| 1. |
- Liu, T. B., et al.
(författare)
-
Synthesis, structures and electrochemical properties of nitro- and amino-functionalized diiron azadithiolates as active site models of Fe-only hydrogenases
- 2004
-
Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 10:18, s. 4474-4479
-
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.
|
|
| 2. |
- Borgstrom, M., et al.
(författare)
-
Electron donor-acceptor dyads and triads based on tris(bipyridine)ruthenium(II) and benzoquinone : Synthesis, characterization, and photoinduced electron transfer reactions
- 2003
-
Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 42:17, s. 5173-5184
-
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.
|
|
| 3. |
- Gao, W. M., et al.
(författare)
-
Synthesis, structures and electrochemical properties of amino-derivatives of diiron azadithiolates as active site models of Fe-only hydrogenase
- 2006
-
Ingår i: Inorganica Chimica Acta. - : Elsevier BV. - 0020-1693 .- 1873-3255. ; 359:4, s. 1071-1080
-
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.
|
|
| 4. |
- 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.
|
|
| 5. |
|
|
| 6. |
- 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.
|
|
| 7. |
|
|
| 8. |
- Berg, K. E., et al.
(författare)
-
Covalently linked ruthenium(II)-manganese(II) complexes : Distance dependence of quenching and electron transfer
- 2001
-
Ingår i: European Journal of Inorganic Chemistry. - 1434-1948 .- 1099-1948. ; 2001:4, s. 1019-1029
-
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.
|
|
| 9. |
- 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.
|
|
| 10. |
|
|
| 11. |
- 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.
|
|
| 12. |
- Hammarstrom, L., et al.
(författare)
-
A biomimetic approach to artificial photosynthesis : Ru(II)-polypyridine photo-sensitisers linked to tyrosine and manganese electron donors
- 2001
-
Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - 1386-1425 .- 1873-3557. ; 57:11, s. 2145-2160
-
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.
|
|
| 13. |
|
|
| 14. |
- 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
|
|
| 15. |
- 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+).
|
|
| 16. |
- Hammarstrom, L., et al.
(författare)
-
Mimicking photosystem II reactions in artificial photosynthesis : Ru(II)-polypyridine photosensitisers linked to tyrosine and manganese electron donors
- 2000
-
Ingår i: Catalysis Today. - 0920-5861 .- 1873-4308. ; 58:03-feb, s. 57-69
-
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,
|
|
| 17. |
- 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
|
|
| 18. |
|
|
| 19. |
|
|
| 20. |
|
|
| 21. |
- He, J. J., et al.
(författare)
-
Phthalocyanine-sensitized nanostructured TiO2 electrodes prepared by a novel anchoring method
- 2001
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 17:9, s. 2743-2747
-
Tidskriftsartikel (refereegranskat)abstract
- A novel method for anchoring phthalocyanines substituted with ester groups onto nanostructured TiO2 films is described. Such phthalocyanines did not adsorb on nanostructured TiO2 film by the ordinary methods. In our new method, the TiO2 film is pretreated with (CH3)(3)COLi to change the surface hydroxyl groups (-OH) into oxygen anions (-O-), thus making the surface more reactive toward the ester functionalities of the dye. The dye can then be anchored onto the semiconductor surface through the produced carboxylate group(s). The amount of anchored dye on the semiconductor shows a dependence on both the time of base treatment and the time of dye treatment. Electrodes treated with the free base phthalocyanine and zinc phthalocyanine were characterized by absorption spectroscopy, photocurrent action spectroscopy, and photocurrent-photovoltage measurements. The homogeneous blue-green color and the absorption bands in the far-red region are indicative of an attachment of the dye on TiO2 film. A monochromatic incident photo-to-current conversion efficiency of 4.3 % was achieved at 690 nm for a cell where the base-treated electrode was treated with ZnPcBu.
|
|
| 22. |
- He, Jianjun, et al.
