High catalytic performance of laccase wired to naphthylated multiwall carbon nanotubes.

The direct electrical connection of laccase on the electrode surface is a key feature in the design of efficient and stable biocathodes. However, laccase can perform a direct electron transfer only when it is in the preferred orientation toward the electrode. Here we report the investigation of the orientation of laccase from white rot fungus on multi-walled carbon nanotube surface modified with a naphthalene group. Naphthylated multi wall carbon nanotubes were synthesized and the kinetics of laccase from white rot fungus adsorption and its direct electro-catalytic activity toward oxygen reduction was investigated by QCM and electrochemical techniques. Compared to pristine multi-walled carbon nanotubes laccase shows a high affinity to be adsorbed onto the surface of naphthylated carbon nanotubes at a very fast rate. The subsequent wiring to the naphthylated multi-walled carbon nanotubes is accompanied by a reorientation and arrangement of adsorbed laccase to create a composite biocathode that exhibits a high-performance for oxygen reduction by direct electron transfer with maximum current densities of 3 mA cm-2.

Enzymatic electrodes nanostructured with functionalized carbon nanotubes for biofuel cell applications.

Nanostructured bioelectrodes were designed and assembled into a biofuel cell with no separating membrane. The glassy carbon electrodes were modified with mediator-functionalized carbon nanotubes. Ferrocene (Fc) and 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonate) diammonium salt (ABTS) bound chemically to the carbon nanotubes were found useful as mediators of the enzyme catalyzed electrode processes. Glucose oxidase from Aspergillus niger AM-11 and laccase from Cerrena unicolor C-139 were incorporated in a liquid-crystalline matrix-monoolein cubic phase. The carbon nanotubes-nanostructured electrode surface was covered with the cubic phase film containing the enzyme and acted as the catalytic surface for the oxidation of glucose and reduction of oxygen. Thanks to the mediating role of derivatized nanotubes the catalysis was almost ten times more efficient than on the GCE electrodes: catalytic current of glucose oxidation was 1 mA cm(-2) and oxygen reduction current exceeded 0.6 mA cm(-2). The open circuit voltage of the biofuel cell was 0.43 V. Application of carbon nanotubes increased the maximum power output of the constructed biofuel cell to 100 µW cm(-2) without stirring of the solution which was ca. 100 times more efficient than using the same bioelectrodes without nanotubes on the electrode surface.

Derivatization of single-walled carbon nanotubes with redox mediator for biocatalytic oxygen electrodes.

Single-walled carbon nanotubes (SWCNTs) were covalently modified with a redox mediator derived from 2,2'-azino-bis-(3-ethylbenzothiazoline)-6-sulfonic acid (ABTS), and implemented in the construction of electrodes for biocatalytic oxygen reduction. The procedure is based on: covalent bonding of mediator to nanotubes, placing the nanotubes directly on the carbon electrode surface and covering the nanostructured electrode with a Nafion film containing laccase as the biocatalyst. The modified electrode is stable and the problem of mediator (ABTS) leaking from the film is eliminated by binding it covalently to the nanotubes. Three different synthetic approaches were used to obtain ABTS-modified carbon nanotubes. Nanotubes were modified at ends/defect sites or on the nanotube sidewalls and characterized by Raman spectroscopy, TGA and electrochemistry. The accessibility of differently located ABTS units by the laccase active center and mediation of electron transfer were studied by cyclic voltammetry. The surface concentrations of ABTS groups electrically connected with the electrode were compared for each of the electrodes based on the charges of the voltammetric peaks recorded in the deaerated solution. The nanotube modification procedure giving the best parameters of the catalytic process was selected.

Determination of the chemical structure of potential organic impurities occurring in the drug substance opipramol.

The tricyclic antipsychotic and antidepressant drug opipramol (opipramole) was examined with regard to the chemical structure of its organic impurities. Impurities were isolated from the technical product by chromatographic methods and their chemical structures were established by 1H NMR, MS and FTIR and further confirmed by comparison with commercially available products or with products obtained by independent synthesis, and in one case additionally by X-ray structure analysis.

Metal-coated fused silica fibers as a support for immobilized compounds yielding a volatile analyte (C2H4).

This paper presents the results of investigations of chemically modified fibers comprising an immobilized compound that yields ethene as the analyte in generated standard gaseous mixtures. Prior to chemical modification, the fibers were coated with a thin aluminum layer to improve their mechanical strength. Commercially available Al-coated fibers were used in this work. During thermal decomposition of the immobilized compound, reproducible quantities of the analyte per unit fiber length were obtained for all the investigated fibers (fiber diameter (microm)/outside diameter (microm) of the Al-coated fiber=110/146, 220/300, and 660/830), amounting to 0.685+/-0.032, 0.8300+/-0.0081, and 1.092+/-0.010 ng cm(-1), respectively. The proposed procedure can be used successfully for the generation of measured component of matrix-free reference materials.

New procedure of silica gel surface modification preparation of gaseous standard mixtures for calibration purposes.

The new type of silica gel surface modification with using the trimethylamine as a reagent is described. The samples of chemically modified silica gel have been used for generation of gaseous standard mixtures (methyl chloride as a measurand) using the technique of thermal decomposition of the surface compound. The main aim of the research was to check the suitability of the new type of silica gel surface modification for obtaining methyl chloride as a measurand of gaseous standard mixture. The gaseous standard mixture obtained with using this technique was used for calibration of a thermal desorber-gas chromatography-flame ionization detector (TD-GC-FID) system. The homogeneity of coverage of silica gel surface with the immobilized compound has been evaluated. The full uncertainty budget of determination of liberated amount of methyl chloride has been calculated. The average amount of methyl chloride liberated from the unit sample of chemically modified silica gel is 3.59 +/- 0.13 mg g(-1). The influence of the modification way on the amount of liberated analyte has also been determined.

Use of porous glass and silica gel as support media of a surface compound for generation of analytes in gaseous standard mixtures. New method for the determination of the amount of analyte generated.

The paper presents a new method for the determination of a volatile component of a gaseous standard mixture obtained by thermal decomposition of a suitable surface compound. The amount of the analyte generated (under given conditions of thermal decomposition) per unit of mass of the chemically modified material has been determined exclusively on the basis of measuring generation time. Therefore, the total error of the determination of the amount of a standard compound depends solely on the respective errors of weighing the material and measuring its decomposition time (both being direct measurements). This new method permits obtaining a few measuring points on the basis of a single sample of the material with chemically modified surface.

Utilization of standards generated in the process of thermal decomposition chemically modified silica gel for a single point calibration of a GC/FID system.

The utilization of a multicomponent gaseous standard mixture, containing CO and CO(2) and obtained by thermal decomposition of a so-called immobilized compound, for a single point calibration of a GC/FID system are described. The generation of such a mixture takes place as a result of thermal decomposition of a sample of chemically modified silica gel placed in a heated chamber of thermal desorber coupled with the device being calibrated via a catalytic methanizer. The mean amount of the analyte librated from unit mass of the gel was 0.71 mg g(-1) (RSD = 3%) for carbon monoxide and 0.86 mg g(-1) (RSD = 3%) for carbon dioxide.