Density Functional Theory studies of dehydrogenated and zwitterionic glycine and alanine on Pd and Cu surfaces

Chiral modification of achiral metal catalysts with chiral auxiliary molecules is a promising method of creating chiral surfaces for heterogeneous catalysis. The ability of a chiral template overlayer to affect the adsorption enantioselectivity of a probe molecule depends on the local adsorption geometry of the template molecule. One potential class of chiral modifiers are the amino acids. Previous experimental studies demonstrated that glycine is adsorbed on the Cu(1 0 0) and Cu(1 1 0) surfaces in its dehydrogenated form, NH2CH2COO, at room temperature. In contrast, recent X-ray photoelectron spectroscopy experiments indicate zwitterionic adsorption of glycine to Pd(1 1 1). Using Density Functional Theory, we have studied the adsorption of glycine on Pd(1 1 1), Cu(1 0 0) and Cu(1 1 0) to examine this apparent difference in chemical states on these surfaces. We conclude that at equilibrium, glycine is adsorbed preferentially to these surfaces in its dehydrogenated form, implying that observation of zwitterions is likely a kinetic effect due to the conditions of the experiment.

Graphical abstractChiral modification of achiral metal catalysts with chiral auxiliary molecules is a promising method of creating chiral surfaces for heterogeneous catalysis. The ability of a chiral template overlayer to affect the adsorption enantioselectivity of a probe molecule depends on the local adsorption geometry of the template molecule. One potential class of chiral modifier are the amino acids. Previous experimental studies demonstrated that glycine is adsorbed on the Cu(1 0 0) and Cu(1 1 0) surfaces in its dehydrogenated form, NH2CH2COO, at room temperature. In contrast, recent X-ray photoelectron spectroscopy experiments indicate zwitterionic adsorption of glycine to Pd(1 1 1). Using Density Functional Theory, we have studied the adsorption of glycine on Pd(1 1 1), Cu(1 0 0) and Cu(1 1 0) to examine this apparent difference in chemical states on these surfaces.Figure optionsDownload full-size imageDownload as PowerPoint slide