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Papers by Alexey Odinokov

Research paper thumbnail of Structural Degradation and Swelling of Lipid Bilayer under the Action of Benzene

The Journal of Physical Chemistry B, 2015

Benzene and other nonpolar organic solvents can accumulate in the lipid bilayer of cellular membr... more Benzene and other nonpolar organic solvents can accumulate in the lipid bilayer of cellular membranes. Their effect on the membrane structure and fluidity determines their toxic properties and antibiotic action of the organic solvents on the bacteria. We performed molecular dynamics simulations of the interaction of benzene with the dimyristoylphosphatidylcholine (DMPC) bilayer. An increase in the membrane surface area and fluidity was clearly detected. Changes in the acyl chain ordering, tilt angle, and overall bilayer thickness were, however, much less marked. The dependence of all computed quantities on the benzene content showed two regimes separated by the solubility limit of benzene in water. When the amount of benzene exceeded this point, a layer of almost pure benzene started to grow between the membrane leaflets. This process corresponds to the nucleation of a new phase and provides a molecular mechanism for the mechanical rupture of the bilayer under the action of nonpolar compounds.

Research paper thumbnail of Computer Simulation of Shallow Traps Created by Impurity Molecules in Anthracene Crystal

The Journal of Physical Chemistry C, 2016

Research paper thumbnail of Microscopic jump mechanism of electron conductivity in photosensitive materials

Russian Journal of Physical Chemistry a, Oct 10, 2014

Research paper thumbnail of Molecular dynamics simulation of the glass transition in 4,4′-N,N′-dicarbazolylbiphenyl

Chemical Physics Letters, 2015

Viscoelastic properties of the molecular liquid consisting of 4,4 -N,N -dicarbazolylbiphenyl (CBP... more Viscoelastic properties of the molecular liquid consisting of 4,4 -N,N -dicarbazolylbiphenyl (CBP) molecules near the glass transition temperature are investigated by molecular dynamics simulations. The relaxation dynamics is analyzed by considering each molecule as a point-like oriented particle. The dependence of the calculated properties on the coarse-grain parameter used in the calculation of orientation correlation is analyzed. The divergence of ˛-relaxation times is described by the Vogel-Fulcher-Tammann law and the mode coupling theory. The basic concepts of the glass transition theory are applied to a real amorphous organic semiconductor.

Research paper thumbnail of Specific Interactions of Neutral Side Chains of an Adsorbed Protein with the Surface of α-Quartz and Silica Gel

The journal of physical chemistry. B, 2015

Many key features of the protein adsorption on the silica surfaces still remain unraveled. One of... more Many key features of the protein adsorption on the silica surfaces still remain unraveled. One of the open questions is the interaction of nonpolar side chains with siloxane cavities. Here, we use nonequilibrium molecular dynamics simulations for the detailed investigation of the binding of several hydrophobic and amphiphilic protein side chains with silica surface. These interactions were found to be a possible driving force for protein adsorption. The free energy gain was larger for the disordered surface of amorphous silica gel as compared to α-quartz, but the impact depended on the type of amino acid. The dependence was analyzed from the structural point of view. For every amino acid an enthalpy-entropy compensation behavior was observed. These results confirm a hypothesis of an essential role of hydrophobic interactions in protein unfolding and irreversible adsorption on the silica surface.

Research paper thumbnail of Molecular Dynamic Simulation of Transmembrane Pore Growth

The Journal of Membrane Biology, 2013

A molecular dynamic approach was applied for simulation of dynamics of pore formation and growth ... more A molecular dynamic approach was applied for simulation of dynamics of pore formation and growth in a phospholipid bilayer in the presence of an external electric field. Processing the simulation results permitted recovery of the kinetic coefficients used in the Einstein-Smoluchowski equation describing the dynamics of pore evolution. Two different models of the bilayer membrane were considered: membrane consisting of POPC and POPE lipids. The simulations permitted us to find nonempirical values of the pore energy parameters, which are compared with empirical values. It was found that the parameters are sensitive to membrane type.

