![Author ORCID: We display the ORCID iD icon alongside authors names on our website to acknowledge that the ORCiD has been authenticated when entered by the user. To view the users ORCiD record click the icon. [opens in a new tab]](https://www.cambridge.org/engage/assets/public/coe/logo/orcid.png){kind=logo}
Abstract
Clay minerals are hypothesized to have played a critical role in prebiotic chemistry by adsorbing organic molecules and catalyzing the formation of the first proto-biopolymers, such as peptides, from smaller molecules, like amino acids, on early Earth and potentially Mars. While most studies focus on proteinogenic amino acids, the influence of non-proteinogenic amino acids, abundant in early planetary environments, remains under-explored. This study employs molecular dynamics simulations to investigate the adsorption of γ-aminobutyric acid (GABA), a non-proteinogenic amino acid, and two positively charged amino acids, l-arginine and l-lysine, onto calcium montmorillonite clay (STx-1b). Baseline adsorption behaviors were quantified for each amino acid in isolation and compared to mixed systems containing GABA with either l-arginine or l-lysine. The results show that GABA decreased the overall adsorption probability of both l-arginine and l-lysine by ~13%, due to competitive interactions for clay surface sites. For l-arginine, backbone nitrogen and oxygen adsorption decreased, while for l-lysine, sidechain nitrogen adsorption decreased, but oxygen adsorption increased. In this case, cationic bridging via the Ca2+ ion was observed in the presence of GABA, though absent for pure l-lysine or any l-arginine systems. Unlike l-arginine and l-lysine, GABA was much more likely to form clusters of molecules. In the solo GABA system, these clusters formed around Ca2+ ions which bridged to the clay. These clusters occurred more often when l-arginine and l-lysine were present. However, in lysine - GABA systems these clusters were less commonly interacting with the clay and more likely to form away from the surface. These findings highlight the complex interplay of amino acids on clay surfaces, offering insights into molecular organization processes relevant to the proto-biomaterial preservation and transfer on early Earth and Mars environments.
