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The topics of DNA adduct structure, biodegradation mechanisms, photo-chemistry, and adsorption of polycyclic aromatic hydrocarbons (PAHs) are discussed using benzo(a)pyrene and its partial oxidation products as an example. The use of classical mechanical, semi-empirical, and ab initio computational techniques are discussed in terms of their ability to answer important questions regarding the environmental fate of this important carcinogenic compound. The role of H-bonding variation with computational technique was analyzed and significant errors are likely when this parameter is predicted by classical force field simulations or semi-empirical calculations. The stability of the conformations of benzo(a)pyrene also change with computational method although the density functional theory (DFT) and second-order Møller-Plessett (MP2) methods used here converge to similar relative energies. Analy- sis of the relationship among HOMO-LUMO gaps, triplet and singlet excitation energies, and phototoxicity suggests that the HOMO-LUMO gaps are not the true parameter related to phototoxicity but a correlation between HOMO-LUMO gaps and excitation energies gives the appearance of a cause-and-effect relationship. Methods for predicting the water-soot partition coefficient of PAHs and the complexation of partial oxidation products with cations and metals in the environment are also discussed.

Computational chemistry applied to studies of organic contaminants in the environment: Examples based on benzo[a]pyrene