Hydration and convergence temperatures: on the use and interpretation of correlation plots

Abstract

An understanding of the energetics of hydration of protein functional groups is essential to understanding the stability and folding of proteins. Much can be learned about hydration energetics by the study of the transfer of model compounds into water. An important feature, common to model compound dissolution and to protein unfolding, is the presence of convergence temperatures at which Δ S°(orΔ H°) for each compound in a series takes on a common value. Here we review the relationship between convergence and group additivity. Analysis of the aqueous dissolution of gaseous alcohols and alkanes shows a large negative entropy change for the alcohols relative to the alkanes. While this has been taken as leading to entropic stabilization of hydrogen bonding in proteins, it is shown that this negative Δ S° arises from changes in internal degrees of freedom and should not be applied to the analysis of protein energetics.