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

对映异构体是两个具有相同化学键排列的分子，但具有彼此镜像的三维结构，就像左手和右手。这些“手性”化学物质在生物体中起着核心作用，其中只有左手或右手形式存在，但不是两者都存在。因此，大多数生物活性分子，如药物，也必须是手性分子，它们必须与生命中发现的生物化学物质的手性相匹配。 然而，生产对映体纯形式的分子是一个具有挑战性的问题。在这个由美国国家科学基金会化学部化学结构动力学和机制A（CSDM-A）计划资助的合作研究项目中，Andrew Gellman教授（卡内基梅隆大学）和Charles Sykes教授（塔夫茨大学）正在研究吸附在金属表面上的手性分子的化学，其中原子结构也具有特定的手性。 Gellman和Sykes教授与他们的学生合作，正在开发弯曲的金属表面，这些表面呈现手性结构的系统变化。所设计的表面使得能够用单个样品研究许多原子构型。 复杂的光谱学绘制了整个表面的化学反应，而孤立的化学反应是使用高分辨率显微镜观察的，该显微镜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行业手性化学品对映体特异性生产的表面设计。 研究了酒石酸（TA）和天冬氨酸（Asp）两种手性化合物在手性Cu（hkl）表面的表面化学。 单晶Cu表面被抛光成球形，使得球体表面上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Cu表面的所有可能结构上的吸附和表面反应非常有效;即所有可能的米勒指数（hkl）。 这些表面的原子结构的成像和不吸附TA和Asp使用扫描隧道显微镜。 TA和天冬氨酸分解动力学的独立测量上数百个不同的铜（hkl）表面，所有在一个单一的样品。 这些数据阐明了表面反应速率常数作为表面取向的函数，KS（HKL），从而使化学和对映体特异性反应的表面结构的影响的理解。 结合，这些数据被用来确定那些表面取向与最高的对映体选择性对TA和Asp的两种对映体的分解。 通过扫描隧道显微镜的成像，确定具有最大对映选择性的表面的原子结构。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值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.