UCLA

In a previous article (Concepts Magn Reson 22A(1) 37-49 (2004)), the initial setup of the C-13 CP/MAS experiment was described. The advantages of the experiment over direct C-13 excitation were also given. In this article, the experiment is applied to three polymorphic structures of glycine. Temperature calibration of the experiment to investigate molecular dynamics as a function of temperature is also described. Though the C-13 CP/MAS experiment is widely applicable, it cannot be universally used. The C-13 CP/MAS experiment works at ambient temperature for both the alpha and gamma polymorphic structures of glycine. However, the cross-polarization technique fails to provide a signal at low temperature from either polymorph. The failure of the technique for both polymorphs arises from the shortened H-1 T-1rho at low temperatures. This shortened T-1rho results from the hindered rotation of the -NH3 group. The technique even fails at ambient temperature for beta-glycine. Again, the reason is a shortened H-1 T-1rho. (C) 2004 Wiley Periodicals, Inc.