Research paper thumbnail of The dielectric continuum solvent model adapted for treating preferential solvation effects

Journal of Electroanalytical Chemistry, 2011

Theoretical investigation of electrostatic solvation effects in binary solvent mixtures composed ... more Theoretical investigation of electrostatic solvation effects in binary solvent mixtures composed of nonpolar and polar ingredients require the elaboration of advanced continuum solvent models in order to treat explicitly the non-uniformity of the dielectric medium, which is an inherent feature of such complicated systems. The present article gives a concise account of the appropriate continuum-level theory developed recently and tested on the solutions of spherical Born ions in the mixtures of benzene and dimethylsulfoxide (DMSO). Its further application for studies of the interaction of ion pairs in the same solvent mixtures with the DMSO contents varying in a wide range is reported. The results are compared with the MD simulations of the same systems which allows for the proper calibration of the parameters of the continuum solvent model.

Research paper thumbnail of Decay kinetics of the excited S1 state of the cyanine dye Cy+I- (thiacarbocyanine iodide): The computation of quantum yields for different pathways

Chemical Physics, 2011

This work explains the unordinary solvent effect which was observed in the photochemical decay ki... more This work explains the unordinary solvent effect which was observed in the photochemical decay kinetics for the cyanine dye thiacarbocyanine iodide (Cy(+)I(-)) in binary solvent mixtures toluene/dimethylsulfoxide. The interpretation is formulated in terms of the probability density F(R) describing the distribution of interionic distances R in the ion pair Cy(+)I(-) and depending on the solvent composition. The proper normalization of this distribution is expressed via the degree of association α for the ion pair in a given solvent mixture. The α values are, in turn, extracted by means of the mass action law from the ionic association constants computed in a separate publication. The detailed kinetic scheme includes the empirical parametrization of the R-dependent kinetic constants for different decay channels. The multiparameter fitting procedure represents, with the reasonable parameter values, the dependence of the observed quantum yields on the solvent composition.

Research paper thumbnail of Association constants and distribution functions for ion pairs in binary solvent mixtures: Application to a cyanine dye system

Chemical Physics, 2011

The computations of the association constants K(ass) were performed at the microscopic level for ... more The computations of the association constants K(ass) were performed at the microscopic level for the ion pair Cy(+)I(-) composed of the complex cyanine dye cation Cy(+) coupled to the negative iodine counterion. The wide array of K(ass) values is arranged by a variation of the composition of the binary solvent mixtures toluene/dimethylsulfoxide with the accompanying change of the solvent polarity. The potentials of mean force (PMFs) are calculated for a set of interionic separations R in the Cy(+)I(-) by a methodology which combines the quantum-chemical techniques for the treatment of the electronic structure of the Cy(+)I(-) system with the recent dielectric continuum approach which accounts for the solvation effects. For a given solute/solvent system the probability function P(R), which describes the distribution of interionic separations, is constructed in terms of the PMFs and implemented for the evaluation of the K(ass).

Research paper thumbnail of Potential of mean force for ion pairs in non-aqueous solvents. Comparison of polarizable and non-polarizable MD simulations

Molecular Physics, 2011

ABSTRACT Potentials of mean force (PMF) are calculated for two model ion pairs in two non-aqueous... more ABSTRACT Potentials of mean force (PMF) are calculated for two model ion pairs in two non-aqueous solvents. Standard non-polarizable molecular dynamics simulation (NPMD) and approximate polarizable simulation (PMD) are implemented and compared as tools for monitoring PMF profiles. For the polar solvent (dimethylsulfoxide, DMSO) the PMF generated in terms of the NPMD reproduces fairly well the refined PMD–PMF profile. For the non-polar solvent (benzene) the conventional NPMD computation proves to be deficient. The validity of the correction found in terms of the approximate PMD approach is verified by its comparison with the result of the explicit PMD computation in benzene. The shapes of the PMF profiles in DMSO and in benzene are quite different. In DMSO, owing to dielectric screening, the PMF presents a flat plot with a shallow minimum positioned in the vicinity of the van der Waals contact of the ion pair. For the benzene case, the observed minimum proves to be unexpectedly deep, which manifests the formation of a tightly-binded contact ion pair. This remarkable effect arises owing to the strong electrostatic interaction that is incompletely screened by a non-polar medium. The PMFs for the binary benzene/DMSO mixtures display intermediate behaviour depending on the DMSO content.

