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Ivanov S.,Bulgarian Academy of Science | Lange U.,University of Regensburg | Tsakova V.,Bulgarian Academy of Science | Mirsky V.M.,Lausitz University of Applied science
Sensors and Actuators, B: Chemical | Year: 2010

The layer by layer (LbL) adsorption technique was used to deposit a new electrocatalytic material consisting of palladium nanoparticles (Pd NPs) and polyaniline (PANI). As far as PANI adsorption did not affect the reactivity of the Pd NPs attached in the former adsorption step, the LbL technique offered the way of increasing the reactive Pd surface within a three-dimensional nanocomposite structure. In situ conductance measurements have shown that depending on the concentration of the PANI solution, used for the LbL adsorption, composites with either PANI-like (dependent on potential and pH) or metal-like (non-dependent on potential and pH) conductive behaviour can be obtained. Metal-like Pd NPs-PANI nanocomposites were studied as electrocatalytic materials for hydrazine oxidation. A linear concentration dependence of the voltammetric peak currents was observed in the 40-800 μM hydrazine concentration range, the sensitivity increasing with the amount of adsorbed Pd NPs. Amperometric measurements showed linear response in the 10-300 μM range with sensitivity 0.5 μA/μmol cm-2 and a theoretical detection limit estimated to be 0.06 μM. © 2010 Published by Elsevier B.V.

Here we report on the stereoselective benzylic hydroxylation and C1-C2 epoxidation of alkylbenzenes and styrene derivatives, respectively, by a heme-thiolate peroxygenase (EC from the fungus Agrocybe aegerita. Benzylic hydroxylation led exclusively to the (R)-1-phenylalkanols. For (R)-1-phenylethanol, (R)-1-phenylpropanol and (R)-1-tetralol, the ee reached >99%. For longer chain lengths, the enantiomeric excesses (ee) and total turnover numbers (TTN) decreased while the number of by-products, e.g. 1-phenylketones, increased. Epoxidation of straight chain and cyclic styrene derivatives gave a heterogeneous picture and resulted in moderate to excellent ee values and TTN: e.g., in the case of (1R,2S)-cis-β-methylstyrene oxide formation, an ee >99% and a TTN of 110000 was achieved. Hydroxylation and epoxidation were true peroxygenations, which was demonstrated by the incorporation of 18O from H 2 18O 2 into the products. The use of fed-batch devices and varying feeding strategies for the substrate and co-substrate turned out to be a suitable approach to optimize peroxygenase catalysis. © 2012 The Royal Society of Chemistry.

Jurk M.,Leibniz Institute for Molecular Pharmacology | Jurk M.,Free University of Berlin | Schramm P.,Leibniz Institute for Molecular Pharmacology | Schramm P.,Lausitz University of Applied science | Schmieder P.,Leibniz Institute for Molecular Pharmacology
Biochemical and Biophysical Research Communications | Year: 2013

Higher organisms as well as bacteria rely on information on the surrounding environment. In Bacillus subtilis, diverse extra-cellular stimuli are transformed into an intra-cellular response via a signal integration hub, called the stressosome. The subsequent signal transduction cascade initiates the general stress response (GSR). One of these stimuli is blue light, which is sensed by the bacterial photoreceptor YtvA. We report here that YtvA is permanently incorporated into the stressosome independent of its illumination state and that RsbT stimulation occurs without direct interaction between the kinase RsbT and YtvA but in a light dependent manner. Furthermore, we show that RsbRA adopts a scaffolding function inside the stressosome explaining on a molecular level why RsbRA is required for light-mediated stress response in vivo. © 2013 Elsevier Inc.

Lange U.,University of Regensburg | Mirsky V.M.,Lausitz University of Applied science
Analytica Chimica Acta | Year: 2011

A new design of conductometric chemical sensors based on conducting polymers as chemosensitive elements was suggested. The sensor includes six electrodes. Four inner electrodes coated by chemosensitive polymer are used for simultaneous two- and four-point resistance measurements thus providing information on the bulk polymer resistance and on the resistance of the polymer/electrode contacts. Two outer electrodes wired to inner electrodes by polymeric electrolyte are used for electrical control of redox state of the chemosensitive polymer. The outer electrodes are connected to potentiostat as reference and counter electrodes. It allows us to control redox state of the inner (working) electrodes. This new measurement configuration, resembling chemosensitive electrochemical transistors, provides an internal test of the sensor integrity and an electrically driven sensor regeneration. It was tested as a sensor for the detection of nitrogen dioxide. Polythiophene or polyaniline was used as receptors. Cyclic voltammograms of these polymers on the sensor surface measured in air atmosphere were very similar to that measured in aqueous electrolyte. A control of conductivity of these chemosensitive polymers by electrical potential applied vs. incorporated reference electrode was demonstrated. This effect was used for the regeneration of the chemosensitive material after exposure to nitrogen dioxide: in comparison to usual chemiresistors displaying an irreversible behavior in such test even in the time scale of hours, a completely reversible sensor regeneration within few minutes was observed. © 2010 Elsevier B.V.

Lange U.,University of Regensburg | Mirsky V.M.,Lausitz University of Applied science
Electrochimica Acta | Year: 2011

A new chemosensitive material based on palladium nanoparticles and PEDOT-PSS is described. The composite was characterized by transmission electron microscopy, cyclic voltammetry and in situ resistance measurements. The material was applied for conductometric detection of hydrazine and NADH. Upon exposure to these analytes PEDOT is reduced leading to an increase in its conductance. This process is catalyzed by palladium. A model for description of the potential dependence of polymer conductivity was suggested, tested and applied for the development of new calibration procedure of chemiresistors based on electroactive polymers. © 2011 Elsevier Ltd. All rights reserved.

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