Comparison between fully deuterated Glycine and hydrogenated Glycine: a single crystal neutron diffraction study

One of the ways of altering the properties of a molecule is to deuterate it. Deuteration leads to change in molecular properties like alteration of spin characteristics, vibrational states, optical properties and even solubility. The recent effort in this direction is to exploit Deuterium kinetic isotope effect (DKIE) in pharmaceutical field to bring out new deuterated drugs with improved pharmacokinetic profiles. It is surprising that Glycine being the simplest amino acid, no neutron structure of deuterated Glycine has been reported till date. In order to study the effect of deutertaion on the hydrogen bonding in Glycine, fully deuterated glycine crystals were grown from deuterated α Glycine in deuterated water. Four circle single crystal diffractometer with BF₃ point detector located at Dhruva Reactor at Trombay was used to collect the single crystal diffraction data at room temperature, neutron wavelength used was 0.995 Å obtained from Cu (220) monochromator crystal. The structural parameters of hydrogenate alpha glycine were used as the starting parameters and were subjected to a series of isotropic and anisotropic full matrix least square refinement using SHELXL. The R-factors obtained were: R[F² > 2 (F²)) = 0. 034, S(goodness of Fit) = 1.15, No. of reflections: 889, No. of parameters: 92. Constrained refinement showed that the hydrogen atoms of amino group were only 40% deuterated, where as C-H hydrogens were fully deuterated. It is observed that partial deuteration of amino group strengthens the hydrogen bonds in deuterated glycine