PHOTO-INDUCED TOXICITY OF PAHs: QSAR
MODELS AND ENVIRONMENTAL SIGNIFICANCE
Ovanes G. MEKENYANQ,b, Gerald T. ANKLEY c ,
Gilman D. VEITH c and Daniel J. CALLb,1
aBourgas University of Technology, Department of Physical Chemistry
8010 Bourgas, Bulgaria
bLake Superior Research Institute, University of Wisconsin-Superior
Superior, WI 54880 USA
CU.S. Environmental Protection Agency, Environmental Research Laboratory -
Duluth, 6201 Congdon Boulevard, Duluth, MN 55804 USA
ABSTRACT
Research with a variety of aquatic species has shown that while polycyclic
aromatic hydrocarbons (PARs) are generally not acutely toxic in conventional
laboratory tests, many are extremely toxic in the presence of sunlight. A QSAR
model was developed for predicting phototoxicity of PARs, which incorporated the
competing effects of stability and light absorbance of the PARs as well as
irradiation parameters. Interaction of these factors produces a complex,
multilinear (bell-shaped) relationship between toxicity and chemical structure.
The molecular descriptor best describing both light absorbency and stability of
ground state PARs was found to be the energy of ROMO-LUMO gap, which could
be computed from structure rather than measured empirically. Thresholds of
ROMO-LUMO gap values were established, classifying PARs according to their
photo-induced toxic properties. The substitution of PAHs, in general, reduced
their HOMO-LUMO gap, which is consistent with the Principle of Absolute
Hardness. Alkane and hydroxy substituents did not significantly reduce the
HOMO-LUMO gap of PAHs. This held less well for nitro, alkene and chloro
substituents.
Interactions (p-n and n-n) between the electronic structures of these substituents
and PAHs provided hyperconjugation effects and eventually "red-shifted" the
parent compounds. It was concluded, however, that the photo-induced properties
of PARs were mainly due to the electronic structure of the parent chemicals.
1 To whom correspondence may be addressed
C. Bardinet et al. (eds.), Geosciences and Water Resources: Environmental Data Modeling
© Springer-Verlag Berlin Heidelberg 1997
MODELS AND ENVIRONMENTAL SIGNIFICANCE
Ovanes G. MEKENYANQ,b, Gerald T. ANKLEY c ,
Gilman D. VEITH c and Daniel J. CALLb,1
aBourgas University of Technology, Department of Physical Chemistry
8010 Bourgas, Bulgaria
bLake Superior Research Institute, University of Wisconsin-Superior
Superior, WI 54880 USA
CU.S. Environmental Protection Agency, Environmental Research Laboratory -
Duluth, 6201 Congdon Boulevard, Duluth, MN 55804 USA
ABSTRACT
Research with a variety of aquatic species has shown that while polycyclic
aromatic hydrocarbons (PARs) are generally not acutely toxic in conventional
laboratory tests, many are extremely toxic in the presence of sunlight. A QSAR
model was developed for predicting phototoxicity of PARs, which incorporated the
competing effects of stability and light absorbance of the PARs as well as
irradiation parameters. Interaction of these factors produces a complex,
multilinear (bell-shaped) relationship between toxicity and chemical structure.
The molecular descriptor best describing both light absorbency and stability of
ground state PARs was found to be the energy of ROMO-LUMO gap, which could
be computed from structure rather than measured empirically. Thresholds of
ROMO-LUMO gap values were established, classifying PARs according to their
photo-induced toxic properties. The substitution of PAHs, in general, reduced
their HOMO-LUMO gap, which is consistent with the Principle of Absolute
Hardness. Alkane and hydroxy substituents did not significantly reduce the
HOMO-LUMO gap of PAHs. This held less well for nitro, alkene and chloro
substituents.
Interactions (p-n and n-n) between the electronic structures of these substituents
and PAHs provided hyperconjugation effects and eventually "red-shifted" the
parent compounds. It was concluded, however, that the photo-induced properties
of PARs were mainly due to the electronic structure of the parent chemicals.
1 To whom correspondence may be addressed
C. Bardinet et al. (eds.), Geosciences and Water Resources: Environmental Data Modeling
© Springer-Verlag Berlin Heidelberg 1997