Complexation of the quinolone antibiotic norfloxacin with DNA

¹H-NMR spectroscopy (500 MHz) was used to study the complexation of the antibacterial agent norfloxacin (NOR) with DNA tetramers 5′-d(TpGpCpA) and 5′-d(CpGpCpG) in aqueous solution. For the first time, the equilibrium parameters (equilibrium constants, enthalpy, and entropy) were obtained for NOR binding with single-stranded and duplex DNA tetramers. By analyzing the complexation parameters and the induced proton chemical shifts in NOR in various complexes, the character of NOR binding was identified as intercalation in the case of the duplex tetramers and as intercalation with external binding in the case of single-stranded tetramers. NOR proved to preferentially bind to GC sites in DNA duplexes.