Nuclear magnetic resonance relaxation studies of proton exchange in methanol–water mixtures

Abstract

The dependence of the hydroxyl proton transverse relaxation rate on pulse spacing has been used to investigate the mechanisms of proton transfer in methanol–water mixtures of varying pH and composition. At pH values outside the range 6–8 the proton exchange is mainly acid–base catalysed. Within this pH range the dominant exchange mechanism involves a neutral, cyclic transfer of protons. Using these mechanisms it is possible to account quantitatively for the dependence of transverse relaxation rate on pulse spacing, composition and pH. The implications for relaxation studies of more complex aqueous carbohydrate and protein systems are discussed.