This work presents a comparative study between two different methods for the preparation of mediator-modified screen-printed electrodes, to be used as detectors in a reliable flow injection system for the determination of the nicotinamide adenine dinucleotide (NADH) coenzyme. The best strategy was selected for the final development of compact biosensors based on dehydrogenase enzymes. For the first immobilisation strategy, different redox mediators were electropolymerised onto the SPE surface. The second immobilisation strategy was carried out using polysulfone–graphite composites, which were deposited by screen-printing technology onto the screen-printed electrode (SPE) surface. Both methods achieved an effective and reliable incorporation of redox mediators to the SPE configuration. Finally, a flow system for ammonium determination was developed using a glutamate dehydrogenase (GlDH)-Meldola's Blue (MB)-polysulfone-composite film-based biosensor.
The stability of the redox mediators inside the composite films as well as the negligible fouling effect observed on the electrode surface improve the repeatability and reproducibility of the sensors, important features for continuous analysis in flow systems. Furthermore, the optimised bio/sensors, incorporated in a flow injection system, showed good sensitivities and short response times. Such a good analytical performance together with the simple and fast sensor construction are interesting characteristics to consider the polysulfone-composite films as attractive electrochemical transducer materials for the development of new dehydrogenase-based SPEs. 相似文献
Summary The conditional protonation constants (=0.1) for 2,2:6,2-terpyridine, logK1=4.93, logK2=3.69, were determined by thepH-metric method. The compositions of complexes of Ag2+ and Ag+ ions with 2,2:6,2-terpyridine (tp) were studied and equilibria of the complex formation process were described. The values of conditional complex formation constants are as follows: for Ag(tp)
2+
:log01=5.79, log02=9.68, for Ag(tp)
22+
:log02=25.31, while the conditional constant of the Ag(tp)NO3 precipitate formation is:KSO=2.45·104. Using coulometric and chronovoltamperometric measurements, the redox systems being formed in the complex solutions of Ag(II) and Ag(I) were determined and described including their formal potentials.
Komplexibildungsgleichgewichte und Redoxpotentiale des Systems Ag(II)/Ag(I) in Gegenwart von 2,2:6,2-Terpyridin in Wasser
Zusammenfassung Mit Hilfe derpH-metrischen Methode wurden die konditionalen Protonationskonstanten (=0.1) von 2,2:6,2-Terpyridin bestimmt: logK1=4.93, logK2=3.69. Es wurde auch die Zusammensetzung der Komplexe von Ag(II) und Ag(I) mit 2,2:6,2-Terpyridin(tp) bestimmt sowie die Gleichgewichte der komplexbildung beschrieben. Die Werte der Konditionalkomplexbildungskonstanten sind: für Ag(tp)
2+
:log01=5.79, log02=9.68, für Ag(tp)
22+
:log02=25.31 und für das Löslichkeitsprodukt Ag(tp)NO3:KSO–1
=4.08·10–5. Die in Komplexlösungen von Ag(II) und Ag(I) vorliegenden Redoxsysteme wurden mittels cyclischer Voltametrie und Coulometrie untersucht und die Formalpotentialwerte dieser Systeme in Wasser bestimmt.
