Interaction of hemoglobin and sulfamethazine: A spectrofluorimetric characterization of the binding thermodynamics

Studies on the interaction of drugs with bio-macromolecules have been of great interest to understand the molecular aspects of such binding correlating with the structural phenomenon. The binding interaction of a well-known antibiotic drug, Sulfamethazine (SMZ) towards hemoglobin (Hb) have been studied extensively using fluorescence spectroscopic technique. The temperature dependent experiments suggested static quenching and ground state complex formation with the number of binding sites around 1 signifying 1:1 binding ratio with the protein. The thermodynamic parameters obtained from the temperature dependent analyses conveyed entropy driven spontaneous, exothermic reaction. The negative enthalpy and a strong positive entropy contribution suggested dominance of electrostatic force(s) between the protein and the drug. The salt dependent analyses denoted destabilization of the complex with increase in the ionic strength, thus signifying decrease in the electrostatic interaction between Hb and SMZ which is in accordance with the thermodynamic calculations. The partition of free energy change concluded non-polyelectrolytic components to be the dominant factor in the bending between the protein and the drug.