Toxicity of aromatic compounds to Tetrahymena estimated by microcalorimetry and QSAR.

The toxicity of six organic aromatic chemicals to Tetrahymena growth metabolism was studied by microcalorimetry. The growth constant k, inhibitory ratio I, and half-inhibiting concentration IC(50) were calculated. The results suggested that the order of toxicity was aniline>nitrobenzene>chlorobenzene>toluene>benzene>phenol. Based on the molecular descriptors (such as K(OW), E(HOMO), E(LUMO), DeltaE, E(T) and logIC(50)), the QSAR equation is obtained by multiple linear regression analysis: logIC(50)=-3.360-1.545 E(HOMO)-0.6850 DeltaE-0.3019logK(OW) (R=0.8643, n=6, s=0.202, F=0.739, Sig.=0.041, R(CV)(2)=0.624). The equation indicates that the toxic action is a two-step process: the pass of the chemicals through the cell membrane (described by logK(OW)) and the electron-transfer reaction of the chemicals with biomolecules (described by E(HOMO) and DeltaE). The substituents on aromatic ring are crucial to the toxicity of the compounds and the reaction between the chemicals and biological macromolecules is important.