扫描电化学显微镜方法研究自组装膜表面氢键协同作用

The understanding of hydrogen bonding self-assembly and disassembly on the surface of self-assembled monolayer (SAM) in liquid phase is important for understanding the molecular recognition. Here we aim to study the synergistic action of intermolecular hydrogen bond of self-assembly and disassembly on the surface of the SAM in liquid phase using SECM. A cyclic process including disassembly (self-assembly) of intermolecular hydrogen bond was constructed by designing a probe molecule that binds the surface group of the SAM substrate to an intermolecular hydrogen bond. In this cycle electrostatic attraction (repulsion) leads to the shift of dissociation equilibrium of the SAM surface group and induces the disassembly (self-assembly) of intermolecular hydrogen bond. Long-range positive (negative) feedback currents are generated away from the substrate base on the regulation of dissociation equilibrium. Then, the application range of the steady limit diffusion current formula (iT.∞ = 4nFDCa) is extended to the calculation of long range positive (negative) feedback current. It is possible to quantitatively study the synergistic action of intermolecular hydrogen bond in experiments. The advantage of SECM is that electron transfer and hydrogen bonding can occur on the probe electrode and substrate electrode, respectively, which avoid the interference of electron transfer on hydrogen bond. At the same time, the open-circuit state of the substrate electrode weakens the interference of the substrate electric field on the synergistic action of intermolecular hydrogen bond. The in situ electrochemical study of intermolecular hydrogen bond of self-assembly and disassembly in liquid phase is realized.

液相中自组装膜（SAM）表面氢键自组装和解组装的认识对理解分子识别有重要意义。本项目运用扫描电化学显微镜（SECM）方法研究液相中SAM表面氢键自组装和解组装中分子间氢键协同作用。通过设计使基底电极的SAM表面基团以分子间氢键键合探针分子，构筑包括分子间氢键解（自）组装的一个循环过程。此循环中，静电吸引（排斥）导致SAM表面基团解离平衡的移动，并诱导上述分子间氢键解（自）组装。借助解离平衡的调控实现远离基底产生持续的长程正（负）反馈电流。将SECM稳态极限扩散电流公式（iT.∞ = 4nFDCa）的应用范围扩展到长程正（负）反馈电流计算中，使实验上定量研究分子间氢键协同作用成为可能。SECM的优势是电子转移和氢键作用可分别发生在探针电极和基底电极上，避免了电子转移对氢键作用的干扰，同时基底电极的开路状态弱化了基底电场对氢键协同作用的干扰。实现液相中分子间氢键自（解）组装的原位电化学研究。

作为细胞膜的简化模型，液相中自组装膜（SAM）表面分子间氢键的认识有助于理解膜表面分子识别的行为。本项目运用扫描电化学显微镜方法（SECM）的反馈、产生收集、成像等模式研究了SAM表面羧基与羟基、羧基与羧基的分子间氢键及正、负电荷的静电。实验表明，基底电极3-巯基丙酸自组装膜（MPA SAM）表面的羧基与探针分子二茂铁甲醇的羟基之间通过氢键自组装形成的分子间氢键（体系1）对电子转移有增强作用，含氧和羟基的部分氧化石墨烯修饰的基底电极作为对比也证实分子间氢键起到电子转移增强作用。Mg2+、Ca2+、Ba2+加入体系1会促进MPA SAM表面羧基解离平衡的正向移动，差异性的诱导上述分子间氢键发生解组装进而实现对分子间氢键解组装的调控。能形成较强离子对的ClO4-加入体系1时，发现了从氢键到静电的转变过程中离子对的竞争优势。乙酸加入体系1，乙酸与MPA SAM之间形成的电荷辅助氢键取代了原分子间氢键。乙腈溶剂中二茂铁甲醇的电化学行为发现水的优先溶剂化现象。体系1中探针改为〖[Fe(CN)_6]〗_4^(4-)时SECM渐进曲线呈现出正反馈向负反馈反转的特点体现出扩散层中MPA SAM表面羧酸根界面静电排斥作用的变化趋势。基底电极构筑成11-巯基十一烷酸和十一烷硫醇的混合SAM时，pH调控膜表面的羧基解离平衡的移动实现了羧基间氢键的合与断的阳离子开关行为。实现了基底电极表面半胱氨酸SAM表面的配位键到静电相互作用的转换。将半胱氨酸修饰在十一烷硫醇自组装单分子膜的缺陷部位形成了基于静电作用的电荷翻转现象，实现对精氨酸和天冬氨酸分子的选择性识别。探针分子改变为多巴胺，分别实现了模拟细胞膜表面基于分子间氢键的多巴胺的可控释放和多巴胺合成前体酪氨酸吸附的“可视化”研究。上述研究有助于在分子水平上理解细胞膜表面氢键、静电协同作用的本质。依托项目培养了3名博士生和5名硕士生，共发表16篇SCI论文，完成预期8篇的目标。