Asymmetric Photolysis ofRacemic Organic Molecules

Since 1929, irradiation of racemic or prochiral precursor molecules with circularly polarized light has been a proposed scenario for the origin of biomolecular asymmetry. Werner Kuhn, a pioneer in the field of asymmetric photolysis, achieved at the University of Heidelberg the first enantioselective photodecomposi-tion (i.e., photolysis) by irradiating solutions of ethyl-a-bromopropionate and N,N-dimethyl-a-azidopropionamide (Kuhn and Braun 1929; Kuhn and Knopf 1930). These molecules were - even for chemists - rather exotic and non-representative of prebiotic conditions during chemical evolution.

In 1974, the research team of Henri Kagan at the University of Paris-Orsay achieved world-wide reputation by the irradiation of racemic camphor (Balavoine et al. 1974), resulting in the highest photochemical induced enantiomeric excess of 20% by carrying the photodecomposition to 99% completion. With the aim of investigating and verifying photochemical theories for the induction of biomolecular homochirality via electronically excited states, topical research focuses on the effect of circularly polarized light on racemic organic molecules such as amino acids.

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