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QSAR ESTIMATED OF EXCITED STATES AND PHOTOINDUCED ACUTE TOXICITY OF POLYCYCLIC AROMATIC HYDROCARBONS
Citation:
Mekeyan, O., G. Ankley, G. Veith, AND D. Call. QSAR ESTIMATED OF EXCITED STATES AND PHOTOINDUCED ACUTE TOXICITY OF POLYCYCLIC AROMATIC HYDROCARBONS. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/J-95/142.
Description:
Direct calculation of the energy of excited states for polycyclic aromatic hydrocarbons using semi-empirical methods on a supercomputer were inadequate in explaining spectroscopic data or measured phytotoxicity. he energy difference between frontier orbitals HOMO-LUMO gap of "average" excited state structures of the PAHs correlated with the measured excited state energies and their observed photoinduced toxicity. he multi-linear relationship between phytotoxicity and hypothetical triplet state HOMO-LUMO gap is similar to that based on ground state structures. his molecular descriptor discriminated phytotoxic PAHs into a narrow range of approximately 6.2+/-0.4 eV. hemicals with a HOMO-LUMO gap in the triplet state greater than 7.1 eV were not phytotoxic in simulated sunlight. hemicals with gaps less than 5.8 eV are likely to be unstable in water and degrade too rapidly to enable determination of photoinduced potency to aquatic organisms. everal preliminary structure-phytotoxicity relationships for PAHs are presented, together with predictions of toxicity for eight untested aromatic chemicals suggested as suitable test chemicals for evaluating the reliability of the QSARs. ractical issues associated with computing ground state and excited state indices for use in QSAR of phytotoxicity are discussed.