Binding mechanism of bioactive cetirizine hydrochloride to sudlow's site i of serum albumins

The mechanism of interaction of an anti-allergic drug, cetirizine dihydrochloride, with the proteins bovine and human serum albumins has been investigated by spectrofluorimetry, FTIR, UV-vis absorption and circular dichroism methods at physiological conditions. The drug was found to quench the fluorescence intensity of the protein through a dynamic quenching mechanism. Various binding parameters were evaluated based on fluorescence quenching studies carried out at 293 K, 301 K and 308 K. The nature of the binding force operating between the drug and protein was proposed, based on the measured thermodynamic parameters. A change in the secondary structure of the protein was evident from the circular dichroism measurements, wherein the α-helicity decreased from 65.69% to 51.23% and from 42.7% to 38.55% for the CTZ-BSA and CTZ-HSA systems, respectively. Based on Förster's theory of non-radiative energy transfer, the distance between the protein and drug was determined. The common blood plasma ions K⁺, Cu²⁺, Ni²⁺, Mn²⁺ and Co²⁺ were found to influence the binding of the drug to the protein. Displacement experiments were carried out to determine the binding site for drug on the protein. These studies, coupled with other spectroscopic results, revealed that the drug was bound to the hydrophobic pocket located in sub domain IIA of site I.