Effect of pH and temperature on physicochemical properties, aggregation behaviour and degradation kinetics of quercetin and baicalein in nearly aqueous media

Recently, flavonoids like quercetin and baicalein have drawn the attention of many researchers worldwide owing to their potential therapeutic applications. But they are still not used for biomedical purposes due to their low solubility and bioavailability. Moreover, there are very few reports available on various factors that can modulate the physicochemical properties of these flavonoids in an aqueous medium. This work explores the physicochemical behaviour of quercetin and baicalein in an aqueous medium under different solution conditions (like pH and temperature). UV–vis and fluorescence studies revealed that quercetin and baicalein show quite different optical properties from each other under same aqueous conditions. Quercetin undergoes autooxidation at alkaline pH and the rate of this autooxidation was enhanced at higher temperature whereas no autooxidation of baicalein was observed at any pH or temperature. Different anionic forms of quercetin and baicalein formed at different pH were characterized with the aid of density functional theory (DFT) and multivariate curve resolution (MCR) approach. Dynamic light scattering (DLS) studies suggest that temperature affects the particle size of both the flavonoids significantly and this aggregation phenomenon was observed to be reversible.