Homochiral Evolution in Self-Assembled Chiral Polymers and Block Copolymers.
Homochiral Evolution in Self-Assembled Chiral Polymers and Block Copolymers.
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DOI：
10.1021/acs.accounts.7b00025
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发表时间：
2017-03
影响因子：
18.3
通讯作者：
Tao Wen;Hsiao-Fang Wang;Ming-Chia Li;R. Ho
中科院分区：
文献类型：
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作者：
Tao Wen;Hsiao-Fang Wang;Ming-Chia Li;R. Ho
手性转移的意义不仅涉及生物系统，如生命中同手性结构的起源，而且涉及人造化学物质和材料。手性偏向如何从分子水平（分子手性）转移到螺旋链（构象手性），然后从自组装转移到螺旋上层结构或相（层次手性），对于自然界的化学和生物过程至关重要，例如通信、复制和酶催化。在这篇文章中，我们根据我们最近对手性聚合物和手性嵌段共聚物（bcp *）自组装的研究，总结了在不同长度尺度下检测同手性进化的方法。由于手性对BCP自组装的影响，在BCP *的自组装中发现了一个螺旋相（H*），以区别于正常的六边形填充柱相的P622对称。合成了对映体聚乳酸bps *，聚苯乙烯-b-聚（l-丙交酯）（PS-PLLA）和聚苯乙烯-b-聚（d-丙交酯）（PS-PDLA），考察了其同手性演化。手性聚乳酸中所构成的手性重复单元的旋光性（分子手性）可用电子圆二色性（ECD）检测，而螺旋型聚乳酸链的构象手性可用振动圆二色性（VCD）明确测定。通过三维透射电子显微镜（3D TEM）技术，可以直接观察到自组装的含聚乳酸的bcp *的H*相，从而确定螺旋纳米结构的手性（分层手性）。通过ECD、VCD和3D TEM对不同长度尺度下bcp *的手性进行了研究，结果表明bcp *的自组装过程具有同手性演化。对于手性聚乳酸来说，在带状球晶中，通过密集的堆积和螺旋链自组装的有效相互作用，可以形成扭曲的片层。利用偏振光显微镜（PLM）的旋转实验可以确定扭曲片的手性。与bcp *的自组装类似，研究结果表明结晶的手性聚乳酸发生了同手性进化。本文的研究结果表明，在检测自组装的手性聚合物和嵌段共聚物的螺旋相的扭曲超结构的分子、构象和层次手性方面，在光谱和形态测定方面取得了显著进展，并表明在手性均聚物和bcp的自组装中可以实现同手性进化。本文提出的不同长度尺度手性转移机理的研究方法，为揭示分子水平上的同手性进化之谜提供了支持信息。
The significance of chirality transfer is not only involved in biological systems, such as the origin of homochiral structures in life but also in man-made chemicals and materials. How the chiral bias transfers from molecular level (molecular chirality) to helical chain (conformational chirality) and then to helical superstructure or phase (hierarchical chirality) from self-assembly is vital for the chemical and biological processes in nature, such as communication, replication, and enzyme catalysis. In this Account, we summarize the methodologies for the examination of homochiral evolution at different length scales based on our recent studies with respect to the self-assembly of chiral polymers and chiral block copolymers (BCPs*). A helical (H*) phase to distinguish its P622 symmetry from that of normal hexagonally packed cylinder phase was discovered in the self-assembly of BCPs* due to the chirality effect on BCP self-assembly. Enantiomeric polylactide-containing BCPs*, polystyrene-b-poly(l-lactide) (PS-PLLA) and polystyrene-b-poly(d-lactide) (PS-PDLA), were synthesized for the examination of homochiral evolution. The optical activity (molecular chirality) of constituted chiral repeating unit in the chiral polylactide is detected by electronic circular dichroism (ECD) whereas the conformational chirality of helical polylactide chain can be explicitly determined by vibrational circular dichroism (VCD). The H* phases of the self-assembled polylactide-containing BCPs* can be directly visualized by 3D transmission electron microscopy (3D TEM) technique at which the handedness (hierarchical chirality) of the helical nanostructure is thus determined. The results from the ECD, VCD, and 3D TEM for the investigated chirality at different length scales suggest the homochiral evolution in the self-assembly of the BCPs*. For chiral polylactides, twisted lamellae in crystalline banded spherulite can be formed by dense packing scheme and effective interactions upon helical chains from self-assembly. The handedness of the twisted lamella can be determined by using rotation experiment of polarized light microscopy (PLM). Similar to the self-assembly of BCPs*, the examined results suggest the homochiral evolution in the crystallized chiral polylactides. The results presented in this Account demonstrate the notable progress in the spectral and morphological determination for the examination of molecular, conformational, and hierarchical chirality in self-assembled twisted superstructures of chiral polymers and helical phases of block copolymers and suggest the attainability of homochiral evolution in the self-assembly of chiral homopolymers and BCPs*. The suggested methodologies for the understanding of the mechanisms of the chirality transfer at different length scales provide the approaches to give Supporting Information for disclosing the mysteries of the homochiral evolution from molecular level.