Dynamic Nuclear Polarization / solid-state NMR of membranes. Thermal effects and sample geometry.

Whereas specially designed dinitroxide biradicals, reconstitution protocols, oriented sample geometries and NMR probes have helped to much increase the DNP enhancement factors of membrane samples they still lag considerably behind those obtained from glasses made of protein solutions. Here we show that not only the MAS rotor material but also the distribution of the membrane samples within the NMR rotor have a pronounced effect on the DNP enhancement. These observations are rationalized with the cooling efficiency and the internal properties of the sample, monitored by their T relaxation, microwave ON versus OFF signal intensities and DNP effect.

Triangular Regulation of Cucurbit[8]uril 1:1 Complexes.

Triangular shapes have inspired scientists over time and are common in nature, such as the flower petals of oxalis triangularis, the triangular faces of tetrahedrite crystals, and the icosahedron faces of virus capsids. Supramolecular chemistry has enabled the construction of triangular assemblies, many of which possess functional features. Among these structures, cucurbiturils have been used to build supramolecular triangles, and we recently reported paramagnetic cucurbit[8]uril (CB[8]) triangles, but the reasons for their formation remain unclear.

Dynamic Nuclear Polarization Efficiency Increased by Very Fast Magic Angle Spinning.

Dynamic nuclear polarization (DNP) has recently emerged as a tool to enhance the sensitivity of solid-state NMR experiments. However, so far high enhancements (>100) are limited to relatively low magnetic fields, and DNP at fields higher than 9.4 T significantly drops in efficiency.

Dynamic Nuclear Polarization/Solid-State NMR Spectroscopy of Membrane Polypeptides: Free-Radical Optimization for Matrix-Free Lipid Bilayer Samples.

Dynamic nuclear polarization (DNP) boosts the sensitivity of NMR spectroscopy by orders of magnitude and makes investigations previously out of scope possible. For magic-angle-spinning (MAS) solid-state NMR spectroscopy studies, the samples are typically mixed with biradicals dissolved in a glass-forming solvent and are investigated at cryotemperatures. Herein, we present new biradical polarizing agents developed for matrix-free samples such as supported lipid bilayers, which are systems widely used for the investigation of membrane polypeptides of high biomedical importance.

Frozen Acrylamide Gels as Dynamic Nuclear Polarization Matrices.

Aqueous acrylamide gels can be used to provide dynamic nuclear polarization (DNP) NMR signal enhancements of around 200 at 9.4 T and 100 K. The enhancements are shown to increase with crosslinker concentration and low concentrations of the AMUPol biradical.