The effect of ternary complex formation on the partitioning of pyrene and anthracene in aqueous solutions containing sodium dodecyl sulfate and M-gamma-cyclodextrin

The partitioning behavior of pyrene and anthracene between n-decane and aqueous solutions containing a partially methylated gamma-cyclodextrin (M-gamma-CD) and sodium dodecyl sulfate (SDS) was studied by extraction experiments. At concentrations below the aqueous solubility of pyrene and anthracene both were found to form 1:1 complexes With M-gamma-CD, Formation constants were determined as 1843 M-1 for pyrene and 624 M-1 for anthracene, In micellar solutions of SDS pyrene was found to be better solubilized than anthracene, At constant concentrations of M-gamma-CD the dependence of the partition coefficients on increasing concentrations of SDS could be divided into three linear regions, At concentrations below a critical surfactant concentration (CSCSDS) the partition coefficients of both polyaromatic hydrocarbons as well as the fluorescence intensity of pyrene increased linearly with the addition of SDS. In the fluorescence spectra of anthracene the addition of SDS led to a shift of the maxima to higher wavelengths, These data suggest the formation of ternary complexes of M-gamma-CD with each of the polyaromatic hydrocarbons and SDS. The ternary complex with anthracene was found to be more stable than that of pyrene, which resulted in higher partition coefficients than seen with pyrene. Increasing the surfactant concentrations above the CSCSDS the partition coefficients remained constant until micelles were formed and another linear increase of the partition coefficients could be observed. CSCSDS and the critical micellization concentration (CMC) were found to increase linearly with cyclodextrin concentration, For CSCSDS a molar ratio of 3/1 was found for M-gamma-CD/SDS. Mixed micelles between SDS and gamma-CD are supposed to be formed above CSCSDS. (C) 1997 Academic Press.