Capillary electrophoresis‐based enzyme assays for β‐lactamase enzymes

Generic in‐capillary as well as offline CE‐based enzyme assays were developed for serine‐β‐lactamases and metallo‐β‐lactamases. The hydrolysis of benzylpenicillin to benzylpenicilloic acid was analyzed using 100 mM sodium phosphate solution, pH 6.0, as a background electrolyte. In‐capillary assays employed an uncoated as well as a polyethylene oxide‐coated capillary, while the offline assays employing long end and short end injection were performed in an uncoated capillary. Using procaine hydrochloride or 4‐hydroxybenzoic acid as internal standard, the respective assays were validated with regard to linearity, LOD and LOQ, repeatability, precision, and accuracy. The assays were applied to the determination of the Michaelis‐Menten parameters K_m and V_max of Bacillus cereus penicillinase as well as New Delhi metallo‐β‐lactamase 1 and Verona integrin‐encoded metallo‐β‐lactamase 2. Furthermore, the inhibition of the enzymes by irreversible and competitive inhibitors was evaluated. Comparable data were obtained with all assays. The use of a simple substrate ensured broad applicability to the various types of β‐lactamases.     

Taking laboratory uncertainties into account in the Hampel estimator

Accreditation and Quality Assurance - According to ISO/IEC 17025:2017, testing and calibration laboratories should apply procedures for estimating measurement uncertainty. It would thus make sense...     

Time-dependent reliability assessment of structures using uncertain fractional rheological models

In this paper, a concept for time-dependent reliability assessment of civil engineering structures is presented. This concept bases on the uncertainty model fuzzy randomness. The time-dependent behaviour of materials with fading memory is captured by means of rheological models using uncertain fractional time derivatives. The presented method can be applied to the reliability assessment of engineering constructions. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electronic non-equilibrium conditions at C60–pentacene heterostructures

The electronic structure of vacuum-sublimed layered organic heterostructures of pentacene (PEN) and fullerene (C₆₀) on conducting polymer substrates was investigated using ultraviolet photoelectron spectroscopy (UPS). The conditions at the PEN/C₆₀interface changed from thermodynamic non-equilibrium (i.e. the onset of the PEN highest occupied molecular orbital above the substrate Fermi-energy) for thin PEN coverages on C₆₀ to thermodynamic equilibrium for thicker PEN coverages (i.e. Fermi-level pinning of PEN). This finding is attributed to a coverage-dependent pinhole connection of PEN through the C₆₀ layer with the substrate. The experiments demonstrate the importance of organic thin film morphology for UPS measurements to assess the energy level alignment at organic/organic heterointerfaces.     

Design of Soluble Hyperbranched Polythiophenes with Tailor‐Made Optoelectronic Properties

Hyperbranched polythiophenes were prepared via a simple one‐pot synthesis approach based on oxidative coupling of branched conjugated monomers. Only small variations in the building unit and architecture lead to large differences of absorption and photoluminescence properties. Interestingly, soluble hyperbranched polythiophenes with relatively small molecular weights show enhanced absorption at low and high wavelengths compared to linear analogues, such as poly(3‐hexyl thiophenes) with high molecular weights. With this versatile approach we present a method to design tailor made, functional materials with potential applications in optoelectronics.

     

Chemomechanical Coupling of Molecular Motors: Thermodynamics, Network Representations, and Balance Conditions

Molecular motors are considered that convert the chemical energy released from the hydrolysis of adenosine triphosphate (ATP) into mechanical work. Such a motor represents a small system that is coupled to a heat reservoir, a work reservoir, and particle reservoirs for ATP, adenosine diphosphate (ADP), and inorganic phosphate (P). The discrete state space of the motor is defined in terms of the chemical composition of its catalytic domains. Each motor state represents an ensemble of molecular conformations that are thermally equilibrated. The motor states together with the possible transitions between neighboring states define a network representation of the motor. The motor dynamics is described by a continuous-time Markov process (or master equation) on this network. The consistency between thermodynamics and network dynamics implies (i) local and nonlocal balance conditions for the transition rates of the motor and (ii) an underlying landscape of internal energies for the motor states. The local balance conditions can be interpreted in terms of constrained equilibria between neighboring motor states; the nonlocal balance conditions pinpoint chemical and/or mechanical nonequilibrium.     

Search for axionlike particles using a variable-baseline photon-regeneration technique

We report the first results of the GammeV experiment, a search for milli-eV mass particles with axionlike couplings to two photons. The search is performed using a "light shining through a wall" technique where incident photons oscillate into new weakly interacting particles that are able to pass through the wall and subsequently regenerate back into detectable photons. The oscillation baseline of the apparatus is variable, thus allowing probes of different values of particle mass. We find no excess of events above background and are able to constrain the two-photon couplings of possible new scalar (pseudoscalar) particles to be less than 3.1x10;(-7) GeV-1 (3.5x10;(-7) GeV-1) in the limit of massless particles.     

Linear phase slope in pulse design: application to coherence transfer

Using optimal control methods, robust broadband excitation pulses can be designed with a defined linear phase dispersion. Applications include increased bandwidth for a given pulse length compared to equivalent pulses requiring no phase correction, selective pulses, and pulses that mitigate the effects of relaxation. This also makes it possible to create pulses that are equivalent to ideal hard pulses followed by an effective evolution period. For example, in applications, where the excitation pulse is followed by a constant delay, e.g. for the evolution of heteronuclear couplings, part of the pulse duration can be absorbed in existing delays, significantly reducing the time overhead of long, highly robust pulses. We refer to the class of such excitation pulses with a defined linear phase dispersion as ICEBERG pulses (Inherent Coherence Evolution optimized Broadband Excitation Resulting in constant phase Gradients). A systematic study of the dependence of the excitation efficiency on the phase dispersion of the excitation pulses is presented, which reveals surprising opportunities for improved pulse sequence performance.