Comparison of the functional properties of trimeric and monomeric CaiT of Escherichia coli

Secondary transporters exist as monomers, dimers or higher state oligomers. The significance of the oligomeric state is only partially understood. Here, the significance of the trimeric state of the L-carnitine/gamma-butyrobetaine antiporter CaiT of Escherichia coli was investigated. Amino acids important for trimer stability were identified and experimentally verified. Among others, CaiT-D288A and -D288R proved to be mostly monomeric in detergent solution and after reconstitution into proteoliposomes, as shown by blue native gel electrophoresis, gel filtration, and determination of intermolecular distances. CaiT-D288A was fully functional with kinetic parameters similar to the trimeric wild-type. Significant differences in amount and stability in the cell membrane between monomeric and trimeric CaiT were not observed. Contrary to trimeric CaiT, addition of substrate had no or only a minor effect on the tryptophan fluorescence of monomeric CaiT. The results suggest that physical contacts between protomers are important for the substrate-induced changes in protein fluorescence and the underlying conformational alterations

Rotamer libraries of spin labelled cysteines for protein studies

ISSN:1463-9084ISSN:1463-907

Polyethylene nanoparticle dispersions studied by X-band CW-ESR spectroscopy

Electron spin resonance spectroscopy (ESR) has been widely used to study properties of polymers, e.g. microviscosity or polarity, on a local scale as sensed by spin probes. The underlying principle is the very high sensitivity of rotational and lateral diffusion of a spin probe to its environment. Nitroxide free radical spin-probes have been studied most intensely for this purpose because of their rather high chemical stabilities. In general, three lines are observed in a continuous-wave (CW) ESR nitroxide spectrum due to hyperfine coupling between the electron spin and the nuclear spin of 14N, which is characterized by the splitting between the outermost extrema in the spectra (2Azz ). In addition, the shape of the ESR spectra can be strongly altered by interactions between spin probes and the surrounding medium. The film formation process from dispersions, and phase transitions, particularly glass transitions, in polymers have been studied by ESR probe or label techniques.We have recently reported aqueous dispersions of nanoscale polyethylene (PE) crystals, consisting of a single lamella of only 6 nm thickness and with a lateral pseudo-diameter of ca. 12 nm. In addition to these dispersions (I) composed of linear PE, dispersions (II) with similar overall particle size but composed of branched (50 methyl branches per 1000 carbon atoms), low crystalline PE are accessible. The uptake of fluorescence probes as guest molecules by the dispersed particles was observed by optical spectroscopy. The environment experienced by these guests can be switched by the melting/crystallization of the PE nanoparticles, and the temperature at which this occurs can be controlled by the degree of branching of the polymer. Here we present preliminary results on spin probes as a reporter for the interactions of guest molecules with the PE particles

Reliable nanometre-range distance distributions from 5-pulse double electron electron resonance

The partial excitation artefact in 5-pulse DEER data can be eliminated by experimental time shifting and signal processing.</p

GaAs thin films grown by LPE under influence of Yb impurity

A comprehensive study of the photoluminescence spectra and the electrophysical parameters have been performed on GaAs epitaxial layers grown by the low temperature liquid phase epitaxy (LPE) method from solution-melts doped with Yb impurity. The characteristic variations of the relative intensity of the components of the PL spectra, electroconductivity, concentration and mobility of the free charge carriers in the grown layers where established as a function of the concentration of the Yb impurity in the initial solutionmelts. A possible mechanism of the influence of the Yb impurity on the native defects and background impurities in the epitaxially grown GaAs is proposed

Regularized dynamical decoupling noise spectroscopy – a decoherence descriptor for radicals in glassy matrices

Decoherence arises from a fluctuating spin environment, captured by its noise spectrum S(ω). Dynamical decoupling (DD) with n π pulses extends the dephasing time if the associated filter function attenuates S(ω). Inversely, DD noise spectroscopy (DDNS) reconstructs S(ω) from DD data by approximating the filters pass band by a δ-function. This restricts application to qubit-like spin systems with inherently long dephasing times and/or many applicable pulses. We introduce regularized DDNS to lift this limitation and thereby infer S(ω) from DD traces of paramagnetic centers in glassy o-terphenyl and water–glycerol matrices recorded with n ≤ 5. For nitroxide radicals at low temperatures, we utilize deuteration to identify distinct matrix- and spin center-induced spectral features. The former extends up to a matrix-specific cut-off frequency and characterizes nuclear spin diffusion. We demonstrate that rotational tunneling of intramolecular methyl groups drives the latter process, whereas at elevated temperatures S(ω) reflects the classical methyl group reorientation. Ultimately, S(ω) visualizes and quantifies variations in the electron spins couplings and thus reports on the underlying spin dynamics as a powerful decoherence descriptor.ISSN:1463-9084ISSN:1463-907

Quantification of Redox Sites during Catalytic Propane Oxychlorination by Operando EPR Spectroscopy

Identification and quantification of redox‐active centers at relevant conditions for catalysis is pivotal to understand reaction mechanisms and requires development of advanced operando methods. Herein, we demonstrate operando EPR spectroscopy as an important technique to quantify the oxidation state of representative CrPO4 and EuOCl catalysts during propane oxychlorination, an attractive route for propylene production. In particular, we show for the first time that the space‐time‐yield of C3H6 correlates with the amount of Cr2+ and Eu2+ ions generated over the catalysts during reaction. These results provide a powerful strategy to gather quantitative understanding of selective alkane oxidation, which could potentially be extrapolated to other functionalization approaches and operating conditions. © 2020 Wiley‐VCH GmbH.ISSN:1433-7851ISSN:1521-3773ISSN:0570-083

Artefact suppression in 5-pulse double electron electron resonance for distance distribution measurements

ISSN:1463-9084ISSN:1463-907