THEORETICAL-STUDIES ON THE BIOCIDAL ACTIVITY OF PHENYLTHIOCYANATES

Molecular orbital calculations are reported on the structure and elect ronic properties of phenylthiocyanates using both the semi-empirical A M1 and MNDO methods and the ab initio 3-21G and 6-31G* methods. The f ungicidal activity of these molecules which is thought to arise from t heir reaction with intracellular thiols does not appear to correlate w ith simple molecular properties such as the calculated atomic charges at the sulfur and cyano-carbon atoms. Reaction coordinate calculations at the AM1-SM1 level in water, using methanethiolate as the attacking nucleophile, strongly suggest that nucleophilic attack will occur at the cyano-carbon in preference to the sulfur atom; in line with experi mental data obtained from the reactions of glutathione with 2-nitro-5- thiocyanatobenzoic acid in aqueous solution.