SPURIOUS COOPERATIVITY IN ALKYLATED SUCCINIC ACIDS

The proton-proton correlation, as measured by the ratio between the se cond and the first dissociation constants of dibasic acid, is sometime s very large and far beyond what could be explained by electrostatic t heories. We propose a novel interpretation of this phenomenon based on the idea of spurious cooperativity. The general theoretical framework underlying the onset of spurious cooperativity is developed first. Th e basic result is that whenever a binding (or dissociating) two-site ( or more) system splits into a mixture of noninterconverting isomers th e binding isotherm (or the titration curve) behaves as if it is more n egatively cooperative compared with the genuine cooperativities of the individual isomer. The theory is applied to a specific system of alph a-alpha' dialkyl succinic acid. It is known that the Meso form of thes e alkylated derivatives show a normal correlation of the same order of magnitude as in succinic acid. On the other hand, the Racemic form of these alkylated derivatives shows anomalous strong negative correlati ons when the alkyl groups become large (e.g., isopropyl and tea butyl) . It is shown that the theory of spurious cooperativity can explain th e different behavior of the Racemic and the Meso forms, as well as the onset of anomalous strong negative correlations when the alkyl groups become large. (C) 1998 American Institute of Physics.