HYDRATION AND CONVERGENCE TEMPERATURES - ON THE USE AND INTERPRETATION OF CORRELATION PLOTS

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