Quantitative structure-activity analyses of nitrobenzene toxicity to Tetrahymena pyriformis

Toxicity data for the 50% growth inhibitory concentration against Tetrahymena pyriformis (log (IGC(50)(-1))) for 42 alkyl- and halogen-substituted nitro- and dinitrobenzenes were obtained experimentally. Log (IGC(50)(-1)) along with the hydrophobicity, the logarithm of the 1-octanol/water partition coefficient (log K-ow), and the molecular orbital properties, the lowest unoccupied molecular orbital energy (E-lumo) and maximum acceptor superdelocalizability (A(max)), were used to develop quantitative structure-activity relationships (QSARs). All the nitroaromatic compounds tested had toxicity in excess of baseline, nonpolar narcosis. The nitrobenzenes were thought to elicit their toxic response through multiple (and mixed) mechanisms. No high-quality relationship was observed between toxicity and hydrophobicity, or E-lumo, individually. However, a strong relationship {log (IGC(50)(-1)) = 16.4(A(max)) - 4.64; n = 42, r(2) = 0.847, s 0.279, F = 229} was obtained. In an effort to improve predictability, two-parameter QSAR, or response surface, analyses were performed. These analyses resulted in the following QSARs: {log (ICG(50)(-1)) = 0.206(log K-ow) - 16.0(A(max)) - 5.04; n. = 42, r(2) = 0.897, s = 0.229, F = 180} and {log (IGC(50)(-1)) = 0.467(log K-ow) - 1.60(E-lumo) - 2.55; n. = 42, r(2) = 0.881, s = 0.246, F = 154}.