Structure-toxicity relationships for phenols to Tetrahymena pyriformis.

Quantitative structure-activity relationships are developed for the toxicity of 166 varied phenol derivatives to the ciliate Tetrahymena pyriformis. A variety of physico-chemical descriptors were calculated but no significant relationship could be obtained for all 166 compounds. When certain chemical groups were omitted from the correlation however, notably the carboxyl-, amino-, nitro, nitroso and acetamide- substituted phenols, an excellent correlation was obtained between toxicity and two parameters. These two parameters (log P and energy of the lowest unoccupied molecular orbital) are explained mechanistically in that they model transport and electrophilicity. The resultant QSAR gave accurate prediction of the toxicity of alkyl, halogenated, alkoxy and aldehyde substituted phenols.