Unraveling the effect of surfactant chain length on the binding interaction of curcumin with cationic and non-ionic micelles

Major drawbacks of using curcumin as a potential multifunctional drug are its very low water solubility and lack of bio-availability. For this purpose we have used surfactants to increase the solubility of curcumin in aqueous medium and to assess its hydrophilic and hydrophobic interactions with micelles. In order to understand the molecular mechanism of the interaction of curcumin with surfactants, we have employed cationic and non-ionic surfactants. We have used hexadecyl(cetyl)trimethylammonium bromide (CTAB), tetradecyltrimethylammonium (TTAB) and dodecyltrimethylammonium bromide (DTAB) as cationic surfactants of varying hydrocarbon tail dimension and octylphenol ethoxylate with 10 moles of ethyelene oxide (OPE-10), octylphenol ethoxylate with 16 moles of ethyelene oxide (OPE-16), octylphenol ethoxylate with 30 moles of ethyelene oxide (OPE-30) as non-ionic surfactants of varying poly(ethylene oxide) hydrophilic head dimension. From the increase in fluorescence intensity of curcumin in the presence of surfactants, we had estimated the apparent binding constant (K-b) of curcumin-micelle complex formation. The evaluated K-b values between curcumin and CTAB, TTAB, and DTAB were 7.75 x 10(5), 3.44 x 10(5), and 0.78 x 10(5) L mol(-1), respectively. In the case of non-ionic surfactants, the estimated K-b values of curcumin with OPE-10, OPE-16, and OPE-30 were 4.90 x 10(6), 3.82 x 10(6), and 0.58 x 10(6) L mol(-1), respectively. Thus, it was found that K-b values were somehow greater in the case of non-ionic surfactants than cationic surfactants. From the fluorescence quenching study it was revealed that the probable location of curcumin was the Stern layer and the palisade layer in the case of cationic and non-ionic micelles, respectively. Our results might be useful to overcome challenges associated with the delivery of curcumin as a multifunctional drug molecule.