(författare)
-
Modified phthalocyanines for efficient near-IR sensitization of nanostructured TiO2 electrode
- 2002
-
Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 124:17, s. 4922-4932
-
Tidskriftsartikel (refereegranskat)abstract
- A zinc phthalocyanine with tyrosine substituents (ZnPcTyr), modified for efficient far-red/near-IR performance in dye-sensitized nanostructured TiO2 solar cells, and its reference, glycine-substituted zinc phthalocyanine, (ZnPcGly), were synthesized and characterized. The compounds were studied spectroscopically, electrochemically, and photoelectrochemically. Incorporating tyrosine groups into phthalocyanine makes the dye ethanol-soluble and reduces surface aggregation as a result of steric effects. The performance of a solar cell based on ZnPcTyr is much better than that based on ZnPcGly. Addition of 3alpha,7alpha-dihydroxy-5beta-cholic acid (cheno) and 4-tert-butylpyridine (TBP) to the dye solution when preparing a dye-sensitized TiO2 electrode diminishes significantly the surface aggregation and, therefore, improves the performance of solar cells based on these phthalocyanines. The highest monochromatic incident photo-to-current conversion efficiency (IPCE) of similar to24% at 690 nm and an overall conversion efficiency (eta) of 0.54% were achieved for a cell based on a ZnPcTyr-sensitized TiO2 electrode. Addition of TBP in the electrolyte decreases the IPCE and eta considerably, although it increases the open-circuit photovoltage. Time-resolved transient absorption measurements of interfacial electron-transfer kinetics in a ZnPoTyr-sensitized nanostructured 702 thin film show that electron injection from the excited state of the dye into the conduction band of TiO2 is completed in similar to500 fs and that more than half of the injected electrons recombines with the oxidized dye molecules in similar to300 ps. In addition to surface aggregation, the very fast electron recombination is most likely responsible for the low performance of the solar cell based on ZnPcTyr.
|
|
| 23. |
|
|
| 24. |
- Johansson, A., et al.
(författare)
-
Synthesis and photophysics of one mononuclear Mn(III) and one dinuclear Mn(III,III) complex covalently linked to a ruthenium(II) tris(bipyridyl) complex
- 2003
-
Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 42, s. 7502-7511
-
Tidskriftsartikel (refereegranskat)abstract
- The preparation of donor (D)-photosensitizer (S) arrays, consisting of a manganese complex as D and a ruthenium tris(bipyridyl) complex as S has been pursued. Two new ruthenium complexes containing coordinating sites for one (2a) and two manganese ions (3a) were prepared in order to provide models for the donor side of photosystem II in green plants. The manganese coordinating site consists of bridging and terminal phenolate as well as terminal pyridyl ligands. The corresponding ruthenium-manganese complexes, a manganese monomer 2b and dimer 3b, were obtained. For the dimer 3b, our data suggest that intramolecular electron transfer from manganese to photogenerated ruthenium(III) is fast, k(ET) > 5 x 10(7) s(-1).
|
|
| 25. |
- Johansson, O., et al.
(författare)
-
Electron donor-acceptor dyads based on ruthenium(II) bipyridine and terpyridine complexes bound to naphthalenediimide
- 2003
-
Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 42:9, s. 2908-2918
-
Tidskriftsartikel (refereegranskat)abstract
- Two series of photosensitizer-electron acceptor complexes have been synthesized and fully characterized: ruthenium(11) tris(bipyridine) {[Ru-II(bpy)(2)(bpy-X-NDI)], where X = -CH2-, tolylene, or phenylene, bpy is 2,2'-bipyridine, and NDI is naphthalenediimide} and ruthenium(II) bis(terpyridine) {[Ru-II(Y-tpy)(tpy-X-NDI)], where Y = H or tolyl and X = tolylene or phenylene, and tpy = 2,2':6',2-terpyridine}. The complexes have been studied by cyclic and differential pulse voltammetry and by steady state and time-resolved absorption and emission techniques. Rates for forward and backward electron transfer have been investigated, following photoexcitation of the ruthenium(II) polypyridine moiety. The terpyridine complexes were only marginally affected by the linked diimide unit, and no electron transfer was observed. In the bipyridine complexes we achieved efficient charge separation. For the complexes containing a phenyl link between the ruthenium(II) and diimide moieties, our results suggest a biphasic forward electron-transfer reaction, in which 20% of the charge-separated state was formed via population of the naphthalenediimide triplet state.
|
|
| 26. |
- Johansson, O., et al.
