Racemate Resolution of Alanine and Leucine on Homochiral Quartz, and Its Alteration by Strong Radiation Damage

Abstract

Homochiral proteins orchestrate biological functions throughout all domains of life, but the origin of the uniform l-stereochemistry of amino acids remains unknown. Here, we describe enantioselective adsorption experiments of racemic alanine and leucine onto homochiral d- and l-quartz as a possible mechanism for the abiotic emergence of biological homochirality. Substantial racemate resolution with enantiomeric excesses of up to 55% are demonstrated to potentially occur in interstitial pores, along grain boundaries or small fractures in local quartz-bearing environments. Our previous hypothesis on the enhanced enantioselectivity due to uranium-induced fission tracks could not be validated. Such capillary tubes in the near-surface structure of quartz have been proposed to increase the overall chromatographic separation of enantiomers, but no systematic positive correlation of accumulated radiation damage and enantioselective adsorption was observed in this study. In general, the natural l-quartz showed stronger enantioselective adsorption affinities than synthetic d-quartz without any significant trend in amino acid selectivity. Moreover, the l-enantiomer of both investigated amino acids alanine and leucine was preferably adsorbed regardless of the handedness of the enantiomorphic quartz sand. This lack of mirror symmetry breaking is probably due to the different crystal habitus of the synthetic z-bar of d-quartz and the natural mountain crystals of l-quartz used in our experiments.

Resolution, quantification, and reliable determination of enantiomeric excess of proteinogenic and non‐proteinogenic amino acids by comprehensive two‐dimensional gas chromatography

“…The former is related to the limitations of the manufacturer's accuracy in determining the ee as well as to the initial syntheses. The latter is a result of differential instrument responses for each enantiomer or erroneous chromatographic quantification caused by co‐eluting impurities, poor enantio‐resolution, or peak tailing [ 40 ]. Consequently, chromatographic techniques do not necessarily provide accurate information on the absolute configuration of the sample.…”

Chirality in Organic and Mineral Systems: A Review of Reactivity and Alteration Processes Relevant to Prebiotic Chemistry and Life Detection Missions

“…There are inherent factors that influence the degree to which chiral minerals (either via their internal structure or having chiral faces) can drive organic ee: the most notable being the degree to which the mineral enantiomers are structurally different (i.e., the chiral index; [196]) and the degree to which organic enantiomers are sorbed to the mineral surface e.g., ref. [197].…”