The use of quantum-chemical descriptors for predicting the photoinduced toxicity of PAHs.

The geometries of 19 polyaromatic hydrocarbons (PAHs) were fully optimized and calculated by a density functional method (B3LYP) with the 3-21G basis set. Various quantum chemical descriptors such as the energy of the highest occupied molecular orbital (E (HOMO)), the energy of the lowest unoccupied molecular orbital (E (LUMO)), the difference in energy between those orbitals (E (GAP)), electronegativity (χ), chemical potential (μ), chemical hardness (η), softness index (S), electrophilicity (ω), and polarizability (α) were employed along with physicochemical descriptors to construct useful quantitative structure-activity relationship (QSAR) models for the photoinduced toxicity of PAHs toward two aquatic species (Daphnia magna and Scenedesmus vacuolatus). E (LUMO), E (HOMO), E (GAP), S, χ, the molar refractivity (MR), and the molecular weight provide valuable information and play a significant role in the assessment of PAH phototoxicity. The resulting models are not expected to be useful per se for making genuine predictions for much larger test sets, but the various results do demonstrate the potential benefits of incorporating quantum-chemical descriptors into QSAR models for predicting the phototoxicity of PAHs.