AIMD Evidence of Inner Sphere Adsorption of Glycine on a Stepped (101) Boehmite AlOOH Surface

Adsorption of glycine, the smallest and simplest amino acid, on the (101) boehmite AlOOH stepped surface has been investigated at the solid/liquid water interface by means of ab initio molecular dynamics simulations at room temperature. The inner-sphere adsorption is shown to be the most favorable in energy, with either a glycinate located at the terrace or a zwitterion located at the step. Such conformations are dissected in terms of covalent and hydrogen bonds formed between the adduct and the surface and between the adduct and the surrounding water solvent at the interface. The outer-sphere adsorption of a zwitterionic glycine at the boehmite interface is found far less favorable in energy, where the compromise in the hydrogen bonds formed by glycine toward the surface and toward the solvent is detailed. Such outer-sphere adsorption is slightly more favorable than the solvation of the glycine molecule within the bulk liquid water. Glycine adsorption is also found to passivate the surface, as it hinders the previously evidenced Grotthus based proton transfer at the step (J. Phys. Chem. C2012, 116, 12514).