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], the conformal change Form Ⅱ→ occurs with decrease of the viscosity; in the second region $-[α]_D$=360 to 140], a guasiend-to-end (Q-E-E) aggregation, which induces viscosity increase, starts to occur while the transition Form II$\rightarrow$I occurs continually and in the third region $-[α]_D$ =140 to 15] a side-by-side (S-S) type aggregation of Form Ⅰ or an end-to-end (E-E) type aggregation occurs according to the solvent situation, i.e., in water-content rich medium (W/PrOH=1/9 or 1/7 v/v), the (S-S) type aggregation with a gross decrease in viscosity occurs while in watercontnet poor medium (W/PrOH=1/29 or 1/15.7 v/v), the (E-E) type aggregation with a large increase in viscosity occurs. The effects of initial concentration $C_0$ (from Ⅱ) and temperature on the (E-E) and (S-S) aggregaion were also studied. In parallel with viscosity measurements, the light-scattering experiment of the PLP system was conducted, the results support the conclusions obtained from the viscosity measurements. By considering the structure of PLP, a reasonable mechanism of the (S-S) and (E-E) aggregation which occurs with the transition Form Ⅱ→Ⅰ is considered.
In Chapter Ⅲ, the conformational transition of Form Ⅱ Form Ⅰ of poly (L-proline) (PLP) and the intermolecular aggregation of the product form Ⅰ during and after the transition in acetic acid/propanol, benzyl alchol/propanol and water/propanol (1/9 v/v) were studied; the molecular weights of PLP being $M_v$ = 54,000, 31,000, 19,000 and 7,6000. For the study, the viscosity change and excess light scattering intensity 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 end-to-end (E-E) type aggregation occurs favorably during and after the transition in high molecular weight PLP irrespective of solvents, but it occurs most favorably in benzyl alchol/propanol (1/9 v/v) than in the solvents of acetic acid/propanol and water/propanol (1/9 v/v). On the contarary, a side-by-side (S-S) type aggregation occurs favorably in water/propanol (1/9 v/v). The quasi-end-to-end (Q-E-E) type aggregation, which induces viscosity increase, occurs in the samples of $M_v$=54,000 and 31, 000 in the middle range of transition. The concentration effect of Form Ⅱ for (S-S) type aggregation in the sample of $M_v$ =19,000 was also studied in acetic acid/propanol and water/propanol (1/9 v/v). The result exhibits that concentration of Form Ⅱ promotes the (S-S) type aggregation during and after the transition Form Ⅱ→Ⅰ. The results of light-scattering experiment support the conclusions obtained from the viscosity measurements.
In Chapter Ⅳ, morphological studies in the micro-end-to-end (m-E-E) and-side-by-side (m-S-S)) aggregation were conducted for the samples precipitated by heating of the end-products of the transition of Form Ⅱ→Ⅰ in poly (L-proline). The observed morphology of the systems shows a rope-type (super helical-type) and pebbles-type aggregate for the (m-E-E) and (m-S-S-) aggregate respectively. The viscosities were also measured during the heatprecipitation in order to know the process of formation of the rope- and pebbles-type aggregates. The result for the (m-E-E) aggregations exhibits two steps, i.e., at first, the viscosity increase with time (step 1), thereafter it decreases until attain the last value (step 2). But the (m-S-S) aggregations shows only one step in the decrease in viscosity. On the basies of all experimental results it is possible to propose a reasonable mechanism for the formation of the two types of aggregates.
Poly-L-proline(PLP)이 acetic acid-, water-propanol (1:9 V/V) 용매에서 Form Ⅱ→ Form Ⅰ 형태 전이와 그 형태 전이 동안에 분자간 응집(aggregation) 현상에 관하여 연구되었다. 이 응집현상의 상세한 원인과 성질을 규명하기 위하여 측정기기로는 점도계(viscometer), 광산란분산기(lighter scattering), 동력학적인 광산란분산기(dynamic lighter scattering) 측정방법들이 이용되었다.
실험결과에서는, PLP 의 분자량이 M$_v$ =31,000 일때 acetic acid-propanol (1:9 V/V) 용매에서는 Form Ⅱ→Form Ⅰ 형태 전이 동안 뿐만 아니라 후에도 end-to-end (E-E) type 의 응집이 일어났다. 또한 이러한 (E-E) type 의 응집은, 극성용매인 acetic acid 의 양이 증가할수록 또 온도가 증가할수록 감소하였다.
그러나, water-propanol (1:9V/V) 용매에서는 PLP 가 그 형태 전이 동안에 생성되는 Form Ⅰ 부분끼리 (서로 반대 방향) side-by-side (S-S)type의 응집이 일어 났었다. 이 용매에서의 (S-S) 응집은 Form Ⅱ→Ⅰ 전이 동안 생성되는 Form Ⅱ 사슬안의 Form Ⅰ 양에 상당히 의존하였다. 즉, Form Ⅰ 분율이 $f_Ⅰ$=0.34일 때 (S-S)응집이 일어나기 시작하고 $f_Ⅰ ＞ 0.76$ 일때 이 (S-S)응집은 매우 강하게 일어 났었다. 이 용매에서의 응집은 water-propanol 공용매에서 water의 양에 상당히 의존하였다. 즉, water의 양이 매우 작을 때 ( ＜ 6.0%) (S-S)응집대신에 (E-E)응집이 일어났다. 또 온도가 증가하면 할수록 (S-S) 응집은 매우 촉진되는 것이 발견되었다.
PLP의 전이 동안의 응집현상은 분자량에 상당히 의존하였는데 Form Ⅱ→Ⅰ 전이를 일으키는 용매에 관계없이, PLP 의 분자량이 높을수록 (S-S) 응집보다 (E-E)응집이 일어나려는 경향이 강하고, 반대로 분자량이 낮을수록 (S-S) 응집이 유리하게 일어났었다. PLP의 (E-E)와 (S-S)응집이 일어난계에 대한 전자현미경 사진에 의한 morphology 의 관찰도 또한 행하였다. 그 관찰의 결과는 (E-E) 응집이 일어난계에서는 기본구조가 모두 rope-type 의 응집물로 이루어져 있고, 반대로 (S-S)응집이 일어난계에서는 기본구조가 pebbles-type의 응집물로 이루어져 있었다. 그리고 열석출이 일어나는 동안에 점성도의 측정결과로 부터 미세-(E-E) 응집물과 미세-(S-S) 응집물이 각각 어떻게 rope-type 응집물과 pebbles-type의 응집물을 형성하는 것에 대한 mechanism을 효과적으로 설명할 수 있었다.
