Hydration Structure around the Methylene Group of Glycine Molecule

Neutron diffraction measurements have been carried out on aqueous 4 mol% glycine solutions. The H/D isotopic substitution technique was applied to both methylene-hydrogen (HM) and water-hydrogen (HW) atoms in order to obtain information concerning the hydration structure around the methylene group within the glycine molecule. Structural parameters for the first hydration shell of the methylene-hydrogen atoms were determined as r(HM···OW) = 2.64(1) A and r(HM···HW) = 2.87(1) A from the least squares fitting analysis of the observed first-order difference function, 0H(delta)H(Q), and the partial structure factor, aHMHex(Q), respectively. The first hydration shell of the methylene group involves ca. 2 water molecules per one glycine molecule.