Spectroscopic study on the interaction of curcumin with single chain and gemini surfactants

Abstract

Curcumin is a natural antioxidant and a polyphenol. The interaction of curcumin with different types of surfactants, (e.g., cationic gemini, anionic, nonionic and bile salt) in an aqueous medium has been studied spectrophotometrically and fluorimetrically in premicellar and post micellar concentration regions. Up to 0.095 mM concentration of cationic gemini surfactant (14-3-14), the absorbance value decreases and after that, increases. In the case of anionic SDMA and anionic sodium cholate (NaC), the absorbance value decreases up to 5.6 mM and 7.0 mM concentration respectively and then increases; after 11.0 mM concentration of SDMA and 17.0 mM concentration of NaC, the absorbance value becomes almost constant. For nonionic Mega 10, absorbance decreases initially and the peak is blue shifted to 371 nm. Then, with further addition of Mega 10, the absorbance value increases and the peak returns to its original position. After 7.4 mM concentration of Mega 10, the absorbance value becomes nearly constant. A fluorescence peak for Curcumin is observed at 537 nm. With increasing concentration of 14-4-14, initially, fluorescence intensity decreases up to 0.077 mM and then, fluorescence intensity increases and the spectra become gradually blue shifted to 501 nm. But for other surfactants used, fluorescence intensity increases with increasing concentration of surfactant and the spectra become gradually blue shifted and after the cmc, the intensity becomes constant. For 14-5-14, initially, anisotropy value increases and then decreases and after the cmc, this value again increases. In the case of SDMA, this value decreases with increasing concentration of SDMA up to 5.6 mM and then increases, after 13.5 mM, this becomes almost constant. For 212, no significant change of this value is observed. In the case of NaC, anisotropy value increases with increasing concentration of NaC and after 16.0 mM, it is almost constant. In the case of Mega 10, it decreases with increasing concentration of surfactant and above the cmc, becomes almost zero. In the premicellar region, curcumin forms complex with surfactant molecules and in the post micellar region, it is incorporated into the hydrophobic core of the micelle. The change in the intensity and wavelength of typical peaks in the absorption and the fluorescence spectra of curcumin shows a considerably different interaction behavior of surfactant molecules with curcumin.