Chemical Physics

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Chemical Physics - Abstracts

Diffusion of carbon and nitrogen in TC4 titanium alloy plasma electrolytic saturation

Publication date: 13 April 2018
Source:Chemical Physics, Volume 505
Author(s): Jing Pang, Wenzhuang Lu, Wei Liu, Sheng Zhang, Yuli Sun, Dunwen Zuo

The study aims at deriving an equation for the temperature field of the specimen- vapour-gaseous envelope (VGE) – electrolyte three-phase system, followed by the calculation of the temperature distribution expression. The diffusion mechanism of carbon and nitrogen, in light of the theory of molecular diffusion, and the mechanism behind the plasma electrolytic saturation, is also discussed. In the PES process, the diffusion of carbon and nitrogen is affected by the strengthening voltage and processing time, which in turn affects the thickness and element distribution of the diffusion layer. Carbon, of which the diffusion depth ranges from 0.5 μm to 2.5 μm, is mainly distributed into the outermost layer. While the nitrogen is able to distribute throughout the diffusion layer as indicated by its several tens microns of diffusion depth. Further, the influence of process parameters on the diffusion of atoms during the strengthening process is verified experimentally.

Graphical abstract

Datum: 25.04.2018

Transitions energies, optical oscillator strengths and partial potential energy surfaces of inner-shell states of water clusters

Publication date: Available online 17 April 2018
Source:Chemical Physics
Author(s): Bruno N.C. Tenório, Carlos E.V. de Moura, Ricardo R. Oliveira, Alexandre B. Rocha

Transitions energies, optical oscillator strengths and partial potential energy surfaces of inner-shell (core–hole) states of water clusters are calculated at the inner-shell multiconfigurational self-consistent field (IS-MCSCF) level. This approach has been applied to diatomic and small polyatomic molecules with high accuracy. In the present work, IS-MCSCF was applied to molecular clusters for the first time. Discussions are carried out based on calculations done at different geometric conformations. It is shown that the transition energy is blue shifted to the first two discrete states at O 1s edge when referred to the isolated water molecule, while the core-electron binding energy is red shifted. Although the results for water clusters can only be compared to liquid water with care, it is worth emphasizing that this same trend is found in the corresponding spectra of the latter, revealing the importance of the first solvation shell to establish the main features of liquid water spectrum.

Datum: 25.04.2018

Mathematics of thermal diffusion in an exponential temperature field

Publication date: 13 April 2018
Source:Chemical Physics, Volume 505
Author(s): Yaqi Zhang, Wenyu Bai, Gerald J. Diebold

The Ludwig-Soret effect, also known as thermal diffusion, refers to the separation of gas, liquid, or solid mixtures in a temperature gradient. The motion of the components of the mixture is governed by a nonlinear, partial differential equation for the density fractions. Here solutions to the nonlinear differential equation for a binary mixture are discussed for an externally imposed, exponential temperature field. The equation of motion for the separation without the effects of mass diffusion is reduced to a Hamiltonian pair from which spatial distributions of the components of the mixture are found. Analytical calculations with boundary effects included show shock formation. The results of numerical calculations of the equation of motion that include both thermal and mass diffusion are given.

Graphical abstract

Datum: 25.04.2018

Effects of Al2O3 atomic layer deposition on interfacial structure and electron transfer dynamics at Re-bipyridyl complex/TiO2 interfaces

Publication date: Available online 3 April 2018
Source:Chemical Physics
Author(s): Jia Song, Aimin Ge, Brandon Piercy, Mark D. Losego, Tianquan Lian

Atomic layer deposition (ALD) of oxide layers on sensitizer- and/or catalyst-functionalized semiconductor surfaces have been used to improve the stability of dye-sensitized solar cells and photoelectrosynthesis cells. However, how the ALD layer affects the interfacial structure of adsorbed molecules and interfacial electron transfer dynamics is still unclear. Herein, we investigated the effects of ALD of Al2O3 on adsorption structure of Re bipyridyl complex on TiO2 nanocrystalline films and rutile (0 0 1) single crystals by IR absorption and sum frequency generation spectroscopy. Further, the electron transfer dynamics between the Re complex and TiO2 film was also examined by ultrafast infrared transient absorption spectroscopy. Our results show that the electron injection yield decreases with the increase of ALD layer thickness.

Graphical abstract

Datum: 25.04.2018

Linking photons and ultra-light particles

Publication date: Available online 27 March 2018
Source:Chemical Physics
Author(s): Dor Ben-Amotz

Similarities between thermally equilibrated photons and an ideal gas composed of highly relativistic (ultra-light) particles have long been noted, as has the fact that the two systems appear to have different energy distribution functions. Here this connection is revisited to show that all the dynamical variable distribution functions of the two systems become identical when results obtained from ultra-light gas kinetic theory are required to be consistent with independently obtained results of thermodynamics and electromagnetic theory. Thus, classical ultra-light particles, whose rest mass approaches zero, are predicted to have equilibrium velocities that are practically indistinguishable from the speed of light, and the corresponding kinetic energy distribution functions are predicted to transform from a Wien distribution to a Planck distribution with increasing particle number density.

Datum: 25.04.2018

Exploring unimolecular dissociation kinetics of ethyl dibromide through electronic structure calculations

Publication date: 13 April 2018
Source:Chemical Physics, Volume 505
Author(s): Nitin R. Gulvi, Priyanka Patel, Purav M. Badani

Pathway for dissociation of multihalogenated alkyls is observed to be competitive between molecular and atomic elimination products. Factors such as molecular structure, temperature and pressure are known to influence the same. Hence present work is focussed to explore mechanism and kinetics of atomic (Br) and molecular (HBr and Br2) elimination upon pyrolysis of 1,1- and 1,2-ethyl dibromide (EDB). For this purpose, electronic structure calculations were performed at DFT and CCSD(T) level of theory. In addition to concerted mechanism, an alternate energetically efficient isomerisation pathway has been exploited for molecular elimination. Energy calculations are further complimented by detailed kinetic investigation, over wide range of temperature and pressure, using suitable models like Canonical Transition State Theory, Statistical Adiabatic Channel Model and Troe’s formalism. Our calculations suggest high branching ratio for dehydrohalogentation reaction, from both isomers of EDB. Fall off curve depicts good agreement between theoretically estimated and experimentally reported values.

