A general model to optimise CuII labelling efficiency of double-histidine motifs for pulse dipolar EPR applications

A multi-site speciation model facilitates double-histidine motif labelling efficiency optimisation for pulse dipolar EPR measurements. Results suggest affinities differing by a factor of 10 between an α-helical and a β-sheet double-histidine motif.

Probing the Y2 Receptor on Transmembrane, Intra- and Extra-Cellular Sites for EPR Measurements

The function of G protein-coupled receptors is intrinsically linked to their conformational dynamics. In conjugation with site-directed spin labeling, electron paramagnetic resonance (EPR) spectroscopy provides powerful tools to study the highly dynamic conformational states of these proteins. Here, we explored positions for nitroxide spin labeling coupled to single cysteines, introduced at transmembrane, intra- and extra-cellular sites of the human neuropeptide Y2 receptor. Receptor mutants were functionally analyzed in cell culture system, expressed in Escherichia coli fermentation with yields of up to 10 mg of purified protein per liter expression medium and functionally reconstituted into a lipid bicelle environment. Successful spin labeling was confirmed by a fluorescence assay and continuous wave EPR measurements. EPR spectra revealed mobile and immobile populations, indicating multiple dynamic conformational states of the receptor. We found that the singly mutated positions by MTSL ((1-oxyl-2,2,5,5-tetramethyl-2,5-dihydro-1H-pyrrol-3-yl) methyl methanesulfonothioate) have a water exposed immobilized conformation as their main conformation, while in case of the IDSL (bis(1-oxyl-2,2,5,5-tetramethyl-3-imidazolin-4-yl) disulfide) labeled positions, the main conformation are mainly of hydrophobic nature. Further, double cysteine mutants were generated and examined for potential applications of distance measurements by double electron–electron resonance (DEER) pulsed EPR technique on the receptor.

Antiferromagnetic coupling in copper(II)porphyrin dimers linked by copper(II) or palladium(II) ion

The synthesis of porphyrin dimers linked by metal ions is described and the X-ray structure of two new dimers is presented. As previously shown for diamagnetic metal ions, strong electronic interactions between the individual subunits were observed. Antiferromagnetic coupling between copper(II)porphyrins linked by palladium(II) or copper(II) ions was studied by EPR and SQUID measurements. For the palladium(II)-linked dimer, the very small antiferromagnetic coupling was estimated by EPR measurements ([Formula: see text] <-1 cm[Formula: see text]. For the trinuclear-copper(II)-linked dimer, a large antiferromagnetic coupling between the copper(II) ions was measured. In this trinuclear compound, the linking copper(II) ion is used as a relay to increase the interaction between the two copper(II)porphyrins.

Magnetization relaxation dynamics of a rare coordinatively unsaturated Co(ii) complex: experimental and theoretical insights

A three-coordinate Co(ii) complex with the molecular formula [Li(DME)3][Co(L)3] (1) was isolated. The influence of the geometry on the SH parameters, and in turn on the magnetization relaxation, is investigated by SQUID and EPR measurements.

Magnetic-field-tuned phase transition of a molecular material from the isolated-spin to the coupled-spin regime

A quantum phase transition, as a consequence of spin-entanglements caused by Cu–Cu exchange couplings, explains EPR measurements in a new monomeric CuII compound.