Exchange mechanisms for sodium dodecyl sulfate micelles: high salt concentration.
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.
Rharbi
Yahya
Y
Department of Chemistry, University of Toronto, 80 St. George St., Toronto, Ontario, Canada M5S 3H6.
Chen
Liusheng
L
Winnik
Mitchell A
MA
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*
D008823:Micelles; D013501:Surface-Active Agents; D012967:Sodium Dodecyl Sulfate; D012965:Sodium Chloride