Research paper thumbnail of Molecular Simulation of Solvent-Induced Stokes Shift in Absorption/Emission Spectra of Organic Chromophores

Journal of Physical Chemistry B, 2007

The values of steady-state solvatochromic Stokes shifts (SS) in absorption/emission electronic sp... more The values of steady-state solvatochromic Stokes shifts (SS) in absorption/emission electronic spectra of organic chromophores are studied theoretically in the framework of the Hush-Marcus model. Charge distributions for chromophore solutes in their S0 and S1 states are found by means of conventional quantum-chemical methods combined with the continuum PCM approach for treating solvation effects. The solvent reorganization energies, which are expected to correlate with the solvent-induced part of 1/2 SS, are found in a molecular dynamics (MD) simulation which invokes a novel method for separation of the inertial piece of the electrostatic response (Vener, et al. J. Phys. Chem. B 2006, 110, 14950). Computations, performed in two solvents (acetonitrile and benzene), consider three organic dyes: coumarin 153 as a benchmark system and two other chromophores, for which experimental spectra are also reported. The results are found to be in reasonable agreement with the experiment. A consistent treatment of nonlinear effect in the solvent response, promoted by the polarizability of solutes and contributing to the solvent reorganization energies (Ingrosso, et al. J. Phys. Chem. B 2005, 109, 3553), improves the results of computations.

Research paper thumbnail of Multiscale Approach to the Structure and Spectra of Nile Red Adsorbed on Polystyrene Nanoparticles

Iop Conference Series: Materials Science and Engineering, 2012

The structure and absorption spectra of the Nile Red (NR) dye adsorbed on the surface of a polyst... more The structure and absorption spectra of the Nile Red (NR) dye adsorbed on the surface of a polystyrene (PS) nanoparticle is studied by DFT/TDDFT based on the results of previous molecular dynamics (MD) simulations. From NR/PS surface structures obtained from MD simulations, relatively small clusters were constructed composed of the adsorbed NR molecule and the nearest PS fragments. These clusters were treated either explicitly by DFT/TDDFT or using the effective fragment potentials (EFP) model. The absorption and emission spectra of the NR/PS system calculated using the EFP model are very close to those calculated with the explicit environment, so that the EFP model can be recommended for use in multiple large-scale calculations. The calculated positions of the absorption and fluorescence bands are in good agreement with experiment.

Research paper thumbnail of Advanced dielectric continuum model of preferential solvation

Chemical Physics, 2009

A continuum model for solvation effects in binary solvent mixtures is formulated in terms of the ... more A continuum model for solvation effects in binary solvent mixtures is formulated in terms of the density functional theory. The presence of two variables, namely, the dimensionless solvent composition y and the dimensionless total solvent density z, is an essential feature of binary systems. Their coupling, hidden in the structure of the local dielectric permittivity function, is postulated at the phenomenological level. Local equilibrium conditions are derived by a variation in the free energy functional expressed in terms of the composition and density variables. They appear as a pair of coupled equations defining y and z as spatial distributions. We consider the simplest spherically symmetric case of the Born-type ion immersed in the benzene/dimethylsulfoxide (DMSO) solvent mixture. The profiles of y(R) and z(R) along the radius R, which measures the distance from the ion center, are found in molecular dynamics (MD) simulations. It is shown that for a given solute ion z(R) does not depend significantly on the composition variable y. A simplified solution is then obtained by inserting z(R), found in the MD simulation for the pure DMSO, in the single equation which defines y(R). In this way composition dependences of the main solvation effects are investigated. The local density augmentation appears as a peak of z(R) at the ion boundary. It is responsible for the fine solvation effects missing when the ordinary solvation theories, in which z=1, are applied. These phenomena, studied for negative ions, reproduce consistently the simulation results. For positive ions the simulation shows that z>1 (z=5-6 at the maximum of the z peak), which means that an extremely dense solvation shell is formed. In such a situation the continuum description fails to be valid within a consistent parametrization.

