Schultz, T.W.; Sinks, G.D.; Cronin, M.T.D. Quinone-induced toxicity to Tetrahymena: structure-activity relationships. Aquat. Toxicol. 1997, 39, 3-4, 267–278.

Abstract

The aquatic toxicities (log(IGC50-1)) of 22 quinones were evaluated in the static Tetrahymena pyriformis population growth assay. A toxicity in excess of baseline was associated with each chemical eliciting a response. The ortho-quinones were the most toxic; internal quinones, with benzenoid substitution on both sides of the quinoid rings, were not toxic at saturation. Ring substitution of 1,4-benzoquinone resulted in a graded toxic response. Substitution by electron-donating, methoxy or hydroxy groups decreased the toxicity. The position of ring substitution was also important, with 2,5-substitution being less toxic than 2,6-substitution. The fully substituted tetramethyl and tetrachloro derivatives, quinones which cannot conjugate or arylate protein thiols, were significantly less toxic than 1,4-benzoquinone. Due to their molecular structure, quinones may act as soft electrophiles and/or redox cyclers. This mixture of mechanisms of toxic action precludes high-quality, quantitative, structure-toxicity relationships. The toxic potency was found to be independent of the 1-octanol/water partition coefficient, one-electron redox potential and lowest unoccupied molecular orbital energy.