A Comparative Study of Molecular Interactions of Three Tetracycline Derivatives with Aqueous β-Cyclodextrin Solution at Different Temperatures

Abstract

A comparative study of complexation behaviour of three tetracycline derivatives viz. doxycycline hydrochloride, oxytetracycline hydrochloride and minocycline hydrochloride with β-cyclodextrin (β-CD) has been done with the help of various thermodynamic and spectroscopic methods. Density (ρ) and conductivity measurements have been carried out for binary drug/water and ternary drug/water/(β-CD) systems at three different temperature viz. 305.15, 310.15 and 315.15 K. The interactions of these tetracycline derivatives with β-cyclodextrin in aqueous solutions are further studied by means of fluorescence spectroscopy and UV-visible spectroscopy. From the measured density (ρ) data, partial molar volume (Φ°ν), partial molar volume expansibility (ϕ°e), Hepler′s constant (∂2ϕ°ν / ∂T2)P and partial molar volume of transfer (Δϕ°ν) have been obtained. From the conductance studies, the energetically favourable interactions are interpreted in the form of free energy change (ΔG) and the apparent association constant (Ka) was estimated from the fluorescence data.