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Fatty Acids Oxidation Studied by Electron Paramagnetic Resonance. 1. Initiation with Coordinated Peroxy Radicals and Reactions with Spin-Trapper DMPO

A. Tkáč and R. Stovíček

Department of Physical Chemistry, Faculty of Chemical Technology, Slovak Technical University, SK-812 37 Bratislava

 

Abstract: tert-Butyl peroxy radicals ROO. with prolonged mean lifetime coordinated to Co(III) chelated in acetylacetonate ligand (acac) or to Fe(IV) in porphyrin ligand can effectively abstract hydrogen atom in nonpolar solvents from organic molecules at physiological temperature or form spin-adducts with the spin-trapper 5,5-dimethyl-1 -pyrroline N-oxide (DMPO). The paramagnetic peroxy and spin-adduct nitroxy radicals, when joined through molecular oxygen present in the solution, form reversible diamagnetic complexes.The experimental conditions controlling the transformation of the primary 12-line EPR signal of ROO. and HOO. spin-adducts to the secondary 7-line alkoxy radical signal in benzene solution, in contrast to the 4-line EPR signal of the high-stable HO. spin-adducts formed in aqueous solutions, are described.The diamagnetic hydroxy derivative[GRAPHICS]as the end product of the reaction of Co(acac)2 with tert-butyl hydroperoxide resulting after the elimination of the original to Co(III)-coordinated ROO' radicals, can catalytically generate DMPO spin-adducts of HO. or HOO. according to the actual polarity of the used solvent.All types of studied DMPO spin-adducts (ROO., HOO., HO.) effectively abstract hydrogen from sterically hindered phenols as well as from biological antioxidants as alpha-tocopherol in hydrophobic or ascorbic acid in hydrophilic environment generating simultaneously the high-stable free radicals of vitamin E or C.

Full paper in Portable Document Format: 476a362.pdf

 

Chemical Papers 47 (6) 362–368 (1993)

Monday, October 21, 2019

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