| 1. |
- Niklasson, Bo, et al.
(författare)
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Diabetes Prevention Through Antiviral Treatment in Biobreeding Rats
- 2016
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Ingår i: Viral immunology. - : Mary Ann Liebert Inc. - 0882-8245 .- 1557-8976. ; 29:8, s. 452-458
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Tidskriftsartikel (refereegranskat)abstract
- A picornavirus (Ljungan virus) has been associated with diabetes in its wild rodent reservoir and in diabetesprone biobreeding (DP-BB) rats. We attempted to alter the development of diabetes in DP-BB rats using two anti-picornavirus compounds (pleconaril and APO-N039), singly or in combination. Antiviral therapy was initiated 2 weeks before expected onset of diabetes. Pleconaril or APO-N039 alone did not affect the debut of diabetes. However, animals receiving a combination of both compounds were protected for at least the entire period of treatment (4 weeks after expected time of diabetes onset). Immunohistochemistry demonstrated that the presence and distribution of virus antigen in the pancreatic islets coincided with the clinical status of the animal. Data indicate that a treatable picornavirus can be involved in the cellular assault resulting in diabetes and in these cases the disease mechanism appears to involve a virus present in the pancreatic beta cell mass itself.
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| 2. |
- Andersson, Claes-Henrik, et al.
(författare)
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Synthesis and IR Spectroelectrochemical Studies of a [60]Fulleropyrrolidine-(tricarbonyl)chromium Complex : Probing C-60 Redox States by IR Spectroscopy
- 2011
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Ingår i: European Journal of Inorganic Chemistry. - : John Wiley & Sons. - 1434-1948 .- 1099-1948 .- 1099-0682. ; :11, s. 1744-1749
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis of a new fulleropyrrolidine-(tricarbonyl)chromium complex: 1-methyl-2-(4-methoxyphenyl)-3,4-[60]fulleropyrrolidine-(tricarbonyl)chromium is described together with its characterization by IR, NMR and cyclic voltammetry. IR spectro-electrochemistry has been used to probe the redox level of the fullerene derivative via the relative position of the vibrational bands of the CO ligands, which are sensitive to the electronic state of the complex. Other strategies to incorporate a tricarbonylchromium moiety to fullerene C60 are also briefly discussed and evaluated.
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| 3. |
- Artero, Vincent, et al.
(författare)
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From Enzyme Maturation to Synthetic Chemistry : The Case of Hydrogenases
- 2015
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Ingår i: Accounts of Chemical Research. - : American Chemical Society (ACS). - 0001-4842 .- 1520-4898. ; 48:8, s. 2380-2387
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Forskningsöversikt (refereegranskat)abstract
- CONSPECTUS: Water splitting into oxygen and hydrogen is one of the most attractive strategies for storing solar energy and electricity. Because the processes at work are multielectronic, there is a crucial need for efficient and stable catalysts, which in addition have to be cheap for future industrial developments (electrolyzers, photoelectrochemicals, and fuel cells). Specifically for the water/hydrogen interconversion, Nature is an exquisite source of inspiration since this chemistry contributes to the bioenergetic metabolism of a number of living organisms via the activity of fascinating metalloenzymes, the hydrogenases. In this Account, we first briefly describe the structure of the unique dinuclear organometallic active sites of the two classes of hydrogenases as well as the complex protein machineries involved in their biosynthesis, their so-called maturation processes. This knowledge allows for the development of a fruitful bioinspired chemistry approach, which has already led to a number of interesting and original catalysts mimicking the natural active sites. More specifically, we describe our own attempts to prepare artificial hydrogenases. This can be achieved via the standard bioinspired approach using the combination of a synthetic bioinspired catalyst and a polypeptide scaffold. Such hybrid complexes provide the opportunity to optimize the system by manipulating both the catalyst through chemical synthesis and the protein component through mutagenesis. We also raise the possibility to reach such artificial systems via an original strategy based on mimicking the enzyme maturation pathways. This is illustrated in this Account by two examples developed in our laboratory. First, we show how the preparation of a lysozyme-{Mn-I(CO)(3)} hybrid and its clean reaction with a nickel complex led us to generate a new class of binuclear Ni-Mn H-2-evolving catalysts mimicking the active site of [NiFe]-hydrogenases. Then we describe how we were able to rationally design and prepare a hybrid system, displaying remarkable structural similarities to an [FeFe]-hydrogenase, and we show here for the first time that it is catalytically active for proton reduction. This system is based on the combination of HydF, a protein involved in the maturation of [FeFe]-hydrogenase (HydA), and a close mimic of the active site of this class of enzymes. Moreover, the synthetic [Fe-2(adt)(CO)(4)(CN)(2)](2-) (adt(2-) = aza-propanedithiol) mimic, alone or within a HydF hybrid system, was shown to be able to maturate and activate a form of HydA itself lacking its diiron active site. We discuss the exciting perspectives this "synthetic maturation" opens regarding the "invention" of novel hydrogenases by the chemists.
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| 4. |
- 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
-
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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| 5. |
- Bacchi, Marine, et al.
(författare)
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Cobaloxime-Based Artificial Hydrogenases
- 2014
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Ingår i: Inorganic Chemistry. - : American Chemical Society. - 0020-1669 .- 1520-510X. ; 53:15, s. 8071-8082
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Tidskriftsartikel (refereegranskat)abstract
- Cobaloximes are popular H2 evolution molecular catalysts but have so far mainly been studied in nonaqueous conditions. We show here that they are also valuable for the design of artificial hydrogenases for application in neutral aqueous solutions and report on the preparation of two well-defined biohybrid species via the binding of two cobaloxime moieties, {Co(dmgH)2} and {Co(dmgBF2)2} (dmgH2 = dimethylglyoxime), to apo Sperm-whale myoglobin (SwMb). All spectroscopic data confirm that the cobaloxime moieties are inserted within the binding pocket of the SwMb protein and are coordinated to a histidine residue in the axial position of the cobalt complex, resulting in thermodynamically stable complexes. Quantum chemical/molecular mechanical docking calculations indicated a coordination preference for His93 over the other histidine residue (His64) present in the vicinity. Interestingly, the redox activity of the cobalt centers is retained in both biohybrids, which provides them with the catalytic activity for H2 evolution in near-neutral aqueous conditions.
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| 6. |
- Beckmann, K., et al.
