-
[show abstract]
[hide abstract]
ABSTRACT: The ability of some liquids to vitrify during supercooling is usually seen as a consequence of the rates of crystal nucleation (and∕or crystal growth) becoming small [D. R. Uhlmann, J. Non-Cryst. Solids 7, 337 (1972)] - and thus a matter of kinetics. However, there is evidence dating back to the empirics of coal briquetting for maximum trucking efficiency [D. Frenkel, Physics 3, 37 (2010)] that some object shapes find little advantage in self-assembly to ordered structures - meaning random packings prevail. Noting that key studies of non-spherical object packing have never been followed from hard ellipsoids [A. Donev, F. H. Stillinger, P. M. Chaikin, and S. Torquato, Phys. Rev. Lett. 92, 255506 (2004); A. Donev, I. Cisse, D. Sachs, E. A. Variano, F. H. Stillinger, R. Connelly, S. Torquato, and P. M. Chaikin, Science 303, 990 (2004)] or spherocylinders [S. R. Williams and A. P. Philipse, Phys. Rev. E 67, 051301 (2003)] (diatomics excepted [S.-H. Chong, A. J. Moreno, F. Sciortino, and W. Kob, Phys. Rev. Lett. 94, 215701 (2005)] into the world of molecules with attractive forces, we have made a molecular dynamics study of crystal melting and glass formation on the Gay-Berne (G-B) model of ellipsoidal objects [J. G. Gay and B. J. Berne, J. Chem. Phys. 74, 3316 (1981)] across the aspect ratio range of the hard ellipsoid studies. Here, we report that in the aspect ratio range of maximum ellipsoid packing efficiency, various G-B crystalline states that cannot be obtained directly from the liquid, disorder spontaneously near 0 K and transform to liquids without any detectable enthalpy of fusion. Without claiming to have proved the existence of single component examples, we use the present observations, together with our knowledge of non-ideal mixing effects, to discuss the probable existence of "ideal glassformers" - single or multicomponent liquids that vitrify before ever becoming metastable with respect to crystals. We find evidence that "ideal glassformer" systems might also be highly fragile systems, approaching the "ideal glass" condition. We link this to the high "volume fragility" behavior observed in recent hard dumbbell studies at similar length∕diameter ratios [R. Zhang and K. S. Schweitzer, J. Chem. Phys. 133, 104902 (2010)]. The discussion suggests some unusual systems for laboratory study. Using differential scanning calorimetry detection of fusion points Tm, liquidus temperatures Tl, and glass transition temperatures Tg, we describe a system that would seem incapable of crystallizing before glass transition, i.e., an "ideal glassformer." The existence of crystal-free routes to the glassy state will eliminate precrystalline fluctuations as a source of the dynamic heterogeneities that are generally considered important in the discussion of the "glassy state problem [P. W. Anderson, Science 267, 1615 (1995)]."
The Journal of chemical physics 03/2013; 138(12):12A549. · 3.09 Impact Factor
-
Dmitry V. Matyushov
[show abstract]
[hide abstract]
ABSTRACT: Spontaneous polarization of the interface, typically found for water in
contact with hydrophobic solutes, couples with the uniform external field to
produce a non-zero force acting on a suspended particle. This force exists even
in the absence of a net particle charge, and its direction is affected by
first-order, dipolar and second-order, qudrupolar orientational order
parameters of the interfacial water. The quadrupolar polarization gives rise to
an effectively negative charge. The corresponding surface charge density is
inversely proportional to the area of the shear surface. The overall
contribution from the quadrupolar polarization of the interface to the particle
mobility becomes negligible compared to experimentally reported values for
particles exceeding a few nanometers in size. The dipolar order of the
interface dominates the zero-charge mobility of sub-micron particles. The
corresponding effective charge is determined by the preferential orientation of
the interfacial dipoles relative to the surface normal.
