Maeda Katsuhiro, Kamiya Nobuto, Yashima Eiji
Department of Molecular Design and Engineering, Graduate School of Engineering, Nagoya University, Chikusa-ku, Nagoya 464-8603, Japan.
Chemistry. 2004 Aug 20;10(16):4000-10. doi: 10.1002/chem.200400315.
Optically active, cis-transoid poly(phenylacetylene) derivatives bearing a poly(gamma-benzyl-L-glutamate) [poly(PBGAm)] or poly(L-glutamic acid) [poly(PGAm)] chain as the pendant were prepared by polymerisation of the corresponding macromonomer with a rhodium catalyst followed by hydrolysis of the pendant ester groups. Their conformational changes in solution, induced by a helix-coil transition of the pendant polypeptides, were investigated using circular dichroism (CD) and absorption spectroscopies. A series of macromonomers with a different peptide chain lengths was synthesised by the polymerisation of the N-carboxyanhydride of gamma-benzyl-L-glutamate with a phenylacetylene bearing an alanine residue as the initiator. The obtained macromonomers (PBGAm) were further polymerised with a rhodium catalyst in N,N-dimethylformamide (DMF) to yield novel poly(phenylacetylene)s [poly(PBGAm)] with a poly(gamma-benzyl-L-glutamate) pendant. The poly(PBGAm) exhibited an induced circular dichroism (ICD) in the UV/Vis region of the polymer backbone in dimethyl sulfoxide (DMSO), probably due to the prevailing one-handed helix formation. The Cotton effect signs of a DMSO solution of the poly(PBGAm) were inverted and accompanied by a visible colour change in the presence of an increasing amount of chloroform or DMF containing lithium chloride. The results suggest that poly(PBGAm) may undergo a conformational change such as a helix-helix transition with a different helical pitch responding to a change in the alpha-helix content of the poly(gamma-benzyl-L-glutamate) pendant. Moreover, a water-soluble poly(PGAm) also showed a similar, but dramatic change in its helical conformation with a visible colour change stimulated by a helix-coil transition of the pendant poly(L-glutamic acid) chains by changing the pH in water.
通过相应的大分子单体与铑催化剂聚合，随后水解侧酯基，制备了带有聚（γ-苄基-L-谷氨酸）[聚（PBGAm）]或聚（L-谷氨酸）[聚（PGAm）]链作为侧基的光学活性顺反式聚（苯乙炔）衍生物。使用圆二色性（CD）和吸收光谱研究了由侧链多肽的螺旋-线圈转变引起的它们在溶液中的构象变化。通过γ-苄基-L-谷氨酸的N-羧基酸酐与带有丙氨酸残基的苯乙炔作为引发剂聚合，合成了一系列具有不同肽链长度的大分子单体。将得到的大分子单体（PBGAm）在N，N-二甲基甲酰胺（DMF）中进一步用铑催化剂聚合，得到带有聚（γ-苄基-L-谷氨酸）侧基的新型聚（苯乙炔）[聚（PBGAm）]。聚（PBGAm）在二甲基亚砜（DMSO）中聚合物主链的紫外/可见区域表现出诱导圆二色性（ICD），这可能是由于主要形成了单手螺旋。在存在越来越多的氯仿或含氯化锂的DMF时，聚（PBGAm）的DMSO溶液的科顿效应符号反转并伴有可见颜色变化。结果表明，聚（PBGAm）可能经历构象变化，例如螺旋-螺旋转变，其螺旋间距不同，响应于聚（γ-苄基-L-谷氨酸）侧基的α-螺旋含量的变化。此外，水溶性聚（PGAm）在水中通过改变pH值，其螺旋构象也表现出类似但显著的变化，并伴有由侧链聚（L-谷氨酸）链的螺旋-线圈转变刺激的可见颜色变化。
