Liu Changxia, Yang Dong, Zhang Li, Liu Minghua
College of Chemistry and Chemical Engineering, Cangzhou Normal University, Cangzhou, 061001, P. R. China.
Beijing National Laboratory for Molecular Science, CAS Key Laboratory of Colloid, Interface and Chemical Thermodynamics, Institute of Chemistry, The Chinese Academy of Sciences, Beijing, 100190, P. R. China.
Soft Matter. 2019 Aug 28;15(32):6557-6563. doi: 10.1039/c9sm01176e. Epub 2019 Jul 30.
The ionic self-assemblies (ISAs) formed by a cationic chiral organogelator (l-glutamide amphiphile, abbreviated as PULG) and anionic dyes exhibited helical nanostructures. And the formed helical structures can be tuned by water amount in the ethanol/water solvent. In pure ethanol, the chirality of the gelator was successfully transferred to the achiral components, which was confirmed by the appearance of an induced CD signal in the achiral components. Meanwhile, the electrostatic interaction between the gelator and achiral dyes contributed to the chirality amplification, causing the nanofibrous structures of the gelator to be transformed to uniform left-handed helices. Upon adding water to ethanol, the induced CD signal exhibited inversion from positive to negative. Interestingly, the left-handed helices formed by ISA of PULG/anionic dyes in ethanol were inverted to right-handed helices with the addition of water. Based on detailed investigations of the XRD patterns, CD and UV/Vis spectra, the mechanism of helicity inversion was proposed: left-handed helices were dominated by hydrogen bonding and right-handed helices were dominated by π-π stacking. This work exemplifies a feasible method to invert the helicity of chiral nanostructures in co-assembly and gives an insight into the conformation change of biomacromolecules in a biological system.
由阳离子手性有机凝胶剂（L-谷氨酰胺两亲物，缩写为PULG）和阴离子染料形成的离子自组装体（ISA）呈现出螺旋纳米结构。并且所形成的螺旋结构可以通过乙醇/水溶剂中的水量进行调节。在纯乙醇中，凝胶剂的手性成功转移到了非手性组分上，这通过非手性组分中诱导圆二色（CD）信号的出现得到了证实。同时，凝胶剂与非手性染料之间的静电相互作用有助于手性放大，导致凝胶剂的纳米纤维结构转变为均匀的左手螺旋。向乙醇中加水后，诱导CD信号呈现从正到负的反转。有趣的是，PULG/阴离子染料在乙醇中通过ISA形成的左手螺旋在加水后转变为右手螺旋。基于对X射线衍射（XRD）图谱、CD和紫外可见（UV/Vis）光谱的详细研究，提出了螺旋反转的机制：左手螺旋以氢键为主导，右手螺旋以π-π堆积为主导。这项工作例证了一种在共组装中反转手性纳米结构螺旋度的可行方法，并深入了解了生物系统中生物大分子的构象变化。
