Distinct local environments of the pyrene chromophores in the covalent DNA adducts of 9,10-epoxy-9,10,11,12-tetrahydrobenzo[e]pyrene and 7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene elucidated by optically detected magnetic resonance

Abstract

The optically detected magnetic resonance (ODMR) spectra of the covalent DNA adduct of 9,10-epoxy-9,10,11,12-tetrahydrobenzo[e]pyrene (BePE) reveal that the excited triplet state chromophore is perturbed by the nucleic acid and that this perturbation is diminished successively by denaturation and enzymatic hydrolysis of the modified DNA, indicating that the adduct resides in an environment with some quasi-intercalative character. In contrast the covalent adduct of 7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene shows little ODMR evidence of interaction with the nucleic acid, which, in view of ODMR's sensitivity demonstrated for the BePE adduct, suggests that the chromophore is situated in an environment resembling the bulk solvent. These results demonstrate that ODMR is more sensitive than conventional phosphorescence techniques to interactions between these pyrene-like chromophores and DNA.

Denaturation and renaturation studies of benzo[a]pyrene metabolite modified DNAs

“…Evidence from spectroscopic measurements presented in this paper strongly suggests that the adduct conformations at the binding sites are grossly different before and after thermal denaturation of the (+)-anrz'-BPDE-modified DNAs. Although interpretation of the results is complicated by the incomplete reannealing of the thermally melted DNA, the finding that the postmelt spectral characteristics of (+)-'-BPDE-modified native DNA exhibit significant stacking interactions, in contrast to those of premelt adducts, is in conformity with the conclusion reached by other spectroscopic evidence (Geacintov et al, 1976(Geacintov et al, , 1978(Geacintov et al, , 1980Lefkowitz & Brenner, 1982) indicating that the covalently bound (+)-'-BPDEs in native DNA are predominantly external in nature. The inability to return to the premelt adduct conformation at the binding sites of negligible stacking interactions appears to conflict with the premise that these original externally bound moieties are the result of reorientation of the intercalated '-BPDE.…”

“…There is strong evidence to suggest that the ultimate carcinogenic metabolite of benzo[a]pyrene (BP), the most widely studied PAH, is (+)-trans-l ,8-dihydroxy-anti-9,10-epoxy-7,8,9,10-tetrahydrobenzo [a] well as stereospecific (Meehan & Straub, 1979), with the dominant covalent adduct resulting from trans addition of the exocyclic amino group of guanine to the CIO position of anti- (Weinstein et al, 1976;Jeffrey et al, 1977;Moore et al, 1977). Spectroscopic studies reveal that the DNA covalent adducts of (+)-a«Z/-BPDE are, to a large extent, not intercalative in nature (Geacintov et al, 1976(Geacintov et al, , 1978(Geacintov et al, , 1980; Lefkowitz & Brenner, 1982). The externally situated pyrenyl moiety does not exhibit strong stacking interactions with the DNA bases, as judged from a mere 2-3-nm spectral red shift.…”

Stereoselective covalent binding of enantiomers of anti-benzo[a]pyrenediol epoxide to DNA as probed by optical detection of magnetic resonance

“…The phosphorescence emission maximum of the (-) adduct is red-shifted by a full 10 nm relative to that of the (+) adduct (Figure 2); moreover, the ODMR frequencies, particularly the 2|£ value, are substantially lower (Figure 3). If one associates red shifts in phosphorescence and zero field splittings with quasi-intercalative binding, as suggested by our earlier work on 9,10-epoxy- 9,10,11,12-tetrahydrobenzo[e] pyrene (BePE) (Lefkowitz & Brenner, 1982), then this would implicate predominantly site Frequency (MHz) figure 3: The 2\E\ ODMR spectra at 1.6 K of the covalent DNA adducts of (+)-BaPDE (panel A) and (-)-BaPDE (panel B). For the (+) adduct, phosphorescence was monitored at 600 nm, and ca.…”

“…These classes of binding sites show distinctive properties in terms of shifts of UV absorbance, chromophore orientation as determined by linear electric dichroism, and differing fluorescence yields (Geacintov, 1985). Previous ODMR studies (Lefkowitz & Brenner, 1982) of DNA adducts of 9,10-epoxy-9,10,l 1,12tetrahydrobenzo [e] pyrene (BePE) have suggested that the triplet zero field splittings of site I (quasi-intercalative) adducts should generally be shifted down in frequency relative to those of solvent-exposed adducts. In this paper, we apply ODMR to the DNA adducts of the (+) and (-) enantiomers of anti-BaPDE [referred to here as simply (+)-and (-)-BaPDE] and find that the complexes show quite dramatically different phosphorescence and zero field splittings, implying that the conformations of the two types of adducts are quite different.…”

Binding of pyrene to DNA, base squence specificity and its implication

“…Site II shows no shift in the absorption spectrum with respect to that of free BPT molecules, an unchanged fluorescence yield and decay time, and susceptibility to oxygen quenching indicative of an e-xternal mode. The spectroscopic properties of the covalent adducts of anti-BPDE with DNA also exhibit outside binding characteristics (12)(13). Since physical binding is dominated by the intercalative mode, it is puzzling that the covalent adduct should be non-intercalative.…”