| 1. |
- Huang, Ping, et al.
(författare)
-
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
- 2002
-
Ingår i: Journal of Inorganic Biochemistry. - 0162-0134 .- 1873-3344. ; 91:1, s. 159-172
-
Tidskriftsartikel (refereegranskat)abstract
- To model the structural and functional parts of the water oxidizing complex in Photosystem 11, a dimeric manganese(II,11) 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), in aqueous solution, in the presence of an electron acceptor, resulted in the stepwise extraction of three electrons by Ru-III(bpy), 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 11, in that the electron transfer to the photosensitizer is fast and results in several electron extractions from the Mn moiety.
|
|
| 2. |
|
|
| 3. |
- Abrahamsson, M. L. A., et al.
(författare)
-
Ruthenium-manganese complexes for artificial photosynthesis : Factors controlling intramolecular electron transfer and excited-state quenching reactions
- 2002
-
Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 41:6, s. 1534-1544
-
Tidskriftsartikel (refereegranskat)abstract
- Continuing our work toward a system mimicking the electron-transfer steps from manganese to P-680(+) in photosystem II (PS II), we report a series of ruthenium(II)-manganese(II) complexes that display intramolecular electron transfer from manganese(II) to photooxidized ruthenium(III). The electron-transfer rate constant (k(ET)) values span a large range, 1 X 10(5)-2 x 10(7) s(-1), and we have investigated different factors that are responsible for the variation. The reorganization energies determined experimentally (lambda = 1.5-2.0 eV) are larger than expected for solvent reorganization in complexes of similar size in polar solvents (typically lambda approximate to 1.0 eV). This result indicates that the inner reorganization energy is relatively large and, consequently, that at moderate driving force values manganese complexes are not fast donors. Both the type of manganese ligand and the link between the two metals are shown to be of great importance to the electron-transfer rate. In contrast, we show that the quenching of the excited state of the ruthenium(II) moiety by manganese(II) in this series of complexes mainly depends on the distance between the metals. However, by synthetically modifying the sensitizer so that the lowest metal-to-ligand charge transfer state was localized on the nonbridging ruthenium(II) ligands, we could reduce the quenching rate constant in one complex by a factor of 700 without changing the bridging ligand. Still, the manganese(II)-ruthenium (III) electrontransfer rate constant was not reduced. Consequently, the modification resulted in a complex with very favorable properties.
|
|
| 4. |
|
|
| 5. |
- Borgström, Magnus, et al.
(författare)
-
Light induced manganese oxidation and long-lived charge separation in a Mn-2(II,II)-Ru-II (bpy)(3)-acceptor triad
- 2005
-
Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 127:49, s. 17504-17515
-
Tidskriftsartikel (refereegranskat)abstract
- The photoinduced electron-transfer reactions in a Mn-2(II.II)-R-II-NDI triad (1) ([Mn-2(bpmp)(OAc)(2)](+), bpmp = 2,6-bis[bis(2-pyridylmethyl)aminomethyl]-4-methyiphenolate and OAc = acetate, R-II = trisbipyridine ruthenium(II), and NDI = naphthalenediimide) have been studied by time-resolved optical and EPR spectroscopy. Complex 1 is the first synthetically linked electron donor-sensitizer-acceptor triad in which a manganese complex plays the role of the donor. EPR spectroscopy was used to directly demonstrate the light induced formation of both products: the oxidized manganese dimer complex (Mn-2(II.III)) and the reduced naphthalenediimide (NDIcenter dot-) acceptor moieties, while optical spectroscopy was used to follow the kinetic evolution of the [Ru(bpy)(3)](2+) intermediate states and the NDIcenter dot- radical in a wide temperature range. The average lifetime of the NDI- radical is ca. 600 mu s at room temperature, which is at least 2 orders of magnitude longer than that for previously reported triads based on a [Ru(bpy)(3)](2+) photosensitizer. At 140 K, this intramolecular recombination was dramatically slowed, displaying a lifetime of 0.1-1 s, which is comparable to many of the naturally occurring charge-separated states in photosynthetic reaction centra. It was found that the long recombination lifetime could be explained by an unusually large reorganization energy (lambda approximate to 2.0 eV), due to a large inner reorganization of the manganese complex. This makes the recombination reaction strongly activated despite the large driving force (-Delta G degrees = 1.07 eV). Thus, the intrinsic properties of the manganese complex are favorable for creating a long-lived charge separation in the "Marcus normal region" also when the charge separated state energy is high.
|
|
| 6. |
- Ekström, Jesper, et al.
