HYDROGEN-BONDED STRUCTURE AND NMR PARAMETERS OF O-17 LABELED POLY(L-ALANINE)S AS STUDIED BY SOLID-STATE O-17 NMR-SPECTROSCOPY

O-17-labeled poly(l-alanine)s with different degrees of polymerization were synthesized. These poly(l-alanine)s take an ct-helix form and a B-sheet form. Solid state O-17 NMR spectra of these polymers were meas ured at different frequencies. By comparing the obtained spectrum and theoretical simulation, the NMR parameters, such as the quadrupolar co upling constant and chemical shift tensor components, were determined. The relationship between the hydrogen-bonded structure and the NMR pa rameters was elucidated in relation to the main-chain conformation. In addition, these results were compared with those of polyglycine as re ported previously, and the feature of O-17 NMR behavior of these polyp eptides, associated with the hydrogen-bonded structure, was discussed. (C) 1998 Elsevier Science B.V.