Collaborative prebiotic adsorption: proteinogenic and non-proteinogenic amino acid mixtures on clay

The puzzling nature of how life can emerge from otherwise non-living matter remains one of the most intriguing open questions in science. Amino acids, the building blocks of proteins, are one set of key compounds of high interest in origins of life. Their interaction with negatively charged clay surfaces, which can serve both as concentrating and catalysing agents, are crucial to abiotic processes leading to chemical complexification such as polymerisation. However, research is highly biased towards the incorporation of protein-forming amino acids, which are expected to undergo polymerisation. It often dismisses the possible role of non-proteinogenic, predominantly extra-terrestrial amino acid species in these processes, despite their universal abundance.

In this work we investigate the adsorption interaction between calcium-montmorillonite (Ca-Mt) and mixtures of proteinogenic L-lysine and L-arginine, and the meteorite-common, non-proteinogenic gamma-aminobutyric acid. These amino acids all bear a structural similarity yet differ in their charge distribution, which in turn affects their interaction with Ca-Mt surfaces. The adsorption behaviour of single component vs. proteinogenic/non-proteinogenic amino acid mixtures is elucidated using attenuated total reflectance Fourier transform infrared spectroscopy and powder X-ray diffraction. This study provides cardinal insights on the nature of collaborative adsorption of proteinogenic amino acids in the presence of non-proteinogenic species on the pathway to chemical complexity.