Stability of Curcumin on Amphiphilic Chitosan

The stability of curcumin (Cur) in different media, such as buffer, modified chitosan, and solvents, was evaluated by using UV-vis and fluorescence. An amphiphilic derivative of chitosan (modified chitosan) was synthesized by substituting diethylamino and dodecyl groups. The critical aggregation concentration of modified chitosan (ChM) was determined by using pyrene as a hydrophobic probe. The ChM aggregates at concentrations above 1.1 × 10^-2 g·L^-1, and hydrophobic environments are formed. For Cur in the presence of ChM (Cur/ChM), it can be seen that the keto form has spectral characteristics, indicating that ChM is stabilizing the Cur molecules in the keto form. These results agree with Cur absorbance spectra obtained in different solvents, in which the tautomeric equilibrium of Cur is shifted to the keto form in nonpolar solvents. The fluorescence intensity of Cur in ChM (at concentrations above the CAC) increased significantly, unlike that of Cur in the buffer. The quantum yield value obtained for Cur was 0.05 g·L^-1 of ChM was higher than that of Cur in the other media. At concentrations of ChM above 0.011 g·L^-1, it aggregates and can incorporate the Cur molecule into the hydrophobic portion, promoting stabilization. This behavior can be confirmed by fluorescence micrographs, which reveal the fluorescent domains of curcumin in the hydrophobic environments of ChM. The percentages of Cur degradation were 96% in the buffer and 71% in 0.05 g·L^-1 Ch, 93% in 0.005 g·L^-1 ChM, 60% in 0.01 g·L^-1 ChM, and 30% in 0.05 g·L^-1 ChM. It is possible to notice that the Cur degradation percentage is 0.05 g·L^-1 ChM (above CAC concentration) was lower compared with the degradation of Cur in the other media. Therefore, these results indicate that the ChM above the CAC, in its aggregated form, can protect the dye molecule from the effects of water.