| 1. |
- Liu, T. B., et al.
(författare)
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Synthesis, structures and electrochemical properties of nitro- and amino-functionalized diiron azadithiolates as active site models of Fe-only hydrogenases
- 2004
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 10:18, s. 4474-4479
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Tidskriftsartikel (refereegranskat)abstract
- Complex [{(mu-SCH2)(2)N(4-NO2C6H4)}Fe-2(CO)(6)] (4) was prepared by the reaction of the dianionic intermediate [(mu-S)(2)Fe-2(CO)(6)](2-) and N,N-bis(chloromethyl)-4-nitroaniline as a biomimetic model of the active site of Fe-only hydrogenase. The reduction of 4 by Pd-C/H-2 under a neutral condition afforded complex [{(mu-SCH2)(2)N(4-NH2C6H4)}Fe-2(CO)(6)] (5) in 67% yield. Both complexes were characterized by IR, H-1 and C-13 NMR spectroscopy and MS spectrometry. The molecular structure of 4, as determined by X-ray analysis, has a butterfly 2Fe2S core and the aryl group on the bridged-N atom slants to the Fe(2) site. Cyclic voltammograms of 4 and 5 were studied to evaluate their redox properties. It was found that complex 4 catalyzed electrochemical proton reduction in the presence of acetic acid. A plausible mechanism of the electrocatalytic proton reduction is discussed.
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| 2. |
- Borgstrom, M., et al.
(författare)
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Electron donor-acceptor dyads and triads based on tris(bipyridine)ruthenium(II) and benzoquinone : Synthesis, characterization, and photoinduced electron transfer reactions
- 2003
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 42:17, s. 5173-5184
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Tidskriftsartikel (refereegranskat)abstract
- Two electron donor-acceptor triads based on a benzoquinone acceptor linked to a light absorbing [Ru(bpy)(3)](2+) complex have been synthesized. In triad 6 (denoted Ru-II-BQ-Co-III), a [Co(bpy)(3)](3+) complex, a potential secondary acceptor, was linked to the quinone. In the other triad, 8 (denoted PTZ-Ru-II-BQ), a phenothiazine donor was linked to the ruthenium moiety. The corresponding dyads Ru-II-BQ (4) and PTZ-Ru-II (9) were prepared for comparison. Upon light excitation in the visible band of the ruthenium moiety, electron transfer to the quinone occurred with a rate constant k(1) = 5 x 10(9) s(-1) (tau(1) = 200 ps) in all the quinone containing complexes. Recombination to the ground state followed, with a rate constant k(b) similar to 4.5 x 10(8) s(-1) (tau(b) similar to 2.2 ns), for both Ru-II-BQ and Ru-II-BQ-Co-III with no indication of a charge shift to generate the reduced Coll moiety. In the PTZ-Ru-II-BQ triad, however, the initial charge separation was followed by a rapid (k > 5 x 10(9) s(-1)) electron transfer from the phenothiazine moiety to give the fairly long-lived PTZ(.+)-Ru-II-BQ(.-) state (tau = 80 ns) in unusually high yield for a [Ru(bPY)(3)](2+)- based triad (> 90%), that lies at DeltaGdegrees = 1.32 eV relative to the ground state. Unfortunately, this triad turned out to be rather photolabile. Interestingly, coupling between the oxidized PTZ(.+) and the BQ(.-) moieties seemed to occur. This discouraged further extension to incorporate more redox active units. Finally, in the dyad PTZ-Ru-II a reversible, near isoergonic electron transfer was observed on excitation. Thus, a quasiequilibrium was established with an observed time constant of 7 ns, with ca. 82% of the population in the PTZ-Ru-*(II) state and 18% in the PTZ(.+)Ru(II)(bpy(.-)) state. These states decayed in parallel with an observed lifetime of 90 ns. The initial electron transfer to form the PTZ(.+)-Ru-II(bpy(.-)) state was thus faster than what would have been inferred from the Ru-*(II) emission decay (tau = 90 ns). This result suggests that reports for related PTZ-Ru-II and PTZ-Ru-II-acceptor complexes in the literature might need to be reconsidered.
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| 3. |
- Gao, W. M., et al.
(författare)
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Synthesis, structures and electrochemical properties of amino-derivatives of diiron azadithiolates as active site models of Fe-only hydrogenase
- 2006
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Ingår i: Inorganica Chimica Acta. - : Elsevier BV. - 0020-1693 .- 1873-3255. ; 359:4, s. 1071-1080
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Tidskriftsartikel (refereegranskat)abstract
- The preparation and characterization of two novel amino-incorporated sulfur-bridged dinuclear iron (I) complexes of the type [NR(mu-SCH2)2]Fe-2(CO)(6), one being amino protected [N(CH2CH2NHTs)(mu-SCH2)(2)]Fe-2(CO)(6) (8) and the other [(mu-SCH2)(2)Fe-2(-CO)(6)NCH2CH2N (mu-SCH2)(2)]Fe-2(CO)(6) (9) are described. These two complexes are readily prepared in a S(N)2 manner between double lithium anion and bis(chloromethyl) amine derivatives. The structures of 8 and 9 were characterized by IR, H-1, C-13 NMR, MS and HRMS spectra and further determined by X-ray analyses. Protonation of complex 8 gave the mono N-protonated product, while for 9 the protonation occurred in both of the N atoms. The redox properties were evaluated by cyclic voltammograms. It was shown that these two complexes can catalyze electrochemical reduction of proton to molecular hydrogen.