(författare)
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Formation of stoichiometrically O-18-labelled oxygen from the oxidation of O-18-enriched water mediated by a dinuclear manganese complex : a mass spectrometry and EPR study
- 2008
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Ingår i: Energy & Environmental Science. - : Royal Society of Chemistry (RSC). - 1754-5692 .- 1754-5706. ; 1:6, s. 668-676
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Tidskriftsartikel (refereegranskat)abstract
- Oxygen formation was detected for the oxidations of various multinuclear manganese complexes by oxone (HSO5-) in aqueous solution. To determine to what extent water was the source of the evolved O-2, (H2O)-O-18 isotope-labelling experiments coupled with membrane inlet mass spectrometry (MIMS) were carried out. We discovered that during the reaction of oxone with [Mn-2(OAc)(2)(bpmp)](+) (1), stoichiometrically labelled oxygen (O-18(2)) was formed. This is the first example of a homogeneous reaction mediated by a synthetic manganese complex where the addition of a strong chemical oxidant yields O-18(2) with labelling percentages matching the theoretically expected values for the case of both O-atoms originating from water. Experiments using lead acetate as an alternative oxidant supported this finding. A detailed investigation of the reaction by EPR spectroscopy, MIMS and Clark-type oxygen detection enabled us to propose potential reaction pathways.
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| 7. |
- Berggren, Gustav, et al.
(författare)
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15.02 - Hydrogenases and Model Complexes in Bioorganometallic Chemistry
- 2022
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Ingår i: Comprehensive Organometallic Chemistry IV. - Oxford : Elsevier. - 9780323913508 ; , s. 3-40
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Hydrogenases are enzymes involved in H2 metabolism, and provide a blue-print for how efficient H2/H+ interconversion can be achieved utilizing base metals. The societal interest in H2 as a future energy carrier, and a desire for fundamental understanding of how their biologically unique cofactors operate, has promoted intense studies of these enzymes and their related biomimetic analogs. This book chapter provides an overview of both the biochemistry of these fascinating enzymes as well the extensive work related to preparing and characterizing organometallic complexes mimicking their catalytic cofactors.
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| 8. |
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| 9. |
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| 10. |
- Berggren, Gustav, et al.
(författare)
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Biomimetic assembly and activation of [FeFe]-hydrogenases
- 2013
-
Ingår i: Nature. - : Nature Publishing Group, a division of Macmillan Publishers Limited. All Rights Reserved.. - 0028-0836 .- 1476-4687. ; 499:7456, s. 66-69
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Tidskriftsartikel (refereegranskat)
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| 11. |
- Berggren, Gustav, et al.
(författare)
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Compounds with capacity to quench the tyrosyl radical in Pseudomonas aeruginosa ribonucleotide reductase
- 2019
-
Ingår i: Journal of Biological Inorganic Chemistry. - : Springer Science and Business Media LLC. - 0949-8257 .- 1432-1327. ; 24:6, s. 841-848
-
Tidskriftsartikel (refereegranskat)abstract
- Ribonucleotide reductase (RNR) has been extensively probed as a target enzyme in the search for selective antibiotics. Here we report on the mechanism of inhibition of nine compounds, serving as representative examples of three different inhibitor classes previously identified by us to efficiently inhibit RNR. The interaction between the inhibitors and Pseudomonas aeruginosa RNR was elucidated using a combination of electron paramagnetic resonance spectroscopy and thermal shift analysis. All nine inhibitors were found to efficiently quench the tyrosyl radical present in RNR, required for catalysis. Three different mechanisms of radical quenching were identified, and shown to depend on reduction potential of the assay solution and quaternary structure of the protein complex. These results form a good foundation for further development of P. aeruginosa selective antibiotics. Moreover, this study underscores the complex nature of RNR inhibition and the need for detailed spectroscopic studies to unravel the mechanism of RNR inhibitors.
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| 12. |
- Berggren, Gustav, et al.
(författare)
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FTIR Study of Manganese Dimers with Carboxylate Donors As Model Complexes for the Water Oxidation Complex in Photosystem II
- 2012
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 51:4, s. 2332-2337
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Tidskriftsartikel (refereegranskat)abstract
- The carboxylate stretching frequencies of two high-valent, di-mu-oxido bridged, manganese dimers has been studied with IR spectroscopy in three different oxidation states. Both complexes contain one monodentate carboxylate donor to each Mn ion, in one complex, the carboxylate is coordinated perpendicular to the Mn-(mu-O)(2)-Mn plane, and in the other complex, the carboxylate is coordinated in the Mn-(mu-O)(2)-Mn plane. For both complexes, the difference between the asymmetric and the symmetric carboxylate stretching frequen-cies decrease for both the Mn-2(IV,IV) to Mn-2(III,IV) transition and the Mn-2(III,IV) to Mn-2(III,III) transition, with only minor differences observed between the two arrangements of the carboxylate ligand versus the Mn-(mu-O)(2)-Mn plane. The IR spectra also show that both carboxylate ligands are affected for each one electron reduction, i.e., the stretching frequency of the carboxylate coordinated to the Mn ion that is not reduced also shifts. These results are discussed in relation to FTIR studies of changes in carboxylate stretching frequencies in a one electron oxidation step of the water oxidation complex in Photosystem II.
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| 13. |
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| 14. |
- Berggren, Gustav, et al.
(författare)
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Mechanistic Studies on the Water-Oxidizing Reaction of Homogeneous Manganese-Based Catalysts : Isolation and Characterization of a Suggested Catalytic Intermediate
- 2011
-
Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 50:8, s. 3425-3430
-
Tidskriftsartikel (refereegranskat)abstract
- The synthesis, isolation, and characterization of two high-valent manganese dimers with isomeric ligands are reported. The complexes are synthesized and crystallized from solutions of low-valent precursors exposed to tert-butyl hydroperoxide. The crystal structures display centrosymmetric complexesconsisting of Mn2 IV,IV(μ-O)2 cores, with one ligand coordinating to each manganese. The ligands coordinate with the diaminoethane backbone, the carboxylate, and one of the two pyridines, while the second pyridine is noncoordinating. The activity of these complexes, under water oxidation conditions, is discussed in light of a proposed mechanism for water oxidation, in which this type of complexes have been suggested as a key intermediate.
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| 15. |
- Berggren, Gustav, 1980-
(författare)
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Mimicking Nature – Synthesis and Characterisation of Manganese Complexes of Relevance to Artificial Photosynthesis
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The development of efficient catalyst for water oxidation is of paramount importance to artificial photosynthesis, but before this can be achieved a deeper understanding of this reaction is essential. In nature this reaction occurs in a tetranuclear Mn-cluster which serves as the work-horse of oxygenic photosynthesis. This thesis summarises my efforts at developing molecular systems capable of mimicking this complex employing a biomimetic approach. Three different approaches towards this goal are described here-in. The first section describes a screening study, in which a number of manganese complexes were tested to see whether or not they were capable of catalysing the formation of dioxygen when treated with different oxidants (Papers I). For those reactions in which dioxygen formation was observed the reactions were repeated in labelled water and the incorporation of labelled O-atoms was studied by mass spectrometry. This allowed us to determine to what extent water was the source of the evolved dioxygen (Papers II-III). In Chapter three a reported catalyst and a derivative thereof is studied in depth. The influence of changes to the ligand on the oxygen–oxygen bond forming reaction could unfortunately not be reliably addressed, because of the instability of the complexes under “catalytic” conditions. Nevertheless, the study allowed us to revise the “carboxylate shift”-mechanism suggested in the literature (Papers IV-V). Chapter four describes the continuation of my work on ligands featuring the carboxylate ligand motif first introduced in Chapter three. In this study ligands containing multiple binding pockets were designed and synthesised (Paper VI). A better understanding of the mechanism in the natural water oxidising enzyme will facilitate the design of biomimetic complexes, this is discussed in Chapter five. In this work model complexes (Paper VII) are used to study the mechanism by which natures own water oxidising catalyst performs this reaction.
