Fluorescence quenching of norfloxacin by divalent transition metal cations

Abstract

Fluorescence quenching of norfloxacin (NOR) by Cu2+, Ni 2+, Co2+ and Mn2+ was studied in water. The change in the fluorescence intensity and lifetime was measured as a function of quencher concentration at various temperatures. According to the Stern-Volmer plots, the NOR was quenched both by collisions and complex formation with the same quencher. However, the static quenching had a more important effect on the emission. Large static and dynamic quenching constants support significant ion-dipole and orbital-orbital interactions between NOR and cations. The both quenching constants by Cu2+ were the largest among quenchers. Also, quenching mechanism of Cu2+ was somewhat different. The change in the absorption spectra due to the quencher provided information on static quenching. The fluorescence of NOR was relatively insensitive to both the dynamic and static quenching compared with other quinolone antibiotics. This property can be explained by the twisted intramolecular charge transfer.