title: Exchange mechanisms for sodium dodecyl sulfate micelles: high salt concentration.
abstract: Solute exchange experiments for the pyrene-labeled triglyceride TG-Py solubilized in sodium dodecyl sulfate (SDS) micelles in the presence and absence of salt show that the "observed" rate constant k(obs) for solute exchange varies by over 6 orders of magnitude as the free sodium ion concentration [Na(+)](aq) is varied between 10 and 850 mM. There is a sharp break in the log-log plot of k(obs) versus [Na(+)](aq) in the range of [Na(+)](aq) = 200 mM, with the exchange rate showing a weaker dependence on [Na(+)](aq) above this concentration. Up to 100 mM added NaCl, this exchange takes place essentially exclusively by a micelle fission mechanism in which each submicelle carries off one of the solutes. At higher salt concentrations, a bimolecular process becomes increasingly important. This fusion process, which involves formation of a transient supermicelle followed by fission back to two normal micelles, becomes the dominant process at high salt concentrations. The fission rate appears to level off for salt concentrations above 300-400 mM. These fission and fusion processes are related in an intimate way to the changes in the size and shape of the SDS micelles with increasing salt concentration.
authors.affiliation: Department of Chemistry, University of Toronto, 80 St. George St., Toronto, Ontario, Canada M5S 3H6.
authors.forename: Yahya
authors.initials: Y
authors.lastname: Rharbi
authors.forename: Liusheng
authors.initials: L
authors.lastname: Chen
authors.forename: Mitchell A
authors.initials: MA
authors.lastname: Winnik
mesh_terms: D000465:Algorithms; D007700:Kinetics; D008823:Micelles; D008968:Molecular Conformation; D010316:Particle Size; D012965:Sodium Chloride / Q000737:chemistry; D012967:Sodium Dodecyl Sulfate / Q000138:chemical synthesis / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D013501:Surface-Active Agents / Q000138:chemical synthesis / Q000737:chemistry*
chemical_list: D008823:Micelles; D013501:Surface-Active Agents; D012967:Sodium Dodecyl Sulfate; D012965:Sodium Chloride