Dehydration of glycine in mixed solvents

Abstract

The analysis of changes in the partial volume of glycine \(\Delta \bar V^0 \) in solutions of substances that have a different effect on water structure is presented. For glycine in mixtures of water with glycerol and ethylene glycol, we derive a single equation for the \(\Delta \bar V^0 \) dependence on the volume fraction of alcohol. The addition of tert-butyl alcohol, ethylene glycol, glycerol, and urea to water leads to a decrease in the hydration number of the amino acid (glycine dehydrates). In 1m solutions the losses of hydration water are 3.2%, 4.5%, 5.7%, and 7.6% respectively. In a 4m solution of tert-butyl alcohol, glycine loses 44% of hydration water, the same as in a 15m urea solution and a 20m glycerol solution. A contribution of the structural dehydration of glycine is observed in dilute aqueous solutions of t-BuOH. In more concentrated solutions, intermolecular interactions in the binary mixed solvent counteract dehydration. These interactions compensate for 15-22% of water lost by glycine in a 20m solution of urea, glycerol, and ethylene glycol and a 4m solution of t-BuOH. The partial volumes are also discussed within preferential solvation concepts.