Stereoelectronic aspects of the intercalative binding of benz[a]anthracene metabolite models to DNA

Abstract

The physical binding of m-electron models of different benz [a]anthracene metabolites to DNA exhibits widely varying properties. In this study, the binding properties of two nonreactive m-electron models of reactive metabolites of benz[a]anthracene were examined. The models investigated are 1,2,3,4-tetrahydrobenz[a]anthracene and 8,9,10,Il-tetrahydrobenz[n]anthracene. Physical binding has been studied by measuring the effects of native DNA, denatured DNA, and DNA components upon the fluorescence intensities and the fluorescence lifetimes of these models. The results indicate that both metabolite models bind to native DNA with association constants that are approximately equal and lie in the range of 2.0 to 3.0 x 103M-'. Furthermore, for both models, binding involves 1-electron interactions between the hydrocarbons and the nucleotide bases. However, the two models exhibit DNA complex conformations that are very different. Results indicate that 1,2,3,4-tetrahydrobenz[a]anthracene binding depends strongly upon DNA secondary structure and involves intercalated complexes. On the other hand, 8,9,10,11-tetrahydrobenz[a]anthracene binding is only weakly dependent upon DNA secondary structure. In native DNA, this binding involves wedged complexes. These two types of complexes may be representative of two important classes of conformations which occur when reactive hydrocarbon metabolites bind to DNA.