Anti-tert-butylperoxyl radical reactivities of copper(II), manganase(II), and iron(III) 3,5-diisopropylsalicylate chelates
作者:Levon A. Tavadyan、Hakop G. Tonikyan、Seyran H. Minasyan、Lusik A. Harutyunyan、Frederick T. Greenaway、Skip Williams、Ronda A. Gray-Kaufman、John R.J. Sorenson
DOI:10.1016/s0020-1693(01)00657-0
日期:2002.1
Copper(II)-, Fe(III)-, and Mn(II)-3,5-di-iso-propylsalicylate (3,5-DIPS) chelates and Cu(II)(2)(acetyl-3,5-DIPS)(4), and 3,5-DIPS acid were examined as antioxidants in scavenging tert-butylperoxyl radical (tert-butylOO(.)). Using kinetic EPR methods it was established that the order of anti-tert-butylOO(.) reactivity is: Mn(II)(3,5-DIPS)(2) >> Cu(II)(2)(3,5-DIPS)(4) - Fe(III)(3,5-DIPS)(3) >> CU(II)(2)(acetyl-3,5-DIPS)(4) and 3,5-DIPS acid. Mn(II)(3,5-DIPS)(2) caused the most rapid rate of removal of tert-butylOO(.) as a result of the oxidation of Mn(II) to Mn(III) by tert-butylOO(.). A slower rate of removal of tert-butylOO(.) was observed for the abstraction of a hydrogen atom from the phenolic hydroxyl group of 3,5-DIPS ligands and subsequent addition of tert-butylOO, to the aromatic ring of the resultant phenoxyl radical. The reaction of tert-butylOO(.) with CU(II)(2)(3,5-DIPS)(4) and Fe(III)(3,5DIPS)(3) is due only to hydrogen atom abstraction from the ligand phenolic OH group by tert-butylOO(.). Introduction of ethylacetate, which is capable of forming a hydrogen bond with the phenolic OH of the ligand, diminished the anti-tert-butylOO(.) reactivity of Cu(II)(2)(3,5-DIPS)(4) and Fe(III)(3,5 -DIPS)(3), similar to its decrease of antioxidant reactivity of phenols, but increased the second-order rate constant for the removal of tert-butylOO(.) by Mn(II)(3,5-DIPS)2 due mainly to the oxidation of Mn(II) to Mn(III). It is concluded that removal of alkylperoxyl radicals by oxidizable Cu(I), Fe(II), and Mn(II) compounds may partially account for biological activity of their chelates. (C) 2002 Elsevier Science B.V. All rights reserved.