CHOLIC-ACID BEHAVIOR IN WATER AND ORGANIC-SOLVENT - STUDY OF NORMAL AND INVERTED AGGREGATES

Water-soluble fluorescent probes, including l-pyrene butyric acid, rho damine B, sodium salt 1,5-diaminoanthraquinone-2,6-disulfonic acid, qu inine hemisulfate and monosodium salt 8-amino-1-naphthol-3,6-disulfoni c acid were used to determine the critical micelle concentration (cmc) of inverted micelles formed by cholic acid in tetrahydrofuran. Anothe r water-insoluble fluorescent probe, namely pyrene, was used to determ ine the cmc of normal micelles formed by sodium cholate in water. Rela tive scattered light intensity measurements give direct evidence of tr ansition concentrations similar to cmc in surfactants. Our results ind icate that in the inverted micelles, hydrophilic sites placed in the c ore are present in cholic acid aggregates above the cmc region at 5-7 mM. In normal micelles, hydrophobic sites in the core are present in s odium cholate aggregates above the cmc region at 15 mM. Another critic al point in the aggregation of cholic acid and sodium cholate occurs a t 1 mM. Normal phase liquid chromatography determination of the cmc re versed micelles has also been performed, and the results obtained agre e well with the spectroscopic studies. (C) 1998 Elsevier Science B.V. All rights reserved.