| 1. |
- Aster, Alexander, et al.
(författare)
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Metal vs. ligand protonation and the alleged proton-shuttling role of the azadithiolate ligand in catalytic H-2 formation with FeFe hydrogenase model complexes
- 2019
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Ingår i: Chemical Science. - : Royal Society of Chemistry. - 2041-6520 .- 2041-6539. ; 10:21, s. 5582-5588
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Tidskriftsartikel (refereegranskat)abstract
- Electron and proton transfer reactions of diiron complexes [Fe(2)adt(CO)(6)] (1) and [Fe(2)adt(CO)(4)(PMe3)(2)] (4), with the biomimetic azadithiolate (adt) bridging ligand, have been investigated by real-time IR- and UV-vis-spectroscopic observation to elucidate the role of the adt-N as a potential proton shuttle in catalytic H-2 formation. Protonation of the one-electron reduced complex, 1(-), occurs on the adt-N yielding 1H and the same species is obtained by one-electron reduction of 1H(+). The preference for ligand vs. metal protonation in the Fe-2(i,0) state is presumably kinetic but no evidence for tautomerization of 1H to the hydride 1Hy was observed. This shows that the adt ligand does not work as a proton relay in the formation of hydride intermediates in the reduced catalyst. A hydride intermediate 1HHy(+) is formed only by protonation of 1H with stronger acid. Adt protonation results in reduction of the catalyst at much less negative potential, but subsequent protonation of the metal centers is not slowed down, as would be expected according to the decrease in basicity. Thus, the adtH(+) complex retains a high turnover frequency at the lowered overpotential. Instead of proton shuttling, we propose that this gain in catalytic performance compared to the propyldithiolate analogue might be rationalized in terms of lower reorganization energy for hydride formation with bulk acid upon adt protonation.
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| 2. |
- Esmieu, Charlène, et al.
(författare)
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Characterization of a monocyanide model of FeFe hydrogenases - highlighting the importance of the bridgehead nitrogen for catalysis
- 2016
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; 45:48, s. 19242-19248
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Tidskriftsartikel (refereegranskat)abstract
- An azadithiolate bridged monocyanide derivative [Fe-2(adt)(CO)(5)(CN)](-) of [Fe-2(adt)(CO)(4)(CN)(2)](2-) has been prepared and extensively characterized as a model of the [FeFe]-hydrogenase active site, using a combination of FTIR spectroscopy, electrochemical methods and catalytic assays with chemical reductants. The presence of two basic nitrogen sites opens up multiple protonation pathways, enabling catalytic proton reduction. To our knowledge [Fe-2(adt)(CO)(5)(CN)](-) represents the first example of a cyanide containing [FeFe]-hydrogenase active site mimic capable of catalytic H-2 formation in aqueous media.
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| 3. |
- Esmieu, Charlène, et al.
(författare)
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From protein engineering to artificial enzymes - biological and biomimetic approaches towards sustainable hydrogen production
- 2018
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Ingår i: Sustainable Energy & Fuels. - : ROYAL SOC CHEMISTRY. - 2398-4902. ; 2:4, s. 724-750
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Forskningsöversikt (refereegranskat)abstract
- Hydrogen gas is used extensively in industry today and is often put forward as a suitable energy carrier due its high energy density. Currently, the main source of molecular hydrogen is fossil fuels via steam reforming. Consequently, novel production methods are required to improve the sustainability of hydrogen gas for industrial processes, as well as paving the way for its implementation as a future solar fuel. Nature has already developed an elaborate hydrogen economy, where the production and consumption of hydrogen gas is catalysed by hydrogenase enzymes. In this review we summarize efforts on engineering and optimizing these enzymes for biological hydrogen gas production, with an emphasis on their inorganic cofactors. Moreover, we will describe how our understanding of these enzymes has been applied for the preparation of bio-inspired/-mimetic systems for efficient and sustainable hydrogen production.
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| 4. |
- Esmieu, Charlene, et al.