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| 4. |
- Huang, Ping, et al.
(författare)
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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
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Ingår i: Journal of Inorganic Biochemistry. - 0162-0134 .- 1873-3344. ; 91:1, s. 159-172
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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.
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| 5. |
- Abrahamsson, M. L. A., et al.
(författare)
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Ruthenium-manganese complexes for artificial photosynthesis : Factors controlling intramolecular electron transfer and excited-state quenching reactions
- 2002
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 41:6, s. 1534-1544
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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.
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| 6. |
- Berg, K. E., et al.
(författare)
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Covalently linked ruthenium(II)-manganese(II) complexes : Distance dependence of quenching and electron transfer
- 2001
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Ingår i: European Journal of Inorganic Chemistry. - 1434-1948 .- 1099-1948. ; 2001:4, s. 1019-1029
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Tidskriftsartikel (refereegranskat)abstract
- Continuing our development of artificial models for photosystem II in green plants, a series of compounds have been prepared in which a RU(bpy)(3)(2+) photosensitizer is covalently Linked to a manganese(II) electron donor. In addition to a trispicolylamine Ligand, two other manganese Ligands, dipicolylamine and aminodiacetic acid, have been introduced in order to study Ligands that are appropriate for the construction of manganese dimers with open coordination sites for the binding of water. Coordination equilibria of the manganese ions were monitored by EPR. The interactions between the ruthenium and manganese moieties were probed by flash photolysis, cyclic voltammetry and steady-state and time-resolved emission measurements. The quenching of the Ru-II excited state by Mn-II was found to be rapid in complexes with short Ru-Mn distances. Nevertheless, each Run species could be photo-oxidized by bimolecular quenching with methylviologen, and the subsequent electron transfer from Mn-II to Ru-III could be monitored.
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| 7. |
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| 8. |
- Ekström, Jesper, et al.
(författare)
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Bio-inspired, side-on attachment of a ruthenium photosensitizer to an iron hydrogenase active site model
- 2006
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; :38, s. 4599-4606
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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.
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| 9. |
- Hammarstrom, L., et al.
(författare)
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A biomimetic approach to artificial photosynthesis : Ru(II)-polypyridine photo-sensitisers linked to tyrosine and manganese electron donors
- 2001
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Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - 1386-1425 .- 1873-3557. ; 57:11, s. 2145-2160
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Forskningsöversikt (refereegranskat)abstract
- The paper describes recent advances towards the construction of functional rr mics of the oxygen evolving complex in photosystem II (PSII) that are coupled to photoinduced charge separation. Some key principles of PSII and artificial systems for light-induced charge accumulation are discussed. Systems are described where biomimetic electron donors - manganese complexes and tyrosine - have been linked to a Ru(II)-polypyridine photosensitiser. Oxidation of the donors by intramolecular electron transfer from the photo-oxidised Ru(III) complex has been studied using optical flash photolysis and EPR experiments. A step-wise electron transfer Mn-2(III,III) --> tyrosine --> Ru(III) has been demonstrated, in analogy to the reaction on the donor side of PSII Electron transfer from the tyrosine to Ru(III) was coupled to tyrosine deprotonation. This resulted in a large reorganisation energy and thus a slow reaction rate, unless the tyrosine was hydrogen bonded or already deprotonated. A comparison with analogous reactions in PSH is made. Finally, light-induced oxidation of a manganese dimer linked to a Ru(II)-photosensitiser has been observed. Preliminary results suggest the possibility of photo-oxidising manganese dimers in several steps, which is an important advancement towards water oxidation.
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| 10. |
- Hammarstrom, L., et al.
(författare)
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Mimicking photosystem II reactions in artificial photosynthesis : Ru(II)-polypyridine photosensitisers linked to tyrosine and manganese electron donors
- 2000
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Ingår i: Catalysis Today. - 0920-5861 .- 1873-4308. ; 58:03-feb, s. 57-69
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Tidskriftsartikel (refereegranskat)abstract
- The paper describes a project aiming at constructing functional mimics of the oxygen evolving complex in photosystem II, coupled to photoinduced charge separation. Biomimetic electron donors, manganese complexes and tyrosine, have been linked to a Ru(II)-polypyridine photosensitiser. Oxidation of the donors by intramolecular electron transfer from the photooxidised Ru(III) complex was demonstrated using optical flash photolysis and EPR experiments. A step-wise electron transfer Mn(III,III)-->tyrosine-->Ru(III) was demonstrated, in analogy to the reaction on the donor side of photosystem II. Electron transfer from the tyrosine to Ru(III) was coupled to tyrosine deprotonation. This resulted in a large reorganisation energy and thus a slow reaction rate, unless the tyrosine was hydrogen bonded or already deprotonated. A comparison with analogous reaction in photosystem II is made. Finally, light-induced oxidation of a manganese dimer linked to a Ru(II)-photosensitiser was observed. Preliminary results suggest the possibility of photooxidising manganese dimers in several steps, which is an important step towards water oxidation,
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