Towards an artificial model for Photosystem II: a manganese(II,II) dimer covalently linked to ruthenium(II) tris-bipyridine via a tyrosine derivative.
In order to model the individual electron transfer steps from the manganese cluster to the photooxidized sensitizer P680+ in Photosystem II (PS II) in green plants, the supramolecular complex 4 has been synthesized. In this complex, a ruthenium(II) tris-bipyridine type photosensitizer has been linked to a manganese(II) dimer via a substituted L-tyrosine, which bridges the manganese ions. The trinuclear complex 4 was characterized by electron paramagnetic resonance (EPR) and electrospray ionization mass spectrometry (ESI-MS). The excited state lifetime of the ruthenium tris-bipyridine moiety in 4 was found to be about 110 ns in acetonitrile. Using flash photolysis in the presence of an electron acceptor (methylviologen), it was demonstrated that in the supramolecular complex 4 an electron was transferred from the excited state of the ruthenium tris-bipyridine moiety to methylviologen, forming a methylviologen radical and a ruthenium(III) tris-bipyridine moiety. Next, the Ru(III) species retrieved the electron from the manganese(II/II) dimer in an intramolecular electron transfer reaction with a rate constant kET > 1.0 x 10(7) s(-1), generating a manganese(II/III) oxidation state and regenerating the ruthenium(II) photosensitizer. This is the first example of intramolecular electron transfer in a supramolecular complex, in which a manganese dimer is covalently linked to a photosensitizer via a tyrosine unit, in a process which mimics the electron transfer on the donor side of PS II.
Sun
L
L
Department of Chemistry, Organic Chemistry, Royal Institute of Technology KTH, Stockholm, Sweden.
Raymond
M K
MK
Magnuson
A
A
LeGourriérec
D
D
Tamm
M
M
Abrahamsson
M
M
Kenéz
P H
PH
Mårtensson
J
J
Stenhagen
G
G
Hammarström
L
L
Styring
S
S
Akermark
B
B
D015082:2,2'-Dipyridyl / Q000031:analogs & derivatives / Q000138:chemical synthesis / Q000737:chemistry / Q000378:metabolism; D056831:Coordination Complexes; D019281:Dimerization; D004578:Electron Spin Resonance Spectroscopy; D004583:Electrons; D008401:Gas Chromatography-Mass Spectrometry; D006860:Hydrogen Bonding; D007202:Indicators and Reagents / Q000737:chemistry; D008345:Manganese / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D015394:Molecular Structure; D019906:Nuclear Magnetic Resonance, Biomolecular; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry / Q000378:metabolism; D010782:Photolysis; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry*; D045332:Photosystem II Protein Complex; D016339:Spectrometry, Mass, Fast Atom Bombardment; D014443:Tyrosine / Q000138:chemical synthesis / Q000737:chemistry / Q000378:metabolism; D017975:Ruthenium Compounds
D015082:2,2'-Dipyridyl; D056831:Coordination Complexes; D007202:Indicators and Reagents; D008345:Manganese; D009942:Organometallic Compounds; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D014443:Tyrosine; C547232:tris(2,2-bipyridine)-ruthenium(II); D017975:Ruthenium Compounds