Research paper thumbnail of Preferential solvation of spherical ions in binary DMSO/benzene mixtures

Chemical Physics, 2009

We consider a new qualitative approach for treating theoretically the solvation of single-atomic ... more We consider a new qualitative approach for treating theoretically the solvation of single-atomic ionic solutes in binary mixtures of polar and nonpolar aprotic solvents. It is based on the implicit continuum electrostatic model of the solvent mixture involving distance-dependent dielectric permittivity epsilon(R) (where R is the distance from the ion) and local concentrations C(1)(R) and C(2)(R) of the solvent ingredients. For a given R, the condition for local thermodynamic equilibrium provides the transcendental equation for explicitly establishing the permittivity and concentration profiles. Computations performed with real Cl(-) and model Cl(+) ions as solutes in benzene/DMSO mixtures are compared with the molecular dynamics simulations of the same systems. A significant discrepancy of molecular and continuum results is revealed for the concentration profiles in the close vicinity of the ion boundary, although the general trends are similar. The continuum methodology cannot account for the formation of rigid solvent structures around ions, which is most significant for the case of Cl(+). Such defect, however, proves to become of less importance in calculations of the solvation free energy, which are quite satisfactory for Cl(-) ion. Free energy calculations for Cl(+) are less successful in the range of low DMSO concentration.

Research paper thumbnail of Structural Degradation and Swelling of Lipid Bilayer under the Action of Benzene

The Journal of Physical Chemistry B, 2015

Benzene and other nonpolar organic solvents can accumulate in the lipid bilayer of cellular membr... more Benzene and other nonpolar organic solvents can accumulate in the lipid bilayer of cellular membranes. Their effect on the membrane structure and fluidity determines their toxic properties and antibiotic action of the organic solvents on the bacteria. We performed molecular dynamics simulations of the interaction of benzene with the dimyristoylphosphatidylcholine (DMPC) bilayer. An increase in the membrane surface area and fluidity was clearly detected. Changes in the acyl chain ordering, tilt angle, and overall bilayer thickness were, however, much less marked. The dependence of all computed quantities on the benzene content showed two regimes separated by the solubility limit of benzene in water. When the amount of benzene exceeded this point, a layer of almost pure benzene started to grow between the membrane leaflets. This process corresponds to the nucleation of a new phase and provides a molecular mechanism for the mechanical rupture of the bilayer under the action of nonpolar compounds.

Research paper thumbnail of Computer Simulation of Shallow Traps Created by Impurity Molecules in Anthracene Crystal

The Journal of Physical Chemistry C, 2016

Research paper thumbnail of Microscopic jump mechanism of electron conductivity in photosensitive materials

Russian Journal of Physical Chemistry a, Oct 10, 2014

Research paper thumbnail of Molecular dynamics simulation of the glass transition in 4,4′-N,N′-dicarbazolylbiphenyl

Chemical Physics Letters, 2015

Viscoelastic properties of the molecular liquid consisting of 4,4 -N,N -dicarbazolylbiphenyl (CBP... more Viscoelastic properties of the molecular liquid consisting of 4,4 -N,N -dicarbazolylbiphenyl (CBP) molecules near the glass transition temperature are investigated by molecular dynamics simulations. The relaxation dynamics is analyzed by considering each molecule as a point-like oriented particle. The dependence of the calculated properties on the coarse-grain parameter used in the calculation of orientation correlation is analyzed. The divergence of ˛-relaxation times is described by the Vogel-Fulcher-Tammann law and the mode coupling theory. The basic concepts of the glass transition theory are applied to a real amorphous organic semiconductor.

