| 1. |
- Berner, Simon, et al.
(author)
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Activity boost of a biomimetic oxidation catalyst by immobilization onto a gold surface
- 2006
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In: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 244:1, s. 86-91
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Journal article (peer-reviewed)abstract
- Thiol-functionalized cobalt porphyrins were used as a model system for investigating catalytic activity in homogeneous and heterogeneous oxidation catalysis. Self-assemble monolayers of thiol-functionalized cobalt porphyrins were prepared on a gold surface and served as heterogenous catalysts. These immoblilized molecules prevented the strong inactivation observed for their homogeneous congener. As a result, the turnover number per molecule in heterogeneous catalysis was at least 100 times higher than that of the corresponding homogeneous catalyst. It is atypical for a heterogenized catalyst to outperform its homogeneous congener. The properties of the molecular layers were characterized on the molecular level by means of X-ray photoelectorn spectroscopy (XPS) and scanning tunneling microscopy (STM). The results demonstrate that the performance of these biomimetic catalysts can be dramatically improved if the catalyst arangement can be controlled on the molecular level.
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| 2. |
- Steen, Robert O., 1978-, et al.
(author)
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Bis-cyclometallated Molecular Switches Based on 4,7-phenantroline and 1,5-naphthyridine Architecture
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Other publication (other academic/artistic)abstract
- Two new bis-terdentate ligands, 3,8-bis-(6-thiophen-2-yl-pyridin-2-yl)-[4,7]phenanthroline (L1) and 2,6-bis(6-(thiophen-2-yl)pyridin-2-yl)-1,5-naphthyridine (L2), capable of reversible double cyclometallation have been synthesized. Both syntheses proceeded via a Skraup synthesis followed by Stille cross-coupling with 2-thiophen-2-yl-6-tributylstannylpyridine to yield the final product. The Ru2(tpy)2-complex of L1 was shown to be capable of reversible cyclometallation, where the bis-cyclometallated (C,C) isomer of the complex had an oxidation potential of +249 mV while the oxidation potential of the doubly S-coordinated (S,S) complex was +987 mV. No ground state interaction between the Ru cores was however found. In theory the complex should display a third, mixed, state. An S,C-coordinated isomer would open the way for molecular electronic applications based on ternary logic. However, despite attempts the S,C-coordinated complex could not be generated.
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| 3. |
- Steen, Robert O., 1978-, et al.
(author)
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Coordination-mode pH-activated Molecular Switches based on Ruthenium(II) Oligopyridine Complex Architecture
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Other publication (other academic/artistic)abstract
- A number of [Ru(tpy)L] complexes (where L is a ligand based on the 6-thien-2-yl-2,2’-bipyridine motif) have been generated to study the ability of this terdentate motif to switch between a N,N,C and a N,N,S binding mode as a function of pH and irradiation. Whilst the parent system 6-thien-2-yl-2,2’-bipyridine (1) displayed facile switching between the orange and purple forms, heavier analogues displayed sluggish switching – most likely resulting from a large moment of inertia about the bond between the S/C-bonded thiophene ring and the chelating bipyridine unit. Prototypic unsymmetrical bimetallic complexes (C7S and C7C) have been generated in order to test if the binding mode of the switching unit can affect the oxidation potential of the remote [Ru(bpy)2(L)] unit. The results of cyclic voltammetry studies suggest that only weak electronic coupling between the metal cores exists, and that the coordination mode (N,N,C or N,N,S) of the thiophene moiety only has a small effect on the oxidation potential of the [Ru(bpy)2(L)] unit.
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| 4. |
- Yu, Xinhai, et al.
