Conformational Transition of Form ￥± to Form ￥° PoLy(L-proline) and the Aggregation of Form ￥° in the Transition: Water-Propanol Solvent System

摘要

The conformational transition of poly(L-proline) (PLP), Form ケ ℃ Form グ and the intermolecular aggregation of the product, Form グ, during and after the transition in water-propanol (1:7, 1:9, 1:15.7, and 1:29 v/v) were studied. For the study, the viscosity change and excess light scattering intensity were measured in the course of the transition which was determined by the Form グ fraction, fI of the sample solution. For the PLP sample of molecular weight Mv=31,000 the experimental results show that the reaction course is roughly divided into three regions: in the first region [fI=0.27 to 0.40 (- [メ]D=400 to 330)], the conformational change of Form ケ ℃ Form グ occurs with decrease of viscosity, in the second region [fI=0.40 to 0.80 (- [メ]D=330 to 120)], a partial side-by-side (p-S-S) type aggregation in which Form グ blocks interact with each other, which induces the increase of viscosity, starts to occur, and in the third region [fI=0.80 to 1.00 (- [メ]D=120 to 15)], a side-by-side type (raft like) aggregation of Form グ or an end-to-end (E-E) type aggregation occurs according to the solvent situation, i.e., in a water-rich medium [water-propanol (1:9 or 1:7 v/v)], the (S-S) type aggregation with a gross decrease in viscosity occurs while in a water-poor medium [water-propanol (1:29 or 1:15.7 v/v), the (E-E) type aggregation with a large increase in viscosity occurs. The (S-S) type aggregation was promoted at high temperatures. Based on the structure of PLP, a reasonable mechanism for the (p-S-S) and (S-S) aggregation which occurs with the transition of Form ケ ℃ Form グ is considered. The suggested mechanism was also supported by the result of chain length effect of PLP for the aggregation.