Research paper thumbnail of Specific Interactions of Neutral Side Chains of an Adsorbed Protein with the Surface of α-Quartz and Silica Gel

The journal of physical chemistry. B, 2015

Many key features of the protein adsorption on the silica surfaces still remain unraveled. One of... more Many key features of the protein adsorption on the silica surfaces still remain unraveled. One of the open questions is the interaction of nonpolar side chains with siloxane cavities. Here, we use nonequilibrium molecular dynamics simulations for the detailed investigation of the binding of several hydrophobic and amphiphilic protein side chains with silica surface. These interactions were found to be a possible driving force for protein adsorption. The free energy gain was larger for the disordered surface of amorphous silica gel as compared to α-quartz, but the impact depended on the type of amino acid. The dependence was analyzed from the structural point of view. For every amino acid an enthalpy-entropy compensation behavior was observed. These results confirm a hypothesis of an essential role of hydrophobic interactions in protein unfolding and irreversible adsorption on the silica surface.

Research paper thumbnail of Molecular Dynamic Simulation of Transmembrane Pore Growth

The Journal of Membrane Biology, 2013

A molecular dynamic approach was applied for simulation of dynamics of pore formation and growth ... more A molecular dynamic approach was applied for simulation of dynamics of pore formation and growth in a phospholipid bilayer in the presence of an external electric field. Processing the simulation results permitted recovery of the kinetic coefficients used in the Einstein-Smoluchowski equation describing the dynamics of pore evolution. Two different models of the bilayer membrane were considered: membrane consisting of POPC and POPE lipids. The simulations permitted us to find nonempirical values of the pore energy parameters, which are compared with empirical values. It was found that the parameters are sensitive to membrane type.

Research paper thumbnail of The dielectric continuum solvent model adapted for treating preferential solvation effects

Journal of Electroanalytical Chemistry, 2011

Theoretical investigation of electrostatic solvation effects in binary solvent mixtures composed ... more Theoretical investigation of electrostatic solvation effects in binary solvent mixtures composed of nonpolar and polar ingredients require the elaboration of advanced continuum solvent models in order to treat explicitly the non-uniformity of the dielectric medium, which is an inherent feature of such complicated systems. The present article gives a concise account of the appropriate continuum-level theory developed recently and tested on the solutions of spherical Born ions in the mixtures of benzene and dimethylsulfoxide (DMSO). Its further application for studies of the interaction of ion pairs in the same solvent mixtures with the DMSO contents varying in a wide range is reported. The results are compared with the MD simulations of the same systems which allows for the proper calibration of the parameters of the continuum solvent model.

Research paper thumbnail of Decay kinetics of the excited S1 state of the cyanine dye Cy+I- (thiacarbocyanine iodide): The computation of quantum yields for different pathways

Chemical Physics, 2011

This work explains the unordinary solvent effect which was observed in the photochemical decay ki... more This work explains the unordinary solvent effect which was observed in the photochemical decay kinetics for the cyanine dye thiacarbocyanine iodide (Cy(+)I(-)) in binary solvent mixtures toluene/dimethylsulfoxide. The interpretation is formulated in terms of the probability density F(R) describing the distribution of interionic distances R in the ion pair Cy(+)I(-) and depending on the solvent composition. The proper normalization of this distribution is expressed via the degree of association α for the ion pair in a given solvent mixture. The α values are, in turn, extracted by means of the mass action law from the ionic association constants computed in a separate publication. The detailed kinetic scheme includes the empirical parametrization of the R-dependent kinetic constants for different decay channels. The multiparameter fitting procedure represents, with the reasonable parameter values, the dependence of the observed quantum yields on the solvent composition.