Graphical abstract

Datum: 25.04.2018

Entropy-enthalpy compensation in conjugated proteins

Publication date: Available online 12 April 2018
Source:Chemical Physics
Author(s): Lavi S. Bigman, Yaakov Levy

Entropy–enthalpy compensation is observed in many reactions, particularly for polymeric biomolecules that often involve large changes in entropy and enthalpy. The imperfect cancelation of entropy and enthalpy dictates many biophysical characteristics, such as protein thermodynamic stability and the free energy barrier for protein folding. In this study, we examine how tethering a conjugate to a protein may affect the thermodynamic stability of the protein. We found that a conjugate mostly affects the unfolded state by eliminating formation of some residual interactions. Consequently, both the enthalpy and the entropy of the unfolded state are affected. We suggest that, because this effect is not localized, the gain in conformational flexibility (i.e., increased entropy) is larger than the loss of some residual interaction (i.e., increased enthalpy). Therefore, the unfolded state of the conjugated protein has a lower free energy than that of the free protein, resulting in thermodynamic destabilization.

Graphical abstract

Datum: 25.04.2018

An investigation about the structures, thermodynamics and kinetics of the formic acid involved molecular clusters

Publication date: 11 May 2018
Source:Chemical Physics, Volume 507
Author(s): Rui Zhang, Shuai Jiang, Yi-Rong Liu, Hui Wen, Ya-Juan Feng, Teng Huang, Wei Huang

Despite the very important role of atmospheric aerosol nucleation in climate change and air quality, the detailed aerosol nucleation mechanism is still unclear. Here we investigated the formic acid (FA) involved multicomponent nucleation molecular clusters including sulfuric acid (SA), dimethylamine (DMA) and water (W) through a quantum chemical method. The thermodynamics and kinetics analysis was based on the global minima given by Basin-Hopping (BH) algorithm coupled with Density Functional Theory (DFT) and subsequent benchmarked calculations. Then the interaction analysis based on ElectroStatic Potential (ESP), Topological and Atomic Charges analysis was made to characterize the binding features of the clusters. The results show that FA binds weakly with the other molecules in the cluster while W binds more weakly. Further kinetic analysis about the time evolution of the clusters show that even though the formic acid’s weak interaction with other nucleation precursors, its effect on sulfuric acid dimer steady state concentration cannot be neglected due to its high concentration in the atmosphere.

Datum: 25.04.2018

Comparison of atmospheric reactions of NH3 and NH2 with hydroxyl radical on the singlet, doublet and triplet potential energy surfaces, kinetic and mechanistic study

Publication date: 11 May 2018
Source:Chemical Physics, Volume 507
Author(s): Morteza Vahedpour, Hamed Douroudgari, Sheida Afshar, Somaie Asgharzade

The NH2 + OH and NH3 + OH reactions on the singlet, doublet and triplet potential energy surfaces carry out using MP2, QCISD, G3MP2, M06-2X, B3LYP, and CCSD(T)//MP2 levels. Three pre-reactive complexes, ¹C1, ³C1 and ³C2 were formed among amidogen and hydroxyl radicals. From variety of the ¹C1, four types of products are obtained that ¹HNO + H2 is thermodynamically stable and three others are being stable after relaxation to triplet state. On the triplet state, five types of adducts are obtained that four of them have enough thermodynamic stability. Two intersystem crossing are presented among triplet and singlet states of the NH2 + OH reaction. 3NH + H2O adduct is spontaneous and exothermic in standard condition. Results lead to different adducts which are playing significant role in the atmospheric and combustion chemistry. The rate constants of selected pathways are calculated at the 300–2500 K temperature range at M06-2X/aug-ccpvqz and CCSD(T)/6-311++G(3df, 3pd) levels of theory.

Datum: 25.04.2018

Generations of even-order harmonics from vibrating H2+ and T2+ in the rising and falling parts of the laser field

Publication date: 13 April 2018
Source:Chemical Physics, Volume 505
Author(s): Liqiang Feng, Henry J. Kapteyn, April Y. Feng

The generations of the even-order harmonics from H2⁺ and one of its isotope T2⁺ have been theoretically investigated beyond the Born-Oppenheimer approximation. Normally, the high-order harmonic generation (HHG) only contains odd-order harmonics for the orbital symmetry along the direction of laser polarization. Here, we showed that due to asymmetric harmonic emission (asymmetric half-wave profile), the even-order harmonics can be generated in the rising and the falling part of the laser field. In detail, in the lower initial vibrational state, the even-order harmonics main come from the falling part of the laser field; while as the initial vibrational state increases, the identified even-order harmonics in the falling part of the laser field are decreased; while some other even-order harmonics coming from the rising part of the laser field can be produced. The interesting phenomena have been proved through studying the spatial distributions and the time profiles of the HHG.

Graphical abstract

Datum: 25.04.2018

Graphical abstract TOC

Publication date: 13 April 2018
Source:Chemical Physics, Volume 505

Datum: 25.04.2018

Ultrafast dynamics of coherent optical phonon in a thin film of Bi3Se2Te

Publication date: Available online 28 March 2018
Source:Chemical Physics
Author(s): Ying-Kuan Ko, Yan-Hao Huang, Phuoc Huu Le, Chih-Wei Luo, Marin Mirtchev Gospodinov, Takayoshi Kobayashi, Atsushi Yabushita

We have performed ultrafast time-resolved spectroscopy of transient absorption for a thin film of Bi3Se2Te, in which recent study result implies the existence of topological surface state. The observed relaxation signal was attributed to the band filling and Auger recombination processes based on the pump power dependence of the signal. After the band filling, bulk-to-surface scattering is thought to proceed being mediated by phonon emission. The dynamics of the phonon was observed from the dumped oscillation appeared on the relaxation curve of the observed signal. The phase of the oscillation indicates that the phonon mode has the period of

519 \pm 3

fs in the electronic excited state.

