| 1. |
- 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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| 2. |
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| 3. |
- Bedin, Michele, 1984-
(författare)
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A dinuclear manganese complex with an asymmetric ligand as a functional mimic of manganese catalase
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Tidskriftsartikel (refereegranskat)abstract
- Reactive Oxygen Species (ROS) in the form of H2O2, OH radicals, and superoxide, are oxygen species generated in the respiratory chain. In high concentrations, these species can cause pathological conditions like ischemia-reperfusion related injuries and neurodegenerative diseases. A series of enzymes exists in nature to protect from this danger: superoxide dismutases (SOD), glutathione peroxidases (GSH), and catalases (CAT). The catalases catalyse the decomposition of H2O2 into water and molecular oxygen. In this work, we focus on mimicking the MnCAT, a subclass of CAT that contains two Mn ions in the cofactor. An asymmetric and dinucleating ligand H2DPCPMP (2-(N-(3-((bis((pyridin-2-yl)methyl)amino)methyl)-2-hydroxy-5-methylbenzyl)-N-((pyridin-2-yl)methyl)amino acetic acid) that contains three pyridine groups, one carboxylate group, and one phenol was used. The ligand can create two pockets where two Mn ions can be accommodated. The dimanganese complex of H2DPCPMP was synthesized and characterized with mass spectrometry, electrochemistry, IR, UV-vis and EPR. The complex can act as a catalyst for the disproportionation of H2O2 but unlike many previously reported mimics of MnCAT, the rate of oxygen evolution is not saturated at high concentrations of H2O2.
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| 4. |
- Bedin, Michele, 1984-, et al.
(författare)
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Dinuclear iron and manganese complex with an asymmetric ligand
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Three complexes using the same asymmetric and dinucleating ligand DPCPMP (2-(N-(3-((bis((pyridin-2-yl)methyl)amino)methyl)-2-hydroxy-5-methylbenzyl)-N-((pyridin-2-yl)methyl)amino acetic acid) have been synthesised. The ligand contains one pocket with three nitrogen donors and another pocket with two nitrogen donors and one oxygen donor. The complexes were containing two iron ions ([Fe2(DPCPMP)(CH3COO)2]), two manganese ions ([Mn2(DPCPMP)(CH3COO)2]) or one iron and one manganese ion ([FeMn(DPCPMP)(CH3COO)2]) mimicing the metal content in the three different subclasses of class I ribonucleotide reductases. The asymmetric ligand was chosen in order to investigate if a small alteration of the coordiantion environment (pyridine versus carboxylate donor) could steer the metal ions in the heterobimetallic complex into a specific pocket of the ligand or not. The complexes have been characterized and investigated with mass spectrometry, electrochemistry, IR, UV-vis, EPR and Mössbauer spectroscopy. From CV and Mössbauer spectroscopy of the heterobimetallic complex it is proposed that the asymmetry is not able to steer the metals into different pockets and instead a mixture of two different isomers is created in the synthesis.
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| 5. |
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| 6. |
- Bedin, Michele, PhD, 1984-
(författare)
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Iron, Manganese and Iridium Complexes From Models of RNR and Catalase to Water Oxidation
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The focus of this thesis has been synthesise and study metal complexes that mimic the structure and function of the active site in two particular metalloenzymes, ribonucleotide reductase (RNR) and manganese catalase (MnCAT). These two metalloenzymes both have two transition metals ions in the cofactor: two manganese ions in MnCAT and either two iron, iron-manganese or two manganese ions in RNR.Three different ligands were synthetized to make model complexes for these cofactors. The first ligand, BPMP, can bind two metal ions and provides two symmetric pockets with two pyridine groups and one amine each, plus a phenolate group that can bridge the two metals. The second ligand DPCPMP had one carboxylate group instead of a pyridine group in one pocket, creating an asymmetric ligand, and the third ligand BPCPMP, had two carboxylate groups, one in each pocket. From the first and the second ligands it was possible to obtain six complexes: low-valent homometallic Mn/Mn and Fe/Fe complexes and a heterometallic complex for each ligand. For the third ligand, only the Fe/Fe complex was synthetized.All seven complexes were characterized by a number of spectroscopic methods. The presence of carboxylate groups in the ligand shifted the redox potential for the metal complexes towards more negative values, particularly in the case of the homometallic Fe/Fe complexes. Surprisingly, for the asymmetric ligand the placement of the metal ions in the two pockets was not dictated by the asymmetry. Additionally, the relative stability of the homometallic complexes versus the heterometallic complexes and the possibility to transform a homometallic complex into a heterometallic complex were investigated. By titrating one metal into a solution containing the other homometallic dimer it was possible to observe that Fe2+ added to a solution of a Mn/Mn complex led to the replacement of one Mn ion in the complex with a Fe ion.The manganese complex of DPCPMP was investigated as a functional model for MnCAT, catalysing the disproportionation of H2O2 to oxygen and water. In the presence of H2O2 this complex also forms a high-valent species with a di-µ-oxo bridge similar to the MnCAT and RNR.Finally, the methodology used for the study of these complexes was also applied to a set of Ir complexes that act as water oxidation catalysts, and we could show that the presence of a pendant group stabilizes the metal at higher oxidation states leading to higher activity for the catalyst.
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| 7. |
- Bedin, Michele, et al.
(författare)
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Synthesis and properties of a heterobimetallic iron-manganese complex and its comparison with homobimetallic analogues
- 2019
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Ingår i: Inorganica Chimica Acta. - : ELSEVIER SCIENCE SA. - 0020-1693 .- 1873-3255. ; 490, s. 254-260
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Tidskriftsartikel (refereegranskat)abstract
- Heterobimetallic cofactors containing one manganese and one iron ion have recently been found within the di-metal carboxylate protein family. Herein we report the synthesis and characterization of three binuclear metal complexes with Fe-Fe, Mn-Mn, and Fe-Mn metal composition. All three complexes use the same ligand framework, the BPMP ligand (HBPMP=2,6-bis[(bis (-2-pyridylmethyl)amine) methyl]-4-methylphenol)) with two additional acetate ligands bridging the two metals. In terms of stability towards metal exchange, the Fe-Mn is more stable than the Mn-Mn complex but less stable than the Fe-Fe complex. Cyclic voltammetry shows that the Fe-Mn complex behaves markedly different than the homobimetallic complexes. The Fe-Mn complex also shows higher reactivity with O-2 than both the Fe-Fe and the Mn-Mn counterparts.
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| 8. |
- 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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| 9. |
- 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
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 50:8, s. 3425-3430
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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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| 10. |
- 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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