New mean-energy formulae for free energy differences

Authors: Raineri, Fernando O.1; Stell, George1; Ben-Amotz, Dor2

Source: Molecular Physics, Volume 103, Numbers 21-23, -23/10 November&U8211;10 December 2005 , pp. 3209-3221(13)

Publisher: Taylor and Francis Ltd

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Abstract:

We report a number of new exact expressions, within the realm of classical statistical mechanics, for the solvation contribution Δ A to the free energy change of a solute that undergoes a transformation between two states that differ in the way they interact with the solvent. Our basic result is a coupling-parameter expression that is equivalent to the usual cumulant expansion of Δ A . In our formula, which is derived from a linear coupling-parameter scheme, all the cumulant terms beyond the first one are collected into an integral over the coupling parameter. From this formula, with the help of the mean-value theorems of calculus, we derive exact one- and two-reference-point mean-energy expressions for the solvation free energy change, neither of which is limited to the linear response regime. Both the one- and the two-reference point formulae are given in terms of one distinguished value of the coupling parameter ( and ξ*, respectively) that is not known a priori (except in the linear response regime where we find it exactly). In the case of the two-reference-point formula, we relate ξ* with the cumulative changes of the solvation structure along the intermediate states sampled in the (ξ=0)→(ξ=1) transformation of the solute. Finally, and based on these developments, we present an analysis of the Linear Interaction Energy and of the Extended Linear Response semi-empirical computational methods (widely used for the determination of binding constants of ligand/receptor biological systems) in an effort to understand their statistical mechanical foundations as well as their domain of applicability.

Document Type: Research article

DOI: http://dx.doi.org/10.1080/00268970500298980

Affiliations: 1: Department of Chemistry, State University of New York at Stony Brook, Stony Brook, NY 11794-3400, USA 2: Department of Chemistry, Purdue University, West Lafayette, Indiana 47907-1393, USA

Publication date: 2005-01-01

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