Research paper thumbnail of Association constants and distribution functions for ion pairs in binary solvent mixtures: Application to a cyanine dye system

Chemical Physics, 2011

The computations of the association constants K(ass) were performed at the microscopic level for ... more The computations of the association constants K(ass) were performed at the microscopic level for the ion pair Cy(+)I(-) composed of the complex cyanine dye cation Cy(+) coupled to the negative iodine counterion. The wide array of K(ass) values is arranged by a variation of the composition of the binary solvent mixtures toluene/dimethylsulfoxide with the accompanying change of the solvent polarity. The potentials of mean force (PMFs) are calculated for a set of interionic separations R in the Cy(+)I(-) by a methodology which combines the quantum-chemical techniques for the treatment of the electronic structure of the Cy(+)I(-) system with the recent dielectric continuum approach which accounts for the solvation effects. For a given solute/solvent system the probability function P(R), which describes the distribution of interionic separations, is constructed in terms of the PMFs and implemented for the evaluation of the K(ass).

Research paper thumbnail of Potential of mean force for ion pairs in non-aqueous solvents. Comparison of polarizable and non-polarizable MD simulations

Molecular Physics, 2011

ABSTRACT Potentials of mean force (PMF) are calculated for two model ion pairs in two non-aqueous... more ABSTRACT Potentials of mean force (PMF) are calculated for two model ion pairs in two non-aqueous solvents. Standard non-polarizable molecular dynamics simulation (NPMD) and approximate polarizable simulation (PMD) are implemented and compared as tools for monitoring PMF profiles. For the polar solvent (dimethylsulfoxide, DMSO) the PMF generated in terms of the NPMD reproduces fairly well the refined PMD–PMF profile. For the non-polar solvent (benzene) the conventional NPMD computation proves to be deficient. The validity of the correction found in terms of the approximate PMD approach is verified by its comparison with the result of the explicit PMD computation in benzene. The shapes of the PMF profiles in DMSO and in benzene are quite different. In DMSO, owing to dielectric screening, the PMF presents a flat plot with a shallow minimum positioned in the vicinity of the van der Waals contact of the ion pair. For the benzene case, the observed minimum proves to be unexpectedly deep, which manifests the formation of a tightly-binded contact ion pair. This remarkable effect arises owing to the strong electrostatic interaction that is incompletely screened by a non-polar medium. The PMFs for the binary benzene/DMSO mixtures display intermediate behaviour depending on the DMSO content.

Research paper thumbnail of Molecular Simulation of Solvent-Induced Stokes Shift in Absorption/Emission Spectra of Organic Chromophores

Journal of Physical Chemistry B, 2007

The values of steady-state solvatochromic Stokes shifts (SS) in absorption/emission electronic sp... more The values of steady-state solvatochromic Stokes shifts (SS) in absorption/emission electronic spectra of organic chromophores are studied theoretically in the framework of the Hush-Marcus model. Charge distributions for chromophore solutes in their S0 and S1 states are found by means of conventional quantum-chemical methods combined with the continuum PCM approach for treating solvation effects. The solvent reorganization energies, which are expected to correlate with the solvent-induced part of 1/2 SS, are found in a molecular dynamics (MD) simulation which invokes a novel method for separation of the inertial piece of the electrostatic response (Vener, et al. J. Phys. Chem. B 2006, 110, 14950). Computations, performed in two solvents (acetonitrile and benzene), consider three organic dyes: coumarin 153 as a benchmark system and two other chromophores, for which experimental spectra are also reported. The results are found to be in reasonable agreement with the experiment. A consistent treatment of nonlinear effect in the solvent response, promoted by the polarizability of solutes and contributing to the solvent reorganization energies (Ingrosso, et al. J. Phys. Chem. B 2005, 109, 3553), improves the results of computations.