Datum: 25.04.2018

Quantitative and sensitive mapping of imidacloprid on plants using Multiphoton Electron Extraction Spectroscopy

Publication date: Available online 4 April 2018
Source:Chemical Physics
Author(s): Anneli Kruve, Valery Bulatov, Israel Schechter

Neonicotinoids, including imidacloprid, are extensively used for plant protection against insects. Unfortunately, these effective pesticides are one of the reasons for the decline of the bee population in recent decades. Ensuring application of minimal pesticide quantity and preventing excess requires a fast method for monitoring the coverage on plants. We present a new, method based on multiphoton electron extraction spectroscopy (MEES), for detecting, quantifying and mapping of imidacloprid coverage on plants. Imaging and quantitative analyses were demonstrated on several plant surfaces including olive and mint leaves and orange peel. Method provides both low detection limits (down to nanogram level) and good trueness. This method is fast and can be directly performed with no sample pre-treatment, thus, it is a good candidate for field analyses.

Datum: 25.04.2018

Editorial Board

Publication date: 13 April 2018
Source:Chemical Physics, Volume 505

Datum: 25.04.2018

Hydrogen storage property of alkali and alkaline-earth metal atoms decorated C24 fullerene: A DFT study

Publication date: 13 April 2018
Source:Chemical Physics, Volume 505
Author(s): Yafei Zhang, Xinlu Cheng

The hydrogen storage behavior of alkali and alkaline-earth metal (AM = Li, Na, K, Mg, Ca) atoms decorated C24 fullerene was investigated by using density functional theory (DFT) study. Our results indicate that the AM atoms prefer to adsorb atop the center of tetragon of C24 fullerene with the largest binding energy than other possible adsorption sites. Moreover, the hydrogen storage gravimetric density of 24H2/6Li/C24, 24H2/6Na/C24 and 36H2/6Ca/C24 configurations reaches up to 12.7 wt%, 10.1 wt% and 12 wt%, higher than the year 2020 target from the US department of energy (DOE). Also, the average adsorption energies of H2 molecules of the 24H2/6Li/C24, 24H2/6Na/C24 and 36H2/6Ca/C24 configurations are −0.198 eV/H2, −0.164 eV/H2 and −0.138 eV/H2, locate the desirable range under the physical adsorption at near ambient conditions. These findings will have important implications on designing new hydrogen storage materials in the future.

Graphical abstract

Datum: 25.04.2018

Entangled photons from single atoms and molecules

Publication date: 11 May 2018
Source:Chemical Physics, Volume 507
Author(s): Bengt Nordén

The first two-photon entanglement experiment performed 50 years ago by Kocher and Commins (KC) provided isolated pairs of entangled photons from an atomic three-state fluorescence cascade. In view of questioning of Bell’s theorem, data from these experiments are re-analyzed and shown sufficiently precise to confirm quantum mechanical and dismiss semi-classical theory without need for Bell’s inequalities. Polarization photon correlation anisotropy (A) is useful: A is near unity as predicted quantum mechanically and well above the semi-classic range,

0 ⩽ A ⩽ 1 / 2

. Although yet to be found, one may envisage a three-state molecule emitting entangled photon pairs, in analogy with the KC atomic system. Antibunching in fluorescence from single molecules in matrix and entangled photons from quantum dots promise it be possible. Molecules can have advantages to parametric down-conversion as the latter photon distribution is Poissonian and unsuitable for producing isolated pairs of entangled photons. Analytical molecular applications of entangled light are also envisaged.

Graphical abstract

Datum: 25.04.2018

Molecular thermal transistor: Dimension analysis and mechanism

Publication date: 13 April 2018
Source:Chemical Physics, Volume 505
Author(s): S. Behnia, R. Panahinia

Recently, large challenge has been spent to realize high efficient thermal transistors. Outstanding properties of DNA make it as an excellent nano material in future technologies. In this paper, we introduced a high efficient DNA based thermal transistor. The thermal transistor operates when the system shows an increase in the thermal flux despite of decreasing temperature gradient. This is what called as negative differential thermal resistance (NDTR). Based on multifractal analysis, we could distinguish regions with NDTR state from non-NDTR state. Moreover, Based on dimension spectrum of the system, it is detected that NDTR state is accompanied by ballistic transport regime. The generalized correlation sum (analogous to specific heat) shows that an irregular decrease in the specific heat induces an increase in the mean free path (mfp) of phonons. This leads to the occurrence of NDTR.

Datum: 25.04.2018

Hydrogen bonding between hydrides of the upper-right part of the periodic table

Publication date: 11 May 2018
Source:Chemical Physics, Volume 507
Author(s): Matjaž Simončič, Tomaz Urbic

One of the most important electrostatic interactions between molecules is most definitely the hydrogen bond. Understanding the basis of this interaction may offer us the insight needed to understand its effect on the macroscopic scale. Hydrogen bonding is for example the reason for anomalous properties in compounds like water and naturally life as we know it. The strength of the bond depends on numerous factors, among them the electronegativity of participating atoms. In this work we calculated the strength of hydrogen bonds between hydrides of the upper-right part of the periodic table (C, N, O, F, P, S, Cl, As, Se, Br) using quantum-chemical methods. The aim was to determine what influences the strength of strong and weak hydrogen bonds in simple hydrides. Various relationships were checked. A relation between the strength of the bond and the electronegativity of the participating atoms was found. We also observed a correlation between the strength of hydrogen bonds and the inter-atomic distances, along with the dependence on the charge transfer on the atom of the donor. We also report characteristic geometries of different dimers.

