Mahapatra Mausumi, Tysoe Wilfred T
Department of Chemistry and Laboratory for Surface Studies, University of Wisconsin-Milwaukee, Milwaukee, WI 53211, USA.
Phys Chem Chem Phys. 2015 Feb 21;17(7):5450-8. doi: 10.1039/c4cp05611f.
The chemisorption of two chiral molecules, propylene oxide and glycidol, is studied on tartaric-acid modified Pd(111) surfaces by using temperature-programmed desorption to measure adsorbate coverage. It is found that R-glycidol shows preferential enantioselective chemisorption on (S,S)-tartaric acid modified Pd(111) surfaces, while propylene oxide does not adsorb enantioselectively. The enantioselectivity of glycidol depends on the tartaric acid coverage, and is exhibited for low tartaric acid coverages indicating that the bitartrate phase is responsible for the chiral recognition. The lack of enantioselectivity when using propylene oxide as a chiral probe implies that the enantiospecific interaction between glycidol and bitartate species is due to hydrogen-bonding interactions of the -OH group of glycidol. Scanning tunneling microscopy images were collected for tartaric acid adsorbed on Pd(111) under the same experimental conditions as used for enantioselective experiments. When tartaric acid is dosed at room temperature and immediately cooled to 100 K for imaging, individual bitartrate molecules were found. Density functional theory (DFT) calculations show that bitartrate binds to Pd(111) through its carboxylate groups and the -OH groups are oriented along the long axis of the bitartrate molecule. An enantiospecific interaction is found between glycidol and bitartate species where R-glycidol binds more strongly than S-glycidol to (S,S)-bitartate species by simultaneously forming hydrogen bonds with both the hydroxyl and carboxylate groups, thereby providing three-point bonding.
通过程序升温脱附测量吸附质覆盖度，研究了两种手性分子环氧丙烷和缩水甘油在酒石酸修饰的Pd(111)表面上的化学吸附。研究发现，R-缩水甘油在(S,S)-酒石酸修饰的Pd(111)表面上表现出优先的对映选择性化学吸附，而环氧丙烷没有对映选择性吸附。缩水甘油的对映选择性取决于酒石酸的覆盖度，并且在低酒石酸覆盖度下表现出来，这表明酒石酸氢盐相负责手性识别。当使用环氧丙烷作为手性探针时缺乏对映选择性，这意味着缩水甘油与酒石酸氢盐物种之间的对映特异性相互作用是由于缩水甘油的-OH基团的氢键相互作用。在与对映选择性实验相同的实验条件下，收集了吸附在Pd(111)上的酒石酸的扫描隧道显微镜图像。当在室温下加入酒石酸并立即冷却至100 K进行成像时，发现了单个酒石酸氢盐分子。密度泛函理论(DFT)计算表明，酒石酸氢盐通过其羧基与Pd(111)结合，并且-OH基团沿着酒石酸氢盐分子的长轴取向。在缩水甘油和酒石酸氢盐物种之间发现了一种对映特异性相互作用，其中R-缩水甘油通过同时与羟基和羧基形成氢键，比S-缩水甘油与(S,S)-酒石酸氢盐物种结合得更强，从而提供三点键合。
