Cetyltrimethylammonium bromide promoted dispersing and incorporation of curcumin into silica particles in alkaline ethanol/water mixture

Silica is one of the most ideal matrixes for curcumin (Cur) since it may improve the dispersing ability and stability of Cur in aqueous media much effectively. In this work, the effect of cetyltrimethylammonium bromide (CTAB) and ammonia on dispersing and stability of curcumin (Cur) in ethanol/water mixture (3:7 in volume) was systemically investigated for the design and preparation of Cur doped silica particles. In the mixture with low ammonia concentration, i.e., 0.2 mM (pH=9.5), in which Cur mainly existed in the protonated form (Cur/ Cur-), the formation of CTAB micelles was effective to promote the dispersing of Cur/Cur- species. In the mixture with high ammonia concentration, i.e., 300 mM (pH=11.5), in which the deprotonated Cur, Cur2-/Cur3- were the dominant species, the addition of CTAB is effective to promote further conversion of Cur/Cur- species into Cur2-/ Cur3- ones and suppress the reverse process to some extent. Due to the protection of CTAB micelles, both stability and emission efficiency of the Cur2-/Cur3- species were significantly improved in the alkaline media. Direct addition of tetraethyl orthosilicate (TEOS) into the mixture with optimized concentrations of ammonia and CTAB allowed the in-situ preparation of Cur doped silica (Cur-SiO2) particles. The Cur-SiO2 particles presented greatly improved dispersing ability and responsive ability towards Cu2+ in aqueous media, attributed to the protection effect of silica matrix.

Automated summary

The influence of CTAB micelles and ammonia on the dispersing and stability of curcumin in ethanol/water mixture was investigated in this study. It was found that CTAB could promote dispersing of Cur at low ammonia concentration and facilitate the conversion of Cur species at high ammonia concentration. The in-situ preparation of Cur doped silica particles was achieved using optimized concentrations of ammonia and CTAB, leading to improved responsiveness towards Cu2+.