Alexander V. Fejzagić  Sebastian Myllek  Fabian Hogenkamp  Julian Greb  Prof. Dr. Jörg Pietruszka  Dr. Thomas Classen 《ChemistryOpen》2020,9(9):959-966

Screening for an interesting biocatalyst and its subsequent kinetic characterization depends on a reliable activity assay. In this work, a fluorometric assay based on the halogenation of 4-methyl-7-diethylamino-coumarin was established to monitor haloperoxidase-activity. Since haloperoxidases utilize hydrogen peroxide and halide ions to halogenate a broad range of substrates by releasing hypohalous acids, a direct quantification of haloperoxidase-activity remains difficult. With the system presented here, 3-bromo-4-methyl-7-diethylaminocoumarin is preferentially formed and monitored by fluorescence measurements. As starting material and product share similar spectroscopical properties, a two-dimensional calibration ap-proach was utilized to allow for quantification of each compound within a single measurement. To validate the system, the two-dimensional Michaelis-Menten kinetics of a vanadium-dependent chloroperoxidase from Curvularia inaequalis were recorded, yielding the first overall kinetic parameters for this enzyme. With limits of detection and quantification in the low μm range, this assay may provide a reliable alternative system for the quantification of haloperoxidase-activity.  相似文献   

    

Dr. Alexander V. Rudnev  Dr. Maria R. Ehrenburg  Elena B. Molodkina  Areeg Abdelrahman  Prof. Dr. Matthias Arenz  Prof. Dr. Peter Broekmann  Prof. Dr. Timo Jacob 《ChemElectroChem》2020,7(2):501-508

Despite a persistent interest in using ionic liquids (ILs) as an electrolyte for various electrochemical applications, the fundamental understanding of the processes at the electrode/IL interface is still at a preliminary stage. Herein, we employ electrochemical in situ scanning tunneling microscopy (STM) to investigate structural changes of a Au(111) single-crystal surface in four ILs: 1-butyl-1-methylpyrrolidinium dicyanamide [BMP][DCA], 1-butyl-1-methylpyrrolidinium bis(trifluoromethane)sulfonimide [BMP][TFSI], 1-ethyl-3-methylimidazolium dicyanamide [EMIm][DCA], and 1-ethyl-3-methylimidazolium acetate [EMIm][OAc]. The STM data demonstrate a significant effect of IL ions on the potential ranges of Au(111) surface stability/instability and on the intensity and pattern of the occurring surface changes. Moreover, the effect of both the anion and cation on the surface stability is considerable in a wide range from high negative to high positive potentials. Apparently, not only strong ion adsorption but also the arrangement of IL ions at the electrolyte side of the interface has a significant impact on the stability of the gold surface.  相似文献   

    

Kevin-P. Gradwohl  Andreas N. Danilewsky  Melissa Roder  Martin Schmidbauer  Jzsef Janicsk-Csthy  Alexander Gybin  Nikolay Abrosimov  R. Radhakrishnan Sumathi 《Journal of Applied Crystallography》2020,53(4):880-884

White‐beam X‐ray topography has been performed to provide direct evidence of micro‐voids in dislocation‐free high‐purity germanium single crystals. The voids are visible because of a dynamical diffraction contrast. It is shown that voids occur only in dislocation‐free parts of the crystal and do not show up in regions with homogeneous and moderate dislocation density. It is further suggested that the voids originate from clustering of vacancies during the growth process. A general method is proposed to verify the presence of voids for any crystalline material of high structural perfection.  相似文献   

    

Maximilian Igelbüscher  Jörg Schröder  Alexander Schwarz 《GAMM-Mitteilungen》2020,43(2):e202000009

Important conditions in structural analysis are the fulfillment of the balance of linear momentum (vanishing resultant forces) and the balance of angular momentum (vanishing resultant moment), which is not a priori satisfied for arbitrary element formulations. In this contribution, we analyze a mixed least-squares (LS) finite element formulation for linear elasticity with explicit consideration of the balance of angular momentum. The considered stress-displacement ( σ − u ) formulation is based on the squared L²(ℬ) -norm minimization of the residuals of a first-order system of differential equations. The formulation is constructed by means of two residuals, that is, the balance of linear momentum and the constitutive equation. Motivated by the crucial point of weighting factors within LS formulations, a scale independent formulation is constructed. The displacement approximation is performed by standard Lagrange polynomials and the stress approximation with Raviart-Thomas functions. The latter ansatz functions do not a priori fulfill the symmetry of the Cauchy stress tensor. Therefore, a redundant residual, the balance of angular momentum (( x − x ₀) × (div σ + f ) + axl[ σ − σ ^T] ), is introduced and the results are discussed from the engineering point of view, especially for coarse mesh discretizations. However, this formulation shows an improvement compared to standard LS σ − u formulations, which is considered here in a numerical study.  相似文献   

