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

对映体是两个分子，它们的化学键排列相同，但它们的三维结构是彼此的镜像，就像你的左手和右手一样。这些“手性”化学物质在只有左手或右手形式存在的生物体中起着核心作用；但不是两者都有。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化学分部化学结构动力学和机理A （CSDM-A）项目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的手性分子的化学性质，其中原子结构也具有特定的手性。Gellman教授和Sykes教授与他们的学生合作，正在开发具有系统变化的手性结构的弯曲金属表面。设计的表面可以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，而使用高分辨率显微镜观察孤立的化学反应，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可以指导制药工业中手性化学品对映体生产的表面设计。研究了两种手性化合物酒石酸（TA）和天冬氨酸（Asp）在手性铜（hkl）表面的表面化学性质。单晶铜表面被抛光成球形，使得球面上的每个点都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）。利用扫描隧道显微镜对这些表面的原子结构进行了成像，并对是否吸附TA和Asp进行了成像。在数百个不同的Cu（hkl）表面上进行了TA和Asp分解动力学的独立测量，所有这些都在单个样品上进行。这些数据阐明了表面反应速率常数是表面取向ks（hkl）的函数，从而使我们能够理解表面结构对化学和对映特异性反应活性的影响。结合这些数据，确定了对TA和Asp两种对映体的分解具有最高对映选择性的表面取向。然后使用扫描隧道显微镜成像来确定具有最大对映体选择性的表面的原子结构。该奖项反映了美国国家科学基金会的法定使命，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 your 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.