Functional molecular films at electrode surfaces

本项目的总体目标是研究沉积在金属电极上的功能性磷脂单层和双层的结构和反应性。这些膜的功能将由多肽和蛋白质的存在来决定。我们的目标是了解磷脂分子是如何聚集形成单层或双层膜的。当电场的大小与作用在生物膜上的电场相当时，这些膜的稳定性如何？这些场如何影响膜内分子的有序性，以及它们如何导致从液晶状态到凝胶状态的相变？我们还有兴趣了解电场如何影响由磷脂和胆固醇组成的混合双层的稳定性，蛋白质进入双层的情况，以及通过结合到支撑双层中的蛋白质进行的电子和离子转移。为了实现这些目标，我们将使用电化学方法、扫描探针显微镜(如扫描隧道显微镜(STM)和原子力显微镜(AFM))、原位光子偏振调制傅里叶变换红外反射吸收光谱(PM-IRRAS)、紫外圆二色光谱和中子散射技术。金属电极表面覆盖一层表面活性剂或磷脂，可以带电，并可在这些支撑膜上施加约10^7-10^8V/m的电场。这些场的大小与作用在生物膜上的场相当。该场可方便地用于操纵单层和双层膜内的有机分子。通过控制电场，人们可以迫使有机分子薄膜中的相变，或者迫使它们在表面分散或聚集。我们将使用电化学技术来控制薄膜的物理状态，并使用扫描探针显微镜来成像薄膜的场驱动转变。此外，还将利用光谱和中子散射技术来研究有机分子的构象变化及其在膜中的有序性。

The general objective of this project is to study the structure and reactivity of functional monolayers and bilayers of phospholipids deposited onto a metal electrode at the metal-solution interface. The functionality of these films will be determined by the presence of peptides and proteins. Our goal is to learn how phospholipid molecules aggregate to form monolayer or bilayer films. What is the stability of these films in the presence of electric fields that are comparable in magnitude to the fields acting on biological membranes? How do these fields affect ordering of molecules within the membrane and how they cause a phase transition from the liquid crystalline to the gel state? We are also interested to learn how the electric field affects the stability of mixed bilayers composed of phospholipids and cholesterol, the incorporation of proteins into the bilayer and electron and ion transfer through proteins incorporated into the supported bilayer. To achieve these goals, we will employ electrochemical methods, scanning probe microscopies such as scanning tunneling microscopy (STM) and atomic force microscopy (AFM), in situ photon polarization modulation Fourier transform infrared reflection absorption spectroscopy (PM-IRRAS), circular dichroism in the UV and neutron scattering techniques. The metal electrode surface, covered by a film of surfactants or phospholipids, can be charged and electric fields on the order of 10^7 - 10^8V/m can be applied to these supported films. These fields have comparable magnitude to the fields acting on biological membranes. The field may be conveniently used to manipulate organic molecules within the monolayer and the bilayer membrane. By controlling the field, one can force phase transitions in the film of organic molecules or force them to disperse or to aggregate at the surface. We will use electrochemical techniques to control the physical state of the film and the scanning probe microscopies to image the field-driven transformations of the membranes. In addition, spectroscopic and neutron scattering techniques will be employed to study conformational changes of organic molecules and their ordering within the membrane.