Novel organometallic conjugated polymer containing (η6-arene)Cr(CO)3 and platinum in the main chain was synthesized by dehydrohalogenation coupling reaction of (η6-1,4-diethynylbenzene)tricarbonylchromium with trans-(PBu3)2PtCl2. The polymer was soluble in common organic solvents and has the number-average molecular weight of 31,000 by GPC analysis. The polymer exhibited an absorption peak derived from π-π∗ interaction at 358 nm in the UV-Vis spectrum, which showed a red shift of approximately 90 nm compared to that of the model compound. The photochemical ligand exchange reaction of the polymer was also investigated. 相似文献
Redox initiated free-radical polymerization of methyl methacrylate (MMA) with allyl alcohol 1,2-butoxylate-block-ethoxylate (AABE) was carried out using cerium(IV) ammonium nitrate/nitric acid (HNO3) redox system to yield AABE-b-PMMA copolymers. The effects of MMA, AABE, Ce(IV) and HNO3 concentrations on the polymerization rate and polymer yield were investigated. The effect of temperature on the rate of polymerization and polymer yield was also investigated in the temperature range of 25-70 °C. Copolymers were characterized using GPC, FT-IR, 1H NMR and viscometry methods. 相似文献
Zeolites are viewed by some as the “philosopher's stone” of modern chemistry.[1] They are more or less indispensable in oil refining and petrochemicals manufacture where they are widely applied as solid acid catalysts. More recently attention has been focused on their use in the manufacture of fine chemicals. The synthetic utility of zeolites and related molecular sieves (zeotypes) has been considerably extended by the incorporation of redox metals into their frameworks. The resulting redox molecular sieves catalyze a variety of selective oxidations under mild conditions in the liquid phase. Their structural diversity–including variation of the redox metal, incorporation of metal complexes, and the size and polarity of the micropores–provides the possibility of designing tailor-made solid catalysts (“mineral enzymes”) for liquid-phase oxidations with clean oxidants such as O2, H2O2, and RO2H. Hence, they have enormous potential in industrial organic synthesis as environmentally friendly alternatives to traditional oxidations employing inorganic oxidants in stoichiometric amounts. A primary aim of this review is to familiarize organic chemists with the synthetic potential of redox molecular sieves. An outline of their synthesis, structures, and chemical properties, highlighting their unique advantages, is followed by a discussion of general (mechanistic) features that influence the choice of a suitable catalyst for a particular type of oxidation. The main part of the review deals with the oxidation of various substrates of synthetic interest–such as alkanes, alkenes, (alkyl)arenes, alcohols, and amines–and emphasizes the advantages of redox molecular sieves (including selectivity and stability) over their homogeneous counterparts. New directions towards truly biomimetic solid catalysts, for example zeolite-encapsulated chiral metal complexes as heterogeneous catalysts for asymmetric oxidations, are high-lighted. 相似文献
The photodissociation of methyl iodide in various matrices at low temperature was studied. The observed Raman spectra excited by 514.5 nm laser radiation showed that there were two different photolytically produced iodine species isolated in the matrices after illumination by a medium pressure mercury lamp. One species which was dominant at lower iodine concentrations and exhibited a progression with an ωe of 201 cm?1, belonged to the matrix isolated iodine monomer (I2). The other species, which was dominant at higher iodine concentrations with an ωe of approximately 180 cm?1, belonged to the iodine aggregate ((I2)n). Five progressions of resonance Raman or resonance fluorescence of these two species were also observed in the other matrices. The iodine aggregate in the methyl iodide matrix at 77 K was formed in a crystalline structure, while the photolytically generated iodine aggregate from CH3I/Ar (2/3) matrix at 10 K, after illumination with a mercury lamp, was in amorphous form. The rearrangement of photolytically produced iodine aggregate in methyl iodide matrix was observed as a function of the duration of illumination. Local heating effects of the laser radiation might induce the iodine monomer to aggregate in matrices. The photodissociation mechanism of methyl iodide in matrices is also proposed. 相似文献
A new iodometric method for quantifying aqueous solutions of iodide-oxidizing and iodine-reducing substances, as well as plain iodine/iodide solutions, is presented. It is based on the redox potential of said solutions after reaction with iodide (or iodine) of known initial concentration. Calibration of the system and calculations of unknown concentrations was performed on the basis of developed algorithms and simple GWBASIC-programs. The method is distinguished by a short analysis time (2–3 min) and a simple instrumentation consisting of pH/mV meter, platinum and reference electrodes. In general the feasible concentration range encompasses 0.1 to 10–6 mol/L, although it goes down to 10–8 mol/L (0.001 mg Cl2/L) for oxidants like active chlorine compounds. The calculated imprecision and inaccuracy of the method were found to be 0.4–0.9% and 0.3–0.8%, respectively, resulting in a total error of 0.5–1.2%. Based on the experiments, average imprecisions of 1.0–1.5% at c(Ox)>10–5 M, 1.5–3% at 10–5 to 10–7 M, and 4–7% at <10–7 M were found. Redox-iodometry is a simple, precise, and time-saving substitute for the more laborious and expensive iodometric titration method, which, like other well-established colorimetric procedures, is clearly outbalanced at low concentrations; this underlines the practical importance of redox-iodometry.An erratum to this article is available at . 相似文献
A series of sulfur-containing compounds was investigated as electron donors in photoinduced free-radical polymerization, in conjunction with 4-carboxybenzophenone (CB) as sensitizer. These compounds included (phenylthio) acetic acid, ethionine, methionine, Gly-Met, Met-Gly and methionine methyl ester. The results were compared with the nonsulfur-containing compounds, alanine and triethanolamine. The best initiation yields is observed for the system CB-(phenylthio)acetic acid. 相似文献