Natural-Abundance Oxygen-17 Magnetic Relaxation in Aqueous Solutions of Apolar Amino Acids and Glycine Peptides

The spin-lattice relaxation times, Ti, of H20 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, nh, and the rotational correlation times, Tc , of water molecules around the amino acids and peptides were estimated and compared with that of pure water, TC°. The value of rc /Tc°=1.87 for norleucine is the largest, while those of Tc/Tc° for glycine peptides are almost the same 1.2. The value of nh(Tc /Tc°—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 coefficent, and limiting diffusion coefficients of amino acids and glycine peptides in aqueous solutions.