| 1. |
- Otrokhov, Grigory, et al.
(author)
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Enzymatic synthesis of polyaniline/multi-walled carbon nanotube composite with core shell structure and its electrochemical characterization for supercapacitor application
- 2014
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In: Electrochimica Acta. - : Elsevier. - 0013-4686 .- 1873-3859. ; 123, s. 151-157
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Journal article (peer-reviewed)abstract
- A new method involving laccase-mediator system has been developed for environmentally friendly synthesis of polyaniline/multi-walled carbon nanotubes (PANI/MWCNT) composite. Fungal laccase, potassium octocyanomolibdate (4+) and atmospheric oxygen served as catalyst, redox-mediator and terminal oxidant, respectively. The structure, morphology and electrical conductivity of composites with different PANI content were investigated. The energy storage of enzymatically obtained composite consists of an electrical double layer capacitance as well as pseudocapacitance of conducting polymer. The obtained PANI/MWCNT composite with PANI content ca. 49 wt.% had high specific capacitance and cycle stability during doping/dedoping. The specific capacitance of this composite measured by cyclic voltammetry technique with potential scan rate of 5 mV/s was ca. 440 F/g. The specific capacitance of the composite decreased by less than 7% of its maximum value after 1000 scan cycles between -0.1 and 0.7 V. Supercapacitor (SC) shell was made from flexible adhesive tape (regular Scotch tape) and current collector was formed after its separation from the surface of graphite foil. The ethanol dispersion of PANI/MWCNT composite was deposited on the current collector surface. The gel polymer electrolyte (polyvinyl alcohol in 1 M phosphoric acid) was employed as both electrolyte medium and separator. The energy and power densities under an operating window of 0.7 V were ca. 7.03 Wh/kg and 5.2 kW/kg, respectively. Crown Copyright (C) 2013 Published by Elsevier Ltd. All rights reserved.
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| 2. |
- Pankratov, Dmitry, et al.
(author)
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A comparative study of biocathodes based on multiwall carbon nanotube buckypapers modified with three different multicopper oxidases
- 2013
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In: Electroanalysis. - : Wiley-VCH Verlagsgesellschaft. - 1040-0397 .- 1521-4109. ; 25:5, s. 1143-1149
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Journal article (peer-reviewed)abstract
- 14 Single- and multi-walled carbon nanotubes from different sources were characterized in detail, and the characteristics obtained were carefully analyzed. The carbon material with the highest capacitance, and also other superior properties ("Taunit-M" from "NanoTechCenter", Russia), was chosen for further modification and fabrication of buckypaper based electrodes. These electrodes were biomodified with plant and fungal laccases, as well as fungal bilirubin oxidase. The designed biocathodes were studied in simple buffers and also in a complex physiol. fluid (human serum). Biocathodes based on immobilized fungal laccase were bioelectrocatalytically inactive in chloride contg. media at neutral pH. In spite of the quite high current densities realized using biodevices based on plant laccase and fungal bilirubin oxidase, the limited thermal stability of the enzymes renders the biocathodes inadequate for practical applications in implanted situations.
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| 3. |
- Shleev, Sergey, et al.
(author)
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Autoreduction and aggregation of fungal laccase in solution phase: possible correlation with a resting form of laccase
- 2006
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In: Biochimie. - : Elsevier BV. - 1638-6183 .- 0300-9084. ; 88:9, s. 1275-1285
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Journal article (peer-reviewed)abstract
- This paper reports results of a reexamination of some poorly understood peculiarities of laccases, an enzyme family which has been extensively studied in our laboratories as well as by others for some years. The issue that is reconsidered here is the previously proposed existence of ''active" and "resting" forms of laccases. The presence of fungal laccases with partly reduced active sites is demonstrated. Of further interest is that an aggregated state in solution, not to our knowledge previously noted for laccase, has been found by using small-angle X-ray scattering as well as thorough analysis of the results of several biochemical experiments. Under some conditions, this aggregated state may correlate with the resting form of the laccases, although this resting form could have a broader significance. It was shown that Trametes ochracea laccase had some anomalous characteristics, which could be correlated with the high concentration of the "resting" enzyme. The mechanism of formation of resting laccase is suggested. Knowledge of the resting state is of importance for in vitro studies. Additionally, a suggestion about the possible regulatory role of this form in vivo is mentioned. (c) 2006 Elsevier SAS. All rights reserved.
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| 4. |
- Shleev, Sergey, et al.
