| 1. |
- Niklasson, Bo, et al.
(author)
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Diabetes Prevention Through Antiviral Treatment in Biobreeding Rats
- 2016
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In: Viral immunology. - : Mary Ann Liebert Inc. - 0882-8245 .- 1557-8976. ; 29:8, s. 452-458
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Journal article (peer-reviewed)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.
(author)
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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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In: European Journal of Inorganic Chemistry. - : John Wiley & Sons. - 1434-1948 .- 1099-1948 .- 1099-0682. ; :11, s. 1744-1749
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Journal article (peer-reviewed)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.
(author)
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From Enzyme Maturation to Synthetic Chemistry : The Case of Hydrogenases
- 2015
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In: Accounts of Chemical Research. - : American Chemical Society (ACS). - 0001-4842 .- 1520-4898. ; 48:8, s. 2380-2387
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Research review (peer-reviewed)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.
(author)
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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
-
In: Chemical Science. - : Royal Society of Chemistry. - 2041-6520 .- 2041-6539. ; 10:21, s. 5582-5588
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Journal article (peer-reviewed)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.
(author)
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Cobaloxime-Based Artificial Hydrogenases
- 2014
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In: Inorganic Chemistry. - : American Chemical Society. - 0020-1669 .- 1520-510X. ; 53:15, s. 8071-8082
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Journal article (peer-reviewed)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.
(author)
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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
-
In: Energy & Environmental Science. - : Royal Society of Chemistry (RSC). - 1754-5692 .- 1754-5706. ; 1:6, s. 668-676
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Journal article (peer-reviewed)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.
(author)
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15.02 - Hydrogenases and Model Complexes in Bioorganometallic Chemistry
- 2022
-
In: Comprehensive Organometallic Chemistry IV. - Oxford : Elsevier. - 9780323913508 ; , s. 3-40
-
Book chapter (other academic/artistic)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. |
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| 11. |
- Berggren, Gustav, et al.
(author)
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Compounds with capacity to quench the tyrosyl radical in Pseudomonas aeruginosa ribonucleotide reductase
- 2019
-
In: Journal of Biological Inorganic Chemistry. - : Springer Science and Business Media LLC. - 0949-8257 .- 1432-1327. ; 24:6, s. 841-848
-
Journal article (peer-reviewed)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.
(author)
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FTIR Study of Manganese Dimers with Carboxylate Donors As Model Complexes for the Water Oxidation Complex in Photosystem II
- 2012
-
In: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 51:4, s. 2332-2337
-
Journal article (peer-reviewed)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.
(author)
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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
-
In: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 50:8, s. 3425-3430
-
Journal article (peer-reviewed)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-
(author)
-
Mimicking Nature – Synthesis and Characterisation of Manganese Complexes of Relevance to Artificial Photosynthesis
- 2009
-
Doctoral thesis (other academic/artistic)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.
(author)
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Semiquinone-Induced Maturation of Bacillus anthracis Ribonucleotide Reductase by a Superoxide Intermediate
- 2014
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In: Journal of Biological Chemistry.
-
Journal article (peer-reviewed)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.
(author)
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Semiquinone-induced Maturation of Bacillus anthracis Ribonucleotide Reductase by a Superoxide Intermediate
- 2014
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In: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 289:46, s. 31940-31949
-
Journal article (peer-reviewed)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.
(author)
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Synthesis and characterisation of low valent Mn-complexes as models for Mn-catalases
- 2010
-
In: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; 39:45, s. 11035-11044
-
Journal article (peer-reviewed)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.
(author)
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Synthesis, Characterization and Reactivity Study of a New Penta-Coordinated Mn(II) Complex
- 2009
-
In: Applied Magnetic Resonance. - : Springer Science and Business Media LLC. - 0937-9347 .- 1613-7507. ; 36:1, s. 9-24
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Journal article (peer-reviewed)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.
(author)
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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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In: Acta Crystallographica Section E. - 1600-5368. ; 63:11, s. M2672-M2673
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Journal article (peer-reviewed)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.
(author)
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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
-
In: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; 45, s. 10044-10054
-
Journal article (peer-reviewed)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.
(author)
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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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In: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 13:15, s. 10435-10446
-
Journal article (peer-reviewed)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.
(author)
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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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In: Nature Communications. - : Springer Nature. - 2041-1723. ; 15:1
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Journal article (peer-reviewed)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.
(author)
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Characterization of a monocyanide model of FeFe hydrogenases - highlighting the importance of the bridgehead nitrogen for catalysis
- 2016
-
In: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; 45:48, s. 19242-19248
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Journal article (peer-reviewed)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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