Enantiospecific equilibrium adsorption and chemistry of d-/l-proline mixtures on chiral and achiral Cu surfaces
Enantiospecific equilibrium adsorption and chemistry of d-/l-proline mixtures on chiral and achiral Cu surfaces
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DOI：
10.1002/chir.23153
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发表时间：
2019-11-24
期刊：
影响因子：
2
通讯作者：
Gellman, Andrew J.
中科院分区：
文献类型：
--
作者：
Dutta, Soham;Gellman, Andrew J.
对手性吸附物之间的对映体特异性相互作用及其与手性表面相互作用的基本理解是解开对映体特异性表面化学起源的关键。本文研究了氨基酸脯氨酸（Pro）在非手性Cu（110）和Cu（111）表面以及手性Cu（643）（R&S）表面的吸附和分解。同位素标记的1-C-13-l-Pro已被用于探测Pro分解机制，并允许质谱鉴别d-Pro和1-C-13-l-Pro作为混合物吸附时。在Cu（111）表面上，X射线光电子能谱显示Pro作为阴离子物种吸附在单分子层中。在手性Cu（643）（R&S）表面上，吸附的Pro对映体以非对映体特异性动力学分解。然而，分解动力学被发现是不同的梯田与扭结的步骤。将手性Cu（643）（R&S）表面暴露于d-Pro和1-C-13-l-Pro的外消旋气相混合物导致外消旋混合物的吸附;即，吸附不是对映体特异性的。然而，暴露于d-Pro和1-C-13-L-Pro的非外消旋混合物导致表面上对映体过量的放大，表明吸附的Pro的纯手性聚集。在共吸附过程中，即使在非常低的覆盖率下也观察到这种扩增，这与其他氨基酸的行为完全不同，其他氨基酸仅在达到单层覆盖率后开始表现出同手性聚集。d-Pro和1-C-13-l-Pro混合物在非手性Cu（110）上的平衡吸附没有显示出任何聚集，与先前dl-Pro/Cu（110）的扫描隧道显微镜（STM）观察一致。这表明从平衡吸附方法和STM实验的结果之间的收敛，并证实了一个二维随机固溶体的形成。
A fundamental understanding of the enantiospecific interactions between chiral adsorbates and understanding of their interactions with chiral surfaces is key to unlocking the origins of enantiospecific surface chemistry. Herein, the adsorption and decomposition of the amino acid proline (Pro) have been studied on the achiral Cu(110) and Cu(111) surfaces and on the chiral Cu(643)(R&S) surfaces. Isotopically labelled 1-C-13-l-Pro has been used to probe the Pro decomposition mechanism and to allow mass spectrometric discrimination of d-Pro and 1-C-13-l-Pro when adsorbed as mixtures. On the Cu(111) surface, X-ray photoelectron spectroscopy reveals that Pro adsorbs as an anionic species in the monolayer. On the chiral Cu(643)(R&S) surface, adsorbed Pro enantiomers decompose with non-enantiospecific kinetics. However, the decomposition kinetics were found to be different on the terraces versus the kinked steps. Exposure of the chiral Cu(643)(R&S) surfaces to a racemic gas phase mixture of d-Pro and 1-C-13-l-Pro resulted in the adsorption of a racemic mixture; i.e., adsorption is not enantiospecific. However, exposure to non-racemic mixtures of d-Pro and 1-C-13-l-Pro resulted in amplification of enantiomeric excess on the surface, indicative of homochiral aggregation of adsorbed Pro. During co-adsorption, this amplification is observed even at very low coverages, quite distinct from the behavior of other amino acids, which begin to exhibit homochiral aggregation only after reaching monolayer coverages. The equilibrium adsorption of d-Pro and 1-C-13-l-Pro mixtures on achiral Cu(110) did not display any aggregation, consistent with prior scanning tunneling microscopy (STM) observations of dl-Pro/Cu(110). This demonstrates convergence between findings from equilibrium adsorption methods and STM experiments and corroborates formation of a 2D random solid solution.