12/2012;
-
[show abstract]
[hide abstract]
ABSTRACT: Elastic network models coarse grain proteins into a network of residue beads connected by springs. We add dissipative dynamics to this mechanical system by applying overdamped Langevin equations of motion to normal-mode vibrations of the network. In addition, the network is made heterogeneous and softened at the protein surface by accounting for hydration of the ionized residues. Solvation changes the network Hessian in two ways. Diagonal solvation terms soften the spring constants and off-diagonal dipole-dipole terms correlate displacements of the ionized residues. The model is used to formulate the response functions of the electrostatic potential and electric field appearing in theories of redox reactions and spectroscopy. We also formulate the dielectric response of the protein and find that solvation of the surface ionized residues leads to a slow relaxation peak in the dielectric loss spectrum, about two orders of magnitude slower than the main peak of protein relaxation. Finally, the solvated network is used to formulate the allosteric response of the protein to ion binding. The global thermodynamics of ion binding is not strongly affected by the network solvation, but it dramatically enhances conformational changes in response to placing a charge at the active site of the protein.
The Journal of chemical physics 10/2012; 137(16):165101. · 3.09 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We show that electrostatic fluctuations of the protein-water interface are globally non-Gaussian. The electrostatic component of the optical transition energy (energy gap) in a hydrated green fluorescent protein is studied here by classical molecular dynamics simulations. The distribution of the energy gap displays a high excess in the breadth of electrostatic fluctuations over the prediction of the Gaussian statistics. The energy gap dynamics include a nanosecond component. When simulations are repeated with frozen protein motions, the statistics shifts to the expectations of linear response and the slow dynamics disappear. We therefore suggest that both the non-Gaussian statistics and the nanosecond dynamics originate largely from global, low-frequency motions of the protein coupled to the interfacial water. The non-Gaussian statistics can be experimentally verified from the temperature dependence of the first two spectral moments measured at constant-volume conditions. Simulations at different temperatures are consistent with other indicators of the non-Gaussian statistics. In particular, the high-temperature part of the energy gap variance (second spectral moment) scales linearly with temperature and extrapolates to zero at a temperature characteristic of the protein glass transition. This result, violating the classical limit of the fluctuation-dissipation theorem, leads to a non-Boltzmann statistics of the energy gap and corresponding non-Arrhenius kinetics of radiationless electronic transitions, empirically described by the Vogel-Fulcher-Tammann law.
The Journal of Physical Chemistry B 08/2012; · 3.70 Impact Factor
-
Dmitry V Matyushov
[show abstract]
[hide abstract]
ABSTRACT: We present a theory of the dielectric response of solutions containing large solutes, of the nanometer size, in a molecular solvent. It combines the molecular dipole moment of the solute with the polarization of a large subensemble of solvent molecules at the solute-solvent interface. The goal of the theory is two-fold: (i) to formulate the problem of the dielectric response avoiding the reliance on the cavity-field susceptibility of dielectric theories and (ii) to separate the non-additive polarization of the interface, jointly produced by the external field of the laboratory experiment and the solute, from specific solute-solvent interactions contributing to the dielectric signal. The theory is applied to experimentally reported frequency-dependent dielectric spectra of lysozyme in solution. The analysis of the data in the broad range of frequencies up to 700 GHz shows that the cavity-field susceptibility, critical for the theory formulation, is consistent with the prediction of Maxwell's electrostatics in the frequency range of 10-200 GHz, but deviates from it outside this range. In particular, it becomes much smaller than the Maxwell result, and shifts to negative values, at small frequencies. The latter observation implies a dia-electric response, or negative dielectrophoresis, of hydrated lysozyme. It also implies that the effective protein dipole recorded by dielectric spectroscopy is much smaller than the value calculated from the protein's charge distribution. We suggest an empirical equation that describes both the increment of the static dielectric constant and the decrement of the Debye water peak with increasing protein concentration. It gives fair agreement with broad-band dispersion and loss spectra of protein solutions, but misses the δ-dispersion region.
Journal of Physics Condensed Matter 07/2012; 24(32):325105, 1-8. · 2.55 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We propose a dissipative electro-elastic network model to describe the dynamics and statistics of electrostatic fluctuations at active sites of proteins. The model combines the harmonic network of residue beads with overdamped dynamics of the normal modes of the network characterized by two friction coefficients. The electrostatic component is introduced to the model through atomic charges of the protein force field. The overall effect of the electrostatic fluctuations of the network is recorded through the frequency-dependent response functions of the electrostatic potential and electric field at the protein active site. We also consider the dynamics of displacements of individual residues in the network and the dynamics of distances between pairs of residues. The model is tested against loss spectra of residue displacements and the electrostatic potential and electric field at the heme's iron from all-atom molecular dynamics simulations of three hydrated globular proteins.
