The Relationship Between Carcinogenic Activities of Polycyclic Aromatic Hydrocarbons and Their Singlet, Triplet, and Singlet‐triplet Splitting Energies and Phosphorescence Lifetimes

Abstract

The energies of the lowest excited singlet, E,, and triplet, E,, states, and singlet-triplet splitting energies, A&,, were determined on 18 carcinogenic and 31 noncarcinogenic polycyclic aromatics. A highly significant correlation was found between carcinogenic activity and the energy of the excited singlet state. Compounds with an E, i 312 kJ/mol were 4.8 times more likely to be carcinogens than those compounds with E, > 312 kJ/mol (P = 0.015). Compounds whose singlet energies fell within the narrow range of 297 < E, < 310 kJ/mol were 22.8 times more likely to be carcinogens than those compounds which fell outside this range (P = 0.00006). A significant correlation between carcinogenic activity and E, energies was not found, while the correlation involving AE,, energies was intermediate between the E, and E, correlations. The phosphorescence lifetimes, tp, of the 18 carcinogenic aromatics and 27 of the noncarcinogenic aromatip were determined, and were shown not to be correlated with carcinogenic activity. When either the E, or AES,* energies were plotted as a function of E, it was found that the carcinogens tended to form in an elliptical cluster. Compounds whose E, and E, energies placed them within the ellipse were 9.7 times more likely to be carcinogens than those compounds which fell outside the ellipse (P = 0.002), while with the Es, AE,,, ellipse, compounds which fell inside were 20.6 times more likely to be carcinogens than those which fell outside (P = O.OOO4). E,, E,, AE,,, and tp values were also determined on 12 carcinogenic and 4 noncarcinogenic alkyl substituted benz [a]anthracenes. There was no significant difference between the carcinogens and noncarcinogens and the "elliptical" correlation predicted both the carcinogens and noncarcinogens to be carcinogenic. The results suggest that either some property(ies) of the lowest excited singlet state, but not its energy, or some molecular property(ies) which runs parallel to singlet state energies may be important in determining carcinogenic activity in polycyclic aromatics.

Low-power green-to-blue and blue-to-UV upconversion in rigid polymer films

“…The triplet energy of fluoranthene of 52.5 kcal mol À1 [22,23] is too high to allow quenching of PtOEP triplets. As expected, no upconverted fluorescence was observed when this film was excited at 533 nm.…”

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

“…The relative correlations for this chemical descriptor are not a problem if one is calibrating calculated values against experimental phototoxicities in order to predict relative toxicities as was done in Mekenyan et al [8]. However, the measured triplet excitation energy is 203 kJ/mol [25], which is in the visible region. For instance, pyrene is predicted to have a HOMO-LUMO gap of 698 kJ/mol with semiempirical calculations [8], which is at the high-energy end of the UV region.…”

Photoinduced Toxicity of PAHs to the Foliar Regions ofBrassica napus(Canola) andCucumbis sativus(Cucumber) in Simulated Solar Radiation

“…By virtue of their extensive -orbitals, PAHs absorb strongly in the ultraviolet-A (UV-A; 320-400 nm) and ultraviolet-B (UV-B; 290-320 nm) regions of the solar spectrum (Suess, 1976;Cook et al, 1983;Nikolaou et al, 1984;Huang et al, 1993). Once excited by actinic radiation, PAHs are good photosensitizers, forming biologically damaging singlet-state oxygen in high yield (Morgan et al, 1977). Additionally, actinic radiation results in the photomodification of PAHs (Katz et al, 1979;Zepp and Schlotzhauer, 1979), defined here as photooxidation and/or photolysis, which increases toxicity McConkey et al, 1996).…”