Research paper thumbnail of Multiscale Approach to the Structure and Spectra of Nile Red Adsorbed on Polystyrene Nanoparticles

Iop Conference Series: Materials Science and Engineering, 2012

The structure and absorption spectra of the Nile Red (NR) dye adsorbed on the surface of a polyst... more The structure and absorption spectra of the Nile Red (NR) dye adsorbed on the surface of a polystyrene (PS) nanoparticle is studied by DFT/TDDFT based on the results of previous molecular dynamics (MD) simulations. From NR/PS surface structures obtained from MD simulations, relatively small clusters were constructed composed of the adsorbed NR molecule and the nearest PS fragments. These clusters were treated either explicitly by DFT/TDDFT or using the effective fragment potentials (EFP) model. The absorption and emission spectra of the NR/PS system calculated using the EFP model are very close to those calculated with the explicit environment, so that the EFP model can be recommended for use in multiple large-scale calculations. The calculated positions of the absorption and fluorescence bands are in good agreement with experiment.

Research paper thumbnail of Advanced dielectric continuum model of preferential solvation

Chemical Physics, 2009

A continuum model for solvation effects in binary solvent mixtures is formulated in terms of the ... more A continuum model for solvation effects in binary solvent mixtures is formulated in terms of the density functional theory. The presence of two variables, namely, the dimensionless solvent composition y and the dimensionless total solvent density z, is an essential feature of binary systems. Their coupling, hidden in the structure of the local dielectric permittivity function, is postulated at the phenomenological level. Local equilibrium conditions are derived by a variation in the free energy functional expressed in terms of the composition and density variables. They appear as a pair of coupled equations defining y and z as spatial distributions. We consider the simplest spherically symmetric case of the Born-type ion immersed in the benzene/dimethylsulfoxide (DMSO) solvent mixture. The profiles of y(R) and z(R) along the radius R, which measures the distance from the ion center, are found in molecular dynamics (MD) simulations. It is shown that for a given solute ion z(R) does not depend significantly on the composition variable y. A simplified solution is then obtained by inserting z(R), found in the MD simulation for the pure DMSO, in the single equation which defines y(R). In this way composition dependences of the main solvation effects are investigated. The local density augmentation appears as a peak of z(R) at the ion boundary. It is responsible for the fine solvation effects missing when the ordinary solvation theories, in which z=1, are applied. These phenomena, studied for negative ions, reproduce consistently the simulation results. For positive ions the simulation shows that z>1 (z=5-6 at the maximum of the z peak), which means that an extremely dense solvation shell is formed. In such a situation the continuum description fails to be valid within a consistent parametrization.

Research paper thumbnail of Preferential solvation of spherical ions in binary DMSO/benzene mixtures

Chemical Physics, 2009

We consider a new qualitative approach for treating theoretically the solvation of single-atomic ... more We consider a new qualitative approach for treating theoretically the solvation of single-atomic ionic solutes in binary mixtures of polar and nonpolar aprotic solvents. It is based on the implicit continuum electrostatic model of the solvent mixture involving distance-dependent dielectric permittivity epsilon(R) (where R is the distance from the ion) and local concentrations C(1)(R) and C(2)(R) of the solvent ingredients. For a given R, the condition for local thermodynamic equilibrium provides the transcendental equation for explicitly establishing the permittivity and concentration profiles. Computations performed with real Cl(-) and model Cl(+) ions as solutes in benzene/DMSO mixtures are compared with the molecular dynamics simulations of the same systems. A significant discrepancy of molecular and continuum results is revealed for the concentration profiles in the close vicinity of the ion boundary, although the general trends are similar. The continuum methodology cannot account for the formation of rigid solvent structures around ions, which is most significant for the case of Cl(+). Such defect, however, proves to become of less importance in calculations of the solvation free energy, which are quite satisfactory for Cl(-) ion. Free energy calculations for Cl(+) are less successful in the range of low DMSO concentration.