Abstract
Understanding the interplay between intrinsic molecular chirality and chirality of the bonding footprint is crucial in exploiting enantioselectivity at surfaces. As such, achiral glycine and chiral alanine are the most obvious candidates if one is to study this interplay on different surfaces. Here, we have investigated the adsorption of glycine on Cu{311} using reflection–absorption infrared spectroscopy, low-energy electron diffraction, temperature-programmed desorption, and first-principles density-functional theory. This combination of techniques has allowed us to accurately identify the molecular conformations present under different conditions and discuss the overlayer structure in the context of the possible bonding footprints. We have observed coverage-dependent local symmetry breaking, with three-point bonded glycinate moieties forming an achiral arrangement at low coverages, and chirality developing with the presence of two-point bonded moieties at high coverages. Comparison with previous work on the self-assembly of simple amino acids on Cu{311} and the structurally similar Cu{110} surface has allowed us to rationalize the different conditions necessary for the formation of ordered chiral overlayers.
Highlights
The study of chirality at metal single-crystal surfaces has relevance to a broad range of applications including biocompatibility, biosensors, and enantioselective heterogeneous catalysis.[1]
In addition to the larger surface unit cell, the registry of adjacent close-packed rows differs on the two surfaces, with a primitive rectangular surface unit cell existing for Cu{110}, but not for Cu{311}. This difference alters the possible bonding footprints[2] that can be adopted by adsorbing α-amino acids; comparison of the bonding configurations adopted and the ordered overlayers formed on the two surfaces will, provide insight into the effect of small changes in surface structure and symmetry on the behavior of adsorbed species
Using temperatureprogrammed desorption (TPD), low-energy electron diffraction (LEED), reflection−absorption infrared spectroscopy (RAIRS), and first-principles density functional theory (DFT), we have elucidated the preparation conditions leading to different phases, and the bonding configurations adopted by the adsorbed species within them
Summary
The study of chirality at metal single-crystal surfaces has relevance to a broad range of applications including biocompatibility, biosensors, and enantioselective heterogeneous catalysis.[1]. Surfaces, with a primitive rectangular surface unit cell existing for Cu{110}, but not for Cu{311} This difference alters the possible bonding footprints (defined according to the surface atoms to which the molecule bonds)[2] that can be adopted by adsorbing α-amino acids; comparison of the bonding configurations adopted and the ordered overlayers formed on the two surfaces will, provide insight into the effect of small changes in surface structure and symmetry on the behavior of adsorbed species. Using temperatureprogrammed desorption (TPD), low-energy electron diffraction (LEED), reflection−absorption infrared spectroscopy (RAIRS), and first-principles density functional theory (DFT), we have elucidated the preparation conditions leading to different phases, and the bonding configurations adopted by the adsorbed species within them This has allowed us to compare the behavior of glycine and alanine on Cu{311} and rationalize the similarities and differences to the behavior of the same adsorbates on Cu{110} by considering the different surface structures in the two cases. Assignment of particular displacement patterns to local-mode descriptions (e.g., carboxylate symmetric stretching, amine scissoring etc.) was achieved by visual inspection
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