Hydration of diglycyl tripeptides with non-polar side chains: a volumetric study

We have determined the apparent molar volumes and the apparent molar adiabatic compressibilities at 25 degrees C of 10 X-Gly-Gly and Gly-Gly-X tripeptides in which X represents a residue with a non-polar side chain. We also have determined the changes in volume and compressibility which accompany neutralization of the amino and carboxyl termini in these tripeptides. The mutual influence of the non-polar side chain of the X residue and the terminal amino and carboxyl groups on the hydration of each other depends on the chemical nature of the side chain and the state of ionization of the termini. We interpret our data in terms of the hydration of the component aliphatic, aromatic, and charged atomic groups, as well as the mutual interactions between these groups.