Selective chiral symmetry breaking: when 'Left' and 'Right' cannot coexist and 'Left' is the best option

Abstract

Chiral symmetry breaking occurs when a physical or chemical process, with no preference for the production of one or other enantiomer, spontaneously generates a large excess of one of the two enantiomers: (L), left-handed or (D), right handed. Inorganic processes involving chiral products commonly yield a racemic mixture of both. However life on Earth uses only one type of amino acids (L) and one type of natural sugars (D). The origin of this selective chirality has remained a fundamental enigma in the origin of life since the time of Pasteur, some 140 years ago. Sodium bromate (NaBrO3) and sodium chlorate (NaClO3) when crystallize from an unstirred solution generates statistically equal numbers of left-handed (L) and right handed (D) chiral crystals. But when these two populations of crystals undergo a dissolution-crystallization phenomenon, they cannot coexist: one of them disappears in an irreversible competition process that nurtures the other one. From the viewpoint of energy, these two enantiomers can exist with an equal probability, thus the result of this competition in different systems would be populations of crystals either (L) or (D). But contradicting this theoretical prediction the handedness of the chiral crystals that win the competition and remain in solution in the different systems is almost always the same (99.2 percent for NaBrO3). We suggest that these results are the consequence of Parity-violating energy difference (PVED) between enantiomers and reinforce the idea of a key role of PVDE theory in the origin of biomolecular chirality on Earth.