Probing the Binding of the Flavonoid Diosmetin to Human Serum Albumin by Multispectroscopic Techniques

The binding mechanism of molecular interaction between diosmetin and human serum albumin (HSA) in a pH 7.4 phosphate buffer was studied using atomic force microscopy (AFM) and various spectroscopic techniques including fluorescence, resonance light scattering (RLS), UV–vis absorption, circular dichroism (CD), and Fourier transform infrared (FT–IR) spectroscopy. Fluorescence data revealed that the fluorescence quenching of HSA by diosmetin was a static quenching procedure. The binding constants and number of binding sites were evaluated at different temperatures. The RLS spectra and AFM images showed that the dimension of the individual HSA molecules were larger after interaction with diosmetin. The thermodynamic parameters, ΔH° and ΔS° were calculated to be −24.56 kJ mol–1 and 14.67 J mol–1 K–1, respectively, suggesting that the binding of diosmtin to HSA was driven mainly by hydrophobic interactions and hydrogen bonds. The displacement studies and denaturation experiments in the presence of urea indicated site I as the main binding site for diosmetin on HSA. The binding distance between diosmetin and HSA was determined to be 3.54 nm based on the Förster theory. Analysis of CD and FT–IR spectra demonstrated that HSA conformation was slightly altered in the presence of diosmetin.