A mechanism for molecular asymmetry

Summary The origin of the molecular asymmetry of biological systems has been speculated upon extensively, and has been the object of numerous inconclusive experimental studies. That circularly polarized light (CPL) might have been the cause of this asymmetry was suggested in 1874 (van't Hoff 1897; Le Bel 1874). During the daylight morning (AM) there is a significant component of left (L) CPL in skylight, which reverses to right (R) CPL in the afternoon (PM) (Wolstencroft 1985). The rates or photochemical reactions of LCPL and RCPL are different for the R (right) and S (left) forms of chiral molecules (Flores et al. 1977). At sunset the ambient temperature at the surface of the earth is approximately 10°C higher than at sunrise. Most chemical reactions proceed faster at higher temperatures and for each 10°C rise in temperature chemical reaction rates increase by a factor of 1.8–4.1 (Taylor 1925). It is proposed that the combination of these four factors, LCPL in the AM compared to the RCPL in the PM, the different rates of photochemical reaction of the R and the S forms of an R-S racemic mixture with RCPL (and LCPL), the higher PM temperature, and the faster reaction rates in the PM could lead to a substantial deviation from equality in the degradation and formation of R and S enantiomeric forms of chiral molecules.