Chiral Amplification Based on Sergeants and Soldiers Effect in Helically Folded Poly(naphthalenecarboxamide)
Chiral Amplification Based on Sergeants and Soldiers Effect in Helically Folded Poly(naphthalenecarboxamide)
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DOI：
10.1021/ma200055g
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发表时间：
2011-04
期刊：
影响因子：
5.5
通讯作者：
K. Mikami;Hiroaki Daikuhara;Yuko Inagaki;A. Yokoyama;T. Yokozawa
中科院分区：
文献类型：
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作者：
K. Mikami;Hiroaki Daikuhara;Yuko Inagaki;A. Yokoyama;T. Yokozawa
手性放大是一种重要的现象，与自然界中同色性的起源有关。1从小分子的手性，如氨基酸，到大分子的手性，如多肽的螺旋螺旋，再到大分子的手性，进一步从大分子的手性到更高级的结构，允许控制生物系统中复杂的反应和功能。2聚合物的手性放大是通过单体单元之间的协同作用，通过小的手性偏向诱导主链螺旋感觉的放大，已在各种人工螺旋聚合物中得到报道。3在这方面，术语“中士和士兵效应”被用来描述在由手性和非手性单体单元组成的共聚物中观察到的手性放大。3a这一效应不仅在人工螺旋聚合物中起作用，而且在超分子系统4和折叠分子5中也起作用，这些超分子系统4和折叠分子5主要采用折叠结构，这些结构是由折叠结构和随机卷曲结构之间的许多构象平衡中的非共价相互作用稳定的局部螺旋择优所稳定的。6WE以前研究了具有手性和非手性三乙二醇侧链的聚对苯甲酰胺S共聚物中的中士和士兵效应，发现在有机溶剂中没有观察到手性放大。7最近，我们报道了具有相同手性侧链的聚(萘甲酰胺)在溶液中采用了以右旋为主的螺旋结构。8在普通有机溶剂中，聚对苯甲酰胺的CD强度随着温度的降低而增加。9另一方面，在水/甲醇=7/3(v/v)的水/甲醇中的CD强度明显大于在有机溶剂中的CD强度，随着温度的降低而增加，然后在0±15℃范围内饱和，不能排除手性聚集的可能性。这些结果表明，聚酰胺的螺旋结构是由疏溶剂效应驱动的分子内自缔合作用稳定的，并且聚酰胺的右旋螺旋偏向在0±15℃的范围内是饱和的。这种从苯环到萘环的简单主链修饰似乎引入了芳香族聚酰胺在水溶液中潜在的分子内自缔合能力。因此，我们预计在水溶液中可以观察到聚(萘甲酰胺)的手性放大。在这篇通讯中，我们报道了带有手性和非手性三(乙二醇基)侧链的聚萘甲酰胺无规共聚物的合成，并观察了基于中士和士兵效应的手性放大。
Chiral amplification is an important phenomenon and is related to the origin of homochirality in nature. 1 Hierarchical chiral amplification from the chirality of small molecules, such as amino acids, to macromolecular chirality, such as the helical sense of theR-helix of peptides, and further from macromolecular chirality to higher-order structures, allows the control of sophisticated reactions and functions in biological systems. 2 Chiral amplification of polymer is based on the amplification of main-chain helical sense induced by a small chiral bias through cooperativity between the monomer units and has been reported in a variety of artificial helical polymers. 3 In this connection, the term “sergeants and soldiers effect” has been used to describe the chiral amplification observed in copolymers composed of chiral and achiral monomer units. 3a This effect operates not only in artificial helical polymers but also in supramolecular systems4 and foldamers, 5 which adopt predominantly folded structures induced by local helical preferences stabilized by noncovalent interactions in many conformational equilibria between folded and random-coil structures. 6We previously investigated the sergeants and soldiers effect in copolymers of poly (p-benzamide) s with chiral and achiral tri-(ethylene glycol) side chains and found that no chiral amplification was observed in an organic solvent. 7 Recently, we have reported that poly (naphthalenecarboxamide) with the same chiral side chain adopts a predominantly right-handed helical structure in solution. 8 In common organic solvents, the CD intensity of the poly (naphthalenecarboxamide) increased with decreasing temperature, as in the case of the poly (p-benzamide). 9 On the other hand, the CD intensity in water/methanol= 7/3 (v/v), which was dramatically larger than that in organic solvents, increased with decreasing temperature and then saturated in the range 0À15 C. No dependence of the concentration of the polymer in the aqueous solvent on the CD spectra can rule out the possibility of chiral aggregation. These results imply that the helical structure is stabilized by an intramolecular self-association driven by a solvophobic effect, and the right-handed helical sense bias of the polyamide is saturated in the range 0À15 C. This simple modification of the main chain from benzene ring to naphthalene ring appears to introduce a potential intramolecular self-association ability of the aromatic polyamides in aqueous solution. Therefore, we expected that the chiral amplification of poly (naphthalenecarboxamide) would be observed in an aqueous solvent. In this Communication, we report the synthesis of random copolymers of poly (naphthalenecarboxamide) with chiral and achiral tri (ethylene glycol) side chains and the observation of chiral amplification based on the sergeants and soldiers effect by