Further studies on the synergistic effect of Ni(II) and Co(II) ions on the sulfite induced autoxidation of Cu(II) penta and hexaglycine complexes

Abstract

A reação de autoxidação dos complexos de Cu(II)/penta e hexaglicina em pH=9 é muito lenta, apresentando um período longo de indução (aproximadamente 4 horas). A presença de S(IV) praticamente não altera a velocidade desta reação. A adição de pequenas quantidades de Ni(II) ou Co(II) aumenta significativamente a velocidade da reação e a eficiência da formação de Cu(III), diminuindo o período de indução para menos de 0,5 s. A constante de velocidade observada para a formação de Cu(III) também depende da concentração de S(IV). A discussão do mecanismo é baseada nas informações disponíveis na literatura e envolve uma cadeia de reações com formação de radicais e um ciclo de oxirredução dos íons metálicos complexados.The autoxidation of Cu(II)/penta and hexaglycine complexes at pH = 9 is very slow showing a large induction period (about 4 h). The presence of S(IV) practically does not affect the rate of this reaction. Addition of small amounts of Ni(II) or Co(II) increases significantly the reaction rate and the effectiveness of Cu(III) formation, the induction period becomes as short as 0.5 s. The observed rate constant for Cu(III) formation also depends on the S(IV) concentration. The mechanism is discussed based on the available literature information and involves a radical chain and redox cycling of the metal ion complexes.

Oxidative DNA damage induced by S(IV) in the presence of Cu(II) and Cu(I) complexes

“…[7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] However, depending on the Cu(II) complex there are some differences related to the products formed (reactive intermediates that could damage the DNA). • was detected.…”

Effect of some antioxidants on oxidative DNA damage induced by autoxidation of microquantities of sulfite in the presence of Ni(II)/Gly–Gly–L–His

“…Detailed kinetics and mechanistic studies have been done for the systems: Mn(II)/(III)/N À 3 , Mn(II)/(III)/ acetate, Co(II)/(III)/TRIS, Ni(II)/(III)/cyclam, Ni(II)/(III)/tetraglycine, Co(II)/(III)/ tetraglycine, and Ni(II) and Cu(II)/(III)/tetra, penta, and hexaglycine [6][7][8][9][10]. Oxidation of the divalent metal ion is accelerated in the presence of S(IV) (a reducing agent) and dissolved oxygen, which may be explained by a radical mechanism.…”