Physical Biology 05/2012; 9(3):036004. · 2.60 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: This paper aims to understand the statistics of the electric field produced by water interfacing a non-polar solute of nanometer dimension. We study, by numerical simulations, the interface between SPC/E water and a Kihara solute, which is a hard-sphere core with a Lennard-Jones layer at its surface. The distribution of the interfacial electric field is monitored as a function of the magnitude of a point dipole placed close to the solute-water interface. The free energy surface as a function of the electric field projected on the dipole direction shows a cross-over with increasing dipole magnitude. While it is a single-well harmonic function at low dipole values, it becomes a double-well surface at intermediate dipole moment magnitudes, transforming into a single-well surface again, with a non-zero minimum position, at still higher dipoles. This transformation, reminiscent of a discontinuous phase transition in bulk materials, has a broad intermediate region where the interfacial waters fluctuate between the two minima. This region is characterized by intense field fluctuations, with non-Gaussian statistics and variance far exceeding expectations from the linear-response approximation. The excited state of the surface water is found to be lifted above the ground state by the energy required to break approximately two hydrogen bonds. This state is pulled down in energy by the external electric field of the solute dipole, making it readily accessible to thermal excitations. The excited state is a surface defect in the hydrogen-bond network, creating a stress in the nearby network, but otherwise relatively localized in the region closest to the solute dipole.
The Journal of chemical physics 09/2011; 135(10):104501. · 3.09 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Electric field produced inside a solute by a uniformly polarized liquid is strongly affected by dipolar polarization of the liquid at the interface. We show, by numerical simulations, that the electric "cavity" field inside a hydrated non-polar solute does not follow the predictions of standard Maxwell's electrostatics of dielectrics. Instead, the field inside the solute tends, with increasing solute size, to the limit predicted by the Lorentz virtual cavity. The standard paradigm fails because of its reliance on the surface charge density at the dielectric interface determined by the boundary conditions of the Maxwell dielectric. The interface of a polar liquid instead carries a preferential in-plane orientation of the surface dipoles thus producing virtually no surface charge. The resulting boundary conditions for electrostatic problems differ from the traditional recipes, affecting the microscopic and macroscopic fields based on them. We show that relatively small differences in cavity fields propagate into significant differences in the dielectric constant of an ideal mixture. The slope of the dielectric increment of the mixture versus the solute concentration depends strongly on which polarization scenario at the interface is realized. A much steeper slope found in the case of Lorentz interfacial polarization also implies a higher free energy penalty for polarizing such mixtures.
The Journal of chemical physics 08/2011; 135(8):084514. · 3.09 Impact Factor
-
Dmitry V Matyushov
[show abstract]
[hide abstract]
ABSTRACT: We report numerical simulations of three hydrated heme proteins, myoglobin, cytochrome c, and cytochrome B562. The properties of interest are the dynamics and statistics of the electric field and electrostatic potential at heme's iron, as well as their separation into the protein and water components. We find that the electric field produced by both the protein and the hydration water relaxes on the time scale of 3-6 ns, and the relaxation time of the electrostatic potential is close to 1 ns. The slow dynamics of the electrostatic observables is accompanied by their large variances. For the electrostatic potential, a large amplitude of its fluctuations leads to a gigantic reorganization energy of a half redox reaction changing the redox state of the protein. Both a large magnitude and a slow relaxation time of the electric field fluctuations are required to explain the onset of large mean-square displacements of iron at the point of protein's dynamical transition. These requirements are met by the simulations which are used to explain the temperature dependence of heme iron displacements measured by Mössbauer spectroscopy. All three phenomena, (i) nanosecond dynamics, (ii) protein dynamical transition and a large high-temperature excess of atomic mean-square displacements, and (iii) the gigantic reorganization energy, are explained here by one physical mechanism. This mechanism involves two components: nanosecond motions of the protein surface residues and polarization of the interfacial water by the protein charges. Global nanosecond conformations of the protein move the surface water. Since water is polarized, these movements create large-amplitude electrostatic fluctuations, sufficient to modify displacements of groups inside the protein and yield reorganization energies of protein electron transfer far exceeding those found for small molecules. Water follows adiabatically the protein motions. Therefore, the relaxation times of the protein and its hydration layer are close, leading to matching temperatures of the dynamical transition for the two components.
