Diffusional Behavior of Poly(beta-benzyl L-aspartate)in the Rodlike,Random-Coil,and Intermediate Forms as Studied by High Field-Gradient ~1H NMR Spectroscopy

摘要

The diffusion coefficients of poly(beta-benzyl L-aspartate)(PBLA)with the alpha-helix (rodlike)form in chloroform and the random-coil form in a mixture of chloroform and trifluoroacetic acid have been measured as a function of the PBLA concentration (CPBLA)by using high field-gradient 'H NMR.The PBLA concentration range for the former is from 0.11 to 9.20 wt % and for the latter it is from 0.20 to 25.2 wt %.From these experimental results,it is found that the diffusion coefficient of PBLA in the rodlike form is much smaller than that of PBLA in the random-coil form at the same PBLA concentration.This implies that the small diffusion coefficients of PBLA in the rodlike form as compared with those in the random-coil form come from the relatively large radius of gyration R_g.Further,it is found that the diffusional behavior of PBLA in the rodlike form is different in the three PBLA concentration regions,that is,region 1 (C_(PBLA)= 0.11 approx0.39 wt %),region 2 (C_(PBLA)= 0.39approx0.86 wt %),and region 3 (C_(PBLA)= 0.86approx9.20 wt %).In the random-coil form,the diffusion is different in the two PBLA concentration regions,that is,region I (C_PBLA)= 0.20approx1.03 wt %)and region II (C_(PBLA)1.03approx25.2 wt %).These diffusional behaviors in the rodlike form and in the random-coil form can be reasonably explained by Tinland-Maret-Rinaudo theory and de Gennes theory,respectively.Further,transitional change from the rodlike form to the random-coil form is discussed on the basis of the diffusional behavior.