First Demonstration of Magnetoelectric Coupling in a Polynuclear Molecular Nanomagnet: Single-Crystal EPR studies of [Fe3O(O2CPh)6(py)3](ClO4)*py under static electric fields

Single-crystal EPR experiments show that the highly symmetric antiferromagnetic half-integer spin triangle [Fe3O(O2CPh)6(py)3](ClO4)·py (1) possesses a ST = 1/2 ground state exhibiting high g-anisotropy due to antisymmetric exchange (Dzyaloshinskii-Moriya) interactions. EPR experiments under static electric fields parallel to the triangle’s plane (i.e. perpendicular to the magnetic z-axis) reveal that this ground state couples to externally applied electric fields. This magnetoelectric coupling causes an increase in the intensity of the intradoublet EPR transition and does not affect its resonance position when B0||z. The results are discussed on the basis of theoretical models correlating the spin chirality of the ground state with the magnetoelectric effect

Nucleic Acids Res

Site-directed spin labeling is emerging as an essential tool to investigate the structural and dynamical features of RNA. We propose here an enzymatic method, which allows the insertion of a paramagnetic center at a specific position in an RNA molecule. The technique is based on a segmental approach using a ligation protocol with T4 RNA ligase 2. One transcribed acceptor RNA is ligated to a donor RNA in which a thio-modified nucleotide is introduced at its 5'-end by in vitro transcription with T7 RNA polymerase. The paramagnetic thiol-specific reagent is subsequently attached to the RNA ligation product. This novel strategy is demonstrated by introducing a paramagnetic probe into the 55 nucleotides long RNA corresponding to K-turn and Specifier Loop domains from the Bacillus subtilis tyrS T-Box leader RNA. The efficiency of the coupling reaction and the quality of the resulting spin-labeled RNA were assessed by Mass Spectrometry, Electron Paramagnetic Resonance (EPR) and Nuclear Magnetic Resonance (NMR). This method enables various combinations of isotopic segmental labeling and spin labeling schemes, a strategy that will be of particular interest to investigate the structural and dynamical properties of large RNA complexes by NMR and EPR spectroscopies

Polyanisotropic Magnetoelectric Coupling in an Electrically Controlled Molecular Spin Qubit

International audienceTwo molecular spin qubits are studied with pulsed Electron Paramagnetic Resonance (EPR) spectroscopy under electric fields to assess their magnetoelectric (ME) couplings and electric spin control. [Fe 3 O(PhCOO) 6 (py) 3 ]ClO 4 ⋅py (Fe 3) is characterized by strong Dzyaloshinskii-Moriya interactions (DMI) which induce important magnetoanisotropy, whereas the DMI in [Cr 3 O(PhCOO) 6 (py) 3 ]ClO 4 ⋅0.5py (Cr 3) is 1-2 orders of magnitude weaker. Fe 3 is observed to demonstrate a clear ME effect whose intensity shows an unprecedented dependence on the molecular orientation within the electric field E (electroanisotropy) and on the relative orientations of the molecular z-axis, the Zeeman field B 0 and E (magnetoelectric anisotropy). The electric control in Fe 3 is shown to be coherent and the ME effect exhibits complex dynamics characterized by saturation and oscillatory effects. On the other hand, Cr 3 exhibits no discernible ME effect, which correlates well with its negligible DMI

Potential of EPR spin-trapping to investigate in situ free radicals generation from skin allergens in reconstructed human epidermis: cumene hydroperoxide as proof of concept

The first step in the development of skin sensitisation to a chemical, and in the elicitation offurther allergic contact dermatitis (ACD), is the binding of the allergen to skin proteins after pene-trating into the epidermis. The so-formed antigenic adduct is then recognised by the immunesystem as foreign to the body. Sensitising organic hydroperoxides derived from autoxidation ofnatural terpenes are believed to form antigens through radical-mediated mechanisms, althoughthis has not yet been established. So far,in vitroinvestigations on reactive radical intermediatesderived from these skin sensitisers have been conducted in solution, yet with experimental condi-tions being far away from real-life sensitisation. Herein, we report for the first time, the potentialuse of EPR spin-trapping to study thein situgeneration of free radicals derived from cumenehydroperoxide CumOOH in a 3D reconstructed human epidermis (RHE) model, thus much closerto what may happenin vivo. Among the undesirable effects associated with dermal exposure toCumOOH, it is described to cause allergic and irritant dermatitis, being reported as a significantsensitiser. We considered exploiting the usage of spin-trap DEPMPO as an extensive view of allsort of radicals derived from CumOOH were observed all at once in solution. We showed that inthe EpiskinTMRHE model, both by incubating in the assay medium and by topical application,carbon radicals are mainly formed by redox reactions suggesting the key role of CumOOH-derived carbon radicals in the antigen formation process

