Sulfite induced autoxidation of Cu(II)/tetra/ penta and hexaglycine complexes: spectrophotometric and rotating-ring-disk glassy carbon electrode studies and analytical potentialities

Abstract

A oxidação de complexos de Cu(II) com tetra, penta e hexaglicina, em solução aquosa de tampão borato, pelo oxigênio dissolvido é fortemente acelerada por sulfito. A formação de complexos de Cu(III) com máximos de absorbância em 250 nm (ε = 9000 mol -1 L cm -1 ) e 365 nm (ε = 7120 mol -1 L cm -1 ) foi também caracterizada usando-se voltametria com eletrodo rotativo disco-anel, na qual componentes anódicos e catódicos foram observados em voltamogramas registrados em solução contendo Cu(II). Voltamogramas, obtidos com várias velocidades de rotação, mostraram que a espécie de Cu(III) gerada eletroquimicamente não é estável em toda a janela de tempo do experimento, e em solução contendo tetraglicina a corrente limite é controlada pela cinética de um equilíbrio envolvendo espécies de Cu(II). O valor calculado da constante de decomposição de primeira ordem foi 4,37x10 -3 s -1 . Experimentos eletroquímicos realizados em solução de Cu(II) após a adição de quantidades relativamente pequenas de sulfito demonstraram que a espécie de Cu(III), formada na reação química, é a mesma que foi coletada no eletrodo anel quando Cu(II) é oxidado no eletrodo disco. A concentração dos complexos de Cu(III) é proporcional à quantidade de sulfito adicionada e os resultados indicaram a possibilidade de desenvolvimento de um método analítico indireto para sulfito, com detecção espectrofotométrica ou amperométrica do produto quimicamente gerado.The oxidation of Cu(II) complexes with tetra, penta and hexaglycine in borate buffer aqueous solution, by dissolved oxygen is strongly accelerated by sulfite. The formation of Cu(III) complexes with maximum absorbances at 250 nm (ε = 9000 mol -1 L cm -1 ) and 365 nm (ε = 7120 mol -1 L cm -1 ) was also characterized by using rotating ring-disk voltammetry, whose anodic and cathodic components were observed in voltammograms recorded in solutions containing Cu(II). Voltammograms, obtained at various rotation speeds, showed that the Cu(III) species electrochemically generated is not stable over the entire time window of the experiment and in solutions containing tetraglycine the overall limiting current is controlled by the kinetics of an equilibrium involving Cu(II) species.The calculated first order rate constant of the decomposition was 4.37x10 -3 s -1 . Electrochemical experiments carried out in Cu(II) solutions after the addition of relatively small amounts of sulfite demonstrated that the Cu(III) species formed in the chemical reaction is the same as the one collected at the ring electrode when Cu(II) is oxidized at the disk electrode in ring-disk voltammetry. The concentration of Cu(III) complexes is proportional to the amount of added sulfite and the results indicated that indirect analytical methods for sulfite may be developed by means of spectrophotometric or amperometric detection of the chemically generated product.Keywords: copper (III), glycines, sulfite, catalysis, autoxidation, rotating ring disc electrode IntroductionThe present article is a comparative study of the sulfite induced oxidat...

Autoxidation of Ni(II) and Co(II) tetra, penta and hexaglycine complexes accelerated by oxy sulfur radicals

“…4,5,10,11,14 The S(IV) induced autoxidation of Ni(II) and Co(II) tetraglycine complexes is very fast. 17,20 On the other hand, Cu(II) tetraglycine complexes react slowly but traces (10 -6 mol L -1 ) of Ni(II) and Co(II) ions accelerate the oxidation.…”

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

“…However, our studies [12][13][14] showed that in fact, this reaction is very slow in the presence of S(IV). The Cu III G 4 formation is efficient and fast only in the presence of S(IV) and trace concentrations of nickel(II) ion, present as impurity in the copper (II) salts (CuClO 4 , Sigma) reagents.…”

“…The intensity of DNA damage in the presence of the different Cu(II) complexes and for S(IV) (10-300 µmol L Figure 1) and previous work. 12,16,19,21,34 Due to the synergistic effect of Ni(II) on the oxidation of Cu II G 4 in the presence of S(IV) and dissolved oxygen, 12,16,17,21 some experiments were carried out to evaluate the DNA strand breakage as shown in Figure 3. …”

“…[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.…”

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 .…”