Datum: 25.04.2018

Graphical abstract TOC

Publication date: 13 April 2018
Source:Chemical Physics, Volume 505

Datum: 25.04.2018

A DFT study on the enthalpies of thermite reactions and enthalpies of formation of metal composite oxide

Publication date: 11 May 2018
Source:Chemical Physics, Volume 507
Author(s): Yu-ying Zhang, Meng-jie Wang, Chun-ran Chang, Kang-zhen Xu, Hai-xia Ma, Feng-qi Zhao

The standard thermite reaction enthalpies (ΔrHm^θ) for seven metal oxides were theoretically analyzed using density functional theory (DFT) under five different functional levels, and the results were compared with experimental values. Through the comparison of the linear fitting constants, mean error and root mean square error, the Perdew-Wang functional within the framework of local density approximation (LDA-PWC) and Perdew-Burke-Ernzerhof exchange-correlation functional within the framework of generalized gradient approximation (GGA-PBE) were selected to further calculate the thermite reaction enthalpies for metal composite oxides (MCOs). According to the Kirchhoff formula, the standard molar reaction enthalpies for these MCOs were obtained and their standard molar enthalpies of formation (ΔfHm^θ) were finally calculated. The results indicated that GGA-PBE is the most suitable one out of the total five methods to calculate these oxides. Tungstate crystals present the maximum deviation of the enthalpies of thermite reactions for MCOs and these of their physical metal oxide mixtures, but ferrite crystals are the minimum. The correlation coefficients are all above 0.95, meaning linear fitting results are very precise. And the molar enthalpies of formation for NiMoO4, CuMoO4, PbZrO3 (Pm/3m), PbZrO3 (PBA2), PbZrO3 (PBam), MgZrO3, CdZrO3, MnZrO3, CuWO4 and Fe2WO6 were first obtained as −1078.75, −1058.45, −1343.87, −1266.54, −1342.29, −1333.03, −1210.43, −1388.05, −1131.07 and − 1860.11 kJ·mol⁻¹, respectively.

Graphical abstract

Datum: 25.04.2018

CO quantum dynamics diffusion on Cu(100)

Publication date: Available online 5 April 2018
Source:Chemical Physics
Author(s): David Zanuttini, Fabien Gatti, Roberto Marquardt

We present a quantum mechanical study of the diffusion of molecules of CO on the Cu(001) surface. We use the Strasbourg-Amsterdam-Postdam potential surface and a “non-tunnel”-variant hereof; to mimic an initial state that is localized in one adsorption well, a “local-potential-shift” concept is introduced; the Multi Configuration Time Dependent Hartree method to perform the calculations. Special emphasis is placed on the effect of the dimensionality of the models. Surprisingly, tunneling plays an important role after typically 1 ps after the beginning of the dynamics and dominates at around 1 ns and might, at least partly, explain the long diffusion rates measured experimentally for the system.

Datum: 25.04.2018

Tautomeric preferences of the cis and trans isomers of axitinib

Publication date: 11 May 2018
Source:Chemical Physics, Volume 507
Author(s): M. Saeed Mirzaei, Avat Arman Taherpour

The tautomeric preferences of axitinib, a potent anticancer drug, as tyrosine kinase inhibitor have been investigated using quantum chemical calculations and docking methods. The energy differences between the two tautomers of trans-isomer are around 4 and 3 kcal mol⁻¹ in vacuo and water, respectively, and for its cis-isomer (major photochemical isomerization product) this equilibrium reversed completely in favour of the second tautomer (not considered previously), which is about 7–8 kcal mol⁻¹ more stable in both gas and aqueous media. The results indicate a very high activation energy for proton exchange for both [1,2] and [1,5] H-shift (around 50 kcal mol⁻¹) in the gas phase, but inclusion of protic solvents (e.g. water) decrease this barrier to around 14 and 35 kcal mol⁻¹ for the both hydrogen shift processes, respectively. In order to have better insight about the electronic structure of axitinib tautomers, the NBO, HOMO-LUMO, NICS and molecular electrostatic potential surfaces (MESP) calculations have been carried out. Docking investigations on the two more stable tautomers revealed that binding of the trans isomer of tautomer I to the active site of the receptor is the most favourable in the terms of energy and structure. This more stability could be attributed to the more hydrogen bonding of this tautomer with the protein residues in comparison to the second tautomer.

Graphical abstract

Datum: 25.04.2018

The Lord Armstrong's experiment in the view of band theory of liquid water

Publication date: Available online 28 March 2018
Source:Chemical Physics
Author(s): Alexander Shimkevich

Liquid water considered in the band theory differs from the ice by localization of electrons in “tails” of the allowed energy bands separated by the wide band gap which defines electrochemical properties of water by means of the allowed energy levels above the middle of the band gap,

ε_{H_{3} O}

, as electronic donors and below,

ε_{OH}

, as their acceptors. The population of electrons

[H_{3} O] / [H_{3} O^{+}]

and holes

[OH] / [{OH}^{-}]

on these levels depends on Fermi level in the band gap. This variable electrochemical potential (as a p-n boundary between the vacant impurity levels and the ones occupied by electrons) becomes the tool for changing physical and chemical properties of liquid water. It turned out that a noticeable shift of Fermi level (more than 1 eV) is possible in the band gap at the expense of an insignificant (

| z | < 10^{- 10}

) deviation of the water composition

H_{2} O_{1 - z}

from the stoichiometric water,

H_{2} O

. This deviation is easily homogenized in the bulk liquid. Then, one can introduce into pure water a negative charge

[H_{3} O + {OH}^{-}] \sim 10^{- 7} M

or the positive one

[H_{3} O^{+} + OH] \sim 10^{- 7} M

by shifting Fermi level up to the donor or acceptor levels in the band gap. These charged molecular pairs

{(H}_{2} {O)}_{2}^{-}

and

{(H}_{2} {O)}_{2}^{+}

organize the two-way “traffic” in the aqueous “floating bridge” between two glass beakers with the pure liquid water under action of the high dc voltage in the Lord Armstrong's experiment.

Datum: 25.04.2018

Numerical simulation of electroosmotic flow in rough microchannels using the lattice Poisson-Nernst-Planck methods

Publication date: 11 May 2018
Source:Chemical Physics, Volume 507
Author(s): Reza Kamali, Mohsen Nasiri Soloklou, Hooman Hadidi

In this study, coupled Lattice Boltzmann method is applied to solve the dynamic model for an electroosmotic flow and investigate the effects of roughness in a 2-D flat microchannel. In the present model, the Poisson equation is solved for the electrical potential, the Nernst– Planck equation is solved for the ion concentration. In the analysis of electroosmotic flows, when the electric double layers fully overlap or the convective effects are not negligible, the Nernst-Planck equation must be used to find the ionic distribution throughout the microchannel. The effects of surface roughness height, roughness interval spacing and roughness surface potential on flow conditions are investigated for two different configurations of the roughness, when the EDL layers fully overlap through the microchannel. The results show that in both arrangements of roughness in homogeneously charged rough channels, the flow rate decreases by increasing the roughness height. A discrepancy in the mass flow rate is observed when the roughness height is about 0.15 of the channel width, which its average is higher for the asymmetric configuration and this difference grows by increasing the roughness height. In the symmetric roughness arrangement, the mass flow rate increases until the roughness interval space is almost 1.5 times the roughness width and it decreases for higher values of the roughness interval space. For the heterogeneously charged rough channel, when the roughness surface potential

ψ_{r}

is less than channel surface potential

ψ_{s}

, the net charge density increases by getting far from the roughness surface, while in the opposite situation, when

ψ_{s}

is more than

ψ_{r}

, the net charge density decreases from roughness surface to the microchannel middle center. Increasing the roughness surface potential induces stronger electric driving force on the fluid which results in larger velocities in the flow.

