Theoretical study of electronic and solvent reorganization associated with a charging process of organic compounds. I. Molecular and atomic level description of solvent reorganization (original) (raw)
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Ion solvation dynamics in an interaction-site model solvent
Chemical Physics, 1991
The molecular theory of the frequency-dependent and wavevectordependent longitudinal dielectric function eL( k, w) is derived for fluids comprising interaction-site model molecules in which point charges are located on the interaction sites. We find that cc( k, w) is a simple functional of a particular charge susceptibility X, O (k, o), which in turn is related to a collective chargecharge equilibrium time correlation function. The electrostatic part F &,.,,(t) of the time-dependent free energy of salvation of a solute that instantaneously changes its charge state is, on the other hand, determined by a charge susceptibility x$(k, k', w) of the solvent in the presence of the solute molecule in its initial charg state. Using an approximate relation between x$ and x,,,o we expnss FBom(t) in terms of x,,+. The restthing theory is applied to calculate the solvation time correlation function of the solute immersed in a dipolar hard sphere (DS) and in dipolar dumbbell (DD) model solvent; the mean spherical approximation and an extended mean spherical approximation are used to compute the structure of the DS and DD solvent models, respectively. With parameters chosen so that the two models have the same molecular volume and the same electric dipole moment, it is found that they have very nearly the same eL( k, o) except at large wavevector, but significantly different solvation time correlation ' Present address:
Chemical Physics, 2002
We propose and demonstrate the usefulness of a method, defined as generalized Born electronegativity equalization method (GBEEM) to estimate solvent-induced charge redistribution. The charges obtained by GBEEM, in a representative series of small organic molecules, were compared to PM3-CM1 charges in vacuum and in water. Linear regressions with appropriate correlation coefficients and standard deviations between GBEEM and PM3-CM1 methods were obtained (R=0.94,SD=0.15,Ftest=234,N=32, in vacuum; R=0.94,SD=0.16,Ftest=218,N=29, in water). In order to test the GBEEM response when intermolecular interactions are involved we calculated a water dimer in dielectric water using both GBEEM and PM3-CM1 and the results were similar. Hence, the method developed here is comparable to established calculation methods.
Structure and dynamics of solvent landscapes in charge-transfer reactions
1996
The dynamics of solvent polarization plays a major role in the control of charge-transfer reactions. Although in principle solvent dynamics looks extremely complicated, the success of Marcus theory describing the solvent influence via a single collective quadratic polarization coordinate has been remarkable. Onuchic and Wolynes have recently proposed (J. Chem. Phys. 1993, 98 (3), 2218) a simple solvent model demostrating how a many-dimensional complex system composed of several dipole moments (representing solvent molecules or polar groups in proteins) can be reduced under the appropriate limits into the Marcus model. This work presents a dynamical study of the same model. It is shown that an effective potential, obtained by a thermodynamic approach, provides an appropriate dynamical description. At high temperatures, the system exibits effective diffusive one-dimensional dynamics in this effective potential, where the Born-Marcus limit is recovered. At low temperatures, a glassy phase emerges with a slow non-self-averaging dynamics. At intermediate temperatures, we will discuss the concept of equiValent diffusion paths and polarization-dependent effects. The equivalent paths are necessary to reduce the problem into the Marcus picture. A discussion of how these different regimes affect the rate of charge transfer is presented. † Current address:
Journal of the American Chemical Society, 1994
In this paper, we combine high-level ab initio quantum chemical calculations with a continuum description of the solvent to obtain accurate solvation free energies of organic solutes in water. By using correlated wave functions at the generalized valence bondperfect pairing (GVB-PP) level, we are able to efficiently produce accurate gas-phase charge distributions. These are then used to obtain solvation energies in a self-consistent formalism which cycles through quantum chemical calculations in the solvent reaction field and continuum electrostatic calculations utilizing polarized solute charges. An average error of 0.6 kcal/mol for solvation energies is obtained for 29 molecules. A systematic discrepancy between theory and experiment is obtained for the difference in solvation free energy between several methylated and unmethylated primary amines and amides. This poses a major puzzle in theoretical modeling of solvation effects.
