High binding yet accelerated guest rotation within a cucurbit[7]uril complex. Toward paramagnetic gyroscopes and rolling nanomachines †

International audienceThe (15-oxo-3,7,11-triazadispiro[5.1.5.3]hexadec-7-yl)oxidanyl, a bis-spiropiperidinium nitroxide derived from TEMPONE, can be included in cucurbit[7]uril to form a strong (K a ∼ 2 × 10 5 M −1) CB[7]@bPTO complex. EPR and MS spectra, DFT calculations, and unparalleled increased resistance (a factor of ∼10 3) toward ascorbic acid reduction show evidence of deep inclusion of bPTO inside CB[7]. The unusual shape of the CB[7]@bPTO EPR spectrum can be explained by an anisotropic Brownian rotational diffusion, the global tumbling of the complex being slower than rotation of bPTO around its " long molecular axis " inside CB[7]. The CB[7] (stator) with the encapsulated bPTO (rotator) behaves as a supramolecular para-magnetic rotor with increased rotational speed of the rotator that has great potential for advanced nano-scale machines requiring wheels such as cucurbiturils with virtually no friction between the wheel and the axle for optimum wheel rotation (i.e. nanopulleys and nanocars)

Peculiarities of the stochastic motion in antiferromagnetic nanoparticles

Antiferromagnetic (AFM) materials are widely used in spintronic devices as passive elements (for stabilization of ferromangetic layers) and as active elements (for information coding). In both cases switching between the different AFM states depends in a great extent from the environmental noise. In the present paper we derive the stochastic Langevin equations for an AFM vector and corresponding Fokker-Planck equation for distribution function in the phase space of generalised coordinate and momentum. Thermal noise is modeled by a random delta-correlated magnetic field that interacts with the dynamic magnetisation of AFM particle. We analyse in details a particular case of the collinear compensated AFM in the presence of spin-polarised current. The energy distribution function for normal modes in the vicinity of two equilibrium states (static and stationary) in sub- and super-critical regimes is found. It is shown that the noise-induced dynamics of AFM vector has pecuilarities compared to that of magnetisation vector in ferromagnets.Comment: Submitted to EPJ ST, presented at the 4-th Conference on Statistical Physics, Lviv, Ukraine, 201

Solid-State NMR/Dynamic Nuclear Polarization of Polypeptides in Planar Supported Lipid Bilayers

Dynamic nuclear polarization has been developed to overcome the limitations of the inherently low signal intensity of NMR spectroscopy. This technique promises to be particularly useful for solid-state NMR spectroscopy where the signals are broadened over a larger frequency range and most investigations rely on recording low gamma nuclei. To extend the range of possible investigations, a triple-resonance flat-coil solid-state NMR probe is presented with microwave irradiation capacities allowing the investigation of static samples at temperatures of 100 K, including supported lipid bilayers. The probe performance allows for two-dimensional separated local field experiments with high-power Lee-Goldberg decoupling and cross-polarization under simultaneous irradiation from a gyrotron microwave generator. Efficient cooling of the sample turned out to be essential for best enhancements and line shape and necessitated the development of a dedicated cooling chamber. Furthermore, a new membrane-anchored biradical is presented, and the geometry of supported membranes was optimized not only for good membrane alignment, handling, stability, and filling factor of the coil but also for heat and microwave dissipation. Enhancement factors of 17-fold were obtained, and a two-dimensional PISEMA spectrum of a transmembrane helical peptide was obtained in less than 2 h

Dynamic Nuclear Polarization NMR Spectroscopy Allows High-Throughput Characterization of Microporous Organic Polymers

Dynamic nuclear polarization (DNP) solid-state NMR was used to obtain natural abundance 13C and 15N CP MAS NMR spectra of microporous organic polymers with excellent signal-to-noise ratio, allowing for unprecedented details in the molecular structure to be determined for these complex polymer networks. Sensitivity enhancements larger than 10 were obtained with bis-nitroxide radical at 14.1 T and low temperature (∼105 K). This DNP MAS NMR approach allows efficient, high-throughput characterization of libraries of porous polymers prepared by combinatorial chemistry methods

