| 1. |
- Csendes, Z., et al.
(författare)
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Synthesis, structural characterisation, and catalytic activity of Mn(II)-protected amino acid complexes covalently immobilised on chloropropylated silica gel
- 2015
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Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861. ; 241, s. 264-269
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Tidskriftsartikel (refereegranskat)abstract
- In this work the syntheses, structure, superoxide dismutase (SOD) activity and the catalytic use in the oxidative transformations of cyclohexene of covalently grafted Mn(II)-complexes formed with various C-protected amino acid (L-histidine, L-cysteine and L-cystine) ligands are presented. The structural features of the surface complexes were studied by EPR, X-ray absorption, and mid/far IR spectroscopies. The superoxide dismutase activities of the materials were determined in a biochemical test reaction. The obtained materials were used as catalysts for the oxidation of cyclohexene with peracetic acid in acetone. Covalent grafting and building the complex onto the surface of the chloropropylated silica gel were successful in all cases. It was found that in many instances the structures obtained and the coordinating groups substantially varied upon changing the conditions of the syntheses. All the covalently immobilised Mn(II)-complexes displayed superoxide dismutase activity and could catalyse the oxidation of cyclohexene. (C) 2014 Elsevier B.V. All rights reserved.
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| 2. |
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| 3. |
- Csendes, Z., et al.
(författare)
-
Superoxide dismutase inspired Fe(III)-amino acid complexes covalently grafted onto chloropropylated silica gel - Syntheses, structural characterisation and catalytic activity
- 2013
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Ingår i: Journal of Molecular Structure. - : Elsevier BV. - 0022-2860. ; 1044, s. 39-45
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Tidskriftsartikel (refereegranskat)abstract
- In this work the syntheses, structure and SOD activity of covalently grafted Fe(III)-complexes formed with various N- or C-protected amino acid ligands (L-histidine and L-tyrosine) inspired by the active site of the Fe SOD enzyme are presented. Chloropropylated silica gel was used as support to mimic the proteomic skeleton of the enzyme. Anchored complexes having uniform amino acids as well as their two-component mixtures have been prepared. The products were characterised by mid and far IR and Raman spectroscopies. SOD activities of the substances were determined via the Beauchamp-Fridovich test reaction. It was found that the preparation of covalently anchored Fe(III)-amino acid complexes was successful in many cases. The structures of the anchored complexes and the coordinating groups varied upon changing the conditions of the syntheses. All the covalently immobilised complexes displayed (in some instances appreciable) SOD activity. (C) 2012 Elsevier B.V. All rights reserved.
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| 4. |
- Kjær, Kasper S., et al.
(författare)
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Finding intersections between electronic excited state potential energy surfaces with simultaneous ultrafast X-ray scattering and spectroscopy
- 2019
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Ingår i: Chemical Science. - : Royal Society of Chemistry (RSC). - 2041-6520 .- 2041-6539. ; 10:22, s. 5749-5760
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Tidskriftsartikel (refereegranskat)abstract
- Light-driven molecular reactions are dictated by the excited state potential energy landscape, depending critically on the location of conical intersections and intersystem crossing points between potential surfaces where non-adiabatic effects govern transition probabilities between distinct electronic states. While ultrafast studies have provided significant insight into electronic excited state reaction dynamics, experimental approaches for identifying and characterizing intersections and seams between electronic states remain highly system dependent. Here we show that for 3d transition metal systems simultaneously recorded X-ray diffuse scattering and X-ray emission spectroscopy at sub-70 femtosecond time-resolution provide a solid experimental foundation for determining the mechanistic details of excited state reactions. In modeling the mechanistic information retrieved from such experiments, it becomes possible to identify the dominant trajectory followed during the excited state cascade and to determine the relevant loci of intersections between states. We illustrate our approach by explicitly mapping parts of the potential energy landscape dictating the light driven low-to-high spin-state transition (spin crossover) of [Fe(2,2′-bipyridine)3]2+, where the strongly coupled nuclear and electronic dynamics have been a source of interest and controversy. We anticipate that simultaneous X-ray diffuse scattering and X-ray emission spectroscopy will provide a valuable approach for mapping the reactive trajectories of light-triggered molecular systems involving 3d transition metals.
