Kinetic EPR-Studies of the Anti-Peroxyl Radical Reactivities with Various Metallochelates of 3,5-Di-Iso-Propylsalicyalte and Salicylidene Schiff Base

Copper(II)-, Fe(III)-, Zn(II)-, 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, salicylidene Schiff base chelates Mn(III), Co(II), Ni(II), were kinetically examined as antioxidants in the scavenging of tert-butyl peroxyl radical ( $$tert - {\text{butylOO}}^{ \bullet }$$ ) in non-polar and polar aprotic solvents. Using kinetic EPR method absolute rate constants and corresponding Arrhenius parameters were determined for reactions of $$tert - {\text{butylOO}}^{ \bullet }$$ with these chelates in the temperature range from − 63 to − 11 °C. It was established that the order of anti- $$tert - {\text{butylOO}}^{ \bullet }$$ reactivity is: Mn(II)(3,5-DIPS)2 >> Cu(II)2(3,5-DIPS)4 > Fe(III)(3,5-DIPS)3 > Zn(II)(3,5-DIPS)2 >> Cu(II)2(acetyl-3,5-DIPS)4 and 3,5-DIPS acid. Mn(II)(3,5-DIPS)2 caused the most rapid removal rate for $$tert - {\text{butylOO}}^{ \bullet }$$ as a result of the oxidation of Mn(II) to Mn(III) by $$tert - {\text{butylOO}}^{ \bullet }$$ . The reaction of $$tert - {\text{butylOO}}^{ \bullet }$$ with Cu(II)2(3,5-DIPS)4, Zn(II)(3,5-DIPS)2 and Fe(III)(3,5-DIPS)3 is due only to hydrogen atom abstraction from the ligand phenolic OH group by $$tert - {\text{butylOO}}^{ \bullet }$$ , owing to their activation by the metalloelement through weakening the intramolecular hydrogen bond. High reactivity of $$tert - {\text{butylOO}}^{ \bullet }$$ with Mn(III) and Co(II) salicylidene Schiff base chelates was established. These salicylidene Schiff base chelates react in a 1:1 stoichiometric ratio with $$tert - {\text{butylOO}}^{ \bullet }$$ without free radical formation and with the single-electron oxidation of central metalloelements. It is concluded that removal of alkylperoxyl radical by Cu(II)-, Fe(III)-, Zn(II)-, and Mn(II)-3,5-di-iso-propylsalicylate chelates, Mn(III) and Co(II) salicylidene Schiff base chelates may partially account for their biological activities.