The aim of this study is to evaluate the binding behavior between pelargonidin-3-O-glucoside (P3G) and bovine serum albumin (BSA) using multi-spectroscopic, transmission electron microscopy (TEM) and molecular docking methods under physiological conditions. Fluorescence spectroscopy and time-resolved fluorescence showed that the fluorescence of BSA could be quenched remarkably by P3G via a static quenching mechanism, and there is a single class of binding site on BSA. In addition, the thermodynamic functions ΔH and ΔS were –21.69 kJ/mol and 24.46 J/mol/K, indicating that an electrostatic interaction was a main acting force. The distance between BSA and P3G was 2.74 nm according to Förster's theory, illustrating that energy transfer occurred. In addition, the secondary structure of BSA changed with a decrease in the α-helix content from 66.2% to 64.0% as seen using synchronous fluorescence, UV/vis, circular dichroism and Fourier transform infrared spectroscopies, whereas TEM images showed that P3G led to BSA aggregation and fibrillation. Furthermore, site marker competitive experiments and molecular docking indicated that P3G could bind with subdomain IIA of BSA. The calculated results of the equilibrium fraction showed that the concentration of free P3G in plasma was high enough to be stored and transported from the circulatory system to its target sites to provide therapeutic effects. Copyright © 2015 John Wiley & Sons, Ltd.

Anthocyanin is one of the flavonoid phytopigments with specific health benefits. The interaction between delphinidin-3-O-glucoside (D3G) and bovine serum albumin (BSA) was investigated by fluorescence spectroscopy, synchronous fluorescence spectroscopy, three-dimensional fluorescence spectroscopy, ultraviolet-visible absorption spectroscopy, circular dichroism spectroscopy and molecular modeling. D3G effectively quenched the intrinsic fluorescence of BSA via static quenching. The number of binding sites and binding constant K_a were determined, and the hydrogen bonds and van der Waals forces played major roles in stabilizing the D3G–BSA complex. The distance r between donor and acceptor was obtained as 2.81 nm according to Förster's theory. In addition, the effects of pH and metal ions on the binding constants were discussed. The results studied by synchronous fluorescence, three-dimensional fluorescence and circular dichroism experiments indicated that the secondary structures of the protein has been changed by the addition of D3G and the α-helix content of BSA decreased (from 56.1% to 52.4%). Furthermore, the study of site marker competitive experiments and molecular modeling indicated that D3G could bind to site I of BSA, which was in the large hydrophobic cavity of subdomain IIA. Copyright © 2014 John Wiley & Sons, Ltd.

Anthocyanin is one of the flavonoid phytopigments that shows strong antioxidant activity. The cyanidin-3-O-glucoside (C3G) is one of the principal types of anthocyanins. To understand the interaction between C3G and bovine serum albumin (BSA), fluorescence spectroscopy, ultraviolet–visible absorption, Fourier transform infrared spectroscopy, circular dichroism and molecular modeling techniques were used. Binding constant (K_a) and the number of binding sites (n) were calculated. The quenching mechanism of fluorescence of BSA by C3G was discussed. The results studied by Fourier transform infrared spectroscopy and circular dichroism experiments indicate that the secondary structures of the protein have been changed by the interaction of C3G with BSA. The result of molecular modeling confirmed that the C3G bound to the site I (sub-domain IIA) of BSA, and that the hydroxyl groups in the B ring of C3G took part in the binding with BSA. Copyright © 2013 John Wiley & Sons, Ltd.

A fluorescence quenching technique is often used to study interactions between small molecules and serum albumin. However, the results are quite different by using spectroscopic techniques on the same drug-protein interaction research and they may be affected by different conditions (e.g. working solution of pH and ionic strength). In this research, using apigenin as an example, the effect of experimental conditions of fluorescence quenching on the binding parameters of drug to bovine serum albumin was investigated using a response surface method (RSM). The effect of pH, the concentration of NaCl and the concentration Mg²⁺ on the quenching constant (K_SV), the apparent association constant (K_a) and the number of binding sites (n) was studied by single-factor experiments with pH, [NaCl] and [Mg²⁺] as independent variables and K_SV, K_a and n as response values. Prediction models were fit to a quadratic polynomial regression equation and the results showed that both K_SV and n displayed a second-order model, whereas Ka displayed linear relation dependence on pH, [NaCl] and [Mg²⁺]. Under these experimental conditions, [NaCl] was the most significant (p < 0.05) impact factor on K_SV and K_a, whereas n was most affected by pH (p < 0.05). Copyright © 2013 John Wiley & Sons, Ltd.