(författare)
-
Intramolecular charge separation in a hydrogen bonded tyrosine-ruthenium(II)-naphthalene diimide triad
- 2004
-
Ingår i: Chemical Communications. - : Royal Society of Chemistry (RSC). - 1359-7345 .- 1364-548X. ; :2, s. 194-195, s. 194-195
-
Tidskriftsartikel (refereegranskat)abstract
- Long-lived charge-separated states in the ns to mus range were observed upon laser flash excitation of a donor-chromophore-acceptor triad based on tris(bipyridine) ruthenium(II) as photosensitizer, naphthalene diimide as acceptor; and a hydrogen bonded phenol as donor.
|
|
| 27. |
- Li, P., et al.
(författare)
-
Influence of tertiary phosphanes on the coordination configurations and electrochemical properties of iron hydrogenase model complexes : Crystal structures of (mu-S2C3H6)Fe-2(CO)(6-n)L-n (L = PMe2Ph, n=1, 2; PPh3 P(OEt)(3), n=1)
- 2005
-
Ingår i: European Journal of Inorganic Chemistry. - : Wiley. - 1434-1948 .- 1099-1948 .- 1099-0682. ; :12, s. 2506-2513
-
Tidskriftsartikel (refereegranskat)abstract
- A series of mono- and disubstituted diiron complexes [(mu-pdt)-Fe-2(CO)(5)L] [pdt = 1,3-propanedithiolato; L = PMe3 (2), PMe2Ph (3), PPh3 (4), P(OEt)(3) (5)] and [(mu-pdt)Fe-2(CO)(4)L-2] [L = PMe2Ph (6), PPh3 (7), P(OEt)3 (8)] were prepared as Fe-only hydrogenase-active-site models by controllable CO displacement of [(mu-pdt)Fe-2(CO)(6)] by tertiary phosphanes. The coordination configurations of 3-6 were characterized by X-ray crystallography. Disubstituted diiron complex 6 features an apical/apical coordination mode, instead of the typical transoid basal/basal configuration. The electrochemistry of 2-6 and 8 was studied by cyclic voltammetry to evaluate the effects of different tertiary phosphane ligands on the redox properties of the iron atoms of model complexes.
|
|
| 28. |
- Lomoth, R., et al.
(författare)
-
Synthesis and characterization of a dinuclear manganese(III,III) complex with three phenolate ligands
- 2002
-
Ingår i: European Journal of Inorganic Chemistry. - 1434-1948 .- 1099-1948. ; 2002:11, s. 2965-2974
-
Tidskriftsartikel (refereegranskat)abstract
- A dinuclear manganese complex ([Mn2L(mu-OAc)(2)]PF6) has been synthesized, where L is the trianion of 2,6-bis{[(2-hydroxy-3,5-di- tert-butylbenzyl) (2-pyridylmethyl) amino] methyl)-4-methylphenol, a ligand with three phenolate groups. The two pseudo-octahedrally coordinated Mn ions are bridged via the two bidentate acetate ligands and the 4-methylphenolate group of the ligand. We have characterized the complex with electrochemistry, spectroelectrochemistry and EPR spectroscopy. Electrochemically the Mn-2(III,III) complex undergoes two metal-centered quasi-reversible one-electron reduction steps (E-1/2 = 0.04 and -0.32 V vs. SCE). Reduction to the Mn-2(II,III) state results in transformation into a modified complex with slightly different redox properties. One-electron oxidation (E-1/2 = 0.96 V vs. SCE) affords the Mn-2(III,IV) state while further one-electron oxidation (E-1/2 = 1.13 V vs. SCE) presumably involves ligand oxidation. High valent Mn complexes involving Mn-IV or Mn-V centers are of particular interest as intermediates in catalytic water oxidation. The redox potentials of [Mn2L(mu-OAC)(2)](+) show the expected stabilization of higher manganese oxidation states compared with the related complex, [Mn-2(bpmp)(mu-OAc)(2)](+).
|
|
| 29. |
- Niburg, M., et al.
