Chemical Models for the Origin of Biological Homochirality

Abstract

Chirality is the property of a molecule to be nonsuperimposable with its mirror image. In biology, basically all chiral molecules exist in only one mirror-image form, or enantiomer, a phenomenon called biological homochirality. For example, chiral amino acids occur nearly exclusively in the l-form and carbohydrates in the d-form. In contrast, chiral molecules on the early Earth should have been racemic, i.e., consisting of equal amounts of both enantiomers, before life came into existence. The emergence of biological homochirality is therefore directly linked with the origin of life but remains an intriguing and unanswered puzzle for scientists. To chemists, it poses a challenge to create model systems for the emergence of homochirality from a racemic state. This chapter gives an overview of such chemical models as well as other experiments and observations that might explain how biological homochirality was achieved.