Thermodynamic studies of iron chelation with doxycycline in acidic medium

Abstract

Doxycycline (DOX) is a broad-spectrum tetracycline antibiotic synthetically derived from oxytetracycline. The complex formation of this drug with iron(III) was studied using spectrophotometry. The thermodynamic parameters of the systems were calculated using the changes in the absorption spectra which occur due to hydrogen bond or complex formation. Thermodynamic parameters of the formation of iron(III) complex with doxycycline (ΔH, ΔG, ΔS, and stability constants) were determined spectrophotometrically at a wavelength corresponding to absorption maximum (374.5 nm) at three different temperatures (22, 35, and 45°C). The obtained data show that the complex has metal to ligand molar ratio of 1: 2 at pH 2–3. The stability constants were calculated to be 13.99 × 10⁶, 7.06 × 10⁵, and 1.29 × 10⁶ by mole ratio method at 22, 35, and 45°C, respectively.