Nanoscale oligopeptide adsorption behaviour on chlorite as revealed by scanning probe microscopy and density functional simulations

In the present work, the interaction between simple oligopeptides of L-alanine (di-L-alanine) and the (001) surface of clinochlore was characterized in details by employing cross-correlated atomic force microscopy (AFM) observations and Density Functional Theory (DFT) simulations. The AFM results showed that the mineral surface is able to stably bind L-alanine peptides preferentially onto the brucite-like sheets of clinochlore during an interaction in a water suspension. In particular, the (001) surface acted as a condensing and agglomerating system, where AFM evidenced di-L-alanine oligopeptides organized in dot-like, agglomerates and filament-like structures up to more than 160 nm in length, in the experimental conditions here used. DFT simulations were conducted to analyse at the atomic scale the interaction between di-L-alanine oligopeptides and the mineral, finding the molecular conformation with the lowest energy, the adsorption (binding) energy between the oligopeptide and the brucitic surface and also the hydrogen bonding scheme. The reported findings constitute a further step towards the comprehension of the interaction mechanisms between fundamental biomolecules and clay mineral surfaces, of paramount importance for environmental sequestration and biotechnological purposes, but also for prebiotic chemistry research.