Conformal transition of form Ⅱ to form Ⅰ in poly(L-proline)and the aggregation of form I in the transition

Abstract

In Chapter Ⅰ, the conformational transition of Form Ⅱ→Ⅰ of poly-L-proline (PLP) and the intermolecular aggregation of the product, Form I, during and after the transition in the acetic acid/propanol (HOAc/PrOH) mixture solvents were studied, the ratio of HOAc:PrOH being changed as 1:9, 1:6 and 1:4 v/v. For the study, the viscosity, light scattering and dynamic light scattering of the system were measured. The experimental results exhibit that the concentration of Form II promotes the end-to-end (E-E) type aggregation during and after the transition Form Ⅱ→Ⅰ. The extent of aggregation is reduced in the order of the ratios of HOAc/PrOH 1:9, 1:6 and 1:4 v/v. The (E-E) type aggregation is also reduced at higher temperatures. It was also observed that the (E-E) type aggregation occurs abrubtly and strongly after the transition Form Ⅱ→Ⅰ occurred in some extent. The point of the abrupt occurrence depends on the solvents and temperature. The light-scattering and translational diffusion-coefficient measurements also showed similiar phenomena. It was also observed that the side-by-side (S-S) type aggregation occurs when the initial concentration of Form Ⅱ of poly-L-proline is relatively small, and the transition temperature is relatively high (35 and 45℃). All the above mentioned experimental results are explained by a simple principle decribed in the text. In Chapter Ⅱ, the conformational transition of Form Ⅱ→→ Form Ⅰ of polyL-proline and the intermolecular aggregation of the product, Form I, during the transition in water/propanol (W/PrOH) (1/7, 1/9, 1/15.7 and 1/29 v/v) were studied. For the study, the viscosity change, excess light scattering intensity and translational diffusion coefficients were measured in the course of the transition which was determined by the $-[α]_D$ (specific optical rotation) of the sample solution. The experimental results exhibit that the reaction course is roughly divides into three regions: in the first region [ $-[α]_D$=440 to 360], t...