TY - JOUR
T1 - Oxidation potentials and electron donation to photosystem II of manganese complexes containing bicarbonate and carboxylate ligands
AU - Kozlov, Yuri N.
AU - Zharmukhamedov, Serguei K.
AU - Tikhonov, Konstantin G.
AU - Dasgupta, Jyotishman
AU - Kazakova, Alevtina A.
AU - Dismukes, G. Charles
AU - Klimov, Vyacheslav V.
PY - 2004/10/21
Y1 - 2004/10/21
N2 - The oxidation potentials of MnII in aqueous solutions of bicarbonate, formate, acetate and oxalate are reported as a function of concentration and compared to the rate of photooxidation of these solutions by the Mn-depleted water-oxidizing complex of photosystem II (apo-WOC-PSII) from peas. Although all the carboxylate species lower considerably the oxidation potential of MnII, only bicarbonate stimulates the electron transfer from MnII to apo-WOC-PSII. On the basis of the electrochemical data it is proposed that the unique capability of Mn-bicarbonate complexes to be photooxidized by PSII could be due to four possible reasons: (i) significantly larger decrease in the oxidation potential of MnII (down to 0.52 V); (ii) electroneutrality of the functional electron transfer complex; (iii) the more favorable energetics reflected in the two pKa values for H 2CO3/HCO3- and HCO3 -/CO32- and greater number of proton transfer sites; and (iv) multiple composition possibilities for the MnIII photo-product as MnIII(HCO3-)3, MnIII(HCO3-)(CO32-) and MnIII(HCO3-)2(OH-) (due to the high Lewis acidity of MnIII (pK < 1).
AB - The oxidation potentials of MnII in aqueous solutions of bicarbonate, formate, acetate and oxalate are reported as a function of concentration and compared to the rate of photooxidation of these solutions by the Mn-depleted water-oxidizing complex of photosystem II (apo-WOC-PSII) from peas. Although all the carboxylate species lower considerably the oxidation potential of MnII, only bicarbonate stimulates the electron transfer from MnII to apo-WOC-PSII. On the basis of the electrochemical data it is proposed that the unique capability of Mn-bicarbonate complexes to be photooxidized by PSII could be due to four possible reasons: (i) significantly larger decrease in the oxidation potential of MnII (down to 0.52 V); (ii) electroneutrality of the functional electron transfer complex; (iii) the more favorable energetics reflected in the two pKa values for H 2CO3/HCO3- and HCO3 -/CO32- and greater number of proton transfer sites; and (iv) multiple composition possibilities for the MnIII photo-product as MnIII(HCO3-)3, MnIII(HCO3-)(CO32-) and MnIII(HCO3-)2(OH-) (due to the high Lewis acidity of MnIII (pK < 1).
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U2 - 10.1039/b406569g
DO - 10.1039/b406569g
M3 - Article
AN - SCOPUS:8144225860
VL - 6
SP - 4905
EP - 4911
JO - Physical Chemistry Chemical Physics
JF - Physical Chemistry Chemical Physics
SN - 1463-9076
IS - 20
ER -