INTERACTIONS OF 4-NITROQUINOLINE 1-OXIDE WITH DEOXYRIBODINUCLEOTIDES

The interactions of 4-nitroquinoline 1-oxide (NQO), a potent mutagen and carcinogen, with several self-and non-self-complementary deoxydinucleotides were probed by using absorption spectra of the charge transfer bands and 1H and 13C NMR spectra. Absorption spectra were analyzed by using Benesi-Hildebrand-type equations to yield stoi-chiometrics and equilibrium constants of complex formation. Non-self-complementary dimers form weak 1:1 complexes [dpTpG:NQO, K(25 °C) = 22 M-1] while self-complementary dimers form strong 2:1 complexes [(dpCpG)2:NQO, K(25 °C) = 2.2 × 104 M-2]. A mixture of dpTpG and dpCpA with NQO gives a 2:1 complex [dpTpG:NQO:dpCpA, K(25 °C) = 8.6 × 103 M-2]. Analyses of the changes in 13C and 1H NMR chemical shifts with complex formation gave approximate orientations for the intercalation of NQO with self-complementary dimer minihelixes. In the (dpCpG)2:NQO and (dpGpC)2:NQO complexes, the NQ2 group of NQO probably lies in the major grove and the NO2, NO containing NQO ring is stacked near the purine imidazole ring. In the (dpTpA)2:NQO and (dpApT)2NQO complexes, the NO2 seems to project into the minor grove and the NQO benzenoid ring is over the purine imidazole ring. © 1979, American Chemical Society. All rights reserved.