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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: 2012

Electroanalytical methods have been applied only in conducting media. An application of conducting polymers allows to overcome this limitation. If such material is in electrochemical equilibrium with dissolved redox active species, its electrical conductivity depends on the redox potential of these species. Therefore, conductometric measurements with conducting polymers can provide about the same information as classical redox electrodes. The approach was applied for redox titration. Equivalent points obtained by this titration in aqueous and organic electrolytes were identical. Then the approach was applied for determination of bromine number by redox titration in non-conducting organic phase. © 2012 Elsevier B.V.

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.

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.

Lange U.,University of Regensburg | Hirsch T.,University of Regensburg | Mirsky V.M.,Lausitz University of Applied science | Wolfbeis O.S.,University of Regensburg
Electrochimica Acta | Year: 2011

A composite material was prepared from graphene and palladium nanoparticles (PdNP) by layer-by-layer deposition on gold electrodes. The material was characterized by absorption spectroscopy, scanning electron microscopy, Raman spectroscopy and surface plasmon resonance. Cyclic voltammetry demonstrated the presence of electrocatalytic centers in the palladium decorated graphene. This material can serve as a sensor material for hydrogen at levels from 0.5 to 1% in synthetic air. Pure graphene is poorly sensitive to hydrogen, but incorporation of PdNPs increases its sensitivity by more than an order of magnitude. The effects of hydrogen, nitrogen dioxide and humidity were studied. Sensor regeneration is accelerated in humid air. The sensitivity of the nanocomposite depends on the number of bilayers of graphene-PdNPs. © 2011 Elsevier Ltd. All rights reserved.

Acker J.,Lausitz University of Applied science | Rietig A.,Lausitz University of Applied science | Steinert M.,Globalfoundries | Hoffmann V.,Leibniz Institute for Solid State and Materials Research
Journal of Physical Chemistry C | Year: 2012

The stoichiometry of the wet-chemical etching of silicon in concentrated HF/HNO 3 mixtures has been studied. By quantifying the major reaction products in solution, the established model that 3 mol of Si are oxidized by 4 mol of HNO 3 to yield 4mol of NO could not be confirmed. In HNO 3-rich HF/HNO 3 mixtures, approximately 1.1 mol of HNO 3 are required to oxidize 1mol of Si. Excess HNO 3 leads to massive accumulation of N(III) species in the etchants and massive formation of nitrous oxides due to incomplete reduction of the HNO 3. An excess of HNO 3 leads to higher consumption and poorer utilization indicated by the massive accumulation of N(III) species in the etchants. In HF-rich mixtures, only 0.9 mol of HNO 3 are needed to oxidize 1 mol of Si yielding a lower accumulation of N(III) species and a higher utilization of the HNO 3. Two parallel pathways contribute to the oxidation of silicon in such solutions: (i) via the oxidation by HNO 3 and reactive intermediates generated by the reduction of HNO 3 and (ii) via the formation of hydrogen. A comprehensive treatment covering alkaline etching, electrochemical etching in HF media, and etching in concentrated HF/HNO 3 mixtures is proposed based on the reactivity of the hydrogen terminated silicon surface against the applied oxidizing agent. © 2012 American Chemical Society.

Hempel N.,Lausitz University of Applied science | Petrick I.,Lausitz University of Applied science | Behrendt F.,TU Berlin
Journal of Applied Phycology | Year: 2012

Microalgae are discussed as an alternative source for the production of biofuels. The lipid content compared to cultivation time of used species is the main reason for any choice of a special strain. This paper reviews more analytical data of 38 screened microalgae strains. After the cultivation period, total content of lipids was analysed. The extracted fatty acids were quantified as fatty acid methyl esters by GC analysis. The amino acids were analysed by HPLC. Chlorella sp., Chlorella saccharophila, Chlorella minutissima and Chlorella vulgaris were identified as species with the highest productivity of fatty acids relevant to transesterification reactions. The components were mainly linoleic acid, palmitic acid and oleic acid. To increase productivity of highly saturated fatty acids, cultivation parameters light intensity and temperature were varied. In this manner, the ideal conditions for biodiesel production were defined in this publication. © 2012 The Author(s).

Nizamov S.,Lausitz University of Applied science | Mirsky V.M.,Lausitz University of Applied science
Biosensors and Bioelectronics | Year: 2011

SPR based biosensors register binding of analytes to the surface with immobilized receptors by measuring changes of the refractive index near this surface. An important task in the improvement of this measurement technology is a separation of signals, corresponding to the changes in the chemosensitive layer, from undesired contributions of bulk phase, for example, due to fluctuations of temperature, concentrations of solutes, pressure. The wavelength of the incident light influences strongly the penetration depth of the corresponding evanescent wave. This dependence was exploited here for compensation of the contribution of the bulk refractive index. It was performed using differential SPR measurements at two wavelengths with differing penetration depths. Theoretical analysis and numerical optimization of the suggested approach, named a Penetration Difference Self-Referencing SPR (PDSR-SPR), were performed. Experimental test was performed using 658 and 980 nm laser diodes. Over 20 times suppression of variations of bulk refractive index with magnitude up to 1000. μRIU was observed. Finally, PDSR-SPR approach was applied for monitoring of antibodies binding to the immobilized antigens. © 2011 Elsevier B.V.

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