The Journal of Physical Chemistry B 08/2011; 115(36):10715-24. · 3.70 Impact Factor
-
Dmitry V. Matyushov
[show abstract]
[hide abstract]
ABSTRACT: Atomic displacements of hydrated proteins are dominated by phonon vibrations at low temperatures and by dissipative large-amplitude motions at high temperatures. A crossover between the two regimes is known as a dynamical transition. Recent experiments indicate a connection between the dynamical transition and the dielectric response of the hydrated protein. We analyze two mechanisms of the coupling between the protein atomic motions and the protein-water interface. The first mechanism considers viscoelastic changes in the global shape of the protein plasticized by its coupling to the hydration shell. The second mechanism involves modulations of the local motions of partial charges inside the protein by electrostatic fluctuations. The model is used to analyze mean-square displacements of iron of metmyoglobin reported by Mössbauer spectroscopy. We show that high displacement of heme iron at physiological temperatures is dominated by electrostatic fluctuations. Two onsets, one arising from the viscoelastic response and the second from electrostatic fluctuations, are seen in the temperature dependence of the mean-square displacements when the corresponding relaxation times enter the instrumental resolution window.
Phys. Rev. E. 07/2011; 84(1).
-
[show abstract]
[hide abstract]
ABSTRACT: Atomic displacements of hydrated proteins are dominated by phonon vibrations at low temperatures and by dissipative large-amplitude motions at high temperatures. A crossover between the two regimes is known as a dynamical transition. Recent experiments indicate a connection between the dynamical transition and the dielectric response of the hydrated protein. We analyze two mechanisms of the coupling between the protein atomic motions and the protein-water interface. The first mechanism considers viscoelastic changes in the global shape of the protein plasticized by its coupling to the hydration shell. The second mechanism involves modulations of the local motions of partial charges inside the protein by electrostatic fluctuations. The model is used to analyze mean-square displacements of iron of metmyoglobin reported by Mössbauer spectroscopy. We show that high displacement of heme iron at physiological temperatures is dominated by electrostatic fluctuations. Two onsets, one arising from the viscoelastic response and the second from electrostatic fluctuations, are seen in the temperature dependence of the mean-square displacements when the corresponding relaxation times enter the instrumental resolution window.
Physical Review E 07/2011; 84(1 Pt 1):011908. · 2.26 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The ability of some liquids to vitrify during supercooling is usually seen as
a consequence of the rates of crystal nucleation (and/or crystal growth)
becoming small- thus a matter of kinetics. However there is evidence, dating
back to the empirics of coal briquetting for maximum trucking efficiency, that
ellipsoids pack efficiently when disordered. Noting that key studies of
non-spherical object packing have never been followed from hard ellipsoids or
spherocylinders (diatomics excepted) into the world of molecules with
attractive forces, we have made a molecular dynamics MD study of crystal
melting and glass formation on the Gay- Berne (G-B) model of ellipsoidal
objects across the aspect ratio range of the hard ellipsoid studies. Here we
report that, in the aspect ratio range of maximum ellipsoid packing efficiency,
various G-B crystalline states, that cannot be obtained directly from the
liquid, disorder spontaneously near 0 K and transform to liquids without any
detectable enthalpy of fusion. Without claiming to have proved the existence of
single component examples, we use the present observations, together with our
knowledge of non-ideal mixing effects, to discuss the probable existence of
"ideal glassformers" - single or multicomponent liquids that vitrify before
ever becoming metastable with respect to crystals. The existence of
crystal-free routes to the glassy state removes any precrystalline fluctuation
perspective from the "glass problem". Unexpectedly we find that liquids with
aspect ratios in the "crystallophobic" range also behave in an unusual
(non-hysteritic) way during temperature cycling through the glass transition.
We link this to the highly volume fraction-sensitive ("fragile") behavior
observed in recent hard dumbbell studies at similar length/diameter ratios.
11/2010;
-
[show abstract]
[hide abstract]
ABSTRACT: Atomic displacements of hydrated proteins are dominated by phonon vibrations at low temperatures and by dissipative large-amplitude motions at high temperatures. A crossover between the two regimes is known as a dynamical transition. Recent experiments indicate a connection between the dynamical transition and the dielectric response of the hydrated protein. We analyze two mechanisms of the coupling between the protein atomic motions and the protein-water interface. The first mechanism considers viscoelastic changes in the global shape of the protein plasticized by its coupling to the hydration shell. The second mechanism involves modulations of the motions of partial charges inside the protein by electrostatic fluctuations. The model is used to analyze mean square displacements of iron of metmyoglobin reported by Moessbauer spectroscopy. We show that high flexibility of heme iron at physiological temperatures is dominated by electrostatic fluctuations. Two onsets, one arising from the viscoelastic response and the second from electrostatic fluctuations, are seen in the temperature dependence of the mean square displacements when the corresponding relaxation times enter the instrumental resolution window.
