Semiempirical Molecular-Orbital Properties of Some Polycyclic Aromatic Hydrocarbons and Correlation with Environmental Toxic Equivalency Factors

Abstract

The similarities and differences in calculated molecular semiempirical (AM1 and PM3) physicochemical properties of a range of polycyclic aromatic hydrocarbons (PAHs) in relation to the published toxic equivalency factors (TEFs) were investigated. The intrinsic clustering of these molecules was examined using a variety of multivariate statistical techniques; namely, principal components analysis, hierarchical cluster analysis, and AutoClass (a Bayesian classification scheme). The association of these compounds with the literature TEFs has been considered using kth nearest neighbor analysis. The general classification of the TEFs with the most important principal component was observed confirming the general classification, although some unusual properties for benzo[ a ]pyrene were noted. From their properties the two most "toxic" PAHs overall (benzo[ a ]pyrene and dibenzo[ ah ]anthracene) showed some distinction from the other PAHs, with anthanthrene the most similar molecule to the former. Clustering of some of the low-molecular-weight and 4-ring PAHs was also found. The implications of the electronic similarity on the reactivity of these compounds, and their TEF values were discussed.