Hydration Structure of Glycine Molecules in Concentrated Aqueous Solutions

A radial distribution study for aqueous 5 mol% glycine solutions was carried out involving time-of-flight neutron diffraction measurements. An isotopic substitution technique was applied to both nitrogen and hydrogen atoms of the sample in order to determine the hydration structure around the amino group of the glycine molecules in an aqueous solution. It has been clarified that there exist 3.0 ± 0.6 water molecules coordinated to the amino group of a glycine molecule with intermolecular distances of rN···O = 2.85 ± 0.05 Å and rN···D = 3.25 ± 0.05 Å. These values suggest that a hydrogen bond is formed between the amino group of a glycine molecule and the nearest-neighbor water molecules in the aqueous glycine solution.