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| 16. |
- Berggren, Gustav, et al.
(författare)
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Semiquinone-Induced Maturation of Bacillus anthracis Ribonucleotide Reductase by a Superoxide Intermediate
- 2014
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Ingår i: Journal of Biological Chemistry.
-
Tidskriftsartikel (refereegranskat)abstract
- Ribonucleotide reductases (RNRs) catalyze the conversion of ribonucleotides to deoxyribonucleotides, and represent the only de novo pathway to provide DNA building blocks. Three different classes of RNR are known, denoted I-III. Class I RNRs are heteromeric proteins built up by α and β subunits and are further divided into different subclasses, partly based on the metal content of the β-subunit. In subclass Ib RNR the β-subunit is denoted NrdF, and harbors a manganese-tyrosyl radical cofactor. The generation of this cofactor is dependent on a flavodoxin-like maturase denoted NrdI, responsible for the formation of an active oxygen species suggested to be either a superoxide or a hydroperoxide. Herein we report on the magnetic properties of the manganese-tyrosyl radical cofactor of Bacillus anthracis NrdF and the redox properties of B. anthracis NrdI. The tyrosyl radical in NrdF is stabilized through its interaction with a ferromagnetically coupled manganese dimer. Moreover, we show through a combination of redox titration and protein electrochemistry that in contrast to hitherto characterized NrdIs, the B. anthracis NrdI is stable in its semiquinone form (NrdIsq) with a difference in electrochemical potential of approximately 110 mV between the hydroquinone and semiquinone state. The under anaerobic conditions stable NrdIsq is fully capable of generating the oxidized, tyrosyl radical-containing form of Mn-NrdF when exposed to oxygen. This latter observation strongly supports that a superoxide radical is involved in the maturation mechanism, and contradicts the participation of a peroxide species. Additionally, EPR spectra on whole cells revealed that a significant fraction of NrdI resides in its semiquinone form in vivo, underscoring that NrdIsq is catalytically relevant.
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| 17. |
- Berggren, Gustav, et al.
(författare)
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Semiquinone-induced Maturation of Bacillus anthracis Ribonucleotide Reductase by a Superoxide Intermediate
- 2014
-
Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 289:46, s. 31940-31949
-
Tidskriftsartikel (refereegranskat)abstract
- Background: Activation of ribonucleotide reductase Ib depends on the flavodoxin-like maturase NrdI.Results: The redox properties of Bacillus anthracis NrdI allow isolation of the semiquinone state, NrdI(sq), which can catalyze formation of the manganese-tyrosyl radical cofactor.Conclusion: The maturation capacity of NrdI(sq) provides evidence that Mn-NrdF is activated via a superoxide radical.Significance: Novel antibiotics may be designed to selectively target the maturation mechanism.
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| 18. |
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| 19. |
- Berggren, Gustav, et al.
(författare)
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Synthesis and characterisation of low valent Mn-complexes as models for Mn-catalases
- 2010
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; 39:45, s. 11035-11044
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Tidskriftsartikel (refereegranskat)abstract
- In this work we report the synthesis of two novel manganese complexes, [L1(3)Mn(6)(II)](ClO4)(6) (1 center dot(ClO4)(6)) and [L2Mn(2)(II)(mu-OAc)(mu-Cl)](ClO4)(2) (2 center dot(ClO4)(2)), where L1(2-) is the 2,2'-(1,3-phenylenebis(methylene))bis-((2-(bis(pyridin-2-ylmethyl)amino)ethyl)azanediyl)diacetic acid anion and L2 is N1,N1'-(1,3-phenylenebis(methylene))bis(N2,N2'-bis(pyridin-2-ylmethyl)ethane-1,2-diamine). The ligands Na(2)L1 and L2 are built on the same backbone, L2 only contains nitrogen donors, while two carboxylate arms have been introduced in Na(2)L1. The two complexes have been characterized by single-crystal X-ray diffraction, magnetic susceptibility, EPR spectroscopy, and electrochemistry. X-Ray crystallography revealed that 1 is a manganese(II) hexamer and 2 is a manganese(II) dimer featuring an unprecedented mono-mu-acetato, mono-mu-chlorido bridging motif. The ability of the complexes to catalyse H2O2 disproportionation, thereby acting as models for manganese catalases, has been investigated and compared to the activity of two other related manganese complexes. The introduction of carboxylate donors in the ligands, leading to increased denticity, resulted in a drop in H2O2 disproportionation activity.
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| 20. |
- Berggren, Gustav, et al.
(författare)
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Synthesis, Characterization and Reactivity Study of a New Penta-Coordinated Mn(II) Complex
- 2009
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Ingår i: Applied Magnetic Resonance. - : Springer Science and Business Media LLC. - 0937-9347 .- 1613-7507. ; 36:1, s. 9-24
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Tidskriftsartikel (refereegranskat)abstract
- A penta-coordinated Mn(II) compound [dqpMnCl2] (1) (dqp = 2,6-di-(8-quinoline-yl)-pyridine) has been synthesized and its X-ray crystallographic structure is reported here. Magnetic susceptibility measurements confirmed a high-spin Mn(II) (S = 5/2) center in 1. The X-band EPR spectrum of 1 in dimethylformamide solution exhibits widely distributed transitions in the spectral range from 0 to 700 mT with particularly well-resolved hyperfine lines due to the 55Mn (I = 5/2) nucleus. The abundance of highly resolved transition lines in the spectrum facilitated the electron paramagnetic resonance spectral simulation which revealed large zero-field splitting and g-anisotropies. When dissolved, 1 exists in equilibrium with a hexa-coordinated species, the latter probably resulting from disassociation of one chlorido-ligand allowing ligation of two solvent molecules. The redox behavior of 1 was studied and was compared to that of a structural analog for which water oxidation in the presence of a chemical oxidant has been shown. The results from water oxidation trials of 1 are discussed
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| 21. |
- Berggren, Gustav, et al.
