Synergistic effect of Ni(ii) and Co(ii) ions on the sulfite induced autoxidation of Cu(ii)/tetraglycine complex

Abstract

The synergistic effect of Ni(II) and Co(II) on the sulfite induced autoxidation of Cu(II)/tetraglycine was investigated spectrophotometrically at 25.0 degrees C, pH = 9.0, 1 x 10(-5) mol dm(-3) < or = [S(IV)] < or = 8 x 10(-5) mol dm(-3), [Cu(II)]= 1 x 10(-3) mol dm(-3), 1 x 10(-6) mol dm(-3) < or = [Ni(II)] or [Co(II)] < or = 1 x 10(-4) mol dm(-3), [O2] approximately 2.5 x 10(-4) mol dm(-3), and 0.1 mol dm(-3) ionic strength. In the absence of added nickel(II) or cobalt(II), the kinetic traces of Cu(III)G4 formation show a large induction period (about 3 h). The addition of trace amounts of Ni(II) or Co(II) increases the reaction rate significantly and the induction period drastically decreases (less than 0.5 s). The effectiveness of Cu(III)G4 formation becomes much higher. The metal ion in the trivalent oxidation state rapidly oxidizes SO3(2-) to SO3*-, which reacts with oxygen to produce SO5*-. The strongly generated oxidants oxidize Cu(II)G4 to Cu(III).

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

“…Our previous studies with tetraglycine as a ligand showed that the Cu(III)/G 4 formation is a linear function with initial sulfite concentration and can be monitored amperometric 22 and spectrophotometically 1,8,23 at 365 nm. For analytical purposes S(IV) could be determined in wine and juices in the range of (0.5-10) × 10 -5 mol L -1 and detection limit 6.0 × 10 -7 mol L -1 .…”

“…However great advances were achieved in some cases, in the presence of complexing medium, where it was possible to follow the formation of one of the metal ion, at trivalent state in large excess (10 -4 -10 -3 mol L -1 ), and the effect of the presence of the second metal ion at very low concentrations (10 -8 -10 -5 mol L -1 ). [2][3][4][5][6][7][8][9] Previous work reported in the literature [1][2][3][4][5][6][7][8][9][10] carried out in complexing medium, using very low concentrations of S(IV) (10 -5 mol L -1 ) and the second metal ion (10 -8 -10 -5 mol L -1 ) showed the complexity of the systems.…”

“…In these systems: Mn(II)/Fe(III)/acetate, 2 Fe(II)/ Mn(II)/H 2 O, 11,12 Co(II)/Mn(II)/N 3 -, 3,6 Ni(II)/Co(III)/cyclam or Ni(II)/Mn(III)/cyclam, 7 Cu(II)/Ni(II)(or Fe(II)/(III), Mn(II), Cr(III))/tetraglycine, 1,8 and Co(II)/Mn(II)/Tris, 9,10 it was possible to follow the concentration of the metal ion (in large excess) at the 3+ state, by measuring the absorbance at a characteristic wavelength.…”

“…However, in the presence of sulfite ((1-8) ×10 -5 mol L -1 ) and traces of Ni(II) and Co(II) (10 -5 mol L -1 ), present as unavoidable impurities in the copper salts (Aldrich) and reagents, the Cu(III)/ tetraglycine formation is efficient and extremely fast (the reaction is complete in 5 s). 1 The metal ions in the trivalent oxidation state react with sulfite to initiate a radical chain reaction in which sulfite is oxidized to sulfate and the metal ion is reduced to the bivalent state, with simultaneous consumption of oxygen.…”

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

“…[19][20][21][22] The literature reports only few studies on DNA damage mediated by Cu(II) (added as a free ion or complex) in the presence of S(IV) and dissolved oxygen. [19][20][21][22][23][24] Previously, we showed that the oxidation of S(IV) in air saturated solution ( 13,14,16,17 In addition, we verified that Cu II G 4 complexes interact with DNA producing strand breaks in significant yields in the presence of S(IV) without or with a second metal ion (traces of Ni(II)). 22 …”