Abstract
Amino acids are some of the simplest biological molecules, yet they nevertheless manifest the ability to construct an incredibly complex variety of structures in which a delicate balance of intermolecular chemical forces drives the dynamics of self-recognition and assembly. Understanding the mechanism by which chiral structures are naturally synthesized is also extremely relevant to pharmaceutical and biochemical industries, in which enantioselectivity and enantiospecificity are vital factors in producing biologically compatible drugs. In this context, the adsorption of simple, naturally occurring amino acids on single crystal surfaces has become the playground for studying chiral self-assembly at the atomic scale and investigating pathways to enantioselective catalytic synthesis using a bottom-up approach. In particular, in the last two decades, several groups have dedicated a concerted effort to understand the formation of chiral self-assembled supramolecular networks of alanine, glycine and proline on Cu{110}, Cu{100}1 and Cu{111} surfaces. In the past, with few exceptions,1 the vast majority of the atomistic studies on supramolecular assembly of amino acids on metal surfaces have been conducted under UHV conditions. It is therefore one of the main challenges ahead of the surface-science community to attempt to bridge the gap between experiments conducted under “dry” vacuum conditions (in which the amino acids adsorb in the absence of a solvent and a co-adsorbate) and the more biologically and pharmaceutically relevant “wet” studies. In fact, when water is present in the system, a competition exists between the formation of hydrogen bonds between an amino acid with another and between an amino acid and the water shell immediately surrounding it. The interaction between amino acids and water is also particularly relevant to corrosion protection, since amino acids have recently become a natural and ecologically compatible alternative to traditional amine-based corrosion inhibitors. In this work we study the co-adsorption of water with glycine, the simplest naturally occurring amino acid, using first-principles density functional theory. Although in the past some authors have tried to account for the solvation of amino acids in the gas-phase, few studies have treated the solvation and interaction between adsorbed glycine and water molecules quantum mechanically.