(författare)
-
A complete sub-system of parallel optical interconnects for telecom applications
- 1996
-
Ingår i: 1996 Proceedings 46th Electronic Components and Technology Conference. ; , s. 259-263
-
Konferensbidrag (refereegranskat)abstract
- Increased throughput and flexibility requirements in large-scale electronic equipment create needs for increased interconnection density capacity and re-configurability. The growing demand for new broadband interactive telecom and computer services is expected to enforce this development, which presents a challenge to traditional electronic interconnection techniques and an opportunity for new optical solutions, provided that the cost of introduction of the optical technology is affordable for both system operators and service users. The authors describe a complete sub-system of parallel optical interconnects (i.e., a total solution including the link itself and the equipment practice supporting the link) which exhibits both cost and performance benefits compared to a pure electrical or a serial optical solution.
|
|
| 30. |
|
|
| 31. |
- Ott, S., et al.
(författare)
-
Model of the iron hydrogenase active site covalently linked to a ruthenium photosensitizer : Synthesis and photophysical properties
- 2004
-
Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 43:15, s. 4683-4692
-
Tidskriftsartikel (refereegranskat)abstract
- A model of the iron hydrogenase active site with the structure [(mu-ADT)Fe-2(CO)(6)] (ADT = azadithiolate (S-CH2-NR-CH2-S), (2: R = 4-bromophenyl, 3: R = 4-iodophenyl)) has been assembled and covalently linked to a [Ru(terpy)(2)](2+) photosensitizer. This trinuclear complex 1 represents one synthetic step toward the realization of our concept of light-driven proton reduction. A rigid phenylacetylene tether has been incorporated as the linking unit in 1 in order to prolong the lifetime of the otherwise short-lived [Ru(terpy)(2)](2+) excited state. The success of this strategy is demonstrated by comparison of the photophysical properties of 1 and of two related ruthenium complexes bearing acetylenic terpyridine ligands, with those of [Ru(terpy)(2)](2+). IR and electrochemical studies reveal that the nitrogen heteroatom of the ADT bridge has a marked influence on the electronic properties of the [Fe-2(CO)(6)] core. Using the Rehm-Weller equation, the driving force for an electron transfer from the photoexcited *[Ru(terpy)(2)](2+) to the diiron site in 1 was calculated to be uphill by 0.59 eV. During the construction of the trinuclear complex 1, n-propylamine has been identified as a decarbonylation agent on the [(mu-ADT)Fe-2(CO)(6)] portion of the supermolecule. Following this procedure, the first azadithiolate-bridged dinuclear iron complex coordinated by a phosphine ligand [(mu-ADT)Fe-2(CO)(5)PPh3] (4, R = 4-bromophenyl) was synthesized.
|
|
| 32. |
|
|
| 33. |
- Pan, Jingxi, et al.
(författare)
-
Stepwise charge separation from a ruthenium-tyrosine complex to a nanocrystalline TiO2 film
- 2004
-
Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 108:34, s. 12904-12910
-
Tidskriftsartikel (refereegranskat)abstract
- A supramolecular complex composed of Ru(II) tris-bipyridine, tyrosine, and dipicolylamine was synthesized and characterized. This complex was attached to TiO2 nanocrystalline films via ester groups at the Ru(II) chromophore, and photoinduced multistep electron transfer was investigated by laser flash photolysis and electron paramagnetic resonance techniques. Following ultrafast electron injection from the metal-ligand charge transfer excited states of Ru(II) to the conduction band of TiO2, fast intramolecular electron transfer from the tyrosine moiety to the photogenerated Ru(III) was observed, characterized by a rate constant of similar to2 x 10(6) s(-1). By comparison of recovery kinetics at the isosbestic point with that of the reference compound lacking the tyrosine, it was found that the intramolecular electron-transfer efficiency is 90%. A hydrogen-bond-promoted electron-transfer mechanism is proposed.
|
|
| 34. |
- Salyi, S., et al.
