Spectroscopic study of benzothiophene partitioning in sodium dodecyl sulfate and cetyl trimethyl ammonium bromide micellar media

This manuscript reports the partitioning of benzothiophene (BNP), a bioactive organic compound, between the aqueous phase and micellar media of an anionic surfactant, sodium dodecyl sulphate (SDS) and a cationic surfactant, cetyl trimethyl ammonium bromide (CTAB). Simple and differential UV/visible spectroscopic studies of said systems have been conducted in premicellar and post-micellar concentration ranges. The experimental results reveal that in the premicellar region, the molecules of BNP get attached with monomeric surfactant molecules, while in the post-micellar region; they are accommodated within the micelle. The bathochromic shift is observed in the UV/visible spectra of BNP in the presence of both surfactants. The water/micelle partition coefficient (K (x)) and binding constant (K (b)) were calculated using differential absorption data and subsequently the values of free energy of partition (a dagger G (p)) and free energy of binding (a dagger G (b)) were calculated. The values of K (x) show that the solubilization of BNP is more spontaneous and takes place to a greater extent in micellar media of SDS than in CTAB.