US EPA

7748066 

Journal Article 

Changes in the redox-potential and catalase activity of Mn2+ ions during formation of Mn-bicarbonate complexes 

Kozlov, YN; Kazakova, AA; Klimov, VV 

1997 

Yes 

Biologicheskie Membrany
ISSN: 0233-4755 

14 

1 

93-97 

English 

WOS:A1997WM49500009 

Changes in the redox-potentials of Mn2+ ions and Mn-bicarbonate complexes were studied because of their possible participation in the photosynthetic oxidation of water in plant photosystem 2 and in the H2O2 decomposition. The electrochemical oxidation of Mn2+ ions was demonstrated by voltammetry on a platinum electrode in 0,1 M LiClO4 solution at the potential of 1,19 V (vs NHE). When added NaHCO3 the oxidation peak of Mn2+ ions was disappeared. New oxidation peaks apeared at 0,92 V and 0,63 V that corresponded to the oxidation of Mn(HCO3)+ and Mn(HCO3)2, respectively, generated by the complex formation between the Mn2+ and HCO-3 ions. The effect of Mn2+-bicarbonate complex on the H2O2 redox decomposition was studied. It was shown that the addition of MnSO4 to the H2O2 solution did not affect the H2O2 oxidation peak height thereby indicating the absence of the H2O2 decomposition by Mn2+ ions. At the same time, subsequent addition of NaHCO3 resulted in the disappearanse of the oxidation peaks of both H2O2 and Mn2+. Since at pH 7, the thermodinamic potential of H2O2 reduction is 1.1 V and the Mn2+ oxidation potential is 1.19V, then the redox reaction between them is hampered. The formation of the Mn2+-bicarbonate complex shifted Mn2+ oxidation potential to 0,63 V, thereby induccing the H2O2 decomposition. It was supposed that the decrease in the Mn2+ oxidation potential resulted from the formation of the bicarbonate complex determines the bicarbonate capability to enhance the Mn2+ abilities in donation of electrons for the PS 2 reaction centers.