Matériau paramagnétique pour l'information quantique : manipulations des spins électroniques et nucléaires dans β − Ga2O3 : Ti

Quantum information processing is a major challenge both on fundamental and technological grounds. In this research field, the spin bus concept relies on the use of both the electronic and nuclear spins in which the electron is used as a reading and writing head over the nuclei system which makes the qubit register. The requested material to build a spin bus must have unpaired electrons delocalized over a great number of nuclear spins having long decoherence time. In this work, we studied a spin system composed of titanium (III) interacting with multiple gallium nuclei in gallium oxide. We synthesized and studied the titanium paramagnetic center in gallium oxide single-crystals by continuous wave EPR and ENDOR spectroscopy and showed that the electron is delocalized over eight neighbouring gallium nuclei. This study also revealed a strong isotopic effect on the nucleus-nucleus interaction mediated by the electron. When the two nearest gallium nuclei surrounding the titanium are identical (same isotopes) this interaction is one order of magnitude higher than in the case of inequivalent nuclei. This effect can be used