(författare)
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Synthesis of a miniaturized [FeFe] hydrogenase model system
- 2019
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Ingår i: Dalton Transactions. - : ROYAL SOC CHEMISTRY. - 1477-9226 .- 1477-9234. ; 48:7, s. 2280-2284
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Tidskriftsartikel (refereegranskat)abstract
- The reaction occurring during artificial maturation of [FeFe] hydrogenase has been recreated using molecular systems. The formation of a miniaturized [FeFe] hydrogenase model system, generated through the combination of a [4Fe4S] cluster binding oligopeptide and an organometallic Fe complex, has been monitored by a range of spectroscopic techniques. A structure of the final assembly is suggested based on EPR and FTIR spectroscopy in combination with DFT calculations. The capacity of this novel H-cluster model to catalyze H-2 production in aqueous media at mild potentials is verified in chemical assays.
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| 5. |
- Khanna, Namita, et al.
(författare)
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In vivo activation of an [FeFe] hydrogenase using synthetic cofactors
- 2017
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Ingår i: Energy & Environmental Science. - : Royal Society of Chemistry (RSC). - 1754-5692 .- 1754-5706. ; 10:7, s. 1563-1567
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Tidskriftsartikel (refereegranskat)abstract
- [FeFe] hydrogenases catalyze the reduction of protons, and oxidation of hydrogen gas, with remarkable efficiency. The reaction occurs at the H-cluster, which contains an organometallic [2Fe] subsite. The unique nature of the [2Fe] subsite makes it dependent on a specific set of maturation enzymes for its biosynthesis and incorporation into the apo-enzyme. Herein we report on how this can be circumvented, and the apo-enzyme activated in vivo by synthetic active site analogues taken up by the living cell.
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| 6. |
- Meszaros, Livia S., et al.
(författare)
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InVivo EPR Characterization of Semi-Synthetic [FeFe] Hydrogenases
- 2018
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Ingår i: Angewandte Chemie International Edition. - : WILEY-V C H VERLAG GMBH. - 1433-7851 .- 1521-3773. ; 57:10, s. 2596-2599
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Tidskriftsartikel (refereegranskat)abstract
- EPR spectroscopy reveals the formation of two different semi-synthetic hydrogenases invivo. [FeFe] hydrogenases are metalloenzymes that catalyze the interconversion of molecular hydrogen and protons. The reaction is catalyzed by the H-cluster, consisting of a canonical iron-sulfur cluster and an organometallic [2Fe] subsite. It was recently shown that the enzyme can be reconstituted with synthetic cofactors mimicking the composition of the [2Fe] subsite, resulting in semi-synthetic hydrogenases. Herein, we employ EPR spectroscopy to monitor the formation of two such semi-synthetic enzymes in whole cells. The study provides the first spectroscopic characterization of semi-synthetic hydrogenases invivo, and the observation of two different oxidized states of the H-cluster under intracellular conditions. Moreover, these findings underscore how synthetic chemistry can be a powerful tool for manipulation and examination of the hydrogenase enzyme under invivo conditions.
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| 7. |
- Nemeth, Brigitta, et al.
(författare)
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Monitoring H-cluster assembly using a semi-synthetic HydF protein
- 2019
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Ingår i: Dalton Transactions. - : ROYAL SOC CHEMISTRY. - 1477-9226 .- 1477-9234. ; 48:18, s. 5978-5986
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Tidskriftsartikel (refereegranskat)abstract
- The [FeFe] hydrogenase enzyme interconverts protons and molecular hydrogen with remarkable efficiency. The reaction is catalysed by a unique metallo-cofactor denoted as the H-cluster containing an organometallic dinuclear Fe component, the [2Fe] subsite. The HydF protein delivers a precursor of the [2Fe] subsite to the apo-[FeFe] hydrogenase, thus completing the H-cluster and activating the enzyme. Herein we generate a semi-synthetic form of HydF by loading it with a synthetic low valent dinuclear Fe complex. We show that this semi-synthetic protein is practically indistinguishable from the native protein, and utilize this form of HydF to explore the mechanism of H-cluster assembly. More specifically, we show that transfer of the precatalyst from HydF to the hydrogenase enzyme results in the release of CO, underscoring that the pre-catalyst is a four CO species when bound to HydF. Moreover, we propose that an electron transfer reaction occurs during H-cluster assembly, resulting in an oxidation of the [2Fe] subsite with concomitant reduction of the [4Fe4S] cluster present on the HydF protein.
