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Characterization of Hydrogen-bond Correlation Involved in the Helical Structure of Polypeptides and Application to the Molecular Design of Synthetic Polymers

多肽螺旋结构中氢键相关性的表征及其在合成聚合物分子设计中的应用

基本信息

批准号：
18550111
负责人：
ABE Akihiro
金额：
$ 2.6万
依托单位：
Tokyo Polytechnic University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2006
资助国家：
日本
起止时间：
2006 至 2007
项目状态：
已结题

项目摘要

The molecular mechanism involved in the helix-sense reversal characteristic of poly(L-aspartic acid ester)s has been investigated. These man-made polymers are known to form an α-helix in either the right-n or left-handed screw depending on the chemical constitution of the ester group (X) in the side chain. While poly(β-benzyl L-aspartate) (PBLA) remains in the left-handed form in conventional helicoidal solution at all temperatures, poly(β-phenethyl L-aspartate) (PPLA) exhibits transformation from the right-to the left-handed form with increasing temperature. In this work, random copolymers comprising residues of the two opposite screw-sense preference, BLA and PLA, were chosen to investigate the stability of the α-helical hydrogen-bond array in a helix-forming solvent such as chloroform or tetrachloroethane (TCE). Sharp S-shaped transitions of the helix sense were observed for copolymers in the range PLA>50%. ^2H NMR studies of partially deuterated samples in the nematic liquid crystalline environment indicate that the thermally induced helix-sense inversion takes place highly cooperatively along the a-helical backbone. These observations strongly suggest a zipper-type propagation process starting from one terminal to the other. The driving force of the transformation has been traced back to the thermal variation of the side chain conformation. For given copolymer samples, the transition temperatures observed in dilute isotropic solution are nearly identical to those obtained in the liquid crystalline state, suggesting that the transition mechanism remains more or less the same in both media. A theoretical formula prescribed within the Zimm-Bragg concept has been successfully used in interpreting these helix-helix transition phenomena.

已经研究了聚（L-天冬氨酸酯）的螺旋方向反转特征所涉及的分子机制。已知这些人造聚合物可在右旋或左旋螺旋中形成 α 螺旋，具体取决于侧链中酯基 (X) 的化学结构。虽然聚（β-L-天冬氨酸苄酯）（PBLA）在常规螺旋溶液中在所有温度下都保持左旋形式，但聚（β-苯乙基L-天冬氨酸）（PPLA）随着温度的升高表现出从右旋到左旋形式的转变。在这项工作中，选择包含两种相反螺旋方向偏好的残基（BLA 和 PLA）的无规共聚物来研究 α-螺旋氢键阵列在螺旋形成溶剂（如氯仿或四氯乙烷 (TCE)）中的稳定性。对于 PLA>50% 范围内的共聚物，观察到螺旋方向的尖锐 S 形转变。对向列液晶环境中部分氘化样品的^2H NMR研究表明，热诱导的螺旋方向反转沿着α-螺旋主链高度协同地发生。这些观察强烈表明从一个终端到另一个终端的拉链式传播过程。转变的驱动力可以追溯到侧链构象的热变化。对于给定的共聚物样品，在稀各向同性溶液中观察到的转变温度几乎与在液晶状态下获得的转变温度相同，这表明两种介质中的转变机制或多或少保持相同。 Zimm-Bragg 概念中规定的理论公式已成功用于解释这些螺旋-螺旋转变现象。