(författare)
-
Bio-inspired, side-on attachment of a ruthenium photosensitizer to an iron hydrogenase active site model
- 2006
-
Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; :38, s. 4599-4606
-
Tidskriftsartikel (refereegranskat)abstract
- The first ruthenium - diiron complex [(mu- pdt) Fe-2(CO)(5){PPh2(C(6)H(4)CCbpy)} Ru(bpy)(2)](2+) 1 (pdt = propyldithiolate, bpy = 2,2'-bipyridine) is described in which the photoactive ruthenium trisbipyridyl unit is linked to a model of the iron hydrogenase active site by a ligand directly attached to one of the iron centers. Electrochemical and photophysical studies show that the light-induced MLCT excited state of the title complex is localized towards the potential diiron acceptor unit. However, the relatively mild potential required for the reduction of the acetylenic bipyridine together with the easily oxidized diiron portion leads to a reductive quenching of the excited state, instead. This process results in a transiently oxidized diiron unit which may explain the surprisingly high light sensitivity of complex 1.
|
|
| 7. |
|
|
| 8. |
- Hammarstrom, L, et al.
(författare)
-
Artificial photosynthesis: towards functional mimics of photosystem II?
- 1998
-
Ingår i: BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS. - : ELSEVIER SCIENCE BV. - 0005-2728. ; 1365:1-2, s. 193-199
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- This paper describes the initial development of a project aiming at the construction of functional mimics of the oxygen-evolving complex of photosystem II, coupled to photoinduced charge separation. Biomimetic electron donors, manganese complexes and tyro
|
|
| 9. |
- HAMMARSTROM, Leif, 1964-, et al.
(författare)
-
MECHANISMS OF TRANSMEMBRANE ELECTRON-TRANSFER - DIFFUSION OF UNCHARGED REDOX FORMS OF VIOLOGEN, 4,4'-BIPYRIDINE, AND NICOTINAMIDE WITH LONG ALKYL CHAINS
- 1993
-
Ingår i: JOURNAL OF PHYSICAL CHEMISTRY. - : American Chemical Society (ACS). - 0022-3654 .- 1541-5740. ; 97:39, s. 10083-10091
-
Tidskriftsartikel (refereegranskat)abstract
- Transmembrane electron transfer in lecithin (phosphatidylcholine) vesicles was studied by pulse radiolysis. Upon reduction, cetylmethylviologen (N-hexadecyl-N'-methyl-4,4'-bipyridinium CMV), cetylbipyridine (4-(N-hexadecylpyridinium-4-yl)pyridine, CB), and cetylnicotinamide (N-hexadecyl-3-(aminocarbonyl)pyridinium, CNA) transferred electrons from the bulk water phase to Fe(CN)63- in the internal water phase of the vesicles. The transmembrane electron transfer was found in all cases to proceed through diffusion of uncharged forms of the redox mediators (CMV0, CB0, and CNA0, respectively) but the kinetic behavior varied considerably. The mechanisms for CB and CNA were simple, the reaction following first-order kinetics, and the transmembrane diffusion was rate limiting (k = (1.5 +/- 0.3) x 10(3) S-1 for CB and k = 3.2 +/- 0.5 s-1 for CNA). The mechanism for CMV was more complicated, and the reaction followed second-order kinetics. The rate-determining step was proposed to be the disproportionation of two viologen radicals formed by the radiation pulse (2CMV+ double-line arrow pointing left and right CMV0 + CMV2+), followed by rapid transmembrane diffusion of CMVO and its subsequent reoxidation by Fe(CN)63-. In pulse radiolysis, and in phosphorescence quenching experiments with Pt2(P2O5)4H84-, CB0 and CB+ were used as models in order to obtain the rates of transmembrane diffusion of CMV0 and CMV+, respectively. Our results exclude the possibility of electron tunneling between viologens on opposite sides of the membrane, and they provide strong arguments against transmembrane diffusion of viologen radical (CMV+).
|
|
| 10. |
- Hammarstrom, L, et al.
(författare)
-
Mimicking photosystem II reactions in artificial photosynthesis
- 1999
-
Ingår i: ZEITSCHRIFT FUR PHYSIKALISCHE CHEMIE-INTERNATIONAL JOURNAL OF RESEARCH IN PHYSICAL CHEMISTRY & CHEMICAL PHYSICS. - : R OLDENBOURG VERLAG. - 0942-9352. ; 213, s. 157-163
-
Tidskriftsartikel (refereegranskat)abstract
- The paper describes a project aiming at the construction of functional mimics of the oxygen evolving complex of Photosystem II, coupled to photoinduced charge separation. Biomimetic electron donors - manganese complexes and tyrosine - have been linked to
|
|
