuclear potential energy, and Coulomb potential energy are calculated numerically using the proposed weight. The computed molecular properties using the proposed weight are compared to those obtained using the Becke weight and as well with molecular properties calculated analytically. Our findings show that the proposed weight gives better bonding-region representations for both \(\rho _{\mathrm{rad}}{({\mathbf {r}} )}\) and \(\rho ^{A-B}{({\mathbf {r}} )}\) than those obtained using the Becke weight. In addition, the proposed weight performs equally well or better than the Becke weight at numerical integration of molecular properties.


Datum: 31.05.2019


The density response kernel, the Fukui function, and other response functions from the Kohn–Sham orbitals

Abstract

A novel approach to the response theory for the Kohn–Sham formalism is presented, and it shows that the linear responses of the electron density to changes in the number of electrons and in the external potential connected and they can be computed simultaneously. This procedure also applies to other quantities related to the density response kernel, such as the Hessian matrix, the dipole polarizability, and the perturbed density. Expressions for the directional Fukui functions go beyond the frontier orbital approximation, showing differential relaxation effects for electron-releasing and electron-withdrawing processes. Even for the simplest approximation, when only the frontier orbitals are included in the sum-over-states, the relaxation effects are different in each direction.


Datum: 28.05.2019


Computational prediction of bioactivity scores and chemical reactivity properties of the Parasin I therapeutic peptide of marine origin through the calculation of global and local conceptual DFT descriptors

Abstract

Eight density functionals, CAM-B3LYP, \(\hbox {LC-}\omega \hbox {PBE}\) , M11, MN12SX, N12SX, \(\omega \hbox {B97}\) , \(\omega \hbox {B97X}\) , and \(\omega \hbox {B97XD}\) , related to the Def2TZVP basis sets, were assessed together with the SMD solvation model for the calculation of the molecular properties and structure of the therapeutic peptide of marine origin Parasin I. All the chemical reactivity descriptors for the system are calculated via conceptual density functional theory (CDFT). The active sites suitable for nucleophilic, electrophilic, and radical attacks are selected by linking them with the Fukui function indices, nucleophilic and electrophilic Parr functions, and condensed dual descriptor \(\Delta {f(r)}\) , respectively. The study reveals that the MN12SX and N12SX density functionals are the most appropriate ones for predicting the chemical reactivity of the molecule under study. Additionally, the pKa value for the peptide is predicted with great accuracy based on our previously published methodology. Moreover, the ability of the studied molecule in acting as an efficient inhibitor of the formation of advanced glycation endproducts (AGEs), which constitutes a useful knowledge for the development of drugs for fighting diabetes, Alzheimer and Parkinson diseases is also presented. Finally, the bioactivity scores for Parasin I are predicted through different methodologies.


Datum: 28.05.2019


Prediction of aqueous solubility by treatment of COSMO-RS data with empirical solubility equations: the roles of global orbital cut-off and COSMO solvent radius

Abstract

Aqueous solubility values of (E)-2-(ethyl(4-((4-nitrophenyl)diazenyl)phenol)amino)ethanol [B1], (E)-2,2′-((4-((4-nitrophenyl)diazenyl)phenyl)azanediyl)diethanol [B2], (E)-2,2′-((3-methyl-4-((4-nitrophenyl)diazenyl)phenyl)azanediyl)diethanol [B3] and (E)-2-((4-((2,4-dinitrophenyl)diazenyl)phenyl)(ethyl)amino)ethanol [B4] were predicted by the treatment of relevant COSMO-RS data with Cramer et al. solubility equation (CSE) and general solubility equation (GSE). DMol3 computational code was employed for the study, where all calculations were carried out using VWN-BP level of theory with double numerical basis set containing polarization functions (DNP). Effects of global orbital cut-off and COSMO solvent radius (CSR) on the predicted results were examined. The results revealed that COSMO-RS data performed very well with both the CSE and GSE, but the latter exhibited a greater prediction strength on average. For nearly all the studied molecules, GSE calculated solubility (SGSE) was found to increase with orbital cut-off and reached an optimum value at a cut-off of 5.5 Å. SGSE values obtained at this and higher cut-off values studied are comparable to experimental solubility values, especially for B1, B3 and B4, while better results were obtained for B2 at lower cut-off values. CSE calculated solubility (SCSE) showed no constant trend with cut-off variation, but at cut-off values ≥ 7.0 Å the SCSE values compare well with the experimental values, especially in the cases of B2 and B3. For all the studied molecules, SGSE decreased with the increase in CSR and the most reliable CSR value for GSE was found to be 1.3 Å. On the contrary, SCSE increased with CSR and for B1 and B4, this increase was followed by a drop in predicted values at CSR > 1.3 Å. However, the best CSR value for CSE was found to be 0.5 Å for almost all the molecules. Our findings have shown that aqueous solubility (in mol/L) of azo dyes can be accurately predicted using CSE or GSE with some COSMO-RS data and that global orbital cut and COSMO solvent radius are essential parameters for accurate prediction.


Datum: 28.05.2019


A theoretical research on intersystem crossing, radiative and nonradiative rates of cyclometalated platinum(II) complexes

Abstract

A series of cyclometalated platinum(II) complexes with similar molecular structures but distinct phosphorescence quantum yields were investigated. To explore the intersystem crossing (ISC) and radiative decay processes, we investigated the absorption and phosphorescence properties, spin–orbit coupling matrix elements, major ISC channels and phosphorescent transition rates. For the temperature-dependent nonradiative decay processes, the metal-centered excited states (3MC), the transition states, and the minimum energy crossing points were investigated with theoretical calculations. The way of temperature-independent nonradiative decay which has weak influence on nonradiative decay rate was also compared through the calculation of reorganization energy (λ).