L’électron : une sonde fantastique

International audienceLe TEMPO (2,2,6,6-tétraméthyl-1-piperidinyloxy), et les nitroxydes en général, constituent une classe particulière de radicaux libres. Leur stabilité en ont fait des outils précieux et efficaces dans de nombreux domaines de la chimie, notamment comme agents d’oxydation en synthèse organique, comme aimants moléculaires ou bien encore comme sondes pour l’étude structurale et dynamique de systèmes complexes, organismes vivants inclus.La présence concomitante de spécificités chimiques, électrochimiques et magnétiques au sein d’une si petite molécule organique a conduit à une large variété d’applications en recherche mais aussi dans l’industrie, et les perspectives inspirantes et excitantes sont nombreuses.En outre, le signal RPE des nitroxydes encode une somme d’informations phénoménale qui est rendue plus accessible avec les récents développements méthodologiques et technologiques de la RPE

L’électron : une sonde fantastique

International audienceLe TEMPO (2,2,6,6-tétraméthyl-1-piperidinyloxy), et les nitroxydes en général, constituent une classe particulière de radicaux libres. Leur stabilité en ont fait des outils précieux et efficaces dans de nombreux domaines de la chimie, notamment comme agents d’oxydation en synthèse organique, comme aimants moléculaires ou bien encore comme sondes pour l’étude structurale et dynamique de systèmes complexes, organismes vivants inclus.La présence concomitante de spécificités chimiques, électrochimiques et magnétiques au sein d’une si petite molécule organique a conduit à une large variété d’applications en recherche mais aussi dans l’industrie, et les perspectives inspirantes et excitantes sont nombreuses.En outre, le signal RPE des nitroxydes encode une somme d’informations phénoménale qui est rendue plus accessible avec les récents développements méthodologiques et technologiques de la RPE

Synthesis of a hemicyanine dye bearing two carboxylic groups and its use as a photosensitizer in dye-sensitized photoelectrochemical cells

Two hemicyanine (aminostilbazium) dyes, one bearing two carboxylic groups while the other being its ester analogue, were synthesized for use as photosensitizers in dye-sensitized photoelectrochemical cells (DSPEC). Only the dye with carboxylic groups is covalently attached on mesoporous TiO2 films. The ester analogue, however, is physically adsorbed and it is easily washed off by several solvents. DSPECs of the Graetzel type, made of mesoporous TiO2 films (in our case, synthesized through the reverse-micellar route), of the aminostilbazium. bicarboxylate photosensitizer and of a I-/I-3(-)/propylenecarbonate electrolyte were tested and were found to yield more than 45% maximum photon to electron conversion efficiency and 0.72% overall photovoltaic efficiency. The cells yielded a linear response within a wide range of illumination intensities

Fonctionnalisation magnétique de surface de nanoparticules de ZnO par génération optique de radicaux méthyles.

International audienceThe combination of nuclear and electron magnetic resonance techniques, in pulse and continuous wave regimes, are used to unravel the nature and features of the light-induced magnetic state arising at the surface of chemically prepared zinc oxide nanoparticles (NPs) occurring under 120 K when subjected to a sub band gap (405 nm) laser excitation. It is shown that the four-line structure observed around g ∼ 2.00 in the as-grown samples (beside the usual core-defect signal at g ∼ 1.96) arises from surface-located methyl radicals (• CH 3), originating from the acetate capped ZnO molecules. By functionalizing the as-grown zinc oxide NPs with deuterated sodium-acetate, the • CH 3 EPR signal is replaced by trideuteromethyl (• CD 3). For • CH 3 , • CD 3 and core-defect signals, an electron spin echo is detected below ∼100 K, allowing for the spin-lattice and spinspin relaxation-time measurements for each of them. Advanced pulse-EPR techniques reveal the protons or deuterons spin-echo modulation for both radicals, and give access to small unresolved superhyperfine couplings between adjacent • CH 3. In addition, electron double resonance techniques show that some correlations exist between the different EPR transitions of • CH 3. These correlations are discussed as possibly arising from cross-relaxation phenomena between different rotational states of radicals