Spectroscopic Investigation of the Effect of Salt on Binding of Tartrazine with Two Homologous Serum Albumins: Quantification by Use of the Debye–Hückel Limiting Law and Observation of Enthalpy–Entropy Compensation

Abstract

Formation of ion pair between charged molecule and protein can lead to interesting biochemical phenomena. We report the evolution of thermodynamics of the binding of tartrazine, a negatively charged azo colorant, and serum albumins with salt. The dye binds predominantly electrostatically in low buffer strengths; however, on increasing salt concentration, affinity decreases considerably. The calculated thermodynamic parameters in high salt indicate manifestation of nonelectrostatic interactions, namely, van der Waals force and hydrogen bonding. Site-marker competitive binding studies and docking simulations indicate that the dye binds with HSA in the warfarin site and with BSA at the interface of warfarin and ibuprofen binding sites. The docked poses indicate nearby amino acid positive side chains, which are possibly responsible for electrostatic interaction. Using the Debye-Hückel interionic attraction theory for binding equilibria, it is shown that, for electrostatic binding the calculated free energy change increases linearly with square root of ionic strength. Also UV-vis, fluorescence, CD data indicate a decrease of interaction with salt concentration. This study quantitatively relates how ionic strength modulates the strength of the protein-ligand electrostatic interaction. The binding enthalpy and entropy have been found to compensate one another. The enthalpy-entropy compensation (EEC), general property of weak intermolecular interactions, has been discussed.

Isothermal titration calorimetry investigation of the interactions between vitamin B6-derived hydrazones and bovine and human serum albumin

“…In principle, a linear correlation between ∆S and ∆H in the binding process for a series of homologous compounds is considered as strong evidence of H-S compensation. The linear correlation occurring for the binding of PLPderived hydrazones with both BSA and HSA clearly indicates enthalpy-entropy compensation, that is, a change in enthalpy is compensated by a corresponding change in the entropic term, as reported for similar systems [55,56].…”

Binding of ascorbic acid and α-tocopherol to bovine serum albumin: a comparative study

“…The results suggest that both warfarin and ibuprofen compete with the two antioxidants binding in the case of BSA and the possible location is at the interface of the warfarin and ibuprofen binding sites. 49 That is, the binding of the two antioxidants to BSA are both nonspecific binding. 48,49 The results are consistent with those derived from ITC.…”

“…49 That is, the binding of the two antioxidants to BSA are both nonspecific binding. 48,49 The results are consistent with those derived from ITC.…”

Interaction of Carrier Protein with Potential Metallic Drug Candidate N-Glycoside ‘GATPT’: Validation by Multi-Spectroscopic and Molecular Docking Approaches

“…The interaction studies of small molecules with proteins are of great importance in determining the ADME properties of a drug molecule with direct implications on its pharmacokinetics and pharmacodynamics [1][2][3][4][5][6][7]. The interaction of the drug with proteins can strongly affect the rate of drug distribution as well as elimination.…”