title: Micellization parameters (number average, aggregation number and critical micellar concentration) of bile salt 3 and 7 ethylidene derivatives: Role of the steroidal skeleton II.
abstract: BACKGROUND
  Bile salts are steroidal biosurfactants. Micellar systems of bile salts are not only important for solubilization of cholesterol, but they also interact with certain drugs thus changing their bioavailability.
  
  
  METHODS
  The number-average aggregation numbers (n¯) are determined using the Moroi-Matsuoka-Sugioka thermodynamic method. Critical micellar concentrations were determined by spectrofluorometric method using pyren and by surface tension measurements.
  
  
  RESULTS
  Micelles of ethylidene derivatives possess the following values for n¯: 7-Eth-D (n¯=11 (50 mM)-n¯=14.8 (100 mM)); 12-Ox-7-Eth-L (n¯≈8.8, without concentration dependence) and 7,12-diOx-3-Eth-Ch (n¯≈2.9, without concentration dependence). In the planes n¯-ln k and ln CMC-ln k derivative 7-Eth-D is outlier in respect to hydrophobic linear congeneric groups.
  
  
  CONCLUSIONS
  Gibbs energy of formation for 7-Eth-D anion micelles in addition to the Gibbs energy of hydrophobic interactions consists excess Gibbs energy (GE) from hydrogen bond formation between building blocks of micelles. Gibbs energy of formation for 7,12-diOx-3-Eth-Ch and 12-Ox-7-Eth-L anion micelle is determined by the Gibbs energy of hydrophobic interactions. Relative increase in hydrophobicity and aggregation number for ethylidene derivatives is larger when ethylidene group is introduced from the C7 lateral side of steroidal skeleton then it is when ethylidene group is on C3 carbon.
  
  
  CONCLUSIONS
  Position of outlier towards hydrophobic congeneric groups from n¯-ln k and ln CMC-ln k planes indicates the existence of excess Gibbs energy (GE) which is not of hydrophobic nature (formation of hydrogen bonds). For the bile salt micelles to have GE (formation of secondary micelles) it is necessary that steroidal skeleton possesses C3-α-(e)-OH and C12-α-(a)-OH groups.
authors.affiliation: Department of Pharmacy, Faculty of Medicine, University of Novi Sad, Hajduk Veljka 3, 21000 Novi Sad, Serbia. Electronic address: mihaljp@uns.ac.rs.
authors.forename: Mihalj
authors.initials: M
authors.lastname: Poša
authors.affiliation: Department of Chemistry, Biochemistry and Environmental Protection, Faculty of Sciences, University of Novi Sad, Trg D. Obradovića 3, 21000 Novi Sad, Serbia.
authors.forename: Srđan
authors.initials: S
authors.lastname: Bjedov
authors.affiliation: Department of Chemistry, Biochemistry and Environmental Protection, Faculty of Sciences, University of Novi Sad, Trg D. Obradovića 3, 21000 Novi Sad, Serbia.
authors.forename: Dušan
authors.initials: D
authors.lastname: Škorić
authors.affiliation: Department of Chemistry, Biochemistry and Environmental Protection, Faculty of Sciences, University of Novi Sad, Trg D. Obradovića 3, 21000 Novi Sad, Serbia.
authors.forename: Marija
authors.initials: M
authors.lastname: Sakač
mesh_terms: D000465:Algorithms; D001647:Bile Acids and Salts / Q000138:chemical synthesis / Q000737:chemistry*; D002784:Cholesterol / Q000737:chemistry*; D003840:Deoxycholic Acid / Q000138:chemical synthesis / Q000737:chemistry; D006860:Hydrogen Bonding; D057927:Hydrophobic and Hydrophilic Interactions; D008823:Micelles; D008956:Models, Chemical; D015394:Molecular Structure; D012995:Solubility; D013050:Spectrometry, Fluorescence; D013256:Steroids / Q000138:chemical synthesis / Q000737:chemistry*; D013500:Surface Tension; D013816:Thermodynamics; D014580:Ursodeoxycholic Acid / Q000138:chemical synthesis / Q000737:chemistry
chemical_list: D001647:Bile Acids and Salts; D008823:Micelles; D013256:Steroids; D003840:Deoxycholic Acid; D014580:Ursodeoxycholic Acid; D002784:Cholesterol
keywords: Aggregation number; Excess Gibbs energy; Hydrophobic linear congeneric group; Micelle of bile salts; Steroidal skeleton