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Ligand exchange upon oxidation of a dinuclear Mn complex - Detection of structural changes by FT-IR spectroscopy and ESI-MS.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry.
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2005 (English)In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, no 6, 1033-1041 p.Article in journal (Refereed) Published
Place, publisher, year, edition, pages
2005. no 6, 1033-1041 p.
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:uu:diva-95874OAI: oai:DiVA.org:uu-95874DiVA: diva2:170240
Available from: 2007-05-04 Created: 2007-05-04 Last updated: 2017-12-14
In thesis
1. Molecular Approaches to Photochemical Solar Energy Conversion: Towards Synthetic Catalysts for Water Oxidation and Proton Reduction
Open this publication in new window or tab >>Molecular Approaches to Photochemical Solar Energy Conversion: Towards Synthetic Catalysts for Water Oxidation and Proton Reduction
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

A molecular system capable of photoinduced water splitting is an attractive approach to solar energy conversion. This thesis deals with the functional characterization of molecular building blocks for the three principal functions of such a molecular system: Photoinduced accumulative charge separation, catalytic water oxidation, and catalytic proton reduction.

Systems combining a ruthenium-trisbipyridine photosensitizer with multi-electron donors in form of dinuclear ruthenium or manganese complexes were investigated in view of the rate constants of electron transfer and excited state quenching. The kinetics were studied in the different oxidation states of the donor unit by combination of electrochemistry and time resolved spectroscopy. The rapid excited state quenching by the multi-electron donors points to the importance of redox intermediates for efficient accumulative photooxidation of the terminal donor.

The redox behavior of manganese complexes as mimics of the water oxidizing catalyst in the natural photosynthetic reaction center was studied by electrochemical and spectroscopic methods. For a dinuclear manganese complex ligand exchange reactions were studied in view of their importance for the accumulative oxidation of the complex and its reactivity towards water. With the binding of substrate water, multiple oxidation in a narrow potential range and concomitant deprotonation of the bound water it was demonstrated that the manganese complex is capable of mimicking multiple aspects of photosynthetic water oxidation.

A dinuclear iron complex was investigated as biomimetic proton reduction catalyst. The complex structurally mimics the active site of the iron-only hydrogenase enzyme and was designed to hold a proton on the bridging ligand and a hydride on the iron centers. Thermodynamics and kinetics of the protonation reactions and the electrochemical behavior of the different protonation states were studied in view of their potential catalytic performance.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2007. 76 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 306
Keyword
Physical chemistry, artificial photosynthesis, solar fuel, WOC, OEC, accumulative electron transfer, hydrogenase mimic, oxygen evolution, proton reduction, water oxidation, Fysikalisk kemi
Identifiers
urn:nbn:se:uu:diva-7875 (URN)978-91-554-6889-7 (ISBN)
Public defence
2007-05-28, Häggsalen, Ångström, Uppsala, 10:00
Opponent
Supervisors
Available from: 2007-05-04 Created: 2007-05-04Bibliographically approved
2. On-line Electrochemistry Electrospray Ionisation Mass Spectrometry: Method Development and Applications
Open this publication in new window or tab >>On-line Electrochemistry Electrospray Ionisation Mass Spectrometry: Method Development and Applications
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis deals with studies of on-line electrochemistry electrospray ionisation mass spectrometry (EC/ESI-MS). It is shown that the use of EC/ESI-MS demands optimal coupling characteristics.

Pre-concentration and desalting, due to matrix exchange, were demonstrated for the model substance 1-hexanethiol in an EC/ESI-MS setup. The setup was also used for investigations of the oxidation states of the manganese complex [Mn2(bpmp)(µ-OAc)2][ClO4], where bpmp is a 2,6-bis[[N,N-di(2-pyridylmethyl)amino]methyl]-4-methylphenol compound. The manganese complex, which is relevant to artificial photosynthesis, was found to be a good model compound for the EC/ESI-MS studies, thanks to its many oxidation states. For the first time, the presence of the Mn(III,IV) state of the manganese complex was demonstrated in the studies.

During the experimental work, the importance of the electrode positioning within the electrochemical cell was investigated. Different EC cell configurations were studied using the manganese complex as a model substance. It was clearly shown that the EC cell design influences the distribution between the peaks in the mass spectra - not only for manganese complexes and Olsalazine but also for 4-chloroaniline.

A previously unknown comproportionation reaction was found for 4-chloroaniline involving the oxidised dimer, 4-[(4-chlorophenyl)imino]-2,5-cyclohexadien-1-imine. This reaction explained the unexpected presence of the signal due to the reduced dimer, 4-amino-4'-chlorodiphenylamine, in the mass spectra.

Furthermore, it was shown that EC/ESI-MS was successful in conjunction with miniaturised gold wire electrodes in a PDMS chip within which dopamine was oxidised with a conversion efficiency of 30%. The oxidation products of dopamine were detected after 0.6-1.2 seconds for 1.0 and 0.5 µl/min, respectively. The combination of electrochemically controlled solid-phase extraction (EC-SPE) with ESI-MS was found to be less straightforward than detecting anions pre-concentrated on a polypyrrole coated electrode with EC-SPE/ICP-MS.

The on-line combination of liquid chromatography with EC/ESI-MS/MS for studying antioxidants in yellow onion extracts was shown to be fast and a relatively easy complement to classical antioxidant activity determinations.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2009. 78 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 622
National Category
Chemical Sciences
Research subject
Analytical Chemistry
Identifiers
urn:nbn:se:uu:diva-99329 (URN)978-91-554-7459-1 (ISBN)
Public defence
2009-04-24, BMC, B42, Husargatan 3, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2009-04-02 Created: 2009-03-12 Last updated: 2009-04-06Bibliographically approved

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