1H and 19F NMR relaxation studies of fleroxacin with Micrococcus luteus.

In order to investigate and characterize interaction processes between the fluoroquinolone fleroxacin and bacterial cells we used non-selective (all resonances are excited), selective (observed resonance is excited) spin-lattice relaxation rates and spin-spin relaxation measurements. The signals of three hydrogens at different moieties of the fleroxacin molecule were considered to get an insight in the complexation behavior. The enhancement of selective relaxation rates was observed with increasing fleroxacin concentrations and keeping the bacterial mass constant. The obtained relaxation rates of the affected hydrogens were analyzed via a Lineweaver-Burk-plot to determine the KD values. Furthermore, 19F NMR spectra were recorded and spin-spin relaxation rates (R2) were determined by a Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence. Because of the dependency of the line width of NMR peaks on transversal relaxation time T2, we compared the line width at half-height at different fleroxacin concentrations in order to investigate the involvement of fluorine atoms in different positions in the complexation. All findings point to core quinolone moiety to be involved in the interaction with bacterial cells.