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Mimicking the Outer Coordination Sphere in [FeFe]-Hydrogenase Active Site Models: From Extended Ligand Design to Metal-Organic Frameworks
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Biomimetic catalysis is an important research field, as a better understanding of nature´s powerful toolbox for the conversion of molecules can lead to technological progress. [FeFe]-hydrogenases are very efficient catalysts for hydrogen production. These enzymes play a crucial role in the metabolism of green algae and certain cyanobacteria. Their active site consists of a diiron complex that is embedded in an interactive protein matrix.

In this thesis, two pathways for mimicking the outer coordination sphere effects resulting from the protein matrix are explored.

The first is the construction of model complexes containing phosphine ligands that are coordinated to the iron center as well as covalently linked to the bridging ligand of the complex. The effect of such linkers is an increased energy barrier for the rotation of the Fe(CO2)(PL3)-subunit, which potentially could stabilize a terminal hydride that is an important intermediate in the proton reduction cycle.

The second pathway follows the incorporation of [FeFe]-hydrogenase active site model complexes into metal-organic frameworks (MOFs). Resulting MOF-catalysts exhibit increased photocatalytic activity compared to homogenous references due to a stabilizing effect on catalytic intermediates by the surrounding framework. Catalyst accessibility within the MOF and the influence of the framework on chemical reactivity are examined in the work presented. Furthermore, an initial step towards application of MOF-catalysts in a device was made by interfacing them with electrodes.

The work of this thesis highlights strategies for the improvement of biomimetic model catalysts and the knowledge gained can be transferred to other systems mimicking the function of enzymes. 

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. , p. 115
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1498
Keywords [en]
[FeFe]-hydrogenases, outer coordination sphere, model complexes, biomimetic catalysis, artificial photosynthesis, metal-organic frameworks
National Category
Inorganic Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-318975ISBN: 978-91-554-9878-8 (print)OAI: oai:DiVA.org:uu-318975DiVA, id: diva2:1085660
Public defence
2017-05-19, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2017-04-28 Created: 2017-03-30 Last updated: 2017-05-05
List of papers
1. Direct Observation of Key Catalytic Intermediates in a Photoinduced Proton Reduction Cycle with a Diiron Carbonyl Complex
Open this publication in new window or tab >>Direct Observation of Key Catalytic Intermediates in a Photoinduced Proton Reduction Cycle with a Diiron Carbonyl Complex
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2014 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 136, no 50, p. 17366-17369Article in journal (Refereed) Published
Abstract [en]

The structure and reactivity of intermediatesin the photocatalytic cycle of a proton reductioncatalyst, [Fe2(bdt)(CO)6] (bdt = benzenedithiolate), wereinvestigated by time-resolved spectroscopy. The singlyreduced catalyst [Fe2(bdt)(CO)6]−, a key intermediate inphotocatalytic H2 formation, was generated by reactionwith one-electron reductants in laser flash-quench experimentsand could be observed spectroscopically on thenanoseconds to microseconds time scale. From UV/visand IR spectroscopy, [Fe2(bdt)(CO)6]− is readilydistinguished from the two-electron reduced catalyst[Fe2(bdt)(CO)6]2− that is obtained inevitably in theelectrochemical reduction of [Fe2(bdt)(CO)6]. For thedisproportionation rate constant of [Fe2(bdt)(CO)6]−, anupper limit on the order of 107 M−1 s−1 was estimated,which precludes a major role of [Fe2(bdt)(CO)6]2− inphotoinduced proton reduction cycles. Structurally [Fe2-(bdt)(CO)6]− is characterized by a rather asymmetricallydistorted geometry with one broken Fe−S bond and sixterminal CO ligands. Acids with pKa ≤ 12.7 protonate[Fe2(bdt)(CO)6]− with bimolecular rate constants of 4 ×106, 7 × 106, and 2 × 108 M−1 s−1 (trichloroacetic,trifluoroacetic, and toluenesulfonic acids, respectively).The resulting hydride complex [Fe2(bdt)(CO)6H] istherefore likely to be an intermediate in photocatalyticcycles. This intermediate resembles structurally andelectronically the parent complex [Fe2(bdt)(CO)6], withvery similar carbonyl stretching frequencies.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2014
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-240552 (URN)10.1021/ja5085817 (DOI)000346682600003 ()
Available from: 2015-01-07 Created: 2015-01-07 Last updated: 2017-12-05
2. Restricted Rotation of an Fe(CO)2(PL3)-subunit in [FeFe ]-Hydrogenase Active Site Mimics by Tethering Phosphine Ligands
Open this publication in new window or tab >>Restricted Rotation of an Fe(CO)2(PL3)-subunit in [FeFe ]-Hydrogenase Active Site Mimics by Tethering Phosphine Ligands
(English)Manuscript (preprint) (Other academic)
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-318973 (URN)
Available from: 2017-03-29 Created: 2017-03-29 Last updated: 2017-03-30
3. Enhanced Photochemical Hydrogen Production by a Molecular Diiron Catalyst Incorporated into a Metal-Organic Framework
Open this publication in new window or tab >>Enhanced Photochemical Hydrogen Production by a Molecular Diiron Catalyst Incorporated into a Metal-Organic Framework
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2013 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 135, no 45, p. 16997-17003Article in journal (Refereed) Published
Abstract [en]

