Quantitative structure-activity relationships of nitroaromatics toxicity to the algae (Scenedesmus obliguus)

The DFT-B3LYP method, with the basis set 6-311G∗∗, was employed to calculate the molecular geometries and electronic structures of 25 nitroaromatics. The acute toxicity (−lg EC50) of these compounds to the algae (Scenedesmus obliguus) along with hydrophobicity described by log KOW, and two quantum chemical parameters-energy of the lowest unoccupied molecular orbital, ELUMO, and the charge of the nitro group, QNO2, were used to establish the quantitative structure-activity relationships (QSARs). For 18 mononitro derivatives, the hydrophobicity parameter log KOW could interpret the toxic mechanism successfully. Dinitro aromatic compounds were susceptible to be reduced to aniline for their electrophilic nature. Their toxicity was controlled mainly by electronic factors instead of hydrophobicity. The electronic parameters, ELUMO and QNO2, were used to yield the following model: -lgEC50=3.746-25.053ELUMO+6.481QNO2 (n = 22, R = 0.926, SE = 0.206, F = 56.854, P < 0.001). The predicted toxic values using the above equation are in good agreement with the experimental values.