Interaction of bisdemethoxycurcumin with cationic (cetyltrimethylammonium) + nonionic (Tween 20/Tween 60) mixed surfactants: Thermodynamic study and functional improvement

Bisdemethoxycurcumin (BDMC), one of the main curcuminoids, has numerous biological activities. However, the low solubility and stability of BDMC limit its application. In this work, in order to improve the solubility and stability of BDMC, we encapsulated BDMC using cetyltrimethylammonium bromide (CTAB) + Tween 20/Tween 60 mixed surfactants. The molar ratio of CTAB to Tween 20/Tween 60 was optimized by response surface analysis. The thermodynamic parameters (binding constant, enthalpy change, entropy change and Gibbs free energy change) for the interaction of BDMC with CTAB + Tween 20/Tween 60 mixed micelles were obtained by fluorescence spectroscopy and UV–visible absorption spectroscopy. Positive enthalpy change and entropy change indicated that hydrophobic interaction was the main driving force. Moreover, due to the longer alkyl chains of Tween 60, the encapsulation of BDMC by CTAB + Tween 60 mixed micelles was stronger. The encapsulation of BDMC in the hydrophobic alkyl chains by the mixed micelles was determined by fluorescence polarization technology, time-resolved fluorescence assay, and 1 H nuclear magnetic resonance spectroscopy. Solubilization and stability experiments showed that the solubility of BDMC was improved and the alkaline hydrolysis of BDMC was inhibited due to the encapsulation of the mixed micelles. The improvement of the solubility and stability of BDMC was more obvious in CTAB + Tween 60 mixed micelles because of the stronger interaction between them. The above results indicated that CTAB + Tween 20/Tween 60 mixed micelles could be used to encapsulate BDMC to improve its solubility and stability.