A molecular proton reduction catalyst [FeFe](dcbdt)(CO)(6) (1, dcbdt = 1,4-dicarboxylbenzene-2,3-dithiolate) with structural similarities to [FeFe]-hydrogenase active sites has been incorporated into a highly robust Zr(IV)-based metal-organic framework (MOF) by postsynthetic exchange (PSE). The PSE protocol is crucial as direct solvothermal synthesis fails to produce the functionalized MOF. The molecular integrity of the organometallic site within the MOF is demonstrated by a variety of techniques, including X-ray absorption spectroscopy. In conjunction with [Ru(bpy)(3)](2+) as a photosensitizer and ascorbate as an electron donor, MOF-[FeFe](dcbdt)(CO)(6) catalyzes photochemical hydrogen evolution in water at pH 5. The immobilized catalyst shows substantially improved initial rates and overall hydrogen production when compared to a reference system of complex 1 in solution. Improved catalytic performance is ascribed to structural stabilization of the complex when incorporated in the MOF as well as the protection of reduced catalysts 1(-) and 1(2-) from undesirable charge recombination with oxidized ascorbate.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-212862 (URN)10.1021/ja407176p (DOI)000327103600042 ()
Available from: 2013-12-17 Created: 2013-12-16 Last updated: 2017-12-06Bibliographically approved
4. Catalyst accessibility to chemical reductants in metal–organic frameworks
Open this publication in new window or tab >>Catalyst accessibility to chemical reductants in metal–organic frameworks
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2017 (English)In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 53, no 22, p. 3257-3260Article in journal (Refereed) Published
Abstract [en]

A molecular H2-evolving catalyst, [Fe2(cbdt)(CO)6] ([FeFe], cbdt = 3-carboxybenzene-1,2-dithiolate), has been attached covalently to an amino-functionalized MIL-101(Cr) through an amide bond. Chemical reduction experiments reveal that the MOF channels can be clogged by ion pairs that are formed between the oxidized reductant and the reduced catalyst. This effect is lessened in MIL-101-NH-[FeFe] with lower [FeFe] loadings. On longer timescales, it is shown that large proportions of the [FeFe] catalysts within the MOF engage in photochemical hydrogen production and the amount of produced hydrogen is proportional to the catalyst loading.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-318972 (URN)10.1039/c7cc00022g (DOI)000398998500023 ()28261731 (PubMedID)
Available from: 2017-03-29 Created: 2017-03-29 Last updated: 2017-12-28Bibliographically approved
5. Functionalization of robust Zr(IV)-based metal-organic framework films via a postsynthetic ligand exchange
Open this publication in new window or tab >>Functionalization of robust Zr(IV)-based metal-organic framework films via a postsynthetic ligand exchange
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2015 (English)In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 51, no 1, p. 66-69Article in journal (Refereed) Published
Abstract [en]

A facile and efficient fabrication approach for homogeneous, crack-free UiO-66 films with exceptionally high crystallinity and tunable thickness on a transparent and conductive glass substrate is reported. Two functionalized species, a catechol ligand and a Fe-2 complex with structural resemblance to the active site of [FeFe] hydrogenase, were introduced into the MOF films via a postsynthetic exchange. Voltammetric studies show the [FeFe] complex in the thinner UiO-66 films (2-5 mu m) can be reduced electrochemically.

National Category
Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-241388 (URN)10.1039/c4cc08218d (DOI)000345909400008 ()25364799 (PubMedID)
Available from: 2015-01-26 Created: 2015-01-12 Last updated: 2017-12-05Bibliographically approved
6. [FeFe] Hydrogenase Active Site Model Chemistry in a UiO-66 Metal-Organic Framework
Open this publication in new window or tab >>[FeFe] Hydrogenase Active Site Model Chemistry in a UiO-66 Metal-Organic Framework
(English)Article in journal (Refereed) Submitted
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-318974 (URN)
Available from: 2017-03-29 Created: 2017-03-29 Last updated: 2017-03-30

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