(author)
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Pt-Co catalyst-coated channel plate reactor for preferential CO oxidation
- 2011
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In: International journal of hydrogen energy. - : Elsevier BV. - 0360-3199 .- 1879-3487. ; 36:5, s. 3778-3788
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Journal article (peer-reviewed)abstract
- To achieve preferential CO oxidation, a Pt-Co catalyst-coated channel plate reactor (CCPR) was produced via conventional mechanical milling and catalyst coating. The proposed reactor performed well under a wide range of operating temperatures and provided satisfactory results at low temperatures (CO concentrations of 1-10 ppm at 413-443 K and 1-50 ppm at 413-453 K). In the proposed CCPR, significant deactivation was not observed during continuous operation for 100 h. In addition, the reactor exhibited excellent tolerance to undesirable conditions, including reaction temperature runaway and feeding stream failure. Characterisation results indicated that the catalytic activity of the proposed CCPR was high due to the formation of Pt3Co intermetallic compounds and nanoscale metal particles. The capacity per channel of the proposed CCPR was approximately 50-100 times greater than those of conventional microchannel reactors; thus, problems associated with excessive reactors were significantly reduced. In general, the results indicated that CCPR has great potential in the small-scale production of hydrogen for fuel cells.
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| 5. |
- Berner, Simon, et al.
(author)
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Electronic and structural studies of immobilized thiol-derivatized cobalt porphyrins on gold surfaces
- 2007
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In: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 253:18, s. 7540-7548
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Journal article (peer-reviewed)abstract
- The immobilisation of thiol-derivatized cobalt porphyrins on gold surfaces has been studied in detail by means of combined scanning tunnelling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). S-thioacetyl has been used as a protective group for the thiol. Different routes for deprotection of the acetyl groups were performed in acidic and in basic conditions. The results show the formation of monolayer films for the different preparation schemes. The immobilisation of the molecules on the gold surface takes place through the thiol-linkers by the formation of multiple thiolate bonds. In the case of layers formed with protected porphyrins approximately 60% of the linkers are bonded to the gold surface whereas for deprotected layers the amount of bonded linkers is increased up to about 80%. STM measurements revealed that the molecules arrange in a disordered overlayer and do not exhibit mobility on the gold surface. Annealing experiments have been performed in order to test the stability of the porphyrin layers. Disordered patterns have been observed in the STM images after annealing at T = 400 °C. XPS revealed that the sulphur content disappeared completely after annealing at T = 180 °C and that the molecules did undergo significant modifications.
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| 6. |
- Olofsson, Jessica, 1975, et al.
(author)
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Scanning electroporation of selected areas of adherent cell cultures
- 2007
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In: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 79:12, s. 4410-4418
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Journal article (peer-reviewed)abstract
- We present a computer-controlled scanning electroporation method. Adherent cells are electroporated using an electrolyte-filled capillary in contact with an electrode. The capillary can be scanned over a cell culture and locally deliver both an electric field and an electroporation agent to the target area without affecting surrounding cells. The instantaneous size of the targeted area is determined by the dimensions of the capillary. The size and shape of the total electroporated area are defined by these dimensions in combination with the scanning pattern. For example, striped and serpentine patterns of electroporated cells in confluent cultures can be formed. As it is easy to switch between different electroporation agents, the method is suitable for design of cell cultures with complex composition. Finite element method simulations were used to study the spatial distributions of the electric field and the concentration of an electroporation agent, as well as the fluid dynamics related to scanning and flow of electroporation agent from the capillary. The method was validated for transfection by introduction of a 9-base-pair-long randomized oligonucleotide into PC12 cells and a pmaxGFP plasmid coding for green fluorescent protein into CHO and WSS cells.
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| 7. |
- Wolf, Matthew J., et al.
(author)
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STM Images of Anionic Defects at CeO2(111)-A Theoretical Perspective
- 2019
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In: Frontiers in Chemistry. - : FRONTIERS MEDIA SA. - 2296-2646. ; 7
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Journal article (peer-reviewed)abstract
- We present a theoretically oriented analysis of the appearance and properties of plausible candidates for the anionic defects observed in scanning tunneling microscopy (STM) experiments on CeO2(111). The simulations are based on density functional theory (DFT) and cover oxygen vacancies, fluorine impurities and hydroxyl groups in the surface and sub-surface layers. In the surface layer, all three appear as missing spots in the oxygen sublattice in filled state simulated STM images, but they are distinguishable in empty state images, where surface oxygen vacancies and hydroxyls appear as, respectively, diffuse and sharp bright features at oxygen sites, while fluorine defects appear as triangles of darkened Ce ions. In the sub-surface layer, all three defects present more complex patterns, with different combinations of brightened oxygen ion triangles and/or darkened Ce ion triangles, so we provide image maps to support experimental identification. We also discuss other properties that could be used to distinguish the defects, namely their diffusion rates and distributions.