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| 8. |
- Queyriaux, Nicolas, et al.
(författare)
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Electrochemical, Spectroscopic, and Computational Investigation of a Series of Polypyridyl Ruthenium(II) Complexes : Characterization of Reduced States
- 2021
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Ingår i: European Journal of Inorganic Chemistry. - : John Wiley & Sons. - 1434-1948 .- 1099-1948 .- 1099-0682. ; 2021:13, s. 1263-1270
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Tidskriftsartikel (refereegranskat)abstract
- A series of polypyridyl ruthenium(II) complexes has been synthesized and characterized by H-1-NMR, electronic absorption and voltammetric techniques. Among this series, hexafluorophosphate salts of eight ruthenium(II) complexes were newly prepared. Due to the well-known ability of this class of compounds to assist electro- and photocatalytic reductive processes (such as the reduction of CO2, H+ and NAD(P)(+) models), particular attention has been paid to investigate the nature of their one- and two-electron reduced species through computational and spectroscopic techniques.
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| 9. |
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| 10. |
- Wang, Vincent Cho-Chien, et al.
(författare)
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The reactivity of molecular oxygen and reactive oxygen species with [FeFe] hydrogenase biomimetics : reversibility and the role of the second coordination sphere
- 2020
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Ingår i: Dalton Transactions. - : ROYAL SOC CHEMISTRY. - 1477-9226 .- 1477-9234. ; 49:3, s. 858-865
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Tidskriftsartikel (refereegranskat)abstract
- The development of oxygen-tolerant H-2-evolving catalysts plays a vital role for a future H-2 economy. For example, the [FeFe] hydrogenase enzymes are excellent catalyst for H-2 evolution but rapidly become inactivated in the presence of O-2. The mechanistic details of the enzyme's inactivation by molecular oxygen still remain unclear. Here, two H-2-evolving diiron complexes [Fe-2(mu-SCH2NHCH2S)(CO)(6)] (1(adt)) and [Fe-2(mu-SCH2CH2CH2S)(CO)(6)] (2(pdt)), inspired by the active site of [FeFe] hydrogenase, were investigated for their reactivity with molecular oxygen and reactive oxygen species. A one-electron reduced and oxygenated 1(adt) species was identified and characterized spectroscopically, which can be directly generated by reacting with molecular oxygen and chemical reductants at room temperature but it is unstable and gradually decomposes. Interestingly, the whole process is reversible and the addition of protons can facilitate the deoxygenation process and prevent further degradation at room temperature. This new identification of intermediate species serves as a model for studying the reversible inactivation and degradation of oxygen-sensitive [FeFe] hydrogenases by O-2, and provides chemical precedence for such processes. In comparison, the complex lacking the nitrogen bridgehead, 2(pdt), exhibits reduced reactivity towards O-2 in the presence of reductants, highlighting that the importance of the second coordination sphere on modulating the oxygenation processes. These results provide new directions to design molecular electrocatalysts for proton reduction operated at ambient conditions and the re-engineering of [FeFe] hydrogenases for improving oxygen tolerance.
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| 11. |
- Wegelius, Adam, et al.
(författare)
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Generation of a functional, semisynthetic [FeFe]-hydrogenase in a photosynthetic microorganism
- 2018
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Ingår i: Energy & Environmental Science. - : Royal Society of Chemistry (RSC). - 1754-5692 .- 1754-5706. ; 11:11, s. 3163-3167
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Tidskriftsartikel (refereegranskat)abstract
- [FeFe]-Hydrogenases are hydrogen producing metalloenzymes with excellent catalytic capacities, highly relevant in the context of a future hydrogen economy. Here we demonstrate the synthetic activation of a heterologously expressed [FeFe]-hydrogenase in living cells of Synechocystis PCC 6803, a photoautotrophic microbial chassis with high potential for biotechnological energy applications. H-2-Evolution assays clearly show that the non-native, semi-synthetic enzyme links to the native metabolism in living cells.
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