Datum: 25.04.2018

Lipid-induced dynamics of photoreceptors monitored by time-resolved step-scan FTIR spectroscopy

Publication date: Available online 20 April 2018
Source:Chemical Physics
Author(s): Michael Jawurek, Jessica Dröden, Benedikt Peter, Clemens Glaubitz, Karin Hauser

The lipid environment plays a crucial role for the function of membrane proteins. We analyzed the influence of various lipid properties on the photoreceptors Bacteriorhodopsin (BR) and Proteorhodopsin (PR) by time-resolved step-scan FTIR spectroscopy. The photoreceptors were reconstituted into liposomes thereby providing an uniform biomimetic membrane, and the physical properties of the lipids were systematically varied. The lipid phase alters significantly the protonation dynamics of both, BR and PR. We also analyzed the conformational changes of the photoreceptors during the proton pumping mechanism and could demonstrate that a lipid-induced altered protonation dynamics is correlated to an altered conformational dynamics. Our results indicate that the fluidity of the membrane environment directly influences the structural-functional correlation.

Graphical abstract

Datum: 25.04.2018

Ternary graphene/amorphous carbon/nickel nanocomposite film for outstanding superhydrophobicity

Publication date: 13 April 2018
Source:Chemical Physics, Volume 505
Author(s): Xiaobo Zhu, Shengguo Zhou, Qingqing Yan

A novel superhydrophobic ternary graphene/amorphous carbon/nickel (G-Ni/a-C:H) carbon-based film was fabricated by a green approach of high-voltage electrochemical deposition without using aqueous solution, which was systematically investigated including the structure and relating applications on self-cleaning and corrosion resistance. Graphene and nickel nano-particle inserts were effective to tailor the feature of nanocrystallite/amorphous microstructure as well as micro-nanoscale hierarchical rose-petal-like surface for G-Ni/a-C:H carbon-based film. Surprisingly, this deposit could present outstanding superhydrophobicity with the contact angle of 158.98 deg and sliding angle of 2.75 deg without any further surface modification meanwhile it could possess fairly well adhesion. Furthermore, the superhydrophobic G-Ni/a-C:H carbon-based film could exhibit excellent corrosion resistance and self-cleaning performances compared to no graphene incorporated deposit. The procedure of fabricating deposit might be simple, scalable, and environmental friendly, indicating a promising prospect for industrial applications in the field of anti-fouling, anti-corrosion and drag resistance.

Graphical abstract

Datum: 25.04.2018

Exciton states and optical absorption in core/shell/shell spherical quantum dot

Publication date: 27 April 2018
Source:Chemical Physics, Volume 506
Author(s): D.B. Hayrapetyan, D.A. Baghdasaryan, E.M. Kazaryan, S.I. Pokutnyi, H.A. Sarkisyan

The exciton states in core/shell/shell spherical quantum dot with three-dimensional Winternitz–Smorodinsky confinement potential are considered. The problem is discussed in the framework of adiabatic approximation when the heavy hole is situated in the effective potential well caused by the electron. The interband optical transitions caused by incident light polarized in z-direction have been considered in such systems. The oscillator strengths and selection rules for the quantum transitions have been obtained. The ensemble of quantum dots and their size dispersion have been taken into account in the calculations. The Gaussian distribution has been chosen to describe the size dispersion of the core/shell/shell quantum dots thickness. The dependence of the absorption coefficient and photoluminescence spectra on the energy of incident light of interband transitions have been obtained.

Graphical abstract

Datum: 25.04.2018

Graphical abstract TOC

Publication date: 11 May 2018
Source:Chemical Physics, Volume 507

Datum: 25.04.2018

Rapid and sensitive detection of synthetic cannabinoids AMB-FUBINACA and α-PVP using surface enhanced Raman scattering (SERS)

Publication date: 27 April 2018
Source:Chemical Physics, Volume 506
Author(s): Syed K. Islam, Yin Pak Cheng, Ronald L. Birke, Omar Green, Thomas Kubic, John R. Lombardi

The application of surface enhanced Raman scattering (SERS) has been reported as a fast and sensitive analytical method in the trace detection of the two most commonly known synthetic cannabinoids AMB-FUBINACA and alpha-pyrrolidinovalerophenone (α-PVP). FUBINACA and α-PVP are two of the most dangerous synthetic cannabinoids which have been reported to cause numerous deaths in the United States. While instruments such as GC–MS, LC–MS have been traditionally recognized as analytical tools for the detection of these synthetic drugs, SERS has been recently gaining ground in the analysis of these synthetic drugs due to its sensitivity in trace analysis and its effectiveness as a rapid method of detection. This present study shows the limit of detection of a concentration as low as picomolar for AMB-FUBINACA while for α-PVP, the limit of detection is in nanomolar concentration using SERS.

Datum: 25.04.2018

Towards first-principles calculation of electronic excitations in the ring of the protein-bound bacteriochlorophylls

Publication date: 13 April 2018
Source:Chemical Physics, Volume 505
Author(s): Igor V. Polyakov, Maria G. Khrenova, Alexander A. Moskovsky, Boris M. Shabanov, Alexander V. Nemukhin

Modeling electronic excitation of bacteriochlorophyll (BChl) molecules in light-harvesting (LH) antennae from photosynthetic centers presents a challenge for the quantum theory. We report on a quantum chemical study of the ring of 32 BChl molecules from the bacterial core complex LH1-RC. Diagonal and off-diagonal elements of the excitonic Hamiltonian matrices are estimated in quantum chemical calculations of relevant fragments using the TD-DFT and CIS approaches. The deviation of the computed excitation energy of this BChl system from the experimental data related to the Qy band maximum of this LH1-RC complex is about 0.2 eV. We demonstrate that corrections due to improvement in modeling of an individual BChl molecule and due to contributions from the protein environment are in the range of the obtained discrepancy between theory and experiment. Differences between results of the excitonic model and direct quantum chemical calculations of BChl aggregates fall in the same range.

