Fried Stephen D, Boxer Steven G
Department of Chemistry; Stanford University, Stanford, California 94305-5080, United States.
Acc Chem Res. 2015 Apr 21;48(4):998-1006. doi: 10.1021/ar500464j. Epub 2015 Mar 23.
Over the past decade, we have developed a spectroscopic approach to measure electric fields inside matter with high spatial (<1 Å) and field (<1 MV/cm) resolution. The approach hinges on exploiting a physical phenomenon known as the vibrational Stark effect (VSE), which ultimately provides a direct mapping between observed vibrational frequencies and electric fields. Therefore, the frequency of a vibrational probe encodes information about the local electric field in the vicinity around the probe. The VSE method has enabled us to understand in great detail the underlying physical nature of several important biomolecular phenomena, such as drug-receptor selectivity in tyrosine kinases, catalysis by the enzyme ketosteroid isomerase, and unidirectional electron transfer in the photosynthetic reaction center. Beyond these specific examples, the VSE has provided a conceptual foundation for how to model intermolecular (noncovalent) interactions in a quantitative, consistent, and general manner. The starting point for research in this area is to choose (or design) a vibrational probe to interrogate the particular system of interest. Vibrational probes are sometimes intrinsic to the system in question, but we have also devised ways to build them into the system (extrinsic probes), often with minimal perturbation. With modern instruments, vibrational frequencies can increasingly be recorded with very high spatial, temporal, and frequency resolution, affording electric field maps correspondingly resolved in space, time, and field magnitude. In this Account, we set out to explain the VSE in broad strokes to make its relevance accessible to chemists of all specialties. Our intention is not to provide an encyclopedic review of published work but rather to motivate the underlying framework of the methodology and to describe how we make and interpret the measurements. Using certain vibrational probes, benchmarked against computer models, it is possible to use the VSE to measure absolute electric fields in arbitrary environments. The VSE approach provides an organizing framework for thinking generally about intermolecular interactions in a quantitative way and may serve as a useful conceptual tool for molecular design.
在过去十年中，我们开发了一种光谱方法，用于以高空间分辨率（<1 Å）和场分辨率（<1 MV/cm）测量物质内部的电场。该方法依赖于利用一种称为振动斯塔克效应（VSE）的物理现象，它最终能在观测到的振动频率和电场之间提供直接映射。因此，振动探针的频率编码了关于探针周围局部电场的信息。VSE方法使我们能够非常详细地理解几种重要生物分子现象的潜在物理本质，例如酪氨酸激酶中的药物 - 受体选择性、酮甾体异构酶的催化作用以及光合反应中心中的单向电子转移。除了这些具体例子，VSE为如何以定量、一致和通用的方式对分子间（非共价）相互作用进行建模提供了概念基础。该领域研究的起点是选择（或设计）一个振动探针来研究感兴趣的特定系统。振动探针有时是所研究系统固有的，但我们也设计了将它们构建到系统中的方法（外在探针），通常对系统的扰动最小。借助现代仪器，振动频率越来越能够以非常高的空间、时间和频率分辨率进行记录，从而得到在空间、时间和场强上相应解析的电场图。在本综述中，我们着手大致解释VSE，以使所有专业的化学家都能理解其相关性。我们的目的不是对已发表的工作进行百科全书式的综述，而是激发该方法的潜在框架，并描述我们如何进行测量以及解释测量结果。使用某些经过计算机模型校准的振动探针，利用VSE可以测量任意环境中的绝对电场。VSE方法为以定量方式全面思考分子间相互作用提供了一个组织框架，并且可能成为分子设计的有用概念工具。
