Oxidation of oleuropein studied by EPR and spectrophotometry

The autoxidation at alkaline pH and enzymatic oxidation by mushroom tyrosinase of oleuropein, the dominant biophenol present in the fruits and leaves of Olea europea, was followed by both electron paramagnetic resonance (EPR) and absorption spectroscopy. For comparison, the same oxidation processes were applied to 4‐methylcatechol, a simple polyphenol present in olive mill wastewaters. EPR spectra of stable o‐semiquinone radicals produced during autoxidation at pH 12 and short‐lived o‐semiquinone free radicals produced during autoxidation at pH 9.0 or tyrosinase action and stabilized by chelation with a diamagnetic metal ion (Mg²⁺) were recorded for both polyphenols, and the corresponding hyperfine splitting constants were determined. The UV‐Vis spectral characteristics of the oxidation of polyphenols were highly dependent on the type of polyphenol, oxidant type and the pH of the reaction. The kinetic behavior of tyrosinase in the presence of oleuropein and 4‐methylcatechol was followed by recording spectral changes at 400 nm (absorption maximum) over time. The tysosinase activity with oleuropein showed a pronounced pH optimum at pH 6.5 and a minor one around pH 8. From the data analysis of the initial rate at pH 6.5, the kinetic parameters K_m = 0.34 ± 0.03 mM and V_max = 0.029 ± 0.002 ΔA₄₀₀ min^–1 were determined for oleuropein.     

Concomitant Crystallization of Copper(II) Sachharinato Complexes with 2-methylpyrazine as a Monomer and an One-dimensional Polymer: Syntheses,Crystal Structures,Spectroscopic and Thermal Properties

The reaction of [Cu(sac)₂(H₂O)₄] · 2H₂O with 2-methylpyrazine (mpyz) leads two complexes, concomitant crystallization of a mononuclear complex [Cu(sac)₂(mpyz)(H₂O)₂] (1) and a polymeric complex [Cu(sac)₂(μ-mpyz)]_n (2). Both complexes have been characterized by elemental analyses, magnetic measurements, FT-IR and ESR, TG-DTA and single-crystal X-ray diffraction analyses. Single-crystal X-ray analyses show that complex 1 consists of discrete molecules in which the copper(II) ions exhibits a square-pyramidal coordination geometry. The individual molecules of 1 are connected into a hydrogen-bonded chain structure, which is further assembled to form a three-dimensional network by π–π stacking interactions. Complex 2 is an 1D coordination polymer in which copper(II) centers are bridged by the mpyz ligand. The chains are further assembled to form two-dimensional frameworks by π–π and C–H···π stacking interactions.     

Aerobic degradation by white‐rot fungi of trichloroethylene (TCE) and mixtures of TCE and perchloroethylene (PCE)

BACKGROUND: Trichloroethylene (TCE) and perchloroethylene (PCE) are considered among the most important groundwater pollutants around the world. These compounds are usually found together in polluted environments but little is known about the ability of microorganisms to simultaneously degrade TCE and PCE. RESULTS: Data showed that several species of white‐rot fungi, including Trametes versicolor, Ganoderma lucidum, and Irpex lacteus, degrade substantial levels of TCE in pure culture. T. versicolor was chosen for further study since it degraded higher levels of TCE than the other organisms. Initial glucose concentration and reoxygenation of samples increased the amount of TCE dechlorination, but no significant difference in percentage TCE degradation was observed. T. versicolor was able to degrade 34.1 and 47.7% of PCE and TCE added as mixtures (containing 5 and 10 mg L⁻¹, respectively). CONCLUSIONS: The degradation ability of TCE was extended to other species of white‐rot fungi. Percentage degradation as well as chloride release from mixtures of TCE and PCE showed that T. versicolor degrades mixtures of TCE and PCE almost as well as its ability to degrade individually added TCE or PCE. The results suggest the potential promise of T. versicolor for bioremediation of TCE and PCE in the environment. Copyright © 2008 Society of Chemical Industry     

Modifizierung des ABSE‐Polycarbosilazans mit Multi‐Walled Carbon Nanotubes zur Herstellung spinnfähiger Massen

Modification of the ABSE polycarbosilazane with multi‐walled carbon nanotubes for the creation of spinable masses An inexpensive method has been found to produce ceramic SiCN‐fibres via the precursor route consisting of five processing steps: synthesis of the polymer, preparation of the spinning mass, melt‐spinning, curing via electron beam and subsequent pyrolysis at 1100 °C in a nitrogen atmosphere. A special solid and meltable fibre polymer, the so‐called polycarbosilazane ABSE, has been developed in the last decade for this purpose. Due to its low molecular weight, an adequate catalytic and thermal aftertreatment was necessary to guarantee a stable melt‐spinning process. This article discusses an alternative way to prepare a qualified spinning mass, i.e. the addition of Multi‐Walled Carbon Nanotubes (MWCNTs) to the ABSE melt. For this purpose a homogeneous dispergation of the MWCNTs in the ABSE matrix is necessary. In this study, spinning masses were fabricated in different ways. By optical analysis and comparison of the level of dispergation in these spinning masses an optimized process for integration of the MWCNTs was identified. The influence of the addition of a dispersing agent is investigated as well. In using a dispersing agent, the level of homogeneous dispersion of the MWCNTs increases whereas the interactions between the particles and the precursor melt decrease. In first spinning experiments a good spinability of the masses were noticed. Thus the addition of MWCNTs represents a new way to modify the ABSE precursor for the melt‐spinning process.     

Synthesis of poly(4-methylstyrene)- graft-poly(ethylene oxide)s and application as polymeric dispersant in coal-water mixture

Poly(4-methylstyrene)-graft-poly(ethylene oxide)s were prepared via polymerisation of ethylene oxide on to poly(4-methylstyrene)s functionalised with hydroxyl groups. In this way, many ‘comb-like’ polymers having different hydrophobic backbone length, hydrophilic branch length and frequency of branches were synthesised. These polymers were tested as dispersants in coal-water mixtures in order to correlate the dispersing properties of this class of polymers with the investigated parameters.     

Series resonant ZCS‐PFM DC‐DC power converter with high‐frequency high‐voltage transformer link for high‐power magnetron drive

This paper presents a single lossless inductive snubber‐assisted ZCS‐PFM series resonant DC‐DC power converter with a high‐frequency high‐voltage transformer link for industrial‐use high‐power magnetron drive. The current flowing through the active power switches rises gradually at a turned‐on transient state with the aid of a single lossless snubber inductor, and ZCS turn‐on commutation based on overlapping current can be achieved via the wide range pulse frequency modulation control scheme. The high‐frequency high‐voltage transformer primary side resonant current always becomes continuous operation mode, by electromagnetic loose coupling design of the high‐frequency high‐voltage transformer and the magnetizing inductance of the high‐frequency high‐voltage transformer. As a result, this high‐voltage power converter circuit for the magnetron can achieve a complete zero current soft switching under the condition of broad width gate voltage signals. Furthermore, this high‐voltage DC‐DC power converter circuit can regulate the output power from zero to full over audible frequency range via the two resonant frequency circuit design. Its operating performances are evaluated and discussed on the basis of the power loss analysis simulation and the experimental results from a practical point of view. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 153(3): 79–87, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20126     

Signals,timers, and continuations for multithreaded user‐level protocols

Precise timing and asynchronous I/O are appealing features for many applications. Unix kernels provide such features on a per‐process basis, using signals to communicate asynchronous events to applications. Per‐process signals and timers are grossly inadequate for complex multithreaded applications that require per‐thread signals and timers that operate at finer granularity. To respond to this need, we present a scheme that integrates asynchronous (Unix) signals with user‐level threads, using the ARIADNE system as a platform. This is done with a view towards support for portable, multithreaded, and multiprotocol distributed applications, namely the CLAM (connectionless, lightweight, and multiway) communications library. In the same context, we propose the use of continuations as an efficient mechanism for reducing thread context‐switching and busy‐wait overheads in multithreaded protocols. Our proposal for integrating timers and signal‐handling mechanisms not only solves problems related to race conditions, but also offers an efficient and flexible interface for timing and signalling threads. Copyright © 2006 John Wiley & Sons, Ltd.     

Photostabilisation of colour formers for heat-sensitive recording systems: Effect of counter-ions on the photofading of fluoran dyes

Fluorans are given considerable attention as functional dyes for heat-and/or pressure-sensitive recording media. Numerous potential metal complexes were synthesised to prolong the life of coloured species. The protecting effect of these compounds against the photofading was examined on cellulose. It was found that the zinc or nickel salts of 3,5-dihydroxy-2-naphthoic acid and its derivatives can be applied as effective stabilisers against the fading of fluoran dyes.     

Study on phase behavior–impact strength relationship of unsaturated polyester/polyurethane hybrid polymer network

The phase behavior of a hybrid polymer network (HPN) composed of poly[(propylene glycol maleate)-co-(propylene glycol phthalate)] crosslinked with styrene and polyester–urethane crosslinked with methylene-bis-ortho-chloroaniline was examined. The correlation between phase separation and impact strength of the HPNs is discussed. The composition of HPNs has an effect on their properties.