Side-chain conformation of poly( l-proline) form II in the crystalline state as studied by high-resolution solid-state 13C NMR spectroscopy

Abstract

High-resolution 13C NMR spectra of poly( l-proline) from II in the solid 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 conformations are different from each other. The behaviour of the main-chain and side-chain conformations of poly( l-proline) was elucidated through the observed 13C NMR chemical shifts and the calculations of the 13C NMR shielding constant and total energy of these polypeptides within the tight-binding INDO/S sum-over-states framework.