title: Polar paradox revisited: analogous pairs of hydrophilic and lipophilic antioxidants in linoleic acid emulsion containing Cu(II).
abstract: BACKGROUND
  Literature data are scarce on the activities of analogous pairs of hydrophilic and lipophilic antioxidants related to the 'polar paradox' distinguishing antioxidants based on their partitioning between lipids and water. The peroxidation of linoleic acid (LA) in the presence of either Cu(II) ions alone or Cu(II) ions combined with Trolox (TR), ascorbic acid (AA), hydroquinone (HQ) and gallic acid (GA), as hydrophilic antioxidants, or with α-tocopherol (TocH), ascorbyl palmitate (AP), tert-butyl hydroquinone (TBHQ) and propyl gallate (PG), as their respective lipophilic analogues, was investigated in aerated and incubated emulsions at 37 °C and pH 7.
  
  
  RESULTS
  LA peroxidation induced by Cu(II) followed pseudo-first-order kinetics with respect to the formation of primary (hydroperoxides) and secondary (aldehyde- and ketone-like) oxidation products, which were determined by ferric thiocyanate (Fe(III)-SCN) and thiobarbituric acid-reactive substances (TBARS) methods respectively. With the exception of TocH at certain concentrations, the tested compounds showed antioxidant behaviour depending on their polarities. The results were evaluated in the light of structure-activity relationships and the polar paradox.
  
  
  CONCLUSIONS
  The results of this study partly confirm the hypothesis that the polar paradox experiences limitations in oil-in-water emulsions and that its validity is also dependent on the concentrations of the antioxidants employed.
authors.affiliation: Chemistry Department, Science and Arts Faculty, Yildiz Technical University, Istanbul, Turkey.
authors.forename: Temelkan
authors.initials: T
authors.lastname: Bakır
authors.forename: Inci
authors.initials: I
authors.lastname: Sönmezoğlu
authors.forename: Filiz
authors.initials: F
authors.lastname: Imer
authors.forename: Reşat
authors.initials: R
authors.lastname: Apak
mesh_terms: D000975:Antioxidants / Q000737:chemistry*; D001205:Ascorbic Acid / Q000031:analogs & derivatives / Q000737:chemistry; D002839:Chromans / Q000737:chemistry; D003300:Copper / Q000737:chemistry*; D004655:Emulsions / Q000737:chemistry*; D005707:Gallic Acid / Q000737:chemistry; D057927:Hydrophobic and Hydrophilic Interactions; D006873:Hydroquinones / Q000737:chemistry; D007501:Iron / Q000737:chemistry; D007700:Kinetics; D019787:Linoleic Acid / Q000737:chemistry*; D015227:Lipid Peroxidation; D010545:Peroxides / Q000737:chemistry; D011435:Propyl Gallate / Q000737:chemistry; D013329:Structure-Activity Relationship; D017392:Thiobarbituric Acid Reactive Substances / Q000737:chemistry; D013861:Thiocyanates / Q000737:chemistry; D024502:alpha-Tocopherol / Q000737:chemistry
chemical_list: D000975:Antioxidants; D002839:Chromans; D004655:Emulsions; D006873:Hydroquinones; D010545:Peroxides; D017392:Thiobarbituric Acid Reactive Substances; D013861:Thiocyanates; C103724:ferric thiocyanate; D005707:Gallic Acid; D003300:Copper; D011435:Propyl Gallate; D019787:Linoleic Acid; D007501:Iron; D024502:alpha-Tocopherol; D001205:Ascorbic Acid; C031226:6-O-palmitoylascorbic acid; C010643:6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid; C031927:hydroquinone