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Mimicking Nature – Synthesis and Characterisation of Manganese Complexes of Relevance to Artificial Photosynthesis
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Photochemistry and Molecular Science.
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2009. , p. 101
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 674
Keywords [en]
Manganese, biomimetic, artificial photosynthesis, water splitting, homogeneous catalysis
National Category
Other Basic Medicine
Research subject
Physical Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-108526ISBN: 978-91-554-7614-4 (print)OAI: oai:DiVA.org:uu-108526DiVA, id: diva2:236509
Public defence
2009-11-06, Polhemsalen, Ångströmslaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2009-10-15 Created: 2009-09-21 Last updated: 2018-01-13Bibliographically approved
List of papers
1. 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
Open this publication in new window or tab >>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
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2008 (English)In: Energy & Environmental Science, ISSN 1754-5692, E-ISSN 1754-5706, Vol. 1, no 6, p. 668-676Article in journal (Refereed) Published
Abstract [en]

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.

National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-108518 (URN)10.1039/b811806j (DOI)000263888600006 ()1754-5692 (ISBN)
Available from: 2009-09-21 Created: 2009-09-21 Last updated: 2017-12-13
2. Sodium [1,2-bis(2-methyl-2-oxopropanamido)-benzene](tetrahydrofuran) manganese(III) methanol solvate
Open this publication in new window or tab >>Sodium [1,2-bis(2-methyl-2-oxopropanamido)-benzene](tetrahydrofuran) manganese(III) methanol solvate
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2005 (English)In: Acta Crystallographica Section E-Structure Reports Online, Vol. 61, p. M1169-Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-75924 (URN)
Available from: 2006-02-24 Created: 2006-02-24 Last updated: 2011-01-11
3. Two tetranuclear Mn-complexes as biomimetic models of the oxygen evolving complex in Photosystem II. A synthesis, characterisation and reactivity study
Open this publication in new window or tab >>Two tetranuclear Mn-complexes as biomimetic models of the oxygen evolving complex in Photosystem II. A synthesis, characterisation and reactivity study
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2009 (English)In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, no 45, p. 10044-10054Article in journal (Refereed) Published
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-108451 (URN)10.1039/b906175d (DOI)
Available from: 2009-09-21 Created: 2009-09-18 Last updated: 2017-12-13
4. Mechanistic Studies on the Water-Oxidizing Reaction of Homogeneous Manganese-Based Catalysts: Isolation and Characterization of a Suggested Catalytic Intermediate
Open this publication in new window or tab >>Mechanistic Studies on the Water-Oxidizing Reaction of Homogeneous Manganese-Based Catalysts: Isolation and Characterization of a Suggested Catalytic Intermediate
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2011 (English)In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 50, no 8, p. 3425-3430Article in journal (Refereed) Published
Abstract [en]

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.

National Category
Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-108524 (URN)10.1021/ic102336a (DOI)000290457700034 ()21428420 (PubMedID)
Available from: 2009-09-21 Created: 2009-09-21 Last updated: 2017-12-13
5. Synthesis and characterisation of low valent Mn-complexes as models for Mn-catalases
Open this publication in new window or tab >>Synthesis and characterisation of low valent Mn-complexes as models for Mn-catalases
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2010 (English)In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 39, no 45, p. 11035-11044Article in journal (Refereed) Published
Abstract [en]

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.

National Category
Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-108525 (URN)10.1039/c0dt00165a (DOI)000284066100028 ()
Available from: 2009-09-21 Created: 2009-09-21 Last updated: 2017-12-13
6. Oxygen evolving reactions catalysed by synthetic manganese complexes: A systematic screening
Open this publication in new window or tab >>Oxygen evolving reactions catalysed by synthetic manganese complexes: A systematic screening
2007 (English)In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, no 38, p. 4258-4261Article in journal (Refereed) Published
Abstract [en]

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.

National Category
Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-11551 (URN)10.1039/b710761g (DOI)000249705100004 ()17893814 (PubMedID)
Available from: 2007-09-27 Created: 2007-09-27 Last updated: 2017-12-11
7. Oxygen Evolving Reactions by Synthetic Manganese Complexes
Open this publication in new window or tab >>Oxygen Evolving Reactions by Synthetic Manganese Complexes
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2008 (English)In: Photosynthesis. Energy from the Sun: 14th International Congress on Photosynthesis, Springer, Netherlands , 2008Chapter in book (Other (popular science, discussion, etc.))
Place, publisher, year, edition, pages
Springer, Netherlands, 2008
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-108452 (URN)978-1-4020-6707-5 (ISBN)
Available from: 2009-09-21 Created: 2009-09-18 Last updated: 2015-04-24

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