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| 8. |
- Kullgren, Jolla, 1978-, et al.
(author)
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Many competing ceria (110) oxygen vacancy structures : From small to large supercells
- 2012
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 137:4, s. 044705-
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Journal article (peer-reviewed)abstract
- We present periodic "DFT+U" studies of single oxygen vacancies on the CeO2(110) surface using a number of different supercells, finding a range of different local minimum structures for the vacancy and its two accompanying Ce(III) ions. We find three different geometrical structures in combination with a variety of different Ce(III) localization patterns, several of which have not been studied before. The desired trapping of electrons was achieved in a two-stage optimization procedure. We find that the surface oxygen nearest to the vacancy either moves within the plane towards the vacancy, or rises out of the surface into either a symmetric or an unsymmetric bridge structure. Results are shown in seven slab geometry supercells, p(2 x 1), p(2 x 2), p(2 x 3), p(3 x 2), p(2 x 4), p(4 x 2), and p(3 x 3), and indicate that the choice of supercell can affect the results qualitatively and quantitatively. An unsymmetric bridge structure with one nearest and one next-nearest neighbour Ce(III) ion (a combination of localizations not previously found) is the ground state in all (but one) of the supercells studied here, and the relative stability of other structures depends strongly on supercell size. Within any one supercell the formation energies of the different vacancy structures differ by up to 0.5 eV, but the same structure can vary by up to similar to 1 eV between supercells. Furthermore, finite size scaling suggests that the remaining errors (compared to still larger supercells) can also be similar to 1 eV for some vacancy structures.
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| 9. |
- Baev, Alexander, et al.
(author)
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Upconverted lasing based on many-photon absorption : an all dynamic description
- 2004
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In: Journal of the Optical Society of America. B, Optical physics. - 0740-3224 .- 1520-8540. ; 21:2, s. 384-396
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Journal article (peer-reviewed)abstract
- A theory is developed for the propagation through a nonlinear medium of strong pump and amplifiedspontaneous-emission pulses. The theory is based on a solution of the density matrix equations that aims at providing an adequate treatment of the nonlinear polarization of the material without addressing the Taylor expansion over the powers of intensity. The theory has been applied for modeling of three-photon absorption induced upconverted stimulated emission of organic molecules in solvents. Numerical results are presented for the organic chromophore 4-[N-(2-hydroxyethyl)-N-(methyl)amino phenyl]-4'-(6-hydroxyhexyl sulfonyl) stilbene dissolved in dimethyl sulfoxide. The results are in good agreement with available experimental results.
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| 10. |
- Bergkvist, Magnus, et al.
(author)
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Surface-dependent conformations of human plasma fibronectin adsorbed to silica, mica, and hydrophobic surfaces, studied with use of Atomic Force Microscopy
- 2003
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In: Journal of biomedical materials research. Part A.. - : Wiley. - 0021-9304 .- 1097-4636. ; 64:2, s. 349-356
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Journal article (peer-reviewed)abstract
- Human plasma fibronectin (Fn) is a large flexible protein stabilized by intermolecular ionic interactions forming a compact structure. On altering solution conditions, the structure can revert to a more expanded state, thereby exposing previously hidden domains (e.g., cell-binding sites). Electron microscopy images of Fn air-sprayed onto mica surfaces show elongated protein structures, indicating a surface-induced structural change. This makes it interesting to investigate the influence of surface properties on the structure of adsorbed Fn. We have used intermittent-contact Atomic Force Microscopy to investigate the structure of Fn adsorbed onto mica, silica, and methylated silica surfaces. We observed that on silica surfaces, which is hydrophilic, most (70%) of the molecules had an elongated structure with partial intramolecular chain interactions, compare to molecules adsorbed on hydrophobic, methylated surfaces, where a compact structure predominated (70%). On mica surfaces, both compact and elongated protein structures were observed, with a slight preference for the elongated form (53%). Results show that surface physical properties influence the molecular structure of fibronectin on adsorption, which could provide useful information in understanding surface-induced in vivo responses.
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