CONFORMATIONAL AND DYNAMICAL BEHAVIORS OF CROSS-LINKED POLY(GAMMA-METHYL L-GLUTAMATE) GEL AS STUDIED BY HIGH-RESOLUTION SOLID-STATE C-13 NMR-SPECTROSCOPY

Cross-linked poly(gamma-methyl L-glutamate) (PMLG) was prepared by the ester-amide exchange reaction using diaminodode cane as a cross-linke r and was swollen by chloroform (CHCl3), trifluoroacetic acid (TFA) an d a mixture of TFA and CHCl3. The structural and dynamical analyses of the PMLG gel were carried out by means of high-resolution solid-state C-13 NMR spectroscopy. From the experimental results on C-13 chemical shifts of amide carbonyl and C, carbons of the polypeptide, it was fo und that the main-chain conformation of cross-linked PMLG was changed from the alpha-helix form to the random-coil form with an increase in the TFA content. Further, from the experimental results on C-13 spin-l attice relaxation time (T-1) and H-1 spin-spin relaxation time (T-2) i t was found that the molecular motion of the amide carbonyl carbon is in the slow-motion region and the ester carbonyl carbon is in the extr eme-narrowing region. The mobility of the cross-linked PMLG becomes mu ch faster with an increase in the TFA content through the helix-coil t ransition. (C) 1998 Elsevier Science B.V.