Structural and ferroelectric phase transitions,Hucisko, Poland, 16–20 May 2016     

Alexander Emelyanenko 《Liquid Crystals Today》2016,25(4):85-87

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Christoph Adam  Alexander K. Belyaev  Hans Irschik  Rudolf Heuer  Franz G. Rammerstorfer  Wilhelm Schneider 《ZAMM - Journal of Applied Mathematics and Mechanics / Zeitschrift für Angewandte Mathematik und Mechanik》2016,96(5):536-537

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Irene Urcelay-Olabarria  Jos Luis García-Muoz  Eric Ressouche  Alexander A. Mukhin  Vassil Skumryev 《Journal of Applied Crystallography》2016,49(2):520-527

(Mn,Co)WO₄ compounds are regarded as reference spin‐induced multiferroics. A comparative study is presented here, within the magnetic symmetry framework, of the incommensurate magnetic orders responsible for the ferroelectric phases of (i) MnWO₄ under a magnetic field ( H || b ) and (ii) Mn_0.90Co_0.10WO₄ in the absence of an external field. On the one hand, although these two ferroelectric phases are stabilized under different external physical conditions, both present the same Xc1′(α0γ)ss magnetic symmetry and practically the same modulation vector. The magnetic ordering in both phases is an elliptical helix with the magnetic moments (as the polarization vector, P ) perpendicular to the b axis, although in most of the ferroelectric compositions of the (Mn,Co)WO₄ family the spins rotate in planes containing b (and have P || b ). On the other hand, the anisotropy of the resulting magnetic modulations is extraordinarily different in the two phases. This is described and explained in the light of the different anisotropies of Co and Mn ions.  相似文献   

    

Alexander V. Evteev  Elena V. Levchenko  Leila Momenzadeh  Irina V. Belova  Graeme E. Murch 《哲学杂志》2016,96(6):596-619

Using results of equilibrium molecular dynamics simulation in conjunction with the Green–Kubo formalism, we present a general treatment of thermal impedance of a crystal lattice with a monatomic unit cell. The treatment is based on an analytical expression for the heat current autocorrelation function which reveals, in a monatomic lattice, an energy gap between the origin of the phonon states and the beginning of the energy spectrum of the so-called acoustic short-range phonon modes. Although, we consider here the f.c.c. Al model as a case example, the analytical expression is shown to be consistent for different models of elemental f.c.c. crystals over a wide temperature range. Furthermore, we predict a frequency ‘window’ where the thermal waves can be generated in a monatomic lattice by an external periodic temperature perturbation.  相似文献   

    

Alexander Frey  Josh Engelhardt  Gabriel Micard  Giso Hahn  Barbara Terheiden 《固体物理学:研究快报》2016,10(2):143-147

Large area (243.36 cm²) back‐junction passivated emitter, rear totally diffused (PERT) solar cells with laser contact opening (LCO) on n‐type mono‐like crystalline Si with efficiencies of 20.2% are presented. Boron emitters with high electrical quality (implied open circuit voltage iV_OC up to 700 mV) are formed during a co‐diffusion step using SiO_x:B layers. Increasing the rear metal contact coverage, we observed a decrease in fill factor (FF) instead of the expected increase due to the decrease of the back side series resistance. We show that it can be attributed to recombination centers (RCs) in the space charge region underneath the contact spots inducing an increasing second diode contribution. The presented empirical model for the RCs implemented in Synopsys Sentaurus TCAD allows for a successful reproduction of the FF, pseudo FF and V_OC behaviour with contact coverage. According to this model, the RCs induced by laser ablation and subsequently evaporation of Al have a shallow exponential distribution with a characteristic length of L_T = 0.2 µm and an effective surface density of N *_T0 = 25 cm^–1. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)  相似文献   

    

Alexander Chizhik  Andrzej Stupakiewicz  Arcady Zhukov  Julian Gonzalez 《physica status solidi (a)》2016,213(2):350-355

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