Equilibrium and nonequilibrium solvation and solute electronic structure
International Journal of Quantum Chemistry, 1990
When a molecular solute is immersed in a polar and polarizable solvent, the electronic wave function of the solute system is altered compared to its vacuum value; the solute electronic structure is thus solvent-dependent. Further, the wave function will be altered depending upon whether the polarization of the solvent is or is not in equilibrium with the solute charge distribution. More precisely, while the solvent electronic polarization should be in equilibrium with the solute electronic wave function, the much more sluggish solvent orientational polarization need not be. We call this last situation "nonequilibrium solvation." We outline a nonlinear Schrodinger equation approach to these issues. The nonlinearity arises from the self-consistent aspect that the solute electronic Hamiltonian depends on the solvent electronic polarization which is induced by the solute charge distribution. We illustrate the predictions of the theory for electron transfer reactions, ionic dissociations, and solvation dynamics in polar solvents. Special features of interest include activation barriers that differ markedly from standard predictions, and novel solvent dynamical features.
Theoretical Chemistry Accounts: Theory, Computation, and Modeling (Theoretica Chimica Acta), 2000
Based on the continuum dielectric model, this work has established the relationship between the solvent reorganization energy of electron transfer (ET) and the equilibrium solvation free energy. The dipolereaction ®eld interaction model has been proposed to describe the electrostatic solute-solvent interaction. The self-consistent reaction ®eld (SCRF) approach has been applied to the calculation of the solvent reorganization energy in self-exchange reactions. A series of redox couples, O 2 /O À 2 , NO/NO + , O 3 /O À 3 , N 3 /N À 3 , NO 2 /NO 2 , CO 2 /CO À 2 , SO 2 /SO À 2 , and ClO 2 /ClO À 2 , as well as (CH 2) 2 C-(-CH 2-) n-C(CH 2) 2 (n 1 $ 3) model systems have been investigated using ab initio calculation. For these ET systems, solvent reorganization energies have been estimated. Comparisons between our single-sphere approximation and the Marcus two-sphere model have also been made. For the inner reorganization energies of inorganic redox couples, errors are found not larger than 15% when comparing our SCRF results with those obtained from the experimental estimation. While for the (CH 2) 2 C±(±CH 2 ±) n ±C(CH 2) 2 (n 1 $ 3) systems, the results reveal that the solvent reorganization energy strongly depends on the bridge length due to the variation of the dipole moment of the ionic solute, and that solvent reorganization energies for dierent systems lead to slightly dierent two-sphere radii.
Partial atomic charges and their impact on the free energy of solvation
Journal of computational chemistry, 2013
Free energies of solvation (DG) in water and n-octanol have been computed for common drug molecules by molecular dynamics simulations with an additive fixed-charge force field. The impact of the electrostatic interactions was investigated by computing the partial atomic charges with four methods that all fit the charges from the quantum mechanically determined electrostatic potential (ESP). Due to the redistribution of electron density that occurs when molecules are transferred from gas phase to condensed phase, the polarization impact was also investigated. By computing the partial atomic charges with the solutes placed in a conductorlike continuum, the charges were effectively polarized to take the polarization effects into account. No polarization correction term or similar was considered, only the partial atomic charges. Results show that free energies are very sensitive to the choice of atomic charges and that DG can differ by several k B T depending on the charge computing method. Inclusion of polarization effects makes the solutes too hydrophilic with most methods and in vacuo charges make the solutes too hydrophobic. The restrained-ESP methods together with effectively polarized charges perform well in our test set and also when applied to a larger set of molecules. The effect of water models is also highlighted and shows that the conclusions drawn are valid for different three-point models. Partitioning between an aqueous and a hydrophobic phase is also described better if the two environment's polarization is taken into account, but again the results are sensitive to the charge calculation method. Overall, the results presented here show that effectively polarized charges can improve the description of solvating a drug-like molecule in a solvent and that the choice of partial atomic charges is crucial to ensure that molecular simulations produce reliable results.