Molecular basis of the Cotton effects induced by the binding of curcumin to human serum albumin

TLDR: It is established that the phenolic OH group of curcumin is the most acidic and that its dissociation is responsible for both the large red-shift of the main absorption band and the binding ofCurcumin to HSA in a right-handed chiral conformation.

Abstract: Curcumin binding to human serum albumin (HSA) has been found recently to induce bisignate CD curves due to intramolecular exciton coupling between the two feruloyl chromophoric parts The present study reports further results on this interaction UV–vis and chiroptical properties of HSA-bound curcumin were analyzed in detail by comparison with bilirubin–albumin complexes Data obtained by UV–vis and fluorescence spectroscopy, CD displacement experiments and molecular modelling methods suggested the primary binding site of curcumin to be located in site I of HSA Since acid–base dissociation of the polyphenol type curcumin molecule plays a fundamental role in albumin binding, light absorption spectra of curcumin and half-curcumin (dehydrozingerone) were studied in ethanol and in water at different pH values It is established that the phenolic OH group of curcumin is the most acidic and that its dissociation is responsible for both the large red-shift of the main absorption band and the binding of curcumin to HSA in a right-handed chiral conformation Additionally, it is demonstrated that pH dependent induced CD spectra can be utilized to determine the acid–base dissociation constant; from chiroptical data the first pKa value of curcumin was calculated (828)