Enantioselective Activity and Toxicity of Chiral Herbicides

Chirality is a natural property that is well known to chemists and has been generally recognized in the life sciences since Pasteur discovered the optical isomers of tartrate and van’t Hoff and LeBel proposed the theory of the stereostructure of carbon compounds (GassmannKuo & Zare, 1985; Koeller & Wong, 2001; KondruWipf & Beratan, 1998). Almost all of the biological macromolecules, such as DNA, RNA, protein, polynucleotides, and even the amino acids, the basic structural units of life, are chiral(Roelfes, 2007). Although the enantiomers of chiral substances have the same physicochemical properties, their biochemical activities, unlike abiotic transformations, can be quite different because biochemical processes usually show high stereoor enantioselectivity (Muller & Kohler, 2004). For instance, enantioselective reactions occur in biological enrichment(Hegeman & Laane, 2002), degradation and other physiological actions(Wong, 2006). For organisms, enantiomers often exhibit different effects or toxicities. The “active” enantiomer of a chiral chemical may have the desired effect on a target species, whereas the other enantiomer may not(Garrison, 2006). It is advisable to use only the biologically active enantiomers, thereby reducing the total amount of chemical pollutants released into the environment.