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| 5. |
- Kjær, Kasper S., et al.
(författare)
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Solvent control of charge transfer excited state relaxation pathways in [Fe(2,2′-bipyridine)(CN)4]2-
- 2018
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 20:6, s. 4238-4249
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Tidskriftsartikel (refereegranskat)abstract
- The excited state dynamics of solvated [Fe(bpy)(CN)4]2-, where bpy = 2,2′-bipyridine, show significant sensitivity to the solvent Lewis acidity. Using a combination of optical absorption and X-ray emission transient spectroscopies, we have previously shown that the metal to ligand charge transfer (MLCT) excited state of [Fe(bpy)(CN)4]2- has a 19 picosecond lifetime and no discernable contribution from metal centered (MC) states in weak Lewis acid solvents, such as dimethyl sulfoxide and acetonitrile.1,2 In the present work, we use the same combination of spectroscopic techniques to measure the MLCT excited state relaxation dynamics of [Fe(bpy)(CN)4]2- in water, a strong Lewis acid solvent. The charge-transfer excited state is now found to decay in less than 100 femtoseconds, forming a quasi-stable metal centered excited state with a 13 picosecond lifetime. We find that this MC excited state has triplet (3MC) character, unlike other reported six-coordinate Fe(ii)-centered coordination compounds, which form MC quintet (5MC) states. The solvent dependent changes in excited state non-radiative relaxation for [Fe(bpy)(CN)4]2- allows us to infer the influence of the solvent on the electronic structure of the complex. Furthermore, the robust characterization of the dynamics and optical spectral signatures of the isolated 3MC intermediate provides a strong foundation for identifying 3MC intermediates in the electronic excited state relaxation mechanisms of similar Fe-centered systems being developed for solar applications.
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| 6. |
- Kunnus, Kristjan, et al.
(författare)
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Vibrational wavepacket dynamics in Fe carbene photosensitizer determined with femtosecond X-ray emission and scattering
- 2020
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Ingår i: Nature Communications. - : Springer Nature. - 2041-1723. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- The non-equilibrium dynamics of electrons and nuclei govern the function of photoactive materials. Disentangling these dynamics remains a critical goal for understanding photoactive materials. Here we investigate the photoinduced dynamics of the [Fe(bmip)2]2+ photosensitizer, where bmip = 2,6-bis(3-methyl-imidazole-1-ylidine)-pyridine, with simultaneous femtosecond-resolution Fe Kα and Kβ X-ray emission spectroscopy (XES) and X-ray solution scattering (XSS). This measurement shows temporal oscillations in the XES and XSS difference signals with the same 278 fs period oscillation. These oscillations originate from an Fe-ligand stretching vibrational wavepacket on a triplet metal-centered (3MC) excited state surface. This 3MC state is populated with a 110 fs time constant by 40% of the excited molecules while the rest relax to a 3MLCT excited state. The sensitivity of the Kα XES to molecular structure results from a 0.7% average Fe-ligand bond length shift between the 1 s and 2p core-ionized states surfaces.
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| 7. |
- Tatsuno, Hideyuki, et al.
