具有光学活性的银纳米溶胶的制备及性能研究

This study explores a new way for the preparation of the optically active Ag nanoparticles under the influence of supramolecular chiral induction. This kind of materials has potential application values in the areas of chiral catalysis, chiral switch, chiral memory and chiral recognization. Silver colloids are to be prepared by the reduction of Ag+ using liquid-phase chemical reduction method with the chiral organic small molecules without mercapto groups in the structures as the chiral inducers. The compositions, morphologies and structures of the as-prepared silver colloids are characterized. The absorption spectra and the chiral dichroism (CD) spectra are to be determined and the optical properties (chirality) are explored in depth. The particle sizes and chirality are controlled by the supramolecular force (especially the coordination force). The stability of Ag nanoparticles is determined by the adding of stabilizers. The optimal experimental conditions are used to prepare the monodispersed silver colloids with high-stability. The relationship of the structures of silver colloids, morphologies and chiral properties are studied. The supramolecular interaction mechanism between the chiral inducers and silver nanoparticles, the photochemical reduction mechanism and the chirality transfer mechanism are to be investigated. Through the study of the project, it will provide a simple, relative facile way for the controllable synthesis of chiral silver nanomaterials. It will also offer significant information for the basic theoretical research in chiral nano devices.

本项目将在超分子手性诱导作用下，探讨制备具有光学活性的银纳米粒子新途径。该类材料在手性催化、手性开关、手性记忆、手性识别等领域有潜在的应用价值。首先我们选取具有简单结构的不含巯基的手性有机小分子作为手性诱导剂，然后通过液相化学还原法，通过滴加硼氢化钠还原银离子制备手性Ag纳米溶胶。对制备的纳米溶胶粒子的组成、结构和形貌进行表征，测定银纳米粒子的吸收光谱和圆二色谱（CD），对光学性能（手性）进行深入的研究。利用超分子作用（特别是配位作用）调控粒子的粒径和手性，通过添加稳定剂控制粒子的稳定性。优化制备条件合成具有稳定性高、单分散好的手性Ag纳米溶胶粒子。探讨银纳米粒子的结构、形貌与手性性能三者之间的关系。重点研究手性诱导剂与银纳米粒子之间的超分子相互作用机理，手性传递作用机理。通过本项目的研究可望为手性银纳米材料的可控合成提供相对简单、易行的技术途径，为手性纳米器件的基础理论研究提供重要信息。

选取脱氧胆酸钠、L-组氨酸、甘胆酸钠、肌苷等手性有机小分子为手性诱导剂，制备具有光学活性的银纳米粒子。对制备的银纳米粒子进行紫外-可见吸收光谱，透射电子显微镜，圆二色谱和傅里叶变换红外光谱表征，并对手性诱导机理进行了研究。以脱氧胆酸钠为还原剂、稳定剂，经紫外光辐照AgNO3溶液在室温下制备出尺寸30 nm左右的类球形的银纳米粒子。红外光谱结果表明，在紫外光激发下，脱氧胆酸钠甾环上12α-OH发生氧化反应，同时还原Ag+为单质银，并聚集生成银纳米粒子。溶液的pH值对光化学氧化还原反应速度有着重要的影响，增加溶液的pH值，Ag+的还原反应速度明显加快。在吸附在银粒子表面的脱氧胆酸钠的手性氛围诱导下，生成的银纳米粒子在其表面等离子体共振区域出现手性信号。以L-组氨酸为稳定剂和手性诱导剂，采用液相化学还原法制备L-组氨酸包覆的银纳米粒子。制备的黄色银纳米溶胶的圆二色谱结果显示其在SPR区域出现手性信号，为正的Cotton Effect (CE)。聚集后的银纳米粒子表现出了与单分散状态粒子截然不同的手性信号，分别在短波和长波的SPR区域表现为相反的双向信号。CD信号发生裂分是由于在光的激发下聚集后的银纳米粒子间发生等离子激元耦合，导致激发态的能级发生分裂。通过液相化学还原法制备出NaDC包覆的银纳米粒子，圆二色谱结果表明处于分散状态的粒子在SPR区域出现一个很强的正的CD信号，而聚集后的银纳米粒子由于粒子间等离子体相互作用呈现裂分的CD信号，并且随粒子聚集程度的增大长波方向的信号发生红移。甘胆酸钠为包覆剂制备的银纳米粒子其圆二色谱在388 nm左右出现正的科顿效应峰。肌苷包覆的银纳米溶胶在400 nm左右出现负的科顿效应峰。