title: Partitioning of nitroxides in dispersed systems investigated by ultrafiltration, EPR and NMR spectroscopy.
abstract: OBJECTIVE
  The partitioning behavior of paramagnetic nitroxides in dispersed systems can be determined by deconvolution of electron paramagnetic resonance (EPR) spectra giving equivalent results with the validated methods of ultrafiltration techniques (UF) and pulsed-field gradient nuclear magnetic resonance spectroscopy (PFG-NMR).
  
  
  METHODS
  The partitioning behavior of nitroxides with increasing lipophilicity was investigated in anionic, cationic and nonionic micellar systems and 10 wt% o/w emulsions. Apart from EPR spectra deconvolution, the PFG-NMR was used in micellar solutions as a non-destructive approach, while UF based on separation of very small volume of the aqueous phase.
  
  
  RESULTS
  As a function of their substituent and lipophilicity, the proportions of nitroxides that were solubilized in the micellar or emulsion interface increased with increasing nitroxide lipophilicity for all emulsifier used. Comparing the different approaches, EPR deconvolution and UF revealed comparable nitroxide proportions that were solubilized in the interfaces. Those proportions were higher than found with PFG-NMR. For PFG-NMR self-diffusion experiments the reduced nitroxides were used revealing a high dynamic of hydroxylamines and emulsifiers. Deconvolution of EPR spectra turned out to be the preferred method for measuring the partitioning behavior of paramagnetic molecules as it enables distinguishing between several populations at their individual solubilization sites.
authors.affiliation: Institute of Human Nutrition and Food Science, Kiel University, 24118 Kiel, Germany. Electronic address: info@foodtech.uni-kiel.de.
authors.forename: Heimke
authors.initials: H
authors.lastname: Krudopp
authors.affiliation: Otto Diels Institute for Organic Chemistry, Kiel University, 24118 Kiel, Germany. Electronic address: fsoennichsen@oc.uni-kiel.de.
authors.forename: Frank D
authors.initials: FD
authors.lastname: Sönnichsen
authors.affiliation: Institute of Human Nutrition and Food Science, Kiel University, 24118 Kiel, Germany. Electronic address: aheins@foodtech.uni-kiel.de.
authors.forename: Anja
authors.initials: A
authors.lastname: Steffen-Heins
mesh_terms: D002592:Cetomacrogol / Q000737:chemistry; D000077286:Cetrimonium; D002593:Cetrimonium Compounds / Q000737:chemistry; D003497:Cyclic N-Oxides / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D045703:Emulsifying Agents / Q000737:chemistry*; D004655:Emulsions; D019811:Hydroxylamine / Q000737:chemistry*; D006898:Hydroxylamines / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008823:Micelles; D012967:Sodium Dodecyl Sulfate / Q000737:chemistry; D014462:Ultrafiltration; D014867:Water / Q000737:chemistry*
chemical_list: D002593:Cetrimonium Compounds; D003497:Cyclic N-Oxides; D045703:Emulsifying Agents; D004655:Emulsions; D006898:Hydroxylamines; D008823:Micelles; D014867:Water; D019811:Hydroxylamine; D012967:Sodium Dodecyl Sulfate; D002592:Cetomacrogol; C505333:TEMPOL-H; C003959:TEMPO; D000077286:Cetrimonium
keywords: Brij58; CTAB; Dispersed systems; PFG-NMR; Partitioning; SDS; Spin probes; TEMPO; TEMPOL; TEMPOL-benzoate