Use of molecular Orbital theory to predict aquatic phototoxicity of substituted polyaromatic hydrocarbons
Polycyclic aromatic hydrocarbons (PAHs) are planar, nonplanar, semi-volatile chemical compounds that are composed of two or more fused aromatic rings. PAHs originate from point sources (e.g. oil spills, industrial processes) and non- point sources (e.g. road runoff, forest fires and motor vehicles). PAHs have low aqueous solubility, and in water absorb on sediment. PAHs can undergo chemical and photochemical transformation to substituted PAHs in vapor, in aqueous state and absorbed to sediment. Reactions of PAHs with reactive species in the environment may give rise to emerging pollutants. Although 16 unsubstituted PAHs are regularly monitored by USEPA, substituted PAHs are not well characterized or monitored regularly.
Computational methods have been used to correlate molecular orbital energy to aquatic photo toxicity in PAHs. Previous researcher found a parabolic relationship for PAH and mono-substituted PAH frontier molecular orbital energy gap and phototoxicity. They interpreted this relationship as a superposition of molecular stability and energy of light absorbed. Our research probes into the extension of molecular orbital energy gaps for prediction of phototoxicity in polysubstituted compounds and other aromatic compounds such as asphaltenes and hydrocarbon nanoribbons. Students Marie Kellemen (LSAMP ‘09) on right and Heather Wontor (URP grant ‘09) on left received research grants to work on this project.