Kazakova A A, Klimov V V
Institute of Soil Science and Photosynthesis, Russian Academy of Sciences, Pushchino, Moscow Region.
Membr Cell Biol. 1997;11(1):115-20.
Changes in the redox potentials of Mn2+ ions and Mn-bicarbonate complexes were studied due to their possible participation in the photosynthetic oxidation of water in plant photosystem 2 and in H2O2 decomposition. Electrochemical oxidation of Mn2+ ions was demonstrated by voltammetry on a platinum electrode in 0.1 M LiClO4 solution at a potential of 1.19 V (vs NHE). When NaHCO3 was added, the oxidation peak of Mn2+ ions disappeared. New oxidation peaks appeared at 0.92 V and 0.63 V which corresponded to the oxidation of Mn(HCO3)+ and Mn(HCO3)2, respectively, generated by complex formation between Mn2+ and HCO3- ions. The effect of the Mn(2+)-bicarbonate complex on 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 H2O2 decomposition by Mn2+ ions. At the same time, subsequent addition of NaHCO3 resulted in the disappearance of the oxidation peaks of both H2O2 and Mn2+. As at pH 7 the thermodynamic potential of H2O2 reduction is 1.1 V and the Mn2+ oxidation potential is 1.19 V, the redox reaction between them is hampered. Formation of the Mn(2+)-bicarbonate complex shifted the Mn2+ oxidation potential to 0.63 V, thereby inducing the decomposition of H2O2. It is suggested that the decrease in the Mn2+ oxidation potential resulting from the formation of the bicarbonate complex determines the bicarbonate capability to enhance the Mn2+ ability to donate electrons for PS 2 reaction centres.
研究了Mn2+离子和锰-碳酸氢盐配合物的氧化还原电位变化，因为它们可能参与植物光系统2中水分子的光合氧化以及过氧化氢的分解。通过伏安法在0.1 M LiClO4溶液中的铂电极上，在1.19 V（相对于标准氢电极）的电位下证明了Mn2+离子的电化学氧化。当加入NaHCO3时，Mn2+离子的氧化峰消失。在0.92 V和0.63 V处出现了新的氧化峰，分别对应于Mn(HCO3)+和Mn(HCO3)2的氧化，这是由Mn2+和HCO3-离子之间形成配合物产生的。研究了Mn(2+)-碳酸氢盐配合物对过氧化氢氧化还原分解的影响。结果表明，向过氧化氢溶液中加入硫酸锰不会影响过氧化氢的氧化峰高度，从而表明Mn2+离子不会分解过氧化氢。同时，随后加入NaHCO3导致过氧化氢和Mn2+的氧化峰均消失。由于在pH 7时过氧化氢还原的热力学电位为1.1 V，Mn2+氧化电位为1.19 V，它们之间的氧化还原反应受到阻碍。Mn(2+)-碳酸氢盐配合物的形成将Mn2+氧化电位移至0.63 V，从而引发过氧化氢的分解。有人认为，碳酸氢盐配合物的形成导致Mn2+氧化电位降低，这决定了碳酸氢盐增强Mn2+向PS 2反应中心提供电子能力的能力。
