Binding studies of caffeine and theophylline to bovine serum albumin: Calorimetric and spectroscopic approach

• Published in: Journal of molecular liquids 2016-11, Vol.223, p.1048-1055
• Main Authors: Banipal, Tarlok S., Kaur, Navalpreet, Banipal, Parampaul K.
• Format: Article
• Language: English
• Subjects: Bovine serum albumin; Fluorescence spectroscopy; Isothermal titration calorimeter; Nuclear magnetic resonance spectroscopy; UV-visible spectroscopy; Xanthine drugs
• ISSN: 0167-7322; 1873-3166
• DOI: 10.1016/j.molliq.2016.09.034

Binding studies of pharmacologically active drugs-caffeine and theophylline to bovine serum albumin (BSA) in phosphate buffer solution, pH=7.4 have been investigated using spectroscopic (UV–visible, fluorescence and nuclear magnetic resonance) and calorimetric (isothermal titration calorimetry) techniques. The derived parameters obtained from all the techniques suggest that the magnitude of binding affinity of BSA-drug follows the order: theophylline>caffeine, which may be attributed to greater acidity of former at physiological pH. UV–visible and fluorescence spectroscopy suggests 1:1 stoichiometry of drug-protein interactions, while calorimetric results support two binding sites. Apart from the tryptophan binding site, a low affinity site also exists which is assessed from the calorimetric measurements. The negative enthalpy and positive entropy, both favors the binding process, and the feasibility of binding is also supported by negative value of Gibbs free energy. The positive heat capacity, consistent with the positive entropy, may be attributed to the exposure of hydrophobic protein surfaces. The observed positive changes in chemical shifts, ∆δ may be due to the deshielding of drug protons owing to hydrophilic-ionic/hydrogen bonding interactions with BSA. [Display omitted] •Binding constant of BSA with TPY is greater than that with CAF.•Positive heat capacity of drug-protein binding.•Blue shifted absorption spectra due to drug-protein interactions.•Drug protons become deshielded in presence of BSA.•Fluorescence of BSA quenched in presence of drugs.