Natural-abundance oxygen-17 magnetic relaxation in aqueous solutions of apolar amino acids and glycine peptides

Abstract

The spin-lattice relaxation times, T1, of H217O have been measured for the aqueous solutions of 11 apolar amino acids and 5 glycine peptides as a function of the concentration at 25°C. The coordination numbers, n(h), and the rotational correlation times, ε(c)(h), of water molecules around the amino acids and peptides were estimated and compared with that of pure water, ε(c)(o). The value of ε(c)(h)/ε(c)(o)=1.87 for norleucine is the largest, while those of ε(c)(h)/ε(c)(o) for glycine peptides are almost the same 1.2. The value of n(h)(ε(c)(h)/ε(c)(o)-1) was defined as the dynamic hydration number (DHN). The DHN showed a good correlation with several physicochemical properties, such as the molecular weights, partial molar volumes, adiabatic compressibilities, heat capacities, B-coefficients of the activity coefficient, and limiting diffusion coefficients of amino acids and glycine peptides in aqueous solutions.