Spectroscopic and Conductometric Investigation of the Interaction of Azithromycin with Iron (II) Ion

The interaction of the antibiotic azithromycin with ferrous sulfate and ferrous perchlorate in methanol has been investigated by spectroscopic and conductometric methods under equilibrium conditions. The interaction of azithromycin with both salts has been found to form one complex with metal to ligand composition of 1:1. The value of log Kf calculated from the absorption spectra for FeSO4-azithromycin complex at 25˚C was 5.16 ± 0.07 (Kf = 1.4 x 105 M-1). The value of log Kf for Fe(ClO4)2-azithromycin complex calculated from the conductivity measurements at 25˚C was 5.20 ± 0.08 (Kf = 1.6 x 105 M-1). The enthalpy and entropy of complexation were determined from the temperature dependence of the complexation constants. The ΔHº and ΔSº were 103.8 kJ/mol and 486.9 J/mol.K, respectively. The calculated molar conductivity of the Fe(ClO4)2-azithromycin complex at 25˚C was 99.7 S cm2 mol-1. This high molar conductivity has been considered indicative of the formation of a charged complex formed from the coordination of the neutral azithromycin ligand to the iron (II) ion without being accompanied by loss of protons.