Datum: 27.05.2019


New insights into Fe–H $$_{2}$$ 2 and Fe–H $$^{-}$$ - bonding of a [NiFe] hydrogenase mimic: a local vibrational mode study

Abstract

In this work, we investigated the strength of the \({\hbox {H}}^{-}\) and \({\hbox {H}}_{2}\) interaction with the Fe atom of a [NiFe] hydrogenase mimic, and how this interaction can be modulated by changing the Fe ligand in trans-position relative to \({\hbox {H}}^{-}\) and \({\hbox {H}}_{2}\) . We used as a quantitative measure of bond strength local vibrational force constants derived from the Konkoli–Cremer local mode analysis, complemented by the topological analysis of the electronic density and the natural bond orbital analysis. Seventeen different ligands were investigated utilizing density functional theory calculations, including \({\sigma }\) -donor ligands such as \({\hbox {CH}}_{3}^{-}\) , \({\hbox {C}}_{2}{\hbox {H}}_{5}^{-}\) , \({\hbox {NH}}_{3}\) , and \({\hbox {H}}_{2}\hbox {O}\) , \({\pi }\) -donor ligands such as \({\hbox {Cl}}^{-}\) , \({\hbox {F}}^{-}\) , and \({\hbox {OH}}^{-}\) , and \({\sigma }\) -donor/ \({\pi }\) -acceptor ligands such as \({\hbox {CN}}^{-}\) and CO. According to the local mode analysis, Fe–H interactions are strengthened by \({\sigma }\) -donor or \({\pi }\) -donor ligands and weakened by \({\sigma }\) -donor/ \({\pi }\) -acceptor ligands. In contrast, the H–H bond of \({\hbox {H}}_{2}\) is weakened by \({\sigma }\) -donor or \({\pi }\) -donor ligands and strengthened by \({\sigma }\) -donor/ \({\pi }\) -acceptor ligands. We also present a new metal–ligand electronic parameter (MLEP) for Fe–H ligands which can be generally applied to evaluate the Fe–H bond strength in iron complexes and iron hydrides. These results form a valuable basis for future [NiFe] hydrogenase-based catalyst design and fine tuning, as well as for the development of efficient biomimetic catalysts for \({\hbox {H}}_{2}\) generation.


Datum: 24.05.2019


Microsolvation of lithium–phosphorus double helix: a DFT study

Abstract

The chemistry of complexes becomes interesting due to their structural diversity in different environments like in aqueous phase, in gas-phase or in the interior of a host. In the last few decades, powerful tools for the determination of gas-phase have been developed. In this context, the microsolvation approach of Li7P7 helix, where the passage from the bare double-strand helix to the hydrated denatured helix, has been addressed through successive attachment of water molecules using density functional theory. The stability of helical structure of the small clusters has been analyzed on the basis of polar bonding interaction between oxygen end of water molecule and Li centers of the Li7P7 helix. The Li7P7 helix is favored when associated with zero to eight water molecules, but the binding of the ninth water molecule brings a drastic change in the structure. Our results suggest that the natural charges on some sites in Li7P7 are large enough to induce partial and eventually total dissociation of water molecules. We shed light on the bonding situation through natural bond orbital, quantum theory of atoms in molecules and energy decomposition analyses which suggest dominant electrostatic interaction between Li centers of Li7P7 and O centers of water molecules (accounting for 60–64% of total bonding attraction). Nevertheless, 31–36% of total attraction is also originated from the orbital interaction. Variation in reactivity on microhydration is also analyzed. In order to check the site selectivity, we have computed conceptual density functional theory-based local reactivity descriptors such as dual descriptor based on the Fukui function, Δf(r), and multiphilic descriptor based on the philicity, Δω(r).


Datum: 20.05.2019


Gold(I)-catalyzed intermolecular dioxolane addition to alkynes: the role of water

Abstract

Density functional theory (DFT) calculations have been performed on a homogeneous gold-catalyzed reaction between acetylene/propyne and the cyclic ketal 2,2-dimethyl-1,3-dioxolane, DMDO, in the presence of water, with the aim of understanding the actual role played by water. After the addition of DMDO to the alkyne, hydrolysis may happen through two possible reaction routes. In the so-called H-route (previously proposed for similar intramolecular reactions), a water proton is initially added to the alkyne C atom still linked to gold and, afterwards, an OH group adds to a DMDO C atom to allow the release of acetone, whereas in the newly proposed OH-route, a water OH group firstly adds to the most substituted DMDO C atom with simultaneous addition of H to the alkyne C atom linked to gold. A 1,3-H transposition from the just added OH group allows the release of acetone. An intramolecular nucleophilic OH addition to the gold-activated alkene intermediate formed from both hydrolysis paths drives the system to the corresponding 1,3-dioxolane product. The H-route is unable to explain the formation of the dioxolane addition products (observed in similar intramolecular reactions) instead of those coming from the direct addition of water to the alkyne, since it is energetically more demanding than the direct hydration. However, OH-route goes through structures that are more stable than those in the water addition, so, it is the one actually happening for the reaction under study. The regioselective addition of DMDO to the internal C atom of propyne is predicted on the basis of the large polarity of the structures formed in this approach, which makes them capable of strong interactions with water.


Datum: 15.05.2019


 


Category: Current Chemistry Research

Last update: 11.04.2018.






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