Graphical abstract

Datum: 25.04.2018

Thermodynamic and transport properties of nitrogen fluid: Molecular theory and computer simulations

Publication date: 27 April 2018
Source:Chemical Physics, Volume 506
Author(s): A. Eskandari Nasrabad, R. Laghaei

Computer simulations and various theories are applied to compute the thermodynamic and transport properties of nitrogen fluid. To model the nitrogen interaction, an existing potential in the literature is modified to obtain a close agreement between the simulation results and experimental data for the orthobaric densities. We use the Generic van der Waals theory to calculate the mean free volume and apply the results within the modified Cohen-Turnbull relation to obtain the self-diffusion coefficient. Compared to experimental data, excellent results are obtained via computer simulations for the orthobaric densities, the vapor pressure, the equation of state, and the shear viscosity. We analyze the results of the theory and computer simulations for the various thermophysical properties.

Datum: 25.04.2018

Graphical abstract TOC

Publication date: 11 May 2018
Source:Chemical Physics, Volume 507

Datum: 25.04.2018

Synthesis of hierarchical flower-like Co3O4 superstructure and its excellent catalytic property for ammonium perchlorate decomposition

Publication date: 27 April 2018
Source:Chemical Physics, Volume 506
Author(s): Gang Li, Weiyang Bai

Hierarchical flower-like cobalt tetroxide (Co3O4) was successfully synthesized via a facile precipitation method in combination with heat treatment of the cobalt oxalate precursor. The samples were systematically characterized by thermo gravimetric analysis and derivative thermo gravimetric analysis (TGA-DTG), X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and N2 adsorption-desorption measurements. The results indicate that the as-fabricated Co3O4 exhibits uniform flower-like morphologies with diameters of 8–12 μm, which are constructed by one-dimensional nanowires. Furthermore, catalytic effect of this hierarchical porous Co3O4 on ammonium perchlorate (AP) pyrolysis was investigated using differential scanning calorimetry (DSC) techniques. It is found that the pyrolysis temperature of AP shifts 142 °C downward with a 2 wt% addition content of Co3O4. Meanwhile, the addition of Co3O4 results in a dramatic reduction of the apparent activation energy of AP pyrolysis from 216 kJ mol⁻¹ to 152 kJ mol⁻¹, determined by the Kissinger correlation. The results endorse this material as a potential catalyst in AP decomposition.

Datum: 25.04.2018

Graphical abstract TOC

Publication date: 13 April 2018
Source:Chemical Physics, Volume 505

Datum: 25.04.2018

New assignment of 14N NQR spectral lines for tetrazoles derivatives

Publication date: 27 April 2018
Source:Chemical Physics, Volume 506
Author(s): Sultonazar Mamadazizov, Marina G. Shelyapina, Galina S. Kupriyanova, George V. Mozzhukhin

In recent years, considerable interest has been shown in the study of tetrazole derivatives, which attract attention as highly nitrogenous compounds for use as an isosteric substitutes for various functional groups that leads to creation of novel biologically active substances. NQR techniques, being sensitive to the local environment of ¹⁴N nuclei, provide great opportunities to study these new substances. To make investigation of complex compounds containing tetrazoles derivatives easier and more reliable a correctly assigned ¹⁴N NQR spectra of tetrazoles are required. Here we report on the results of our DFT B3LYP calculations of ¹⁴N NQR spectral parameters (quadrupole coupling constant Qcc and the asymmetry parameter of the electric field gradient

η

) for tetrazole, 5-aminotetrazole and 5-aminotetrazole monohydrate. It has been found that the commonly accepted assignment of the ¹⁴N NQR spectral lines for these molecules is incorrect. A new assignment for these molecules is proposed.

Datum: 25.04.2018

Editorial Board

Publication date: 27 April 2018
Source:Chemical Physics, Volume 506

Datum: 25.04.2018

Graphical abstract TOC

Publication date: 27 April 2018
Source:Chemical Physics, Volume 506

Datum: 25.04.2018

Self assembly and gelation in solutions of chiral N-trifluoroacetylated α-aminoalcohols

Publication date: Available online 12 April 2018
Source:Chemical Physics
Author(s): Sergey V. Stovbun, Aleksey A. Skoblin, Dmitry V. Zlenko

The low molecular weight (

Mr \sim 200

 Da) chiral N-trifluoroacetylated

α

-aminoalcohols (TFAAAs) are able for gelate various organic solvents and water in very low concentrations (

\sim 10^{- 3}

 M). The gelation was not observed in the racemic solutions or solution of achiral TFAAA. The gelation is temperature-reversible and demonstrates the memory effect. The gel scaffold is composed of thin supramolecular elements (strings) having a helical structure. The thinnest (elementary) strings have a crystalline, highly ordered structure and braid together to form thicker elements. The sign of the helicity changes with the growing of the strings in course of the gelation process, so that the thicker strings have the opposite helicity as compared to thinner ones. We provide a theoretical description of the strings growing process.

