Conformational and dynamical behaviors of cross-linked poly(γ-methyl l-glutamate) gel as studied by high-resolution solid-state 13C NMR spectroscopy

Abstract

Cross-linked poly(γ-methyl l-glutamate) (PMLG) was prepared by the ester-amide exchange reaction using diaminododecane as a cross-linker and was swollen by chloroform (CHCl 3), trifluoracetic acid (TFA) and a mixture of TFA and CHCl 3. The structural and dynamical analyses of the PMLG gel were carried out by means of high-resolution solid-state 13C NMR spectroscopy. From the experimental results on 13C chemical shifts of amide carbonyl and C α carbons of the polypeptide, it was found that the main-chain conformation of cross-linked PMLG was changed from the α-helix form to the random-coil form with an increase in the TFA content. Further, from the experimental results on on 13C spin-lattice relaxation time ( T 1) and 1H spin-spin relaxation time ( T 2) it 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 extreme-narrowing region. The mobility of the cross-linked PMLG becomes much faster with an increase in the TFA content through the helix-coil transition.