(författare)
-
Synthesis of an amino-functionalized model of the Fe-only hydrogenase active site
- 2003
-
Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 9:2, s. 557-560
-
Tidskriftsartikel (refereegranskat)abstract
- A dinuclear 2Fe2S mimic 6 of the active site of the Fe-only hydrogenases has been synthesized. Complex 6 contains a free amino group which enables linkage to a protein backbone or to a redox active species for the study of electron transfer processes in proteins or in supramolecular systems. The structures of the complex 6 and its Boc-protected precursor 5 could be verified by X-ray crystallography.
|
|
| 35. |
- Schmitt, H., et al.
(författare)
-
Synthesis, redox properties, and EPR spectroscopy of manganese(III) complexes of the ligand N,N-bis(2-hydroxybenzyl)-N '-2-hdroxybenzylidene-1,2-diaminoethane : Formation of mononuclear, dinuclear, and even higher nuclearity complexes
- 2002
-
Ingår i: Chemistry - A European Journal. - 0947-6539 .- 1521-3765. ; 8:16, s. 3757-3768
-
Tidskriftsartikel (refereegranskat)abstract
- The synthesis and characterization of the title trisphenolate ligand are described. From its reaction with manganese(iii) three complexes were isolated. The crystal structures revealed one pentacoordinate monomer and two similar dimers with different solvents of crystallization. In the dimers the metal ions are hexacoordinate and connected through bridging of two phenolates. A combination of electrochemistry and EPR spectroscopy showed that, in acetonitrile, the isolated batches were all identical and mainly monomeric, indicating that the mononuclear complex is in equilibrium with the dimer and perhaps also with complexes of higher nuclearity, as suggested by the detection of both the trimer and the tetramer by electrospray ionization mass spectrometry (ESI-MS). The successful use of the monomer batch as an epoxidation catalyst indicated that a high-valent manganese-oxo species can be formed, although it is probably short-lived. This is also suggested by EPR studies of the species formed by electrochemical oxidation of the complex. Upon one-electron oxidation, a manganese(iv) species was formed, which was at least partly converted to another species containing a phenoxy radical.
|
|
| 36. |
- Shi, F., et al.
(författare)
-
Synthesis and characterization of two novel high valent dinuclear complexes with a triphenolate ligand bearing functional groups
- 2005
-
Ingår i: Chinese Chemical Letters. - 1001-8417 .- 1878-5964. ; 16:1, s. 89-92
-
Tidskriftsartikel (refereegranskat)abstract
- Two novel high valent complexes [M-2(III, III)L(mu-OAc)(2)](PF6)-P-. (M=Mn, Fe; 9) were prepared, where L was the tri-anion of 2,6-bis{[(2-hydroxy-3-(morpholin-4-yl methyl)-5-tertbutyl benzyl)(pyridyl-2-methyl)amino]methyl}-4-methyl phenol which contained additional phenolic, tert-butyl and morpholin-4-yl methyl groups compared to its parent [Mn-2(II, II)(bpmp) (mu-OAc)(2)](CIO4)-C-. (10). These improvements decreased the difference between the new model and (Mn)(4) cluster (OEC in nature).
|
|
| 37. |
- Sjodin, M., et al.