(författare)
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Tetraethylammonium [12,12-diethyl-2,2,9,9-tetramethyl-1,4,7,10-tetraza-5,6-benzotridecane-3 ,8,11,13-tetraone(4-)]oxidomanganate(V)
- 2007
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Ingår i: Acta Crystallographica Section E. - 1600-5368. ; 63:11, s. M2672-M2673
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Tidskriftsartikel (refereegranskat)abstract
- The Mn-V complex in the title compound, (C8H20N)[ Mn(C21H26N4O4)O], is interesting as it has been suggested that Mn-V oxospecies are intermediates both in epoxidation of alkenes and in water oxidation in PSII, i.e. photosystem II, the protein found in oxygenic photosynthetic organisms, which uses light to split water into O-2, protons and electrons. The Mn atom has a square-pyramidal coordination of four N atoms with an apical O atom. The four N atoms coordinating to Mn [Mn-N = 1.872 (2)-1.882 (2) angstrom] form a plane within 0.03 (3) angstrom from which the Mn ion is displaced by 0.582 (2) angstrom.
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| 22. |
- Berggren, Gustav, et al.
(författare)
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Two tetranuclear Mn-complexes as biomimetic models of the oxygen evolving complex in Photosystem II - A synthesis, characterisation and reactivity study
- 2009
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; 45, s. 10044-10054
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Tidskriftsartikel (refereegranskat)abstract
- In this work we report the preparation of two metallamacrocyclic tetranuclear manganese(II) complexes, [L1(4)Mn(4)](ClO4)(4) and [L2(4)Mn(4)](ClO4)(4) where L1 and L2 are the anions of the heptadentate ligands 2-((2-(bis(pyridin-2-ylmethyl) amino) ethyl)(methyl) amino) acetic acid and 2-(benzyl(2-(bis(pyridin-2-ylmethyl) amino) ethyl) amino) acetic acid), respectively. The complexes have been fully characterized by ESI-MS, elemental analysis, single-crystal X-ray diffraction, magnetic susceptibility, and EPR spectroscopy. Electrochemical reactions as well as reactions with different chemical redox reagents have been performed and a reversible two electron oxidation per manganese ion has been identified. The reaction of [L1(4)Mn(4)](ClO4)(4) with oxone or cerium(IV) results in the evolution of oxygen which makes this system interesting for future studies in the search for a functional mimic of the oxygen evolving complex in Photosystem II.
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| 23. |
- Cabotaje, Princess R., et al.
(författare)
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Probing Substrate Transport Effects on Enzymatic Hydrogen Catalysis : An Alternative Proton Transfer Pathway in Putatively Sensory [FeFe] Hydrogenase
- 2023
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Ingår i: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 13:15, s. 10435-10446
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Tidskriftsartikel (refereegranskat)abstract
- [FeFe] hydrogenases, metalloenzymes catalyzing proton/dihydrogeninterconversion, have attracted intense attention due to their remarkablecatalytic properties and (bio-)technological potential for a futurehydrogen economy. In order to unravel the factors enabling their efficientcatalysis, both their unique organometallic cofactors and proteinstructural features, i.e., "outer-coordination sphere"effects have been intensively studied. These structurally diverseenzymes are divided into distinct phylogenetic groups, denoted asGroup A-D. Prototypical Group A hydrogenases display high turnoverrates (10(4)-10(5) s(-1)).Conversely, the sole characterized Group D representative, Thermoanaerobacter mathranii HydS (TamHydS), shows relatively low catalytic activity (specific activity10(-1) & mu;mol H-2 mg(-1) min(-1)) and has been proposed to serve a H-2-sensory function. The various groups of [FeFe] hydrogenaseshare the same catalytic cofactor, the H-cluster, and the structuralfactors causing the diverging reactivities of Group A and D remainto be elucidated. In the case of the highly active Group A enzymes,a well-defined proton transfer pathway (PTP) has been identified,which shuttles H+ between the enzyme surface and the activesite. In Group D hydrogenases, this conserved pathway is absent. Here,we report on the identification of highly conserved amino acid residuesin Group D hydrogenases that constitute a possible alternative PTP.We varied two proposed key amino acid residues of this pathway (E252and E289, TamHydS numbering) via site-directed mutagenesisand analyzed the resulting variants via biochemical and spectroscopicmethods. All variants displayed significantly decreased H-2-evolution and -oxidation activities. Additionally, the variantsshowed two redox states that were not characterized previously. Thesefindings provide initial evidence that these amino acid residues arecentral to the putative PTP of Group D [FeFe] hydrogenase. Since theidentified residues are highly conserved in Group D exclusively, ourresults support the notion that the PTP is not universal for differentphylogenetic groups in [FeFe] hydrogenases.
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| 24. |
- Cheng, Fangwen, et al.
(författare)
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Embedding biocatalysts in a redox polymer enhances the performance of dye-sensitized photocathodes in bias-free photoelectrochemical water splitting
- 2024
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Ingår i: Nature Communications. - : Springer Nature. - 2041-1723. ; 15:1
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Tidskriftsartikel (refereegranskat)abstract
- Dye-sensitized photoelectrodes consisting of photosensitizers and molecular catalysts with tunable structures and adjustable energy levels are attractive for low-cost and eco-friendly solar-assisted synthesis of energy rich products. Despite these advantages, dye-sensitized NiO photocathodes suffer from severe electron-hole recombination and facile molecule detachment, limiting photocurrent and stability in photoelectrochemical water-splitting devices. In this work, we develop an efficient and robust biohybrid dye-sensitized NiO photocathode, in which the intermolecular charge transfer is enhanced by a redox polymer. Owing to efficient assisted electron transfer from the dye to the catalyst, the biohybrid NiO photocathode showed a satisfactory photocurrent of 141±17 μA·cm−2 at neutral pH at 0 V versus reversible hydrogen electrode and a stable continuous output within 5 h. This photocathode is capable of driving overall water splitting in combination with a bismuth vanadate photoanode, showing distinguished solar-to-hydrogen efficiency among all reported water-splitting devices based on dye-sensitized photocathodes. These findings demonstrate the opportunity of building green biohybrid systems for artificial synthesis of solar fuels.
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| 25. |
- 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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| 26. |
- 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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| 27. |
- Esmieu, Charlene, et al.
(författare)
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Synthesis of a miniaturized [FeFe] hydrogenase model system
- 2019
-
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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| 28. |
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| 29. |
- Fasano, Andrea, et al.
