Electrostatic solvation energy component

This equation corresponds to the following three-step process. First, the cavity inside a solvent is created and the molecule is inserted into the cavity. Next, nonpolar interactions between the solute and the solvent are switched on. Finally, the electrostatic interactions between the solute and the solvent are switched on. Of the three components in Eq. (5), the electrostatic component of the solvation energy (AGeie) is by far the largest and is typically of an order of several thousands kcal/mol for an average protein. Consequently, it is convenient to start the examination of different approaches from the electrostatic solvation energy component. 

Given the somewhat ad hoc nature of most specific schemes for evaluating the non-electrostatic components of the solvation free energy, a reliance on a simpler, if somewhat more empirical, scheme has become widely accepted within available continuum models. In essence, the more empirical approach assumes that the free energy associated with the non-electrostatic solvation of any atom will be characteristic for that atom (or group) and proportional to its solvent-exposed surface area. Thus, the molecular Geos may be computed simply as... 

Bliznyuk AA, Gready JE. A new approach to estimation of the electrostatic component of the solvation energy in molecular mechanics calculations. J Phys Chem 1995 99 14506-14513. 

The non-polar component of the solvation free energy is especially important for implicit membrane models as it decreases from a significant positive contribution in aqueous solvent to near zero at the center of the phospholipid bilayer. Without a non-polar term, even hydrophobic solutes would in fact prefer the high-dielectric environment where the electrostatic solvation free energy is more favorable than in a low-dielectric medium. The functional form of the non-polar term may follow a simple switching function [79,80], a calculated free energy insertion profile for molecular oxygen [82,84], or may be parameterized as well with respect to simulation or experimental data. 

Over the recent years implicit solvent models have undergone a transition to relatively mature methodology that is now widely employed in molecular dynamics simulations and related applications. Most popular are implicit solvent models based on a decomposition of the solvation free energy into electrostatic and nonpolar components. The electrostatic free energy is typically obtained according to a continuum electrostatics model that is described by Poisson theory or by the more approximate but much more efficient Generalized Born formalism. 

Atomic radii from Rashin et al. [122] the electrostatic component of the solvation energies are calculated at B3LYP/6-311 + G(d,p) level. 

For solvent models where the cavity/dispersion interaction is parameterized by fitting to experimental solvation energies, the use of a few explicit solvent molecules for the first solvation sphere is not recommended, as the parameterization represents a best fit to experimental data without any explicit solvent present. The electrostatic component of eq. (14.49) can be described at several different levels of approximation, as discussed in the following sections. 

Solvating ability of mixed solvent differs from solvating ability of individual components. In addition to the permittivity change and the correspondent electrostatic interaction energy change, this is also caused by a number of reasons, the most important of which are discussed in the chapter. 

The terms u ° and Wg are associated with the changes in solvation energy and ionic atmosphere experienced by the reactants and products in the mixed-solvent region. The second and third terms in Eqs (41 and 42) reflect the work involved to displace the ions in and out of the electrified interfaces. Effectively, A and are the potential drop developed between the reaction plane and the bulk of the corresponding electrolyte phase. In the original analysis by Samec [7], these electrostatic components provide the most important contributions to the work terms. This is simply because of the assumption that chemical changes in the ionic environment can be neglected outside the inner compact layer. ... 

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