COMMENT TO C-13-NMR STUDIES OF ALPHA-POLYMORPHS AND GAMMA-POLYMORPHS OF GLYCINE

Glycine provided to research laboratories by chemical companies can co ntain different polymorphs and/or mixture of polymorphs. The alpha- an d gamma-glycine differ slightly in C-13 Shielding parameters and very much in dynamic properties. The isotropic values of chemical shifts fo r carboxyl groups of alpha- and gamma-glycine are found to be delta(is o) =176.50 ppm and delta(iso) = 174.60 ppm, respectively. By using cro ss-polarization contact time equal to 20 ms, the intensity of carboxyl signal arising from gamma-glycine is reduced almost to zero, while th at of alpha-glycine is only slightly depleted compared to the intensit y of signal recorded at contact time of 1 ms. In contrast, for alpha-f orm, the C-13 T-1 relaxation time of carboxyl carbon is five times sho rter compared to gamma-form. (C) 1998 Elsevier Science B.V. All rights reserved.