title: Determination of critical micellar concentrations of two monoketo derivatives of cholic acid.
abstract: 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 ((1)H 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.
authors.affiliation: Laboratory of Physical Pharmacy, Department of Pharmacy, Faculty of Medicine, University of Novi Sad, Hajduk Veljkova 3, 21000 Novi Sad, Serbia. junposam@eunet.yu
authors.forename: Mihalj
authors.initials: M
authors.lastname: Posa
authors.forename: Valéria
authors.initials: V
authors.lastname: Guzsvány
authors.forename: János
authors.initials: J
authors.lastname: Csanádi
mesh_terms: D000042:Absorption / Q000187:drug effects; D001647:Bile Acids and Salts / Q000737:chemistry; D002635:Chenodeoxycholic Acid / Q000031:analogs & derivatives; D019826:Cholic Acid / Q000737:chemistry*; D002793:Cholic Acids / Q000737:chemistry*; D003217:Conductometry; D004553:Electric Conductivity; D006860:Hydrogen Bonding / Q000187:drug effects; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D009682:Magnetic Resonance Spectroscopy; D008823:Micelles; D009567:Nitrazepam / Q000737:chemistry; D012235:Rhodamines / Q000378:metabolism; D012965:Sodium Chloride / Q000494:pharmacology; D013053:Spectrophotometry; D014508:Urea / Q000494:pharmacology
chemical_list: C545300:3,12-dihydroxy-7-ketocholanoic acid; D001647:Bile Acids and Salts; D002793:Cholic Acids; D008823:Micelles; D012235:Rhodamines; C026188:rhodamine 6G; D002635:Chenodeoxycholic Acid; C025576:3,7-dihydroxy-12-oxocholanoic acid; D012965:Sodium Chloride; D014508:Urea; D009567:Nitrazepam; D019826:Cholic Acid