Huang Xin, Liu Minghua
Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Colloid and Interface Science, Institute of Chemistry, CAS, 100080, Beijing, P. R. China.
Langmuir. 2006 Apr 25;22(9):4110-5. doi: 10.1021/la0530586.
Previously, we have found that an achiral barbituric acid (BA) derivative, 5-(4-(N-methyl-N-hexadecylaminobenzylidene))-2,4,6-(1H,3H)-pyrimidinetrione (BAC16), could form molecular assemblies showing supramolecular chirality through the organization at the air/water interface. To acquire more knowledge of the formation mechanism of such supramolecular assemblies, some achiral molecules, such as stearic acid (SA), octadecylamine (ODA), and an analogue of BA without an alkyl chain, were mixed into the BAC16 system. The effects of these matrix molecules on the supramolecular chirality and surface morphologies of Lanmuir-Blodgett (LB) films were investigated. It was observed that, at a low molar ratio of the matrix molecules (below 10%), the chirality of the BAC16 assemblies could be maintained with only a reduction in the intensity. When the matrix fraction was increased, the supramolecular chirality of the mixed films disappeared. The addition of the matrix molecules can greatly change the surface morphologies of the mixed films. When SA was mixed with BAC16, the spiral nanofibers of BAC16 were changed to long nanofibers. When ODA was mixed, the hydrolytic cleavage reaction of BAC16 took place at the air/water interface and disordered spirals were obtained. When the analogous BA derivate without an alkyl chain was mixed, the phase-separating morphology was observed. These changes in the chirality and surface morphologies indicated firmly that the supramolecular chirality of BAC16 films were formed due to the cooperative arrangement of the molecules. A certain amount of matrix molecules will destroy the cooperative arrangement and thus the chirality.
此前，我们发现一种非手性巴比妥酸（BA）衍生物，5-(4-(N-甲基-N-十六烷基氨基苄叉基))-2,4,6-(1H,3H)-嘧啶三酮（BAC16），能够通过在空气/水界面的自组装形成具有超分子手性的分子聚集体。为了深入了解此类超分子聚集体的形成机制，将一些非手性分子，如硬脂酸（SA）、十八胺（ODA）以及一种不含烷基链的BA类似物，混入BAC16体系中。研究了这些基质分子对朗缪尔-布洛杰特（LB）膜超分子手性和表面形貌的影响。结果发现，当基质分子的摩尔比很低（低于10%）时，BAC16聚集体的手性能够得以维持，只是强度有所降低。当基质比例增加时，混合膜的超分子手性消失。基质分子的加入能极大地改变混合膜的表面形貌。当SA与BAC16混合时，BAC16的螺旋纳米纤维转变为长纳米纤维。当ODA混合时，BAC16在空气/水界面发生水解裂解反应，得到无序的螺旋结构。当混入不含烷基链的类似BA衍生物时，观察到相分离形貌。手性和表面形貌的这些变化有力地表明，BAC16膜的超分子手性是由于分子的协同排列形成的。一定量的基质分子会破坏这种协同排列，进而破坏手性。
