4.7 Author:
   Kehrer, Armin; Weiden, Norbert; Weiss, Alarich
Reference:
   Journal, ZPCFAX, Z.Phys.Chem.(Munich), EN, 178, 1, 1992, 1-24
Title:
   The Electric Field Gradient at the Bromine and Deuteron Sites in Deuterated Glycyl-L-alanine Hydrobromide Monohydrate and the Iodine Site in Glycyl-L-alanine Hydroiodide Monohydrate. A Single Ctystal NMR/NQR Study
Abstract:
The electric field gradient tensor, EFGT, of 81Br and the EFGT`s of 2H were studied by NMR (4.7 T) at room temperature in deuterated single crystals of glycyl-L-alanine hydrobromide monohydrate. eQFzzh-1 (81Br) is 19.750 MHz, the asymmetry parameter h(81Br) = 0.833.The EFGT(81Br) is oriented in such a way that Fzz is nearly parallel to the shortest hydrogen bond H***Br. Fyy points in the direction of a neighboring positive charge (nitrogen).The 2H EFGT of the ND3 group deuterons is averaged by the dynamics of the ND3 group.One tensor only results, eFzzh-1 (2H) = 53.7 kHz, h(2H) = 0.103.The deuteron at the COOD group shows eFzzh-1 (2H) = 165.5 kHz, h(2H) = 0.088.The direction of Fzz is in the bond direction O-D with a deviation therefrom of 6.8 deg.The D2O molecule in the lattice is flipping at room temperature.Only one EFGT(2H) is observed, eQFzzh-1 = 125.6 kHz, h(2H) = 0.815.The direction of Fzz deviates from the normal of the D2O plane by 13.4 deg.We have not observed the 2H spectrum of the amido hydrogen atom.The EFGT(127I) of glycyl-L-alanine hydroiodide monohydrate was measured by observing the transition ½ <*> 3/2.The orientation of Fzz is strongly dependent from the positive charges of the next nearest neighbors.The results found for the EFGT’s of 81Br, 2H, and 127I are discussed in view of the crystal structure of the isotypic compounds Gly-L-Ala*HX*H2O, X = Br, I.