(författare)
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Kinetic Modeling of the Reversible or Irreversible Electrochemical Responses of FeFe-Hydrogenases
- 2024
-
Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 146:2, s. 1455-1466
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Tidskriftsartikel (refereegranskat)abstract
- The enzyme FeFe-hydrogenase catalyzes H2 evolution and oxidation at an active site that consists of a [4Fe-4S] cluster bridged to a [Fe2(CO)3(CN)2(azadithiolate)] subsite. Previous investigations of its mechanism were mostly conducted on a few “prototypical” FeFe-hydrogenases, such as that from Chlamydomonas reinhardtii(Cr HydA1), but atypical hydrogenases have recently been characterized in an effort to explore the diversity of this class of enzymes. We aim at understanding why prototypical hydrogenases are active in either direction of the reaction in response to a small deviation from equilibrium, whereas the homologous enzyme from Thermoanaerobacter mathranii (Tam HydS) shows activity only under conditions of very high driving force, a behavior that was referred to as “irreversible catalysis”. We follow up on previous spectroscopic studies and recent developments in the kinetic modeling of bidirectional reactions to investigate and compare the catalytic cycles of Cr HydA1 and Tam HydS under conditions of direct electron transfer with an electrode. We compare the hypothetical catalytic cycles described in the literature, and we show that the observed changes in catalytic activity as a function of potential, pH, and H2 concentration can be explained with the assumption that the same catalytic mechanism applies. This helps us identify which variations in properties of the catalytic intermediates give rise to the distinct “reversible” or “irreversible” catalytic behaviors.
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| 30. |
- Fasano, Andrea, et al.
(författare)
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Reversible or Irreversible Catalysis of H+/H2 Conversion by FeFe Hydrogenases
- 2021
-
Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 143:48, s. 20320-20325
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Tidskriftsartikel (refereegranskat)abstract
- Studies of molecular catalysts traditionally aim at understanding how a certain mechanism allows the reaction to be fast. A distinct question, which has only recently received attention in the case of bidirectional molecular catalysts, is how much thermodynamic driving force is required to achieve fast catalysis in either direction of the reaction. “Reversible” catalysts are bidirectional catalysts that work either way in response to even a small departure from equilibrium and thus do not waste input free energy as heat; conversely, “irreversible” catalysts require a large driving force to proceed at an appreciable rate [Fourmond et al. Nat. Rev. Chem.2021, 5, 348–360]. Numerous mechanistic rationales for these contrasting behaviors have been proposed. To understand the determinants of catalytic (ir)reversibility, we examined the steady-state, direct electron transfer voltammetry of a particular FeFe hydrogenase, from Thermoanaerobacter mathranii, which is very unusual in that it irreversibly catalyzes H2 oxidation and production: a large overpotential is required for the reaction to proceed in either direction [Land et al. Chem. Sci.2020, 11, 12789–12801]. In contrast to previous hypotheses, we demonstrate that in this particular enzyme catalytic irreversibility can be explained without invoking slow interfacial electron transfer or variations in the mechanism: the observed kinetics is fully consistent with the same catalytic pathway being used in both directions of the reaction.
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| 31. |
- Gamache, Mira T., et al.
(författare)
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E. coli-based semi-artificial photosynthesis : biocompatibility of redox mediators and electron donors in [FeFe] hydrogenase driven hydrogen evolution
- 2023
-
Ingår i: Energy Advances. - : Royal Society of Chemistry. - 2753-1457. ; 2:12, s. 2085-2092
-
Tidskriftsartikel (refereegranskat)abstract
- Semi-artificial photosynthesis aims to harness the power of biocatalysis while breaking away from the limitations of Nature's photosynthetic machinery, by merging artificial light harvesters with enzyme catalysts. However, the artificial photocatalytic components are generally toxic towards the biological components. In this study, we investigate a system wherein Escherichia coli cells, heterologously expressing an [FeFe] hydrogenase, act as hydrogen evolution catalyst in combination with an artificial photosensitizer, sacrificial electron donor, and redox mediator. Previously, the use of artificial components or their reaction products was found to be toxic to E. coli cells. To overcome this challenge, we examined alternative electron donors and redox mediators, achieving turnover numbers (TON, 39.6 mu mol H-2 per 1 mL sample with OD600 = 5) and turnover frequencies (TOF, 812 nmol H-2 h(-1) per 1 mL sample with OD600 = 5) on par with previously reported high performing E. coli-based systems while greatly reducing cytotoxic effects. Transient absorption spectroscopy revealed how the choice of photosensitizer, electron donor, and redox mediator affects the observed photocatalytic TOFs. Following optimization of the redox mediator and electron donor the biocatalyst demonstrated remarkable stability throughout the experiments. We identified the availability of electrons from the electron donor as the primary limiting factor, with approximately 85% of electrons being effectively utilized for hydrogen production. Furthermore, the observed activity with different [FeFe] hydrogenases verified the broad applicability of the identified photocatalytic components to promote light-driven catalysis in bio-hybrid systems.
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| 32. |
- Gamache, Mira T., et al.
(författare)
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Elucidating Electron Transfer Kinetics and Optimizing System Performance for Escherichia coli-Based Semi-Artificial H-2 Production
- 2023
-
Ingår i: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 13:14, s. 9476-9486
-
Tidskriftsartikel (refereegranskat)abstract
- Both photo- and biocatalysis are well-established andintensivelystudied. The combination of these two approaches is also an emergingresearch field, commonly referred to as semi-artificial photosynthesis.Semi-artificial photosynthesis aims at combining highly efficientsynthetic light harvesters with the self-healing and potent catalyticproperties of biocatalysis. In this study, a semi-artificial photocatalyticsystem featuring Escherichia coli bacteria,which heterologously express the [FeFe] hydrogenase enzyme HydA1 fromgreen algae, is employed as a hydrogen gas production catalyst. Toprobe the influence of photochemistry on overall system performance,the E. coli whole-cell catalyst iscombined with two different photosensitizers and redox mediators.The addition of a redox mediator greatly improves the rates and longevityof the photocatalytic system, as reflected in increases of both theturn-over number (0.777 vs 10.9 & mu;mol H-2 mL(-1) OD600 (-1)) and the turn-over frequency(175 vs 334 & mu;mol H-2 mL(-1) h(-1) OD600 (-1)). The redoxmediator is found to both protect from photobleaching and enable electrontransport to the hydrogenase from an extracellular photosensitizer.However, E. coli cells are stronglyaffected by the photocatalytic system, leading to a decrease in cellintegrity and cell viability, possibly due to toxic decompositionproducts formed during the photocatalytic process. We furthermoreemployed steady-state and transient absorption spectroscopy to investigatesolution potentials and the kinetics of electron transfer processesbetween the sacrificial electron donor, photosensitizer, redox mediator,and the [FeFe] hydrogenase as the final electron acceptor. These resultsallowed us to rationalize the different activities observed in photocatalyticassays and offer a better understanding of the factors that influencethe photocatalytic performance of E. coli-based whole-cell systems.
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| 33. |
- Grāve, Kristīne, et al.