Datum: 25.04.2018

Graphical abstract TOC

Publication date: 27 April 2018
Source:Chemical Physics, Volume 506

Datum: 25.04.2018

Resonant heating of Fe3O4 and hemozoin nanoparticles dispersed in D2O by RF excitation of transitions between Zeeman components

Publication date: 27 April 2018
Source:Chemical Physics, Volume 506
Author(s): I.V. Khmelinskii, V.I. Makarov

Presently we evaluated the natural relaxation frequency of the spin angular momentum of Fe3O4 and hemozoin superparamagnetic (SP) nanoparticles in D2O solutions in function of the sample temperature. The sample was composed of 1% H2O in D2O with dispersed Fe3O4 or hemozoin nanoparticles at variable number density. The natural relaxation frequencies are in the sub-MHz and MHz range for the Fe3O4 and hemozoin nanoparticles, respectively. We studied resonance heating of the same samples. We found that scanning the external magnetic field strength in a constant-frequency radio-frequency (RF) electromagnetic field, with its magnetic field component perpendicular to the external magnetic field, we obtain resonant heating at the magnetic field strength of 50 or 100 Gs for the RF excitation at 150 or 300 MHz, respectively. The measured resonance line has a Lorentzian form, with the heating amplitude dependent on the number density of SP nanoparticles, RF power and time. The resonance width correlates with the natural relaxation frequency of the spin angular momentum of the SP nanoparticles. We describe a theoretical model explaining the experimental results. As the achievable heating rate is directly proportional to the spin relaxation rate of the SP nanoparticles, we expect two orders of magnitude higher heating rates in suspensions based on water with natural isotopic composition.

Graphical abstract

Datum: 25.04.2018

A Combined Time-Resolved Infrared and Density Functional Theory Study of the Lowest Excited States of 9-Fluorenone and 2-Naphthaldehyde

Publication date: Available online 24 April 2018
Source:Chemical Physics
Author(s): Magnus W.D. Hanson-Heine, James A. Calladine, Jixin Yang, Michael Towrie, Raphael Horvath, Nicholas A. Besley, Michael W. George

A combined experimental and theoretical study of the infrared (IR) spectra of 2-naphthaldehyde and 9-fluorenone in their ground and first excited singlet and triplet electronic states is presented. IR studies have also been carried out using supercritical krypton (scKr) as a solvent to measure spectra in the ground and triplet excited states. This solvent provides a weakly interacting environment that is closer to the gas phase and allows a direct comparison with the calculated spectra for a single molecule. The IR spectra for the three different states are computed with Kohn-Sham density functional theory. For the first excited singlet state it is necessary to use an overlap procedure that allows the excited state to be studied by preventing variational collapse to the ground state. This allows the excited singlet state to be studied in an analogous approach to the ground and excited triplet state, in contrast to using time-dependent density functional theory. The good agreement between the calculated excited state spectra and the experiment provides insight into the nature of the excited states. For the ground and excited triplet state the anharmonic vibrational frequencies are computed using the transition optimized shifted Hermite method, and for these molecules the hybrid B97-1 functional is found to provide the closest agreement with experiment in the ground state.

Datum: 25.04.2018

The protonated water trimer and its giant Fermi resonances

Publication date: Available online 3 April 2018
Source:Chemical Physics
Author(s): Nagaprasad Reddy Samala, Noam Agmon

The protonated water trimer is a prototype “proton wire” that can transport two protons nearly concertedly. This “proton transfer mode” (PTM) is an important contributor to the infrared spectrum of the isolated gas-phase cluster. We have simulated its infrared spectrum for both the hydrated and deuterated isotopologues, using vibrational 2nd order perturbation theory (VPT2) and ab initio molecular dynamics (AIMD) trajectories. VPT2 calculations explain quantitatively the experimental spectra at both high and low frequencies, provided that high-level quantum chemistry is utilized. In the D2-tagged hydrated cluster, the PTM undergoes giant Fermi resonances (FR’s) with two combination bands. In the deuterated analogue, one observes a single FR of “normal” intensity, manifested as the doublet recently reported experimentally. We provide band assignment for both isotopologues, with and without the D2 tag applied in experiment. We discuss possible manifestations of the giant resonance on proton transfer through water wires.

Datum: 25.04.2018

Structural Transformations of 3-Fluoro and 3-Fluoro-4-methoxy Benzaldehydes under Cryogenic Conditions: A Computational and Low Temperature Infrared Spectroscopy Investigation

Publication date: Available online 22 April 2018
Source:Chemical Physics
Author(s): G.O. Ildiz, J. Konarska, R. Fausto

Structural transformations of 3-fluorobenzaldehyde (C7H5FO; 3FBA) and 3-fluoro-4-methoxybenzaldehyde (C8H7FO2; 3F4MBA), taking place in different solid phase environments and at low temperature, were investigated by infrared spectroscopy, complemented by quantum chemistry calculations undertaken at the DFT(B3LYP)/6-311++G(d,p) level of approximation. The studied compounds were isolated from gas phase into cryogenic inert matrices (Ar, Xe), allowing to characterize their equilibrium conformational composition in gas-phase at room temperature. In both cases, two conformers differing by the orientation of the aldehyde moiety (with the carbonyl aldehyde bond cis or trans in relation to the aromatic ring fluorine substituent) were found to coexist, with the cis conformer being slightly more populated than the trans form. In situ narrowband UV irradiation of the as-deposited matrices led either to preferential isomerization of the cis conformer into the trans form or decarbonylation of both conformers, depending on the used excitation wavelength. Deposition of the vapours of 3F4MBA only, onto the cold (15 K) substrate, produced an amorphous solid containing also both the cis and trans conformers of the compound. Subsequent heating of the amorphous phase up to 268 K led to crystallization of the compound, which is accompanied by conformational selection, the cis form being the single species present in the crystal. The experimentally observed transformations of the studied compounds, together with the structural and vibrational results obtained from the performed quantum chemical calculations, allowed a detailed structural and vibrational characterization of the individual conformers.

Graphical abstract

Datum: 25.04.2018

Mesoporous activated carbon from corn stalk core for lithium ion batteries

Publication date: 27 April 2018
Source:Chemical Physics, Volume 506
Author(s): Yi Li, Chun Li, Hui Qi, Kaifeng Yu, Ce Liang

A novel mesoporous activated carbon (AC) derived from corn stalk core is prepared via a facile and effective method which including the decomposition and carbonization of corn stalk core under an inert gas atmosphere and further activation process with KOH solution. The mesoporous activated carbon (AC) is characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer-Emmett-Teller (BET) measurements. These biomass waste derived from activated carbon is proved to be promising anode materials for high specific capacity lithium ion batteries. The activated carbon anode possesses excellent reversible capacity of 504 mAh g⁻¹ after 100 cycles at 0.2C. Compared with the unactivated carbon (UAC), the electrochemical performance of activated carbon is significantly improved due to its mesoporous structure.

