SIDE-CHAIN CONFORMATION OF POLY(L-PROLINE) FORM-II IN THE CRYSTALLINESTATE AS STUDIED BY HIGH-RESOLUTION SOLID-STATE C-13 NMR-SPECTROSCOPY

High-resolution C-13 NMR spectra of poly(L-proline) form II in the sol id state were measured using the CP MAS and PST/MAS techniques over a wide range of temperatures. From these results. it was found that the pyrrolidine ring in the form II takes two types of conformations, and the mobilities of the pyrrolidine rings in the two types of conformati ons are different from each other. The behaviour of the main-chain and side-chain conformations of poly(L-proline) was elucidated through th e observed C-13 NMR chemical shifts and the calculations of the C-13 N MR shielding constant and total energy of these polypeptides within th e tight-binding INDO/S sum-over-states framework.