Physicochemical Properties and Complexity of Amino Acids beyond Our Biosphere: Analysis of the Isoleucine Group from Meteorites

Abstract

Understanding the physicochemical properties of biomolecules and how these properties drive the emergence of complexity in the assembly/condensation of such systems is important for understanding a variety of reactions taking place in astrophysical environments, in particular those where polymerization processes occur on mineral surfaces or solid organic matter form in cold-chemistry processes. Here, a computational study of the structural and electronic properties of the gas and condensed phases of the isoleucine group of amino acids, found with large enantiomeric excess in Antarctic meteorites, is presented. An analysis of a statistical complexity measure related to their electronic properties, of the degree of chirality, and of the H-bond patterns is also reported. The results, based on Density Functional Theory, Many Body Perturbation Theory, and Moller–Plesset perturbation theory, show that a) the condensed amino acids keep reminiscence of structural and electronic properties of the gas phase molecules, b) the proteinogenic l-isoleucine gains in complexity and chirality upon condensation, contrary to its diastereomer, which is absent in living systems, and c) the complexity based on electronic properties can contrast with the notion of structural/geometrical complexity. The findings suggest that future scoring strategies of organic molecules should rely on both structural/geometrical molecular complexity and on the electronic properties, which in different states of matter are determined by other degrees of freedom (configurational or chiral) to a different extent, as well as on information storage capability of self-assembly configurations constrained by an atomistic chemistry perspective.