CHANGES IN THE REDOX-POTENTIAL AND CATALA SE ACTIVITY OF MN2-BICARBONATE COMPLEXES( IONS DURING FORMATION OF MN)

Changes in the redox-potentials of Mn2+ ions and Mn-bicarbonate comple xes were studied because of their possible participation in the photos ynthetic oxidation of water in plant photosystem 2 and in the H2O2 dec omposition. The electrochemical oxidation of Mn2+ ions was demonstrate d by voltammetry on a platinum electrode in 0,1 M LiClO4 solution at t he 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 an d 0,63 V that corresponded to the oxidation of Mn(HCO3)(+) and Mn(HCO3 )2, respectively, generated by the complex formation between the Mn2and HCO3- ions. The effect of Mn2+-bicarbonate complex on the H2O2 red ox decomposition was studied. it was shown that the addition of MnSO4 to the H2O2 solution did not affect the H2O2 Oxidation peak height the reby indicating the absence of the H2O2 decomposition by Mn2+ ions. At the same time, subsequent addition of NaHCO3 resulted in the disappea ranse 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+ oxida tion potential is 1.19 V, then the redox reaction between them is hamp ered. The formation of the Mn2+-bicarbonate complex shifted Mn2+ oxida tion potential to 0,63 V, thereby induccing the H2O2 decomposition. It was supposed that the decrease in the Mn2+ oxidation potential result ed from the formation of the bicarbonate complex determines the bicarb onate capability to enhance the Mn2+ abilities in donation of electron s for the PS 2 reaction centers.