(författare)
-
Proton-coupled electron transfer from tyrosine in a tyrosine-ruthenium-tris-bipyridine complex : Comparison with Tyrosine(z) oxidation in photosystem II
- 2000
-
Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 122:16, s. 3932-3936
-
Tidskriftsartikel (refereegranskat)abstract
- The pH- and the temperature dependence of the rate constant for electron transfer from tyrosine to ruthenium in Ru(II)(bpy)(2)(4-Me-4'CONH-L-tyrosine etyl ester-2,2'-bpy) 2PF(6) was investigated using flash photolysis. At a pH below the tyrosine pK(a) approximate to 10 the rate constant increased monotonically with pH. This increase was consistent with a concerted electron transfer/deprotonation mechanism. Also indicative of a concerted reaction was the unusually high reorganization energy, 2 eV, extracted from temperature-dependent measurements. Deprotonation of the tyrosine group, at pH > pK(a), resulted in a 100-fold increase in rate constant due to a decreased reorganization energy, lambda = 0.9 eV. Also, the rate constant became independent of pH, In Mn-depleted photosystem II a similar pH dependence has been found for electron transfer from tyrosine(Z) (Tyr(Z)) to the oxidized primary donor P680(+). On the basis of the kinetic similarities we propose that the mechanisms in the two systems are the same, that is, the electron transfer occurs as a concerted proton-coupled electron-transfer reaction, and at pH < 7 the Tyr(Z) proton is released directly to the bulk water.
|
|
| 38. |
|
|
| 39. |
- Sjodin, M., et al.
(författare)
-
The mechanism for proton-coupled electron transfer from tyrosine in a model complex and comparisons with Y-z oxidation in photosystem II
- 2002
-
Ingår i: Philosophical Transactions of the Royal Society of London. Biological Sciences. - : The Royal Society. - 0962-8436 .- 1471-2970. ; 357:1426, s. 1471-1478
-
Tidskriftsartikel (refereegranskat)abstract
- In the water-oxidizing reactions of photosystem II (PSII), a tyrosine residue plays a key part as an intermediate electron-transfer reactant between the primary donor chlorophylls (the pigment P-680) and the water-oxidizing Mn cluster. The tyrosine is deprotonated upon oxidation, and the coupling between the proton reaction and electron transfer is of great mechanistic importance for the understanding of the water-oxidation mechanism. Within a programme on artificial photosynthesis, we have made and studied the proton-coupled tyrosine oxidation in a model system and been able to draw mechanistic conclusions that we use to interpret the analogous reactions in PSII.
|
|
| 40. |
|
|
| 41. |
- Sun, Licheng C., et al.
(författare)
-
Iron hydrogenase active site mimics in supramolecular systems aiming for light-driven hydrogen production
- 2005
-
Ingår i: Coordination chemistry reviews. - : Elsevier BV. - 0010-8545 .- 1873-3840. ; 249:15-16, s. 1653-1663
-
Forskningsöversikt (refereegranskat)abstract
- Models of the iron hydrogenase active site [(mu-DT)Fe-2(CO)(6)] (DT: dithiolate) have been synthesized where the dithiolate co-factor bears a functional group to allow for their incorporation into supramolecular systems. Covalently linked to ruthenium(II) polypyridyl photosensitizers, the resulting ruthenium-diiron complexes represent the first members of a new class of dyads designed to promote the light-driven production of hydrogen. The functionalized diiron complexes have been characterized by X-ray crystallography. The redox properties of all complexes were investigated by cyclic voltammetry and the interactions between the photo-excited ruthenium moiety and the diiron unit in these dyads were evaluated by time-resolved spectroscopy.
|
|
| 42. |
- Sun, Licheng C., et al.
(författare)
-
Towards an artificial model for Photosystem II : a manganese(II,II) dimer covalently linked to ruthenium(II) tris-bipyridine via a tyrosine derivative
- 2000
-
Ingår i: Journal of Inorganic Biochemistry. - 0162-0134 .- 1873-3344. ; 78:1, s. 15-22
-
Tidskriftsartikel (refereegranskat)abstract
- In order to model the individual electron transfer steps from the manganese cluster to the photooxidized sensitizer P-680(+) 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 k(ET)>1.0X10(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.
|
|
| 43. |
- Sun, Licheng C., et al.