(författare)
-
Redox-induced structural changes in the di-iron and di-manganese forms of Bacillus anthracis ribonucleotide reductase subunit NrdF suggest a mechanism for gating of radical access
- 2019
-
Ingår i: Journal of Biological Inorganic Chemistry. - : Springer Science and Business Media LLC. - 0949-8257 .- 1432-1327. ; 24:6, s. 849-861
-
Tidskriftsartikel (refereegranskat)abstract
- Class Ib ribonucleotide reductases (RNR) utilize a di-nuclear manganese or iron cofactor for reduction of superoxide or molecular oxygen, respectively. This generates a stable tyrosyl radical (Y center dot) in the R2 subunit (NrdF), which is further used for ribonucleotide reduction in the R1 subunit of RNR. Here, we report high-resolution crystal structures of Bacillus anthracis NrdF in the metal-free form (1.51 angstrom) and in complex with manganese (Mn-II/Mn-II, 1.30 angstrom). We also report three structures of the protein in complex with iron, either prepared anaerobically (Fe-II/Fe-II form, 1.32 angstrom), or prepared aerobically in the photo-reduced Fe-II/Fe-II form (1.63 angstrom) and with the partially oxidized metallo-cofactor (1.46 angstrom). The structures reveal significant conformational dynamics, likely to be associated with the generation, stabilization, and transfer of the radical to the R1 subunit. Based on observed redox-dependent structural changes, we propose that the passage for the superoxide, linking the FMN cofactor of NrdI and the metal site in NrdF, is closed upon metal oxidation, blocking access to the metal and radical sites. In addition, we describe the structural mechanics likely to be involved in this process.
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| 34. |
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| 35. |
- Grāve, Kristīne, et al.
(författare)
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The Bacillus anthracis class Ib ribonucleotide reductase subunit NrdF intrinsically selects manganese over iron
- 2020
-
Ingår i: Journal of Biological Inorganic Chemistry. - : Springer Science and Business Media LLC. - 0949-8257 .- 1432-1327. ; 25:4, s. 571-582
-
Tidskriftsartikel (refereegranskat)abstract
- Correct protein metallation in the complex mixture of the cell is a prerequisite for metalloprotein function. While some metals, such as Cu, are commonly chaperoned, specificity towards metals earlier in the Irving-Williams series is achieved through other means, the determinants of which are poorly understood. The dimetal carboxylate family of proteins provides an intriguing example, as different proteins, while sharing a common fold and the same 4-carboxylate 2-histidine coordination sphere, are known to require either a Fe/Fe, Mn/Fe or Mn/Mn cofactor for function. We previously showed that the R2lox proteins from this family spontaneously assemble the heterodinuclear Mn/Fe cofactor. Here we show that the class Ib ribonucleotide reductase R2 protein from Bacillus anthracis spontaneously assembles a Mn/Mn cofactor in vitro, under both aerobic and anoxic conditions, when the metal-free protein is subjected to incubation with Mn-II and Fe-II in equal concentrations. This observation provides an example of a protein scaffold intrinsically predisposed to defy the Irving-Williams series and supports the assumption that the Mn/Mn cofactor is the biologically relevant cofactor in vivo. Substitution of a second coordination sphere residue changes the spontaneous metallation of the protein to predominantly form a heterodinuclear Mn/Fe cofactor under aerobic conditions and a Mn/Mn metal center under anoxic conditions. Together, the results describe the intrinsic metal specificity of class Ib RNR and provide insight into control mechanisms for protein metallation.
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| 36. |
- Greening, Chris, et al.
(författare)
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Minimal and hybrid hydrogenases are active from archaea
-
Ingår i: Cell. - 1097-4172. ; 187
-
Tidskriftsartikel (refereegranskat)abstract
- Microbial hydrogen (H 2) cycling underpins the diversity and functionality of diverse anoxic ecosystems. Among the three evolutionarily distinct hydrogenase superfamilies responsible, [FeFe] hydrogenases were thought to be restricted to bacteria and eukaryotes. Here, we show that anaerobic archaea encode diverse, active, and ancient lineages of [FeFe] hydrogenases through combining analysis of existing and new genomes with extensive biochemical experiments. [FeFe] hydrogenases are encoded by genomes of nine archaeal phyla and expressed by H 2-producing Asgard archaeon cultures. We report an ultraminimal hydrogenase in DPANN archaea that binds the catalytic H-cluster and produces H 2. Moreover, we identify and characterize remarkable hybrid complexes formed through the fusion of [FeFe] and [NiFe] hydrogenases in ten other archaeal orders. Phylogenetic analysis and structural modeling suggest a deep evolutionary history of hybrid hydrogenases. These findings reveal new metabolic adaptations of archaea, streamlined H 2 catalysts for biotechnological development, and a surprisingly intertwined evolutionary history between the two major H 2-metabolizing enzymes.
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| 37. |
- Grinter, Rhys, et al.
(författare)
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Structural basis for bacterial energy extraction from atmospheric hydrogen
- 2023
-
Ingår i: Nature. - : Springer Nature. - 0028-0836 .- 1476-4687. ; 615:7952, s. 541-547
-
Tidskriftsartikel (refereegranskat)abstract
- Diverse aerobic bacteria use atmospheric H2 as an energy source for growth and survival1. This globally significant process regulates the composition of the atmosphere, enhances soil biodiversity and drives primary production in extreme environments2,3. Atmospheric H2 oxidation is attributed to uncharacterized members of the [NiFe] hydrogenase superfamily4,5. However, it remains unresolved how these enzymes overcome the extraordinary catalytic challenge of oxidizing picomolar levels of H2 amid ambient levels of the catalytic poison O2 and how the derived electrons are transferred to the respiratory chain1. Here we determined the cryo-electron microscopy structure of the Mycobacterium smegmatis hydrogenase Huc and investigated its mechanism. Huc is a highly efficient oxygen-insensitive enzyme that couples oxidation of atmospheric H2 to the hydrogenation of the respiratory electron carrier menaquinone. Huc uses narrow hydrophobic gas channels to selectively bind atmospheric H2 at the expense of O2, and 3 [3Fe-4S] clusters modulate the properties of the enzyme so that atmospheric H2 oxidation is energetically feasible. The Huc catalytic subunits form an octameric 833 kDa complex around a membrane-associated stalk, which transports and reduces menaquinone 94 Å from the membrane. These findings provide a mechanistic basis for the biogeochemically and ecologically important process of atmospheric H2 oxidation, uncover a mode of energy coupling dependent on long-range quinone transport, and pave the way for the development of catalysts that oxidize H2 in ambient air.
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| 38. |
- Habib, Iman, et al.
