HYDRATION STRUCTURE OF GLYCINE MOLECULES IN CONCENTRATED AQUEOUS-SOLUTIONS

A radial distribution study for aqueous 5 mol% glycine solutions was c arried out involving time-of-flight neutron diffraction measurements. An isotopic substitution technique was applied to both nitrogen and hy drogen atoms of the sample in order to determine the hydration structu re around the amino group of the glycine molecules in an aqueous solut ion. It has been clarified that there exist 3.0+/-0.6 water molecules coordinated to the amino group of a glycine molecule with intermolecul ar distances of tau(N...o)=2.85+/-0.05 Angstrom and tau(N...D)=3.25+/- 0.05 Angstrom. These values suggest that a hydrogen bond is formed bet ween the amino group of a glycine molecule and the nearest-neighbor wa ter molecules in the aqueous glycine solution.