Photo-induced oxidation of a dinuclear Mn(2)(II,II) complex to the Mn(2)(III,IV) state by inter- and intramolecular electron transfer to Ru(III)tris-bipyridine.
To model the structural and functional parts of the water oxidizing complex in Photosystem II, a dimeric manganese(II,II) complex (1) was linked to a ruthenium(II)tris-bipyridine (Ru(II)(bpy)(3)) complex via a substituted L-tyrosine, to form the trinuclear complex 2 [J. Inorg. Biochem. 78 (2000) 15]. Flash photolysis of 1 and Ru(II)(bpy)(3) in aqueous solution, in the presence of an electron acceptor, resulted in the stepwise extraction of three electrons by Ru(III)(bpy)(3) from the Mn(2)(II,II) dimer, which then attained the Mn(2)(III,IV) oxidation state. In a similar experiment with compound 2, the dinuclear Mn complex reduced the photo-oxidized Ru moiety via intramolecular electron transfer on each photochemical event. From EPR it was seen that 2 also reached the Mn(2)(III,IV) state. Our data indicate that oxidation from the Mn(2)(II,II) state proceeds stepwise via intermediate formation of Mn(2)(II,III) and Mn(2)(III,III). In the presence of water, cyclic voltammetry showed an additional anodic peak beyond Mn(2)(II,III/III,III) oxidation which was significantly lower than in neat acetonitrile. Assuming that this peak is due to oxidation to Mn(2)(III,IV), this suggests that water is essential for the formation of the Mn(2)(III,IV) oxidation state. Compound 2 is a structural mimic of the water oxidizing complex, in that it links a Mn complex via a tyrosine to a highly oxidizing photosensitizer. Complex 2 also mimics mechanistic aspects of Photosystem II, in that the electron transfer to the photosensitizer is fast and results in several electron extractions from the Mn moiety.
Department of Biochemistry, Center for Chemistry and Chemical Engineering, Lund University, P.O. Box 124, S-221 00 Lund, Sweden.
P
P
Huang
A
A
Magnuson
R
R
Lomoth
M
M
Abrahamsson
M
M
Tamm
L
L
Sun
B
B
van Rotterdam
J
J
Park
L
L
Hammarström
B
B
Akermark
S
S
Styring
D015082:2,2'-Dipyridyl / Q000031:analogs & derivatives* / Q000737:chemistry*; D000097:Acetonitriles / Q000737:chemistry; D004563:Electrochemistry; D004578:Electron Spin Resonance Spectroscopy; D007854:Lead / Q000737:chemistry; D008027:Light; D046911:Macromolecular Substances; D008345:Manganese / Q000737:chemistry*; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D016877:Oxidants / Q000737:chemistry; D010084:Oxidation-Reduction; D010777:Photochemistry; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry*; D045332:Photosystem II Protein Complex; D012428:Ruthenium / Q000737:chemistry; D014867:Water / Q000737:chemistry
D000097:Acetonitriles; D046911:Macromolecular Substances; D009942:Organometallic Compounds; D016877:Oxidants; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D014867:Water; C058901:tris(2,2'-bipyridine)ruthenium III; D007854:Lead; D008345:Manganese; D015082:2,2'-Dipyridyl; D012428:Ruthenium; C032159:acetonitrile