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

Yuri N. Kozlov, Serguei K. Zharmukhamedov, Konstantin G. Tikhonov, Jyotishman Dasgupta, Alevtina A. Kazakova, G Charles Dismukes, Vyacheslav V. Klimov

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Abstract

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 -/CO3 2- and greater number of proton transfer sites; and (iv) multiple composition possibilities for the MnIII photo-product as MnIII(HCO3 -)3, MnIII(HCO3 -)(CO3 2-) and MnIII(HCO3 -)2(OH-) (due to the high Lewis acidity of MnIII (pK <1).

Original languageEnglish
Pages (from-to)4905-4911
Number of pages7
JournalPhysical Chemistry Chemical Physics
Volume6
Issue number20
DOIs
Publication statusPublished - Oct 21 2004

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Photosystem II Protein Complex
Manganese
Bicarbonates
carboxylates
manganese
carbonates
formic acid
Ligands
Oxidation
ligands
oxidation
Electrons
electron transfer
Proton transfer
electrons
Photooxidation
Oxalates
photooxidation
formates
oxalates

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Atomic and Molecular Physics, and Optics

Cite this

Oxidation potentials and electron donation to photosystem II of manganese complexes containing bicarbonate and carboxylate ligands. / Kozlov, Yuri N.; Zharmukhamedov, Serguei K.; Tikhonov, Konstantin G.; Dasgupta, Jyotishman; Kazakova, Alevtina A.; Dismukes, G Charles; Klimov, Vyacheslav V.

In: Physical Chemistry Chemical Physics, Vol. 6, No. 20, 21.10.2004, p. 4905-4911.

Research output: Contribution to journalArticle

Kozlov, Yuri N. ; Zharmukhamedov, Serguei K. ; Tikhonov, Konstantin G. ; Dasgupta, Jyotishman ; Kazakova, Alevtina A. ; Dismukes, G Charles ; Klimov, Vyacheslav V. / Oxidation potentials and electron donation to photosystem II of manganese complexes containing bicarbonate and carboxylate ligands. In: Physical Chemistry Chemical Physics. 2004 ; Vol. 6, No. 20. pp. 4905-4911.
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AU - Dasgupta, Jyotishman

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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 -/CO3 2- and greater number of proton transfer sites; and (iv) multiple composition possibilities for the MnIII photo-product as MnIII(HCO3 -)3, MnIII(HCO3 -)(CO3 2-) and MnIII(HCO3 -)2(OH-) (due to the high Lewis acidity of MnIII (pK <1).

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