Chapter 5: Isotope Chirality and Cosmochemistry¹

Isotope substitution can generate centers of asymmetry in molecules or molecule fragments which are usually regarded as achiral. Thus simple achiral molecules, such as e.g. glycine, become chiral by ¹H ⇒ ²D monosubstitution in the methylene group. Such chiral molecules, enantioisotopomers, can provide more–less enantiomeric excess (ee) according to laws of probability theory. It has been experimentally demonstrated by variants of the Soai autocatalysis that enantiomeric excesses of chiral isotopomers can induce huge amounts of excess chirality in achiral-to-chiral reactions. In the present study calculations are described, which started from terrestrial stable isotope abundances of H, C, N, and O, and quantify the possible effects in inducing chirality by the unusually high concentrations of heavy isotopes of these elements in interplanetary and interstellar space objects. Simple organic molecules considered as ‘prebiotic’ precursors of living organisms have been chosen as model systems. The results show that statistical enantiomeric excesses in chiral isotopomers are substantially increasing, as a consequence of higher abundances of the heavy isotopes, detected recently by cosmochemical/astrophysical methods. This effect might have had an important role in the evolution of the prebiotic phase of biological chirality.