Oxidation potentials and electron donation to photosystem II of manganese complexes containing bicarbonate and carboxylate ligands

Autor:	Yuri Kozlov, Vyacheslav V. Klimov, Jyotishman Dasgupta, Konstantin G. Tikhonov, G. Charles Dismukes, Serguei K. Zharmukhamedov, Alevtina A. Kazakova
Rok vydání:	2004
Předmět:	Photosystem II Ligand Bicarbonate Inorganic chemistry General Physics and Astronomy chemistry.chemical_element Manganese Medicinal chemistry Oxalate chemistry.chemical_compound Electron transfer chemistry Formate Carboxylate Physical and Theoretical Chemistry
Zdroj:	Physical Chemistry Chemical Physics. 6:4905
ISSN:	1463-9084 1463-9076
DOI:	10.1039/b406569g
Popis:	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 H2CO3/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).
Databáze:	OpenAIRE
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