Interaction between oxidised state of quercetin and bovine serum albumin in presence of surfactant aggregates with different charges

Abstract

The present investigation focuses on the role of surfactant and its charge on the interaction of flavonoid Quercetin (QCT) and Bovine serum albumin (BSA). QCT is known to undergo autoxidation in many chemical environments which has different characteristics compared to its non-oxidised structure. In this experiment, two ionic surfactants used. They are anionic surfactant, Sodium dodecyl sulfate (SDS) and Cationic surfactants Cetyl pyridinium bromide (CPB). The characterizations employed are conductivity, FT-IR, UV–visible spectroscopy, Dynamic light scattering (DLS) and Zeta potential measurements. The critical micellar concentration (CMC) as well as the counter-ion binding constant (β) have been calculated by making use of specific conductance values, in aqueous medium at 300 K. Various thermodynamic parameters, ΔG0 m, standard free energy of micellization, ΔH0 m, standard enthalpy of micellization and ΔS0 m, standard entropy of micellization are calculated. The negative value of ΔG0 m in all systems is indicative of spontaneous binding occurring in both QCT + BSA + SDS (−23.35 kJ mol−1) and QCT + BSA + CPB (−27.18 kJ mol−1). The higher negative value infers the latter is a more stable system with greater spontaneity. The UV-visible spectroscopy study points at stronger binding of QCT and BSA in presence of surfactants and also there is stronger binding of CPB in ternary mixture with higher binding constant compared to SDS ternary mixture. Which is evident from the binding constant calculated from Benesi-Hildebrand plot (QCT + BSA + SDS, 244.46 M−1; QCT + BSA + CPB, 336.53 M−1). Further, the structural alterations occurring in the above systems has been observed by FT-IR spectroscopy. The DLS and Zeta potential measurements also support the above finding. Communicated by Ramaswamy H. Sarma