Chenhua Zhao

Diffusional behavior of polypeptides in the thermotropic liquid crystalline state as studied by the pulse field-gradient spin-echo 1H nuclear magnetic resonance method

The self-diffusion coefficients (D) and 1H spin–spin relaxation times (T2) of poly(γ-oleyl L-glutamate)(POLLG) with long oleyl side chains and poly(γ-n-octadecyl L-glutamate)(POLG) with n-alkyl side chains have been measured by the pulse field-gradient spin-echo 1H nuclear magnetic resonance (NMR) method and the Carr–Purcell/Meiboom–Gill (CPMG) 1H NMR method, respectively, over a wide range of temperatures from 30 to 80 °C, in order to elucidate the dynamic behavior of polypeptides in the thermotropic liquid crystalline state, which take the α-helical conformation. From these experiments, it was found that the diffusion coefficients of POLLG and POLG chains in the thermotropic liquid crystalline state at 60 °C are 9.97×10−7 and 3.53×10−7 cm2/s, respectively, and the former diffuses faster than the latter. The diffusion coefficients of POLG in the directions parallel (D∥) and perpendicular (D⊥) to the α-helical chain axis were determined over a wide range of temperatures, and the D∥ value was found to be m...

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 13 C NMR spectroscopy. From the experimental results on 13 C 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 13 C spin-lattice relaxation time ( T 1 ) and 1 H 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.