Collaborative Research: Structure Sensitive Surface Chemistry - Enantioselectivity on Chiral Surfaces

对映体是两个分子，它们具有相同的化学键排列，但具有相互镜像的三维结构，如左手和右手。这些“手性”化学物质在生物体中发挥着核心作用，在生物体中只存在左手或右手形式，但不能同时存在两者。因此，大多数生物活性分子，如药物，也必须是手性分子，而且它们必须与生活中发现的生物化学物质的利手性相匹配。然而，生产具有对映体纯度的分子形式是一个具有挑战性的问题。在这项由美国国家科学基金会化学部化学结构动力学与机理A(CSDM-A)计划资助的合作研究项目中，卡内基梅隆大学的Andrew Gellman教授和塔夫茨大学的Charles Sykes教授正在研究吸附在金属表面的手性分子的化学，金属表面的原子结构也具有特定的利手性。盖尔曼教授和赛克斯教授与他们的学生合作，正在开发呈现手性结构系统变化的曲面金属表面。所设计的表面可以用一个样品来研究许多原子构型。复杂的光谱绘制了整个表面的化学反应，而孤立的化学反应是用高分辨率显微镜观察的，它可以绘制单个原子的位置。除了为未来的科学家提供培训机会外，从该项目中获得的见解还可以指导制药业手性化学品对映体生产表面的设计。本研究以酒石酸(TA)和天冬氨酸(Asp)两种手性化合物在手性铜(HKl)表面的表面化学为研究对象。单晶铜表面被抛光成球形，使得球体表面的每个点暴露出具有不同原子结构的平面。这使得研究TA和Asp在铜表面所有可能的结构上的吸附和表面反应是非常有效的，即所有可能的米勒指数(Hkl)。用扫描隧道显微镜对吸附了TA和Asp前后的表面原子结构进行了成像。TA和Asp分解动力学的独立测量是在数百个不同的铜(HKl)表面上进行的，都是在一个样品上进行的。这些数据阐明了表面反应速率常数作为表面取向Ks(Hkl)的函数，从而使我们能够理解表面结构对化学反应和对映异构体反应性的影响。结合这些数据，这些数据被用来确定对TA和Asp两个对映体的分解具有最高对映体选择性的表面取向。然后，使用扫描隧道显微镜进行成像，以确定具有最高对映选择性表面的原子结构。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Enantiomers are two molecules that have the same arrangement of chemical bonds, but have three-dimensional structures that are mirror images of each other, like left and right hands. These 'chiral' chemicals play a central role in living-organisms, where only the left- or right-handed forms are present; but not both. As a result, most biologically active molecules, such as pharmaceuticals, must also be chiral molecules, and they must match the handedness of the biochemicals found in life. However, producing enantiomerically pure forms of molecules is a challenging problem. In this collaborative research project funded by the Chemical Structure Dynamics and Mechanism A (CSDM-A) program of the National Science Foundation Division of Chemistry, Professors Andrew Gellman (Carnegie Mellon University) and Charles Sykes (Tufts University) are studying the chemistry of chiral molecules adsorbed on metal surfaces where the atomic structure also has a specific handedness. Working with their students, Professors Gellman and Sykes are developing curved metal surfaces that present a systematic variation in chiral structures. The designed surfaces enable the study of many atomic configurations with a single sample. Sophisticated spectroscopies map the chemical reactivity across the surface, while isolated chemical reactions are observed using a high-resolution microscope that can map the positions of individual atoms. In addition to providing training opportunities for future scientists, insights gained from the project could guide the design of surfaces for enantiospecific production of chiral chemicals in the pharmaceutical industry. The research targets the surface chemistry of two chiral compounds, tartaric acid (TA) and aspartic acid (Asp), on chiral Cu(hkl) surfaces. Single crystal Cu surfaces are polished into spherical shapes such that each point on the surface of the sphere exposes a plane with a different atomic structure. This makes it very efficient to study the adsorption and surface reactions of TA and Asp on all possible structures of a Cu surface; i.e. all possible Miller indices (hkl). The atomic structures of these surfaces are imaged with and without adsorbed TA and Asp using scanning tunneling microscopy. Independent measurements of TA and Asp decomposition kinetics are made on hundreds of different Cu(hkl) surfaces, all on a single sample. These data elucidate surface reaction rate constants as a function of surface orientation, ks(hkl), and hence enable an understanding of the effect of surface structure on chemical and enantiospecific reactivity. Combined, these data are used to identify those surface orientations with the highest enantioselectivities towards decomposition of the two enantiomers of TA and Asp. Imaging with the scanning tunneling microscope is then used to determine the atomic structure of the surfaces having greatest enantioselectivity.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.