(författare)
-
Towards artificial photosynthesis : ruthenium-manganese chemistry for energy production
- 2001
-
Ingår i: Chemical Society Reviews. - : Royal Society of Chemistry (RSC). - 0306-0012 .- 1460-4744. ; 30:1, s. 36-49
-
Forskningsöversikt (refereegranskat)abstract
- The synthesis and characterisation of supramolecular model systems mimicking the light reactions on the donor side of Photosystem II (PSII) in green plants have been reviewed. In these systems, manganese complexes and tyrosine are electron donors, modelling the manganese cluster and tyrosine(Z) in PSII. The donors have been covalently linked to a photosensitizer, a ruthenium(ii) tris-bipyridyl complex, that plays the role of the P-680 chlorophylls in PSII. It has been demonstrated that, in the presence of an external electron acceptor in solution, the model systems can undergo an intermolecular electron transfer from the photoexcited state of Ru-II to an acceptor, followed by an intramolecular electron transfer from the coordinated Mn complexes or the tyrosine unit to the photogenerated Ru-III. This leads to regeneration of the Ru-II and oxidation of the Mn complexes or generation of a tyrosine radical. The process closely mimics the primary reaction steps on the donor side of PSII.
|
|
| 44. |
|
|
| 45. |
|
|
| 46. |
|
|
| 47. |
- Sun, LC, et al.
(författare)
-
Toward solar energy conversion into fuels: Design and synthesis of ruthenium-manganese supramolecular complexes to mimic the function of photosystem II
- 2003
-
Ingår i: ACS Symposium Series. - 0097-6156. ; 852, s. 219-244
-
Forskningsöversikt (refereegranskat)abstract
- To mimic the electron donor side of Photosystem II (PSII), a number of supramolecular model complexes have been designed and synthesized. Ruthenium(II) tris-bipyridyl complexes have been used in most cases as photosensitizers, mimicking the function of P-680 in PSII. As electron donors, monomeric and dimeric manganese complexes and tyrosine have been introduced into the supramolecular systems, modelling the Mn cluster and Tyrosinez respectively in PSII For monomeric manganese complexes, di-, tri- and tetradentate ligands have been linked to a Ruthenium(II) trisbipyridyl type complex; and for dimeric manganese complexes hepta-dentate ligands containing pyridines have been used. Some related ligands, where two pyridines have been replaced by phenolate groups have also been synthesized, in order to get ligands that can stabilize manganese complex in high valence states. Photophysical and photochemical studies showed that the electron transfer rate from monomeric Mn complex to photo-generated Ru(III) was low when Mn-Ru distance was long, while the electron transfer rate was enhanced when the Mn-Ru distance was short. However, the excited state of ruthenium complex was quenched if Mn got close to the Ru, leading to a short lifetime. By synthetically inserting a tyrosine unit between Ru and Mn moieties, quenching of the excited state lifetime of Ru was reduced, and the electron transfer from Mn to Ru(III) was very fast although the Mn-Ru distance was long. These supramolecular Ru-Mn systems are closely modelling the electron donor side of PSII both functionally and structurally. The design and synthesis of these model systems are summarized and discussed in this chapter.
|
|
| 48. |
- Sun, LC, et al.
(författare)
-
Towards artificial photosynthesis: ruthenium-manganese chemistry for energy production
- 2001
-
Ingår i: CHEMICAL SOCIETY REVIEWS. - : ROYAL SOC CHEMISTRY. ; 30:1, s. 36-49 Language: English
-
Recension (övrigt vetenskapligt/konstnärligt)abstract
- The synthesis and characterisation of supramolecular model systems mimicking the light reactions on the donor side of Photosystem II (PSII) in green plants have been reviewed. In these systems, manganese complexes and tyrosine are electron donors, modelli
|
|
| 49. |
|
|
| 50. |
|
|
