Determination of critical micellar concentrations of two monoketo derivatives of cholic acid

• Published in: Colloids and surfaces, B, Biointerfaces B, Biointerfaces, 2009-11, Vol.74 (1), p.84-90
• Main Authors: Posa, M, Guzsvany, V, Csanadi, J
• Format: Article
• Language: English
• Subjects: Absorption - drug effects; Bile Acids and Salts - chemistry; Chenodeoxycholic Acid - analogs & derivatives; Cholic Acid - chemistry; Cholic acid monoketo derivatives; Cholic Acids - chemistry; Conductometry; Critical micellar concentration; Electric Conductivity; Hydrogen Bonding - drug effects; Hydrogen-Ion Concentration - drug effects; Magnetic Resonance Spectroscopy; Micelles; Nitrazepam - chemistry; Primary and secondary micelles; Rhodamines - metabolism; Sodium Chloride - pharmacology; Spectrophotometry; Urea - pharmacology
• ISSN: 0927-7765; 1873-4367
• DOI: 10.1016/j.colsurfb.2009.06.029

Critical micellear concentrations (CMC) were determined for two novel promoters of membrane permeability—7-monoketocholic acid (7-MKC) and 12-monoketocholic acid (12-MKC), using two non-invasive ( 1H NMR relaxation experiment and conductometry) and two invasive (spectral shift and partition coefficient of the probe molecule) methods. Studies by the former methods suggest the different aggregation abilities of the investigated bile acid derivatives. In an aqueous solution, 7-MKC has a somewhat lower CMC value (43 mM) than 12-MKC (50 mM). Further, it was found that, in addition to primary micelles, 7-MKC forms also secondary micelles. In the experiments with probe (hydrophobic) molecules, the aggregation properties of investigated bile acids did not differ in water, whereas the presence of urea altered the aggregation of 7-MKC. Based on the CMC value, 7-MKC is more hydrophobic than 12-MKC. The apparent hydrophobicity of 7-MKC is a consequence of the formation of secondary micelles, shifting the monomer equilibrium to the direction of primary micelles, which is manifested as a decrease in the CMC value.