QSAR study of the toxicity of nitrobenzenes to Tetrahymena pyriformis

A QSAR analysis has been carried out of the toxicity of 47 monosubstituted nitrobenzenes to the aquatic ciliate Tetrahymena pyriformis. The single most important parameter was the logarithm of the apparent partition coefficient (log D) at pH 7.35. 2- and 3-derivatives yielded an excellent correlation of toxicity with log D, Swain-Lupton field parameter and modulus of change of charge on the nitro group oxygen upon substitution. This is consistent with their behaving as pro-electrophiles. 4-derivatives, however, clearly had a different mode of action, with the best correlation being found with log D, molar refractivity and the Shannon index.