Application of fluorescence and linear dichroism techniques to the characterization of the covalent adducts derived from interaction of (±)-trans-9,10-dihydroxy-anti-11,12-epoxy-9,10,11,12-tetrahydrobenzo[e]pyrene with DNA

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Abstract
Spectroscopic techniques including absorption, fluorescence excitation and emission spectra, fluorescence decay profiles (determined by single photon counting techniques), and electric linear dichroism are applied to a study of the conformation of covalent adducts derived from a reaction of 9,10-dihydroxy-11,12-epoxy-9,10,11,12-tetrahydro[e]pyrene (B[e]PDE) with DNA. The characteristics of non-covalent adducts obtained from the intercalative binding of 9,10,11,12-tetrahydroxytetrahydrobenzo[e]pyrene (B[e]PT) (derived from the hydrolysis of B[e]PDE) with DNA are compared to those of the covalent B[e]PDE–DNA adducts. It is shown that there are two types of binding sites in B[e]PDE–DNA adducts: (1) an exterior binding site similar to the one observed with the isomeric 7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (B[a]PDE)–DNA adducts, and (2) a quasi-intercalative type of binding site in which the properties of the pyrene chromophore are similar to those of an intercalated pyrene moiety, but in which the red shift in the absorption maximum, and fluorescence quenching are less pronounced. This latter conformation is not observed in covalent B[a]PDE–DNA adducts. It is shown that the DNA concentration is an important parameter in determining the relative number of pyrene chromophores at these two binding sites. The extent of covalent binding of B[e]PDE is 4–8 times less than the binding of B[a]PDE to DNA under the same experimental conditions. The reduced reactivity of B[e]PDE is tentatively attributed to steric hindrance due to quasi-diaxial conformations of the two hydroxyl groups in one of the two bay-regions of B[e]PDE.

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