The Study of Chiral Adsorption Systems Using Synchrotron-Based Structural and Spectroscopic Techniques: Stereospecific Adsorption of Serine on Au-Modified Chiral Cu{531} Surfaces

Abstract

We apply modern synchrotron-based structural techniques to the study of serine adsorbed on the pure and Au-modified intrinsically chiral Cu{531} surface. XPS and NEXAFS data in combination with DFT show that on the pure surface both enantiomers adsorb in μ4 geometries (with de-protonated β-OH groups) at low coverage and in μ3 geometries at saturation coverage. Significantly larger enantiomeric differences are seen for the μ4 geometries, which involve substrate bonds of three side groups of the chiral center, i.e. a three-point interaction. The μ3 adsorption geometry, where only the carboxylate and amino groups form substrate bonds, leads to smaller but still significant enantiomeric differences, both in geometry and the decomposition behavior. When Cu{531} is modified by the deposition of 1 and 2 ML Au the orientations of serine at saturation coverage are significantly different from those on the clean surface. In all cases, however, a μ3 bond coordination is found at saturation involving different numbers of Au atoms, which leads to relatively small enantiomeric differences.