Quantitative structure-toxicity relationships for chlorophenols to bioluminescent lux-marked bacteria using atom-based semi-empirical molecular-orbital descriptors

Literature data on the toxicity of chlorophenols for three luminescent bact eria (Vibrio fischeri, and the lux-marked Pseudomonas fluorescens 10586s pU CD607 and Burkholderia spp. RASC c2 (Tn4431)) have been analysed in relatio n to a set of computed molecular physico-chemical properties. The quantitative structure-toxicity relationships of the compounds in each species showed marked differences when based upon semi-empirical molecular- orbital molecular and atom based properties. For mono-, di- and tri-chlorop henols multiple linear regression analysis of V. fischeri toxicity showed a good correlation with the solvent accessible surface area and the charge o n the oxygen atom. This correlation successfully predicted the toxicity of the heavily chlorinated phenols, suggesting in V. fischeri only one overall mechanism is present for all chlorophenols. Good correlations were also fo und for RASC c2 with molecular properties, such as the surface area and the nucleophilic superdelocalisability of the oxygen. In contrast the best QST R for P. fluorescens contained the 2nd order connectivity index and ELUMO s uggesting a different, more reactive mechanism. Cross-species correlations were examined, and between V. fischeri and RASC c2 the inclusion of the minimum value of the nucleophilic susceptibility on the ring carbons produced good results. Poorer correlations were found wit h P, fluorescens highlighting the relative similarity of V, fischeri and RA SC c2, in contrast to that of P. fluorescens.