Norf loxacin La(III)-based complex: synthesis, characterization, and DNA-binding studies

A La(III) complex, [(LaCl2)-Cl-III(NOR)(2)] Cl (2), containing norfloxacin (NOR) (1), a synthetic fluoroquinolone antibacterial agent, has been synthesized and characterized by elemental analysis, IR, UV-vis spectra and H-1 NMR spectroscopy, and molar conductance measurements. The interaction between 2 and CT-DNA was investigated by steady-state absorption and fluorescence techniques in different pH media, and showed that 2 could bind to CT-DNA presumably via non-intercalative mode and the La(III) complex showed moderate ability to bind CT-DNA compared to other La(III) complexes. The binding site number n, and apparent binding constant K-A, corresponding thermodynamic parameters Delta G(#), Delta H-#, Delta S-# at different temperatures were calculated. The binding constant (K-A) values are 0.23 +/- 0.05, 0.56 +/- 0.05, and 0.18 +/- 0.08 x 10(5) L mol(-1) for pH 4, 7, and 11, respectively. It was also found that the fluorescence quenching mechanism of CT-DNA by La(III) complex was a static quenching process.