Molecular models of benzene and selected polycyclic aromatic hydrocarbons in the aqueous and adsorbed states

Journal Article · Sun Aug 01 04:00:00 EDT 1999 · Environmental Toxicology and Chemistry

DOI:https://doi.org/10.1897/1551-5028(1999)018<1656:MMOBAS>2.3.CO;2· OSTI ID:20012719

Kubicki, J D; Blake, G A; Apitz, S E

Energy gaps between the highest-occupied molecular orbital and lowest-unoccupied molecular orbital ({Delta}E{sub HOMO-LUMO}) for a suite of common polycyclic aromatic hydrocarbons (PAHs) in the gas-phase were calculated with three different molecular modeling methods: semiempirical, ab initio Hartree-Fock, and density functional calculations. Results indicate that semiempirical, Hartree-Fock, and density functional calculations may provide useful relative HOMO-LUMO gap information, but these methods overestimate the actual {Delta}E{sub HOMO-LUMO}. Based on vibrational frequency analyses, density functional calculations reliably produce dynamically stable structures that can be used to predict model {Delta}E{sub HOMO-LUMO} values. Both the semiempirical and ab initio Hartree-Fock methods were unreliable in predicting dynamically stable structures; hence predictions of {Delta}E{sub HOMO-LUMO} values was not possible for several PAHs. Changes in the HOMO-LUMO gap of benzene and selected PAHs due to solvation effects were calculated using self-consistent reaction field methods and explicit solvation. Self-consistent isodensity polarized continuum model calculations modeling water and octanol solvation do not change calculated {Delta}E{sub HOMO-LUMO} values enough to affect predicted phototoxicities; thus, gas-phase values may be used for PAHs in solution and in vivo. Energetics of PAH bonding to mineral surface groups were also modeled. In some cases, interaction of PAHs with model aluminate surface defects suggests that {Delta}E{sub HOMO-LUMO} values may be lowered significantly by adsorption that would lower chemical stabilities. Significant increases in calculated {Delta}E{sub HOMO-LUMO} that would increase chemical stability of the compounds were not predicted.

• Research Organization: Computer Sciences Corp., San Diego, CA (US)
• OSTI ID: 20012719
• Journal Information: Environmental Toxicology and Chemistry, Journal Name: Environmental Toxicology and Chemistry Journal Issue: 8 Vol. 18; ISSN ETOCDK; ISSN 0730-7268
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
ADSORPTION
BENZENE
BIODEGRADATION
BIOLOGICAL AVAILABILITY
H CODES
POLYCYCLIC AROMATIC HYDROCARBONS
STABILITY