title: pH dependence of the composition and stability of Mn(III)-bicarbonate complexes and its implication for redox interaction of Mn(II) with photosystemII.
abstract: Dependence of the electrochemical potential of oxidation of Mn(II) to Mn(III) on logarithm of bicarbonate concentration at different pH is considered. Slope values of the dependence are equal to -60, -120 and -180mV/log C(HCO)₃ at pH6.20, 6.50 and 8.35 respectively, that corresponds to binding of one, two and three HCO(3)(-) ligands to Mn(III). Extrapolation of these dependences to log C(HCO)₃=0 shows that at pH6.20 complex [Mn(III)HCO(3)](2+) with E(0)=0.99V and K(st)=6.5×10(8)M(-1), at pH6.50 complex [Mn(III)(HCO(3))(2)](+) with E(0)=0.77V and K(st)=3.5×10(12)M(-2), and at pH8.35 complex [Mn(III)(HCO(3))(3)](0) with E(0)=0.67V and K(st)=1.73×10(14)M(-3) are formed. From the dependence of oxidation potential of Mn(II) to Mn(III) on pH at initial concentration of NaHCO(3) equal to 28mM the limits of pH stability of the complexes were determined: pH5.0-6.35 for [Mn(III)HCO(3)](2+), pH6.35-7.0 for [Mn(III)(HCO(3))(2)](+) and pH7.0-8.35 for [Mn(III)(HCO(3))(3)](0). The obtained data may be important for understanding the mechanism of stimulating action of HCO(3)(-) ions on photoinduced electron transfer from Mn(II) to reaction centres of photosystem2 or to reaction centres of anoxygenic photosynthetic bacteria.
authors.affiliation: Institute of Basic Biological Problems, Russian Academy of Sciences, Institutskaya 2, Pushchino, Moscow Region 142290, Russia.
authors.forename: Yu N
authors.initials: YN
authors.lastname: Kozlov
authors.forename: K G
authors.initials: KG
authors.lastname: Tikhonov
authors.forename: O M
authors.initials: OM
authors.lastname: Zastrizhnaya
authors.forename: V V
authors.initials: VV
authors.lastname: Klimov
mesh_terms: D001639:Bicarbonates / Q000737:chemistry*; D056831:Coordination Complexes / Q000737:chemistry*; D004579:Electron Transport; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008345:Manganese / Q000737:chemistry*; D010084:Oxidation-Reduction; D045332:Photosystem II Protein Complex / Q000737:chemistry* / Q000378:metabolism
chemical_list: D001639:Bicarbonates; D056831:Coordination Complexes; D045332:Photosystem II Protein Complex; D008345:Manganese