(författare)
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DGTS: Integrated Typing and Pointing
- 2009
-
Ingår i: Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics). - Berlin, Heidelberg : Springer Berlin Heidelberg. - 1611-3349 .- 0302-9743. - 9783642036576 ; , s. 232-235
-
Konferensbidrag (refereegranskat)abstract
- Capacitive sensing is used in many different fields of application. Ithas been implemented in such devices as mobile phones and remote controls. However, up until now the physical sensing area has remained limited despite the widespread use of larger input devices such as keyboards. We present DGTS, which seamlessly integrates keyboard typing and cursor pointing. This input device offers multi-finger operation for scrolling and other specialized input commands. The objective of this work is to replace computer mice and touchpads by integrating capacitive sensing into a layer within the keyboard thereby reducing the space required for pointing devices. This paper gives the technical background, shows our contribution, and concludes with initial tests.
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| 39. |
- Habib, Iman, et al.
(författare)
-
Multi-touch keyboard device
- 2009
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The present invention is in the technical field of computer input devices. More particularly, the present invention is in the technical field of computer keyboards. More particularly, a computer keyboard comprising capacitive multi-touch technology. Conventional computer input devices consist of a keyboard and a pointing device. These devices are often separated spatially thus decreasing the efficiency of user input due to time spent moving hands and fingers between the different input devices.
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| 40. |
- Hola, Katerina, et al.
(författare)
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Carbon Dots and [FeFe] Hydrogenase Biohybrid Assemblies for Efficient Light-Driven Hydrogen Evolution
- 2020
-
Ingår i: ACS Catalysis. - : AMER CHEMICAL SOC. - 2155-5435. ; 10:17, s. 9943-9952
-
Tidskriftsartikel (refereegranskat)abstract
- Artificial photosynthesis is seen as a path to convert and store solar energy into chemical energy for our society. In this work, highly fluorescent aspartic acid-based carbon dots (CDs) are synthesized and employed as a photosensitizer to drive photocatalytic hydrogen evolution with an [FeFe] hydrogenase (CrHydA1). The direct interaction in CDs from L-aspartic acid (AspCDs)/CrHydA1 self-assembly systems, which is visualized from native gel electrophoresis, has been systematically investigated to understand the electron-transfer dynamics and its impact on photocatalytic efficiency. The study discloses the significant influence of the electrostatic surrounding generated by sacrificial electron donors on the intimate interplay within the oppositely charged subunits of the biohybrid assembly as well as the overall photocatalytic performance. The system reaches an external quantum efficiency of 1.7% at 420 nm and an initial activity of 1.73 mu mol(H-2) mg(-1) (hydrogenase) min(-1) under favorable electrostatic conditions. Owing to the ability of the synthesized AspCDs to operate efficiently under visible light, in contrast to other materials that require UV illumination, the stability of the biohybrid assembly in the presence of a redox mediator extends beyond 1 week.
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| 41. |
- Khanna, Namita, et al.
(författare)
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In vivo activation of an [FeFe] hydrogenase using synthetic cofactors
- 2017
-
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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| 42. |
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| 43. |
- Kurz, Philipp, et al.
(författare)
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Oxygen evolving reactions catalysed by synthetic manganese complexes : A systematic screening
- 2007
-
Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; :38, s. 4258-4261
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Tidskriftsartikel (refereegranskat)abstract
- A set of six multinuclear manganese complexes was screened for the ability to catalyse reactions yielding O(2) under coherent experimental conditions; we identify a much larger number of manganese compounds than previously known that catalyse oxygen formation.
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| 44. |
- Land, Henrik, et al.
(författare)
-
Characterization of a putative sensory [FeFe]-hydrogenase provides new insight into the role of the active site architecture
- 2020
-
Ingår i: Chemical Science. - : The Royal Society of Chemistry. - 2041-6539. ; 11:47, s. 12789-12801
-
Tidskriftsartikel (refereegranskat)abstract
- [FeFe]-hydrogenases are known for their high rates of hydrogen turnover, and are intensively studied in the context of biotechnological applications. Evolution has generated a plethora of different subclasses with widely different characteristics. The M2e subclass is phylogenetically distinct from previously characterized members of this enzyme family and its biological role is unknown. It features significant differences in domain- and active site architecture, and is most closely related to the putative sensory [FeFe]-hydrogenases. Here we report the first comprehensive biochemical and spectroscopical characterization of an M2e enzyme, derived from Thermoanaerobacter mathranii. As compared to other [FeFe]-hydrogenases characterized to-date, this enzyme displays an increased H2 affinity, higher activation enthalpies for H+/H2 interconversion, and unusual reactivity towards known hydrogenase inhibitors. These properties are related to differences in active site architecture between the M2e [FeFe]-hydrogenase and “prototypical†[FeFe]-hydrogenases. Thus, this study provides new insight into the role of this subclass in hydrogen metabolism and the influence of the active site pocket on the chemistry of the H-cluster.
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| 45. |
- Land, Henrik, et al.
(författare)
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Current State of [FeFe]-Hydrogenase Research : Biodiversity and Spectroscopic Investigations
- 2020
-
Ingår i: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 10:13, s. 7069-7086
-
Tidskriftsartikel (refereegranskat)abstract
- Hydrogenases are redox enzymes that catalyze the conversion of protons and molecular hydrogen (H-2). Based on the composition of the active site cofactor, the monometallic [Fe]-hydrogenase is distinguished from the bimetallic [NiFe]- or [FeFe]-hydrogenase. The latter has been reported with particularly high turnover activities for both H-2 release and H-2 oxidation, notably at neutral pH, ambient temperatures, and negligible electric overpotential. Due to these properties, [FeFe]-hydrogenase represents the "gold standard" in enzymatic hydrogen turnover. Understanding hydrogenase chemistry is crucial for the design of transition metal complexes that serve as potentially sustainable proton reduction or H-2 oxidation catalysts, e.g., in electrolytic devices or fuel cells. However, even 20 years after the crystal structures of [FeFe]-hydrogenase have been published, several aspects of biological hydrogen turnover are heatedly discussed. In this perspective, we give an overview on how the diversity of naturally occurring and artificially prepared, semisynthetic [FeFe]-hydrogenases deepens our understanding of hydrogenase chemistry. In parallel, we cover recent results from biophysical techniques that go beyond the scope of conventional X-ray diffraction, EPR, and FTIR spectroscopy. Taking into account both proton transfer and electron transfer as well as the notorious sensitivity of [FeFe]-hydrogenase toward carbon monoxide, the discussion further touches upon the molecular proceedings of biological hydrogen turnover.
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| 46. |
- Land, Henrik, et al.