Intrinsic decoherence and Rabi oscillation damping of Mn 2+and Co 2+ electron spin qubits in bulk ZnO

We demonstrate by pulse EPR that two electron spin qubits in bulk ZnO, the Mn2+ and the Co2+ spin qubits, which have, respectively, long $(T_{2}(6\ \text{K})= 178\ \mu\text{s})$ and short $(T_{2}(1.7\ \text{K})= 9\ \mu\text{s})$ transverse spin coherence time T2 at low temperature, have however very short and similar Rabi oscillation damping times, on the order of $T_{R}\approx250\ \text{ns}$ at low temperature. A detailed study of Mn2+ spin qubits has shown that the main contribution to the Rabi oscilation damping rate is temperature independent and proportional to the Rabi frequency. This main contribution to the damping rate during coherent microwave manipulation of spins is interpreted as due to the changes of the dipolar couplings induced by the long microwave pulse used in this kind of EPR nutation experiment. Strategies are suggested for overcoming this problem of Rabi oscillation overdamping in future spin-based quantum computers

Toward a better understanding of the dynamic characteristics of single-storey braced steel frame buildings in Canada

International audienceSingle-storey braced steel frame buildings (SSBSFs) are currently the most widely used commercial structures, which include strip malls, power centres, warehouses, small and medium-sized industrial plants. The lateral seismic or wind forces acting on such low-rise structures are usually transferred from a metal roof-deck diaphragm to a system of vertical bracing members. Because these flexible roof diaphragms have a considerable effect on the dynamic response of SSBSFs during an earthquake, they also play an important role in the evaluation of the fundamental vibration period, a key parameter in determining the magnitude of the design seismic forces. It is therefore of utmost importance to reliably predict the fundamental period of SSBSFs. This paper presents the results of a four-year field measurement research project on the dynamic behaviour of SSBSFs. The goal of the project was to create a reliable database for the dynamic characteristics of SSBSFs (periods, mode shapes, and damping) and to find a relationship between them and the geometric parameters (height and plan dimensions). The field tests are described, along with the selected buildings and experimental setup. The measured fundamental periods are then compared to the National building code of Canada (NBCC) empirical equations. A statistical analysis of the data, based on different regression models, yielded new proposed building geometric parameters to be used in simple equations for the prediction of the fundamental period of SSBSFs

High-temperature ferromagnetism in Co-doped CeO2 synthesized by the coprecipitation technique

The aim of the present study is to check the influence of annealing under vacuum and a mixture of N-2-H-2 atmosphere on the magnetic properties of polycrystalline Co-doped CeO2 diluted magnetic oxides (DMOs) with Co concentrations of 5 at% synthesized using the coprecipitation technique. X-Ray diffraction (XRD) patterns and transmission electron microscopy (TEM) showed for all samples the expected CeO2 cubic fluorite-type structure and that Co ions are uniformly distributed inside the samples. Room-temperature Raman and photoluminescence (PL) spectroscopies indicate an increase in the concentration of oxygen vacancies upon Co doping and further annealing. Field dependent magnetization measurements revealed a paramagnetic behavior for as-prepared Co-doped CeO2, while a ferromagnetic behavior appears when the same samples are annealed under vacuum or N-2-H-2 atmosphere. Temperature dependent magnetization measurements suggest that the observed ferromagnetism is due to the presence of metallic Co clusters with nanometric size and broad size distribution. These results are supported by electron paramagnetic resonance studies

Magnetic Properties of Gold Nanoparticles: A Room-Temperature Quantum Effect:

Persistent currents: The magnetism of Au nanoparticles might result from persistent currents. Limited portions of a given sample may even support self‐sustained currents, thus exhibiting remnant magnetization and hysteresis. Observing such a quantum effect at room temperature with user‐friendly samples opens unforeseen possibilities