(author)
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Characterization of two new multiforms of Trametes pubescens laccase
- 2007
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In: Bioorganic Chemistry. - : Elsevier BV. - 0045-2068. ; 35:1, s. 35-49
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Journal article (peer-reviewed)abstract
- Electrochemical properties of two multiforms of laccase from Trametes pubescens basidiomycete (LACI and LAC2) have been studied. The standard redox potentials of the T1 sites of the enzymes were found to be 746 and 738 mV us. NHE for LACI and LAC2, respectively. Bioelectroreduction of oxygen based on direct electron transfer between each of the two forms of Trametes pubescens laccase and spectrographic graphite electrodes has been demonstrated and studied. It. is concluded that the T1 site of laccase is the first electron acceptor, both in solution (homogeneous case) and when the enzymes are adsorbed on the surface of the graphite electrode (heterogeneous case). Thus, the previously proposed mechanism of oxygen bioelectroreduction by adsorbed fungal laccase was additionally confirmed using two forms of the enzyme. Moreover, the assumed need for extracellular laccase to communicate directly and electronically with a solid matrix (lignin) in the course of lignin degradation is discussed. In summary, the possible roles of multiforms of the enzyme based on their electrochemical, biochemical, spectral, and kinetic properties have been suggested to consist in broadening of the substrate specificity of the enzyme, in turn yielding the possibility to dynamically regulate the process of lignin degradation according to the real-time survival needs of the organism.
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| 5. |
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| 6. |
- Shleev, Sergey, et al.
(author)
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Direct heterogeneous electron transfer reactions of Trametes hirsuta Laccase at bare and thiol-modified gold electrodes
- 2006
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In: Electroanalysis. - : Wiley. - 1040-0397 .- 1521-4109. ; 18:19-20, s. 1901-1908
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Journal article (peer-reviewed)abstract
- Direct electron transfer reactions of high redox potential Trametes hirsuta laccase on bare and 15 different thiol-modified gold electrodes were studied using cyclic voltammetry and potentiometry: Well-pronounced Faradaic processes were obtained for the enzyme adsorbed on bare gold, whereas reproducible and stable electrochemistry was obtained only when 4-aminothiophenol was used for gold modification. Moreover, the laccase-4-aminothiophenol-modified gold electrode showed the highest value of the steady-state potential under aerobic conditions equal to 660 mV vs. NHE compared with the other 15 different thiol modified electrodes and also the bare electrodes with immobilized enzyme. However, this value is still too far away from the equilibrium potential of the oxygen electrode and Trametes hirsuta laccase-modified graphite electrode, for which a well-pronounced high potential process of oxygen bioelectroreduction is shown at 800 mV vs. NHE. Possible mechanisms of the enzyme function on bare and thiol-modified gold electrodes are discussed in correlation with the structure and orientation of the enzyme on the surface of the various electrodes.
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| 7. |
- Shleev, Sergey, et al.
(author)
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Interaction of fungal laccases and laccase-mediator systems with lignin
- 2006
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In: Enzyme and Microbial Technology. - : Elsevier BV. - 0141-0229 .- 1879-0909. ; 39:4, s. 841-847
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Journal article (peer-reviewed)abstract
- The interaction between fungal laccases from Trametes basidiomycetes and different lignins has been studied using electrochemical and chromatographic methods. The kinetic parameters for the oxidation reaction of hydroquinone and for Kraft lignin by molecular oxygen catalysed by Trametes hirsuta laccase have been investigated. Polymerisation of lignin by laccase was shown. The process was independent on the source of lignin as well as on the origin and purity of the enzymes. A complex pattern of interaction between the laccase-mediator system (LMS) and lignin was shown. Along with the polymerisation of lignin, the ability to degrade lignin using the LMS was observed. Data generated by combining size exclusion chromatographic separation of lignin with the use of a laccase modified electrode as post column detector, strongly suggest that laccase can oxidise natural lignin by a long-range electron transfer mechanism. The influence of the origin of lignin as well as source of the enzyme on this process was also shown. (c) 2006 Elsevier Inc. All rights reserved.
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| 8. |
- Shleev, Sergey, et al.
(author)
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Laccase-based biosensors for monitoring lignin
- 2006
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In: Enzyme and Microbial Technology. - : Elsevier BV. - 0141-0229. ; 39:4, s. 835-840
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Journal article (peer-reviewed)abstract
- Four different ways to detect Kraft and soluble pine lignin using either soluble or immobilised Trametes hirsuta laccase have been investigated. In the first, the concentration of lignin was measured using laccase in homogeneous medium with a Clark electrode. In the second, laccase immobilised onto aminated porous glass beads was used in a reactor submerged into the lignin containing solution and the reaction was followed with a Clark electrode. The third and fourth techniques involved lignin detection using laccase modified spectrographic graphite electrodes, either used in flow injection mode or in batch mode, where lignin solutions were injected into an electrochemical cell. It was shown that the use of laccase modified graphite electrodes in conjunction with flow injection for amperometric lignin detection is an attractive perspective and our data form the basis for designing laccase-based biosensors to be applied for measuring lignin and its model compounds in waste water, e.g. from the pulp and paper industry. (c) 2006 Elsevier Inc. All rights reserved.
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