QSPR analysis of the toxicity of aromatic compounds to the algae (Scenedesmus obliquus).

The quantitative structure-property relationship (QSPR) model was developed for the 50% effective inhibition concentration (48h - EC(50)) of 36 selected substituted benzenes for the algae Scenedesmus obliquus by the application of the Characteristic Root Index (CRI) model. To increase the predictive power of the CRI-based model, the following semi-empirical molecular descriptors calculated by the quantum chemical PM3 method were included: the energy of the highest occupied molecular orbital (E(HOMO)), the energy of the lowest unoccupied molecular orbital (E(LUMO)), and the dipole moment (mu). A two-descriptor model with a correlation coefficient of r=0.926 was developed without the outliers from multiple regression analysis [-logEC(50)=0.494 (+/-0.072) CRI-0.798 (+/-0.063) E(LUMO)+1.985 (+/-0.169)]. E(LUMO) was the most important parameter, followed by the CRI. E(LUMO) reflects electronic properties, whereas the CRI reflects hydrophobicity, molecular size, and branching. The statistical robustness of the developed model was validated by the modified jackknife test. The predictive accuracy of the proposed model was compared with the recently published study in which a toxicity model was developed for the same algae. Because of its high statistical significance, the validated model has been used to predict -logEC(50) values of compounds for which there are no experimental measurements.