| 1. |
- Larsson, Henrik, et al.
(författare)
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Charge propagation in [Os(bpy)2(PVP)xCl]Cl polymers. An example of mean field behavior in a system with constrained diffusion of redox sites?
- 1995
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Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier. - 0022-0728 .- 1873-2569. ; 381:1-2, s. 133-142
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Tidskriftsartikel (refereegranskat)abstract
- Chronocoulometry and impedance spectroscopy were used to study the dynamics of charge transport in a series of methylated [Os(bpy)(2)(PVP)(x)Cl]Cl polymers (PVP = poly(4-vinylpyridine); bpy = 2,2'-bipyridine; 5 less than or equal to x less than or equal to 40) which were deposited as thin firms on glassy carbon electrodes. Apparent charge propagation diffusion coefficients D-app were of the order of 10(-8) cm(2) s(-1) and were approximately linearly dependent on the total concentration of redox sites but independent of the ratio of oxidized to reduced centres present in a particular coating. Attempts were made to explain these observations in terms of a recent theory of charge transport appropriate for systems in which the redox sites are permanently attached to the polymer chains. It was found that the concentration dependence and magnitude of D-app could be explained satisfactorily by a mean field model of charge propagation.
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| 2. |
- Larsson, Henrik, et al.
(författare)
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Electron transport in quaternized poly(4-vinylpyridine) films containing pentacyanoferrate(II/III) on electrodes. The influence of the binding type of the electroactive complex
- 1992
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Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier. - 0022-0728 .- 1873-2569 .- 1572-6657. ; 336:1-2, s. 263-279
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Tidskriftsartikel (refereegranskat)abstract
- This study is an attempt to investigate how charge transport in thin redox polymer films spin-coated onto glassy carbon electrode surfaces is affected by the way in which the electroactive group is bound to the polymeric matrix. Two different redox polymers based on methylated and cross-linked poly(4-vinylpyridine) and pentacyanoferrate(II/III) have been synthesized. In the first case, an anionic complex formed by coordinating pyridine to pentacyanoferrate(II) was electrostatically bound to the methylated pyridine groups in the polymer matrix. In the other case, pentacyanoferroate(II) was coordinated directly to unmethylated pyridine groups in the partly methylated polymer film. The film thicknesses were estimated with ellipsometric measurements. Their electrochemical characteristics were investigated using cyclic voltammetry, chronocoulometry and impedance spectroscopy. The apparent charge-transport diffusion coefficient D(app) was almost two orders of magnitude greater in the ion-exchange polymer than in the redox polymer with coordinatively bound electroactive groups. The temperature dependence of D(app) was evaluated using Arrhenius plots.
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| 3. |
- Larsson, Henrik
(författare)
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Ellipsometric determinations of the thicknesses of dry and electrolyte-immersed poly(4-vinylpyridine) films containing coordinated light-absorbing [Os(bpy)2pvpCl]2+/+ redox groups
- 1994
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Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier. - 1572-6657 .- 1873-2569. ; 365:1-2, s. 229-237
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Tidskriftsartikel (refereegranskat)abstract
- Ellipsometry has been used to measure the dimensions of quaternized poly(4-vinylpyridine) films containing [Os(bpy)2pvpCl]2+/+ redox groups on glassy carbon electrodes. Film thicknesses and complex refractive indices were deduced using molar absorptivities obtained from photometry or a combination of photometry and cyclic voltammetry. The precision in the film thicknesses was estimated using data obtained from thick and thin films with the same polymer + redox group compositions and from data recorded at 60-degrees and 70-degrees angles of incidence of 633 nm laser light. The effects of errors in the experimentally determined molar absorptivity of the redox groups on film thickness were also assessed. The results of this study suggest that reliable thicknesses can be obtained for both dry and electrolyte-swollen films, and that the presence of light-absorbing redox groups within coatings such as these presents no real obstacle for ellipsometric determinations.
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| 4. |
- Sharp, Michael, et al.
(författare)
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Studies of the temperature dependence of charge propagation rates in quaternized poly(4-vinylpyridine) polymers containing electrostatically bound and coordinated redox sites
- 1995
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Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier. - 0022-0728 .- 1873-2569. ; 386:1-2, s. 189-195
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Tidskriftsartikel (refereegranskat)abstract
- The activation parameters associated with charge propagation in a series of quaternized poly(4-vinylpyridine) polymers, which contained both electrostatically hound and coordinated redox sites and which were deposited as thin films on electrode surfaces, were derived from the temperature dependence of apparent charge transport diffusion coefficients. The values of the activation energies and entropies obtained are discussed in terms of models of charge transport that are appropriate for redox polymers in which physical displacements of the redox sites are either free or constrained.
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| 9. |
- Ademark, Pia, et al.
(författare)
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Hydrolytic properties of a beta-mannosidase purified from Aspergillus niger. J. Biotechnol. 75: 281-289.
- 1999
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Ingår i: Journal of Biotechnology. - 1873-4863. ; 75:2-3, s. 281-289
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Tidskriftsartikel (refereegranskat)abstract
- A β-mannosidase was purified to homogeneity from the culture filtrate of Aspergillus niger. A specific activity of 500 nkat mg−1 and a 53-fold purification was achieved using ammonium sulfate precipitation, anion-exchange chromatography, and gel filtration. The isolated enzyme has an isoelectric point of 5.0 and appears to be a dimer composed of two 135-kDa subunits. It is a glycoprotein and contains 17% N-linked carbohydrate by weight. Maximal activity was observed at pH 2.4–5.0 and at 70°C. The β-mannosidase hydrolyzed β-1,4-linked manno-oligosaccharides of degree of polymerization (DP) 2–6 and also released mannose from polymeric ivory nut mannan and galactomannan. The Km and Vmax values for p-nitrophenyl-β-Image-mannopyranoside were 0.30 mM and 500 nkat mg−1, respectively. Hydrolysis of Image-galactose substituted manno-oligosaccharides showed that the β-mannosidase was able to cleave up to, but not beyond, a side group. An internal peptide sequence of 15 amino acids was highly similar to that of an Aspergillus aculeatus β-mannosidase belonging to family 2 of glycosyl hydrolases.
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| 10. |
- Amine, A., et al.
(författare)
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A Microdialysis probe coupled with a miniaturized thermal glucose sensor for in vivo monitoring
- 1995
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Ingår i: Analytical Letters. - : Informa UK Limited. - 0003-2719 .- 1532-236X. ; 28:13, s. 2275-2286
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Tidskriftsartikel (refereegranskat)abstract
- A miniaturized thermal flow injection analysis biosensor has been coupled with a microdialysis probe for continuous subcutaneous glucose monitoring. Thermal biosensors are based on the principle of measuring the heat evolved during enzyme catalysed reactions. The system presented here consists of a miniaturized thermal biosensor with a small column containing coimmibolized glucose oxidase and catalase. The analysis buffer passes through the column at a flow rate of 60μL/min via an 1μL sample loop which is connected to a microdialysis probe. Invitro results showed constant permeability of the probe and stability of the biosensor response during 24 hours. The response time was 85 sec giving a sample rate of 42 samples/hour. During a load experiment, the glucose profile in a healthy volunteer was followed both in the subcutaneous tissue and blood using the microdialysis set-up proposed and comparing to blood glucose analyser.
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