(författare)
-
Discovery of novel [FeFe]-hydrogenases for biocatalytic H-2-production
- 2019
-
Ingår i: Chemical Science. - : Royal Society of Chemistry (RSC). - 2041-6520 .- 2041-6539. ; 10:43, s. 9941-9948
-
Tidskriftsartikel (refereegranskat)abstract
- A new screening method for [FeFe]-hydrogenases is described, circumventing the need for specialized expression conditions as well as protein purification for initial characterization. [FeFe]-hydrogenases catalyze the formation and oxidation of molecular hydrogen at rates exceeding 10(3) s(-1), making them highly promising for biotechnological applications. However, the discovery of novel [FeFe]-hydrogenases is slow due to their oxygen sensitivity and dependency on a structurally unique cofactor, complicating protein expression and purification. Consequently, only a very limited number have been characterized, hampering their implementation. With the purpose of increasing the throughput of [FeFe]-hydrogenase discovery, we have developed a screening method that allows for rapid identification of novel [FeFe]-hydrogenases as well as their characterization with regards to activity (activity assays and protein film electrochemistry) and spectroscopic properties (electron paramagnetic resonance and Fourier transform infrared spectroscopy). The method is based on in vivo artificial maturation of [FeFe]-hydrogenases in Escherichia coli and all procedures are performed on either whole cells or non-purified cell lysates, thereby circumventing extensive protein purification. The screening was applied on eight putative [FeFe]-hydrogenases originating from different structural sub-classes and resulted in the discovery of two new active [FeFe]-hydrogenases. The [FeFe]-hydrogenase from Solobacterium moorei shows high H-2-gas production activity, while the enzyme from Thermoanaerobacter mathranii represents a hitherto uncharacterized [FeFe]-hydrogenase sub-class. This latter enzyme is a putative sensory hydrogenase and our in vivo spectroscopy study reveals distinct differences compared to the well established H-2 producing HydA1 hydrogenase from Chlamydomonas reinhardtii.
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| 47. |
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| 48. |
- Lorenzi, Marco, et al.
(författare)
-
Investigating the role of the strong field ligands in [FeFe] hydrogenase: spectroscopic and functional characterization of a semi-synthetic mono-cyanide active site
- 2022
-
Ingår i: Chemical Science. - : Royal Society of Chemistry (RSC). - 2041-6520 .- 2041-6539. ; 13:37, s. 11058-11064
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Tidskriftsartikel (refereegranskat)abstract
- Artificial maturation of hydrogenases provides a path towards generating new semi-synthetic enzymes with novel catalytic properties. Here enzymes featuring a synthetic asymmetric mono-cyanide cofactor have been prepared using two different hydrogenase scaffolds. Their structure and reactivity was investigated in order to elucidate the design rationale behind the native di-cyanide cofactor, and by extension the second coordination sphere of the active-site pocket. Surprisingly, the choice of host enzyme was found to have a dramatic impact on reactivity. Moreover, the study shows that synthetic manipulations of the active-site can significantly increase inhibitor tolerance, as compared to native [FeFe] hydrogenase, while retaining the enzyme's native capacity for reversible catalysis.
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| 49. |
- Lorenzi, Marco, et al.
(författare)
-
Light-Driven [FeFe] Hydrogenase Based H-2 Production in E. coli : A Model Reaction for Exploring E. coli Based Semiartificial Photosynthetic Systems
- 2022
-
Ingår i: ACS Sustainable Chemistry and Engineering. - : American Chemical Society (ACS). - 2168-0485. ; 10:33, s. 10760-10767
-
Tidskriftsartikel (refereegranskat)abstract
- Biohybrid technologies like semiartificial photosynthesis are attracting increased attention, as they enable the combination of highly efficient synthetic light-harvesters with the self-healing and outstanding performance of biocatalysis. However, such systems are intrinsically complex, with multiple interacting components. Herein, we explore a whole-cell photocatalytic system for hydrogen (H2) gas production as a model system for semiartificial photosynthesis. The employed whole-cell photo catalytic system is based on Escherichia coli cells heterologously expressing a highly efficient, but oxygen-sensitive, [FeFe] hydrogenase. The system is driven by the organic photosensitizer eosin Y under broad-spectrum white light illumination. The direct involvement of the [FeFe] hydrogenase in the catalytic reaction is verified spectroscopically. We also observe that E. coli provides protection against O-2 damage, underscoring the suitability of this host organism for oxygen-sensitive enzymes in the development of (photo) catalytic biohybrid systems. Moreover, the study shows how factorial experimental design combined with analysis of variance (ANOVA) can be employed to identify relevant variables, as well as their interconnectivity, on both overall catalytic performance and O-2 tolerance.
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| 50. |
- Lorenzi, Marco, 1990-
(författare)
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New Roads for an Ancient Enzyme : Whole-Cell Studies and New Cofactors for [FeFe] Hydrogenases
- 2022
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- [FeFe] hydrogenases rare Nature’s best H2-processing catalysts, and one of the best candidates to satisfy societal need for cheap and efficient catalyst for H2-evolution. These enzymes owe their remarkable catalytic activities to their organometallic active site, called “H-cluster”. The H-cluster can be described as a canonical [4Fe4S] cluster linked via a bridging cysteine residue to a [2Fe] subsite, which is in turn coordinated by three CO, two CN− and one bidentate azadithiolate ligand. This unique cofactor allows these enzymes to function with virtually no overpotential requirements and TOFs up to 20 000 s-1. We have now reached a good understanding of the catalytic cycle by which these enzymes operate, yet many questions remain open especially regarding the physiological relevance of some the proposed intermediates. In this thesis, we have used FTIR and EPR spectroscopies on whole-cell samples of [FeFe] hydrogenases to study the influence of the intracellular environment on the catalytic cycle of these enzymes. Moreover, we have investigated how the bacterial cytoplasm influences the stability of the H-cluster and favours the formation of sulfide-inhibited states, and we have studied the role of the proton-transfer chain and of steric factor related to the active site pocket in promoting this inhibition. Today, whole-cell systems attract a lot of interest due to the possibility to couple living cells with artificial photosensitizer to create whole-cell photocatalytic systems endowed with self-healing capabilities and broadband light absorption properties. We have built a system consisting of an E. coli-encapsulated [FeFe] hydrogenase coupled to the organic photosensitizer eosin Y, and we have verified the occurrence of light-induced electron transfer from eosin Y to the enzyme with consequent H2 production. We have also applied a simple design-of-experiments approach to look into how the different system parameters interact with each other, and we have demonstrated that such approaches represent a viable strategy to guide the optimization of this type of photocatalytic systems. Finally, we have moved our attention to semi-artificial hydrogenases. We have used artificial maturation to generate asymmetric monocyanide versions of the H-cluster using two different model hydrogenases, CrHydA1 and DdHydAB. Through the application of FTIR, EPR and Protein-Film Electrochemistry we characterized these variants, studied the effect of this ligand exchange on the overall catalytic performance, and shed light on the effect of second-coordination sphere interaction on parameters such as catalytic rate, overpotential, affinity for H2 and inhibitor sensitivity.
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