Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA.
Langmuir. 2010 Nov 2;26(21):16412-23. doi: 10.1021/la102074a.
Temperature programmed desorption methods have been used to probe the enantioselectivity of achiral Cu(100), Cu(110), and Cu(111) single crystal surfaces modified by chiral organic molecules including amino acids, alcohols, alkoxides, and amino-alcohols. The following combinations of chiral probes and chiral modifiers on Cu surfaces were included in this study: propylene oxide (PO) on L-alanine modified Cu(110), PO on L-alaninol modified Cu(111), PO on 2-butanol modified Cu(111), PO on 2-butoxide modified Cu(100), PO on 2-butoxide modified Cu(111), R-3-methylcyclohexanone (R-3-MCHO) on 2-butoxide modified Cu(100), and R-3-MCHO on 2-butoxide modified Cu(111). In contrast with the fact that these and other chiral probe/modifier systems have exhibited enantioselectivity on Pd(111) and Pt(111) surfaces, none of these probe/modifier/Cu systems exhibit enantioselectivity at either low or high modifier coverages. The nature of the underlying substrate plays a significant role in the mechanism of hydrogen-bonding interactions and could be critical to observing enantioselectivity. While hydrogen-bonding interactions between modifier and probe molecule are believed to induce enantioselectivity on Pd surfaces (Gao, F.; Wang, Y.; Burkholder, L.; Tysoe, W. T. J. Am. Chem. Soc. 2007, 129, 15240-15249), such critical interactions may be missing on Cu surfaces where hydrogen-bonding interactions are believed to occur between adjacent modifier molecules, enabling them to form clusters or islands.
程序升温脱附方法已被用于探测手性 Cu(100)、Cu(110)和 Cu(111)单晶表面的对映选择性，这些表面由手性有机分子如氨基酸、醇、烷氧基和氨基醇修饰。在这项研究中，包括了以下在 Cu 表面上的手性探针和手性修饰剂的组合：L-丙氨酸修饰的 Cu(110)上的环氧丙烷 (PO)、L-丙醇胺修饰的 Cu(111)上的 PO、2-丁醇修饰的 Cu(111)上的 PO、2-丁氧基修饰的 Cu(100)上的 PO、2-丁氧基修饰的 Cu(111)上的 PO、2-丁氧基修饰的 Cu(100)上的 R-3-甲基环己酮 (R-3-MCHO) 和 2-丁氧基修饰的 Cu(111)上的 R-3-MCHO。与这些和其他手性探针/修饰剂系统在手性 Pd(111)和 Pt(111)表面上表现出对映选择性的事实相反，在低或高修饰剂覆盖率下，这些探针/修饰剂/Cu 系统都没有表现出对映选择性。底层底物的性质在手性氢键相互作用的机制中起着重要作用，并且对于观察对映选择性可能至关重要。虽然在 Pd 表面上，氢键相互作用被认为会诱导手性选择性（Gao, F.; Wang, Y.; Burkholder, L.; Tysoe, W. T. J. Am. Chem. Soc. 2007, 129, 15240-15249），但在 Cu 表面上，由于氢键相互作用被认为发生在相邻修饰剂分子之间，从而使它们能够形成簇或岛，因此这种关键相互作用可能缺失。
