Spectrometric study on the hydrophobic hydration in the formation of Tween-60 micelles with curcumin

The hydrophobic hydration in the formation of Tween-60 micelles upon entrapping bioactive curcumin has been observed and studied. The atypically increased values of pyrene polarity index suggest that Tween-60/curcumin complexes with bigger bulk hydrophobic part have stronger hydrophobic hydration than curcumin alone. The low-field shifts of water proton by 1H NMR method can also confirm the formation of stronger hydrogen bond network of water molecules surrounding Tween-60/curcumin complexes. However, the hydrophobic aggregation of surfactant alkyl chains into Tween-60 premicelles and micelles may destroy the hydrophobic hydration of Tween-60/curcumin complexes, which is indicated by the decreasing change of pyrene polarity index with increasing Tween-60 concentration. The fluorescence anisotropy of curcumin is observed to have sharply decreased values for Tween-60/curcumin complexes, which correlates positively with the hydrogen bonding strength of water molecules around curcumin. The fluorescence anisotropy, fluorescence spectroscopy and stability of curcumin cooperatively suggest that there is gradually weakened contact of curcumin with water in the order of curcumin alone, Tween-60/curcumin complexes, curcumin with Tween-60 premicelles and micelles. This work demonstrates that the hydrophobic hydration plays an important role in the entrapment of curcumin from a polar medium of water to surfactant micelles.