SOLID-STATE NMR OF GLYCINE IN FROZEN SOLUTION

The properties of a solute dissolved in aqueous solution under a variety of freezing conditions have been investigated by solid-state NMR spectroscopy. A mixing apparatus similar to that used in biological ESR studies has been used to freeze solutions rapidly (∼ 105 K s-1) for study by NMR with a view to applying this to study enzymatic reaction mechanisms. In order to learn more about the structure of the frozen sample, a small molecule with a simple and well-defined molecular motion was studied by solid-state NMR in frozen solution. The relaxation properties of crystalline glycine have been characterized and are dominated by the rotational motion of the ammonium group. The temperature dependence of T1H, T1C, T1ρH, and T1ρC have been determined for α-crystalline glycine and frozen-solution samples prepared with different freezing rates. From these data, activation energies for the molecular motion have been calculated and rationalized in terms of the structures within each state. © 1993 Academic Press, Inc.