Study of inclusion complex of β-cyclodextrin and levofloxacin and its effect on the solution equilibria between gadolinium(III) ion and levofloxacin

The formation of host-guest inclusion complex of levofloxacin with beta-cyclodextrin (beta-CD) was studied by fluorescence spectroscopy in buffer solution (pH 7.4) at 298 K. The experimental results confirmed the existence of 1:1 inclusion complex of levofloxacin with beta-CD. The association constant of the beta-CD inclusion complex was obtained from the Benesi-Hildebrand equation. The formation of the inclusion complex was confirmed by the IR and H-1 NMR technique. The complex formation equilibria between Gd(III) ion and levofloxacin were investigated in aqueous solutions without and in the presence of beta-cyclodextrin. The stoichiometry and stability constants of the formed complexes are reported, and the concentration distribution of the various complex species has been evaluated as a function of pH. The effect of beta-cyclodextrin on dissociation constants, K (a), of levofloxacin and stability constants of gadolinium(III)- levofloxacin complexes, beta (p,q,r), were examined. Furthermore, effect of levofloxacin on the speciation and distribution Gd(III) in human blood plasma was evaluated by computer simulation.