Role of Hydrogen Bond in Polypeptides - ^2HNMR Studies in the Lyotropic Liquid Crystalline State

1. 用固态多肽合成器制备了DP值为25 ~ 50的单分散PBLG样品。在含有CHCl_3和DCA的混合溶剂中，螺旋线圈跃迁用^1H-和^<13>C-NMR记录。这些样品在整个双相区域表现出两种不同的化学位移：一种来自螺旋部分，另一种来自线圈部分。这些观察结果与Nagayame等人先前报道的结果相反。对于聚（β-对氯苯- l -天冬氨酸）和聚（β-五氟苯乙基l -天冬氨酸）等体系，研究了聚（天冬氨酸酯）特有的螺旋感反转现象。发现侧链末端的化学修饰引起聚合物溶解度的明显变化，并最终改变了螺旋-螺旋转变温度。这些结果表明，α-螺旋构象中氢键的稳定性随着侧链结构和周围溶剂的性质而敏感地改变。进一步的研究正在进行中，以阐明内部氢键的这些独特特征。

1. Monodisperse PBLG samples having DP of 25 〜 50 have been prepared by using a solid-state peptide synthesizer. The helix-coil transitions in a mixed solvent comprising CHCl_3 and DCA were followed by ^1H- and ^<13>C-NMR. These samples exhibited two separate chemical shifts over the entire biphasic region : one from the helical and the other from the coil part. These observations are in contraditoin to those previously reported by Nagayame et al.2. The helix-sense inversion phenomena peculiar to poly(aspartic acid ester)s has been studies for systems such as poly (β-p-chlorobenzyl L-aspartate) and poly(β-pentafluorophenethyl L-aspartate). Chemical modifications at the sidechain terminal were found to cause appreciable changes in the solubility of polymers, and eventually the helix-helix transition temperatures were shifted. These results indicate that the stability of hydrogen bonds involved in the α-helix conformation sensitively alters with the sidechain structure as well as the character of the surrounding solvents. Further investigations are underway to elucidate these unique characteristics of the internal hydrogen-bonds.