11/2010;
-
[show abstract]
[hide abstract]
ABSTRACT: Despite its diversity, life universally relies on a simple basic mechanism of energy transfer in its energy chains-hopping electron transport between centers of electron localization on hydrated proteins and redox cofactors. Since many such hops connect the point of energy input with a catalytic site where energy is stored in chemical bonds, the question of energy losses in (nearly activationless) electron hops, i.e., energetic efficiency, becomes central for the understanding of the energetics of life. We show here that standard considerations based on rules of Gibbs thermodynamics are not sufficient, and the dynamics of the protein and the protein-water interface need to be involved. The rate of electronic transitions is primarily sensitive to the electrostatic potential at the center of electron localization. Numerical simulations show that the statistics of the electrostatic potential produced by hydration water are strongly non-Gaussian, with the breadth of the electrostatic noise far exceeding the expectations of the linear response. This phenomenon, which dramatically alters the energetic balance of a charge-transfer chain, is attributed to the formation of ferroelectric domains in the protein's hydration shell. These dynamically emerging and dissipating domains make the shell enveloping the protein highly polar, as gauged by the variance of the shell dipole which correlates with the variance of the protein dipole. The Stokes-shift dynamics of redox-active proteins are dominated by a slow component with the relaxation time of 100-500 ps. This slow relaxation mode is frozen on the time-scale of fast reactions, such as bacterial charge separation, resulting in a dramatically reduced reorganization free energy of fast electronic transitions. The electron transfer activation barrier becomes a function of the corresponding rate, self-consistently calculated from a non-ergodic version of the transition-state theory. The peculiar structure of the protein-water interface thus provides natural systems with two "non's"-non-Gaussian statistics and non-ergodic kinetics-to tune the efficiency of the redox energy transfer. Both act to reduce the amount of free energy released as heat in electronic transitions. These mechanisms are shown to increase the energetic efficiency of protein electron transfer by up to an order of magnitude compared to the "standard picture" based on canonical free energies and the linear response approximation. In other words, the protein-water tandem allows both the formation of a ferroelectric mesophase in the hydration shell and an efficient control of the energetics by manipulating the relaxation times.
Physical Chemistry Chemical Physics 10/2010; 12(47):15335-48. · 3.57 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Numerical simulations of hydrated proteins show that protein hydration shells are polarized into a ferroelectric layer with large values of the average dipole moment magnitude and the dipole moment variance. The emergence of the new polarized mesophase dramatically alters the statistics of electrostatic fluctuations at the protein-water interface. The linear response relation between the average electrostatic potential and its variance breaks down, with the breadth of the electrostatic fluctuations far exceeding the expectations of the linear response theories. The dynamics of these non-Gaussian electrostatic fluctuations are dominated by a slow (approximately = 1 ns) component that freezes in at the temperature of the dynamical transition of proteins. The ferroelectric shell propagates 3-5 water diameters into the bulk.
The Journal of Physical Chemistry B 07/2010; 114(28):9246-58. · 3.70 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We present the results of numerical simulations of the electrostatics and dynamics of water hydration shells surrounding Kihara cavities given by a Lennard-Jones (LJ) layer at the surface of a hard-sphere cavity. The local dielectric response of the hydration layer substantially exceeds that of bulk water, with the magnitude of the dielectric constant peak in the shell increasing with the growing cavity size. The polar shell propagates into bulk water to approximately the cavity radius. The statistics of the electrostatic field produced by water inside the cavity follow linear response and approach the prediction of continuum electrostatics with increasing cavity size. Comment: 4 pages, 4 figures
04/2010;
-
Dmitry V Matyushov
[show abstract]
[hide abstract]
ABSTRACT: A theory of radiation absorption by dielectric mixtures is presented. The coarse-grained formulation is based on the wave-vector-dependent correlation functions of molecular dipoles of the host polar liquid and a density structure factor of the solutes. A nonlinear dependence of the dielectric absorption coefficient on the solute concentration is predicted and originates from the mutual polarization of the liquid surrounding the solutes by the collective field of the solute dipoles aligned along the radiation field. The theory is applied to terahertz absorption of hydrated saccharides and proteins. While the theory gives an excellent account of the observations for saccharides, without additional assumptions and fitting parameters, experimental absorption coefficient of protein solutions significantly exceeds theoretical calculations with dipole moment of the bare protein assigned to the solute and shows a peak against the protein concentration. A substantial polarization of protein's hydration shell, resulting in a net dipole moment, is required to explain the disagreement between theory and experiment. When the correlation function of the total dipole moment of the protein with its hydration shell from numerical simulations is used in the analytical model, an absorption peak, qualitatively similar to that seen in experiment, is obtained. The existence and position of the peak are sensitive to the specifics of the protein-protein interactions. Numerical testing of the theory requires the combination of dielectric and small-angle scattering measurements. The calculations confirm that "elastic ferroelectric bag" of water shells observed in previous numerical simulations is required to explain terahertz dielectric measurements.