Graphical abstract

Datum: 25.04.2018

A Quasi Quantum treatment of the Spin Orbit state changing and conserving rotationally inelastic NO(X)-He collisions

Publication date: Available online 22 April 2018
Source:Chemical Physics
Author(s): Xia Zhang, Steven Stolte

A Quasi Quantum treatment (QQT) of the rotational inelastic NO(X)-He collisions in the pure Hund’s case (a) spin orbit state conserving transitions is extended to the mixed Hund’s case (a) spin orbit state conserving and changing transitions. To enable this extension a polar and azimuthal angle dependent intermolecular hard-shell PES,

V_{S} (R_{S}, γ_{R}, χ_{R}) = E_{S}

, has been developed. The DCSs and ICSs calculated by QQT are compared with those obtained from QM exact calculations onto a full R-range ab initio PES. The rotationally inelastic scattering of NO(X) from He presents a paradigm for the rotationally inelastic scattering at a thermal collision energy of molecules residing in a

Π

electronic rotational eigenstate.

Datum: 25.04.2018

Editorial Board

Publication date: 11 May 2018
Source:Chemical Physics, Volume 507

Datum: 25.04.2018

State-to-state quantum dynamics of the H + LiF → Li + HF reaction on an accurate ab initio potential energy surface

Publication date: Available online 22 April 2018
Source:Chemical Physics
Author(s): Changjian Xie, Xinguo Liu, Hua Guo

Quantum state-to-state dynamics calculations are reported for the H + LiF(vi, ji) → HF(vf, jf) + Li reaction on a recently reported ground state

({\tilde{X}}^{2} A^{'})

potential energy surface. It was found that at low collision energies the title reaction is dominated by long-lived resonances, while the lifetimes of resonances become shorter at higher energies. The existence of resonances is also supported by the differential cross section, which has mostly forward and sideways bias. The integral cross section rises with collision energy slowly, and the opacity function suggests that the reaction is dominated by small impact parameter collisions. The HF product has cold vibrational state distributions in range of the collision energy studied here, although its rotational state distributions peak near the highest accessible rotational states. This early-barrier reaction shows some enhancement by translational energy, but internal excitations of the LiF reactant have more complex behaviors.

Graphical abstract

Datum: 25.04.2018

Facilely prepared, N, O-codoped nanosheet derived from pre-functionalized polymer as supercapacitor electrodes

Publication date: 27 April 2018
Source:Chemical Physics, Volume 506
Author(s): Jun Wang, Ting Yang, Zheling Zeng, Shuguang Deng

Nitrogen and oxygen codoped carbon nanosheets derived from pre-functionalized polymer were prepared using a facile direct pyrolysis method. The carbon microstructures are tunable with micro- and mesopore size distribution and a large specific surface area (1628.9–2146.1 m² g⁻¹). Furthermore, a significant morphology change, from carbon granules to carbon nanosheets, occurred at an annealing temperature of 1273 K. The unique carbon sheet morphology guaranteed a good specific capacitance of 246.4 F g⁻¹ at 0.5 A g⁻¹ in 1 M H2SO4 aqueous solution and an excellent rate capability with a retention of 87.9% at 5 A g⁻¹ as coin cell. The outstanding capacitance attributes to the combination of pseudocapacitance due to the N,O dual-doping and unique nanosheet morphology. Moreover, its outstanding cycling performance with 95% retention over 10,000 cycles at 10 A g⁻¹ and an acceptable energy density of 8.6 Wh kg⁻¹ at 0.2 A g⁻¹ make the N,O-codoped carbon nanosheet potent and promising electrode material for high performance supercapacitors.

Graphical abstract

Datum: 25.04.2018

Solvent induced fluorescence enhancement of graphene oxide studied by ultrafast spectroscopy

Publication date: 31 May 2018
Source:Chemical Physics, Volume 508
Author(s): Litao Zhao, Jinquan Chen, Xiaoxiao He, Xiantong Yu, Shujun Yan, Sanjun Zhang, Haifeng Pan, Jianhua Xu

Femtosecond transient absorption (TA) spectroscopy combined with picosecond time resolved fluorescence (TRF) were used to reveal the fluorescence kinetics of graphene oxide (GO) in water, ethanol and water-ethanol mixtures. Size-independent fluorescence of GO were observed in water, and pH-dependent fluorescence spectra could be fitted well by a triple emission relaxation with peaks around 440 nm, 500 nm, and 590 nm respectively. The results indicate that polycyclic aromatic hydrocarbons (PAHs) linked by oxygen-containing functional groups dominate GO’s fluorescence emission. GO’s fluorescence quantum yield was measured to be 2.8% in ethanol but 1.2% in water. The three decay components fluorescence decay, as well as the transient absorption dynamics with an offset, confirmed this solvent induced fluorescence enhancement. GO’s Raman spectral signals showed that GO in ethanol has a smaller average size of PAHs than that of GO in water. Therefore, besides other enhancement effects reported in literatures, we proposed that solvents could also change the size of PAHs, resulting in a photoluminescence enhancement. Our experimental data demonstrates that GO’s quantum yield could be up to 2.8% in water and 8.4% in ethanol and this observation may help ones to improve GO’s photoluminescence efficiency as well as its applications in solution.

Datum: 25.04.2018

Thermodynamic study of quercetin and rutin mixtures with alcohols

Publication date: 13 April 2018
Source:Chemical Physics, Volume 505
Author(s): Katarzyna Szymczyk, Anna Taraba

The paper presents interactions between quercetin (3,3′,4′,5,7-pentahydroxyflavone) and its glycoside, rutin with short chain alcohols, methanol, ethanol and 1-propanol studied by the surface tension measurements. An attempt was made to investigate the effect of flavonoid and alcohol concentrations as well as temperature on the thermodynamic parameters of alcohols adsorption at the water-air interface that is the standard free enthalpy, enthalpy and entropy of adsorption as well as the infinite dilution activity coefficient. The obtained results show that the mixtures of quercetin with methanol and rutin with ethanol are characterized by the best adsorption properties but all studied systems become less structured after adsorption.

Graphical abstract

Datum: 25.04.2018

Category: Current Chemistry Research

Last update: 28.03.2018.

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