Partial Molar Volumes and Adiabatic Compressibilities of a Series of Aliphatic Amino Acids and Oligoglycines in D₂O

Abstract

This paper reports the first characterization of the hydration properties of some amino acids and oligoglycines, low molecular weight analogues of proteins, in D2O. Specifically, the partial molar volumes, V°, and adiabatic compressibilities, K°S, of five α-amino acids and five oligoglycines have been determined in D2O at 25 °C. The resulting data have been used to estimate the volume and compressibility contributions of the component nonpolar (methylene group), polar (peptide group), and charged (oppositely charged amino and carboxyl terminal groups) chemical groups. It was found that the volume and compressibility contributions of these charged, polar, and nonpolar groups in D2O are “measurably” distinct from those in H2O. This distinction, in principle, may allow one to develop a method by which differential volumetric measurements of proteins in D2O and H2O can be used to gain insight into the nature of the solvent-exposed protein groups in the absence of detailed structural information.