Physical Review E 02/2010; 81(2 Pt 1):021914. · 2.26 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We report the results of extensive numerical simulations and theoretical calculations of electronic transitions in the reaction center of Rhodobacter sphaeroides photosynthetic bacterium. The energetics and kinetics of five electronic transitions related to the kinetic scheme of primary charge separation have been analyzed and compared to experimental observations. Nonergodic formulation of the reaction kinetics is required for the calculation of the rates due to a severe breakdown of the system ergodicity on the time scale of primary charge separation, with the consequent inapplicability of the standard canonical prescription to calculate the activation barrier. Common to all reactions studied is a significant excess of the charge-transfer reorganization energy from the width of the energy gap fluctuations over that from the Stokes shift of the transition. This property of the hydrated proteins, breaking the linear response of the thermal bath, allows the reaction center to significantly reduce the reaction free energy of near-activationless electron hops and thus raise the overall energetic efficiency of the biological charge-transfer chain. The increase of the rate of primary charge separation with cooling is explained in terms of the temperature variation of induction solvation, which dominates the average donor-acceptor energy gap for all electronic transitions in the reaction center. It is also suggested that the experimentally observed break in the Arrhenius slope of the primary recombination rate, occurring near the temperature of the dynamical transition in proteins, can be traced back to a significant drop of the solvent reorganization energy close to that temperature.
The Journal of Physical Chemistry B 09/2009; 113(36):12424-37. · 3.70 Impact Factor
-
Dmitry V Matyushov
[show abstract]
[hide abstract]
ABSTRACT: Equilibrium in the electronic subsystem across the solution-metal interface is considered to connect the standard electrode potential to the statistics of localized electronic states in solution. We argue that a correct derivation of the Nernst equation for the electrode potential requires a careful separation of the relevant time scales. An equation for the standard metal potential is derived linking it to the thermodynamics of solvation. The Anderson-Newns model for electronic delocalization between the solution and the electrode is combined with a bilinear model of solute-solvent coupling introducing nonlinear solvation into the theory of heterogeneous electron transfer. We therefore are capable of addressing the question of how nonlinear solvation affects electrochemical observables. The transfer coefficient of electrode kinetics is shown to be equal to the derivative of the free energy, or generalized force, required to shift the unoccupied electronic level in the bulk. The transfer coefficient thus directly quantifies the extent of nonlinear solvation of the redox couple. The current model allows the transfer coefficient to deviate from the value of 0.5 of the linear solvation models at zero electrode overpotential. The electrode current curves become asymmetric in respect to the change in the sign of the electrode overpotential.
The Journal of chemical physics 07/2009; 130(23):234704. · 3.09 Impact Factor
-
Dmitry V Matyushov
[show abstract]
[hide abstract]
ABSTRACT: A theoretical formulation is developed for the activated kinetics when some subset of nuclear modes of the thermal bath is slower than the reaction and ergodicity of the thermal bath is not maintained. Nonergodic free energy profiles along the reaction coordinate are constructed by using restricted canonical ensembles with the phase space available to the system found by solving a self-consistent kinetic equation. The resulting activation barrier incorporates not only thermodynamic parameters but also dynamical information from the time autocorrelation function of the solute-solvent interaction energy. The theory is applied to the reactions of solvolysis and charge transfer in polar media.
The Journal of chemical physics 05/2009; 130(16):164522. · 3.09 Impact Factor