(författare)
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Hot Branching Dynamics in a Light-Harvesting Iron Carbene Complex Revealed by Ultrafast X-ray Emission Spectroscopy
- 2020
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Ingår i: Angewandte Chemie - International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 59:1, s. 364-372
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Tidskriftsartikel (refereegranskat)abstract
- Iron N-heterocyclic carbene (NHC) complexes have received a great deal of attention recently because of their growing potential as light sensitizers or photocatalysts. We present a sub-ps X-ray spectroscopy study of an FeIINHC complex that identifies and quantifies the states involved in the deactivation cascade after light absorption. Excited molecules relax back to the ground state along two pathways: After population of a hot 3MLCT state, from the initially excited 1MLCT state, 30 % of the molecules undergo ultrafast (150 fs) relaxation to the 3MC state, in competition with vibrational relaxation and cooling to the relaxed 3MLCT state. The relaxed 3MLCT state then decays much more slowly (7.6 ps) to the 3MC state. The 3MC state is rapidly (2.2 ps) deactivated to the ground state. The 5MC state is not involved in the deactivation pathway. The ultrafast partial deactivation of the 3MLCT state constitutes a loss channel from the point of view of photochemical efficiency and highlights the necessity to screen transition-metal complexes for similar ultrafast decays to optimize photochemical performance.
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| 8. |
- Varga, G., et al.
(författare)
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Building, characterising and catalytic activity testing of Co-C-protected amino acid complexes covalently grafted onto chloropropylated silica gel
- 2015
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Ingår i: Journal of Molecular Structure. - : Elsevier BV. - 0022-2860. ; 1090, s. 138-143
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Tidskriftsartikel (refereegranskat)abstract
- Co-C-protected amino acid (C-protected L-histidine, L-tyrosine, L-cysteine and L-cystine) complexes were covalently grafted onto chloropropylated silica gel, and the materials thus obtained were structurally characterised by mid/far IR and X-ray absorption spectroscopies. The superoxide dismutase-like activities of the substances were determined via the Beauchamp-Fridovich test reaction. It was found that covalent grafting and the preparation of the anchored complexes were successful in most cases. The coordinating groups varied upon changing the conditions of the syntheses. All materials displayed catalytic activity, although catalytic activities differed widely. (C) 2014 Elsevier B.V. All rights reserved.
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| 9. |
- Gustafson, Karl P. J., et al.
(författare)
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In Situ Structural Determination of a Homogeneous Ruthenium Racemization Catalyst and Its Activated Intermediates Using X-Ray Absorption Spectroscopy
- 2020
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 26:15, s. 3411-3419
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Tidskriftsartikel (refereegranskat)abstract
- The activation process of a known Ru-catalyst, dicarbonyl(pentaphenylcyclopentadienyl)ruthenium chloride, has been studied in detail using time resolved in situ X-ray absorption spectroscopy. The data provide bond lengths of the species involved in the process as well as information about bond formation and bond breaking. On addition of potassium tert-butoxide, the catalyst is activated and an alkoxide complex is formed. The catalyst activation proceeds via a key acyl intermediate, which gives rise to a complete structural change in the coordination environment around the Ru atom. The rate of activation for the different catalysts was found to be highly dependent on the electronic properties of the cyclopentadienyl ligand. During catalytic racemization of 1-phenylethanol a fast-dynamic equilibrium was observed.
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| 10. |
- Sranko, D., et al.
(författare)
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A SEM, EDX and XAS characterization of Ba(II)Fe(III) layered double hydroxides
- 2011
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Ingår i: Journal of Molecular Structure. - : Elsevier BV. - 0022-2860. ; 993:1-3, s. 62-66
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Konferensbidrag (refereegranskat)abstract
- The structural characteristics of Ba-Fe double hydroxides were studied by various methods, such as scanning electron microscopy (SEM), energy dispersive X-ray (EDX) fluorescence and X-ray absorption spectroscopies (XAS). It was verified that under hyperalkaline conditions (using 10 M or 20 M NaOH solution for precipitating the substances) layered double hydroxides could be prepared and the structure collapsed on heat treatment at 523 K. Important structural parameters could also be obtained through the quantitative analysis of the XAS spectrum of Ba3Fe-LDH made using 20 M NaOH for precipitating the material. (C) 2010 Elsevier B.V. All rights reserved.
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