Methode zur enzymatischen Bestimmung vond (+)-Malat

Zusammenfassung Zur Bestimmung des unnatürlichen Enantiomers von Äpfelsäure wird eine enzymatische Methode zur quantitativen Analyse vond(+)-Malat beschrieben. Mit einem ausPseudomonas luorescens isoliertend-Malat-Enzym (d(+)-Malat: NAD Oxidoreduktase, decarboxylierend), dasd-Malat spezifisch zu Pyruvat decarboxyliert, wobei NADH entsteht, wurde eine Analysenmethode entwickelt, die es ermöglicht, 20 bis 200 mgd-Malat je Liter in Fruchtsäften zu bestimmen. Mit dem optischen Test wurden bei der Untersuchung verschiedener Fruchtsäfte keine Störungen beobachtet.

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A method for the enzymatic determination

Summary An enzymatic method is described for the quantitative determination ofd(+)-malate, the unnatural enantiomer of malic acid. From a strain ofPseu-domonas fluorescens that was originally isolated by the enrichment technique ad-malic enzyme (d(+)-malate NAD oxidoreductase, decarboxylating) was purified that oxidatively decarboxylates D-malate to pyruvate and reduces NAD. The amount of NADH formed in this reaction is measured in an optical test. Amounts of 20 to 200 mg D-malate per liter can be assayed in fruit juices. No interfering substances were observed in experiments with orange, grape fruit, apple, black currant, grape and cherry juices.

     

Chemical short range order in liquid Sb-Sn alloys proved with the aid of the dependence of the mixing enthalpies on temperature

The mixing enthalpies of liquid Sb-Sn alloys were measured as a function of the concentration and of the temperature by means of a high-temperature calorimeter. The deviations found from the behaviour of a regular solution and the small dependences on temperature can be interpreted assuming the existence of associates, having the compositions SbSn and SbSn₂. The results are reproduced quantitatively by an association model.     

Biomimetic synthesis of gold nanocrystals using a reducing amphiphile

The first synthesis of a chelating and reactive surfactant derived from citric acid and a short silicone as hydrophobic tail is described. Aqueous solutions of this reactive amphiphile spontaneously induce gold ion reduction, particle nucleation, and further direct crystal growth. The process, both pH and light dependent, occurs through lipid-directed assembly of metal ions, their reduction and subsequent lipid-directed growth to yield ultrathin (approximately 7 nm thick) quasi two-dimensional gold nanocrystals.     

Anhydrous formation of foamed silicone elastomers using the Piers–Rubinsztajn reaction

Elastomeric silicone foams are generally produced by the generation of hydrogen through reaction of Si-H groups with active hydrogen compounds, including water and alcohols, in a process catalyzed by platinum or tin complexes. It can be very difficult to control the rate and magnitude of bubble formation, particularly because of adventitious water. Silicone foams in a variety of densities (0.08–0.46 g/cm³) were obtained using a newly developed Piers–Rubinsztajn reaction by combining α,ω-hydride-terminated poly(dimethylsiloxane) with an alkoxysilane crosslinker such as tetraethyl orthosilicate with catalysis by B(C₆F₅)₃. A single reaction leads both to crosslinking and bubble evolution. The reaction is not significantly impacted by humidity: foams are generated by the release of alkane gases derived from the alkoxysilane crosslinker, typically methane or ethane, rather than hydrogen. It was found that crosslinker reactivity and concentration, and silicone molecular weight, can be used to effectively control bubble nucleation, coalescence, viscosity build and, therefore, final foam density and the formation of open or closed cell foams. Better quality foams normally resulted when hexane, which acts as a blowing agent, was added to the pre-foam mixture. In addition to these advantages, and excellent reproducibility, the Piers–Rubinsztajn reaction benefits from a very fast induction time.     

Quantification of metallic coating failure on carbon fiber reinforced plastics using acoustic emission

Carbon fiber reinforced plastic substrates were subsequently coated with an electrochemically applied nickel and an electroplated copper layer. The coating-substrate system was loaded in four-point bending and the acoustic emission from coating failure was recorded during loading. The acoustic emission signals were analyzed using pattern recognition and frequency analysis techniques. This approach yields three distinguishable types of acoustic emission signals, which are correlated to three different failure mechanisms: i) nickel cracking ii) copper cracking and iii) delamination between the two coating layers. To confirm the correlation between the types of acoustic emission signals and the respective failure mechanisms and to assess the validity of the acoustic emission method to describe mechanical failure, the micro-mechanical fracture energies released during mechanical loading were calculated based on microscopic measurements of the crack progress utilizing scanning electron microscopy and scanning acoustic microscopy. These energies were compared to the associated acoustic emission signals energy for each failure mechanism. We found the calculated micro-mechanical energy values to be proportional to the measured accumulated acoustic emission energy of the associated acoustic emission signal type. We conclude that the reported failure classification method offers the possibility to compare fracture toughness values in multilayered coatings with multiple failure types, derived solely from acoustic emission energies.     

Adsorption kinetics of zeolite coatings directly crystallized on metal supports for heat pump applications (adsorption kinetics of zeolite coatings)

A series of theoretical studies had previously indicated that the utilization of zeolite coatings directly crystallized on metal surfaces might improve the performance of adsorption heat pumps significantly. In this study, for the first time, kinetic measurements were performed to determine the rate of adsorption of zeolite coatings, which is the relevant parameter for increasing the power density of heat pump applications. The zeolite coatings investigated were prepared by using the substrate heating method. A scale-up of the substrate heating system was made in order to be able to grow zeolite coatings on 5 × 5 cm² stainless steel plates, instead of the 1 × 1 cm² plates, conventionally used in synthesis experiments. Two different reactors were constructed in which zeolite A and X coatings, with mass equivalent thicknesses of about 38 μm and 230 μm, respectively, could be obtained. The zeolite X coating, which had a quite open nature, exhibited quite favorable overall adsorption kinetics when compared to a reference sample, a paper-like polymer structure containing zeolite laminated on a metal layer.     

Intrinsic and Effective Kinetics of Cobalt‐Catalyzed Fischer‐Tropsch Synthesis in View of a Power‐to‐Liquid Process Based on Renewable Energy

The production of liquid hydrocarbons based on CO₂ and renewable H₂ is a multi‐step process consisting of water electrolysis, reverse water‐gas shift, and Fischer‐Tropsch synthesis (FTS). The syngas will then also contain CO₂ and probably sometimes H₂O, too. Therefore, the kinetics of FTS on a commercial cobalt catalyst was studied with syngas containing CO, CO₂, H₂, and H₂O. The intrinsic kinetic parameters as well as the influence of pore diffusion (technical particles) were determined. CO₂ and H₂O showed only negligible or minor influence on the reaction rate. The intrinsic kinetic parameters of the rate of CO consumption were evaluated using a Langmuir‐Hinshelwood (LH) approach. The effectiveness factor describing diffusion limitations was calculated by two different Thiele moduli. The first one was derived by a simplified pseudo first‐order approach, the second one by the LH approach. Only the latter, more complex model is in good agreement with the experimental results.     

Transient modeling of an adsorber using finned-tube heat exchanger

This paper presents a heat and mass transfer simulation of an adsorber, taking into consideration the geometry of the heat exchanger and the diffusion in the adsorbent medium. In this model, an increment in the direction of heating/cooling fluid containing one (or more) fin pitch was considered. In the domain of this increment, the distribution of the adsorbent temperature was evaluated in the radial and axial directions. The model is validated by experimental data of different adsorbents, volume flows and temperatures. All data were collected in an adsorber test-bench at Fraunhofer ISE. As a result it was found a coefficient of multiple determination of around 0.94 and an error of 20% during the transient. Finally, the model was run on typical operation for cooling application and compared with data from literature. A numerical energy balance was also evaluated. In summary, the results obtained by a independent group shows the same range of confidence of the model developed here, in terms of the tendency of the curves and even the absolute values.