<scp>l</scp>-Cysteine on Ag(111): A Combined STM and X-ray Spectroscopy Study of Anchorage and Deprotonation

Abstract

Thiols adsorbed on noble metals are prominent model systems for self-assembly and nanotechnology research. l-cysteine is the only proteinogenic amino acid containing a thiol group. A detailed knowledge of the interaction of this molecule with well-defined surfaces is essential to rationalize and advance interfacial amino acid self-assembly and the metal-mediated anchoring of proteins. Here, we address the exemplary system l-cysteine on Ag(111) in UHV, examined by direct STM observations, synchrotron-based XPS, and NEXAFS. Following adsorption, the molecules build up a dense-packed layer of zwitterions, attached to the surface via their sulfur atom. Upon annealing to 390 K, the cysteine molecules undergo pronounced chemical and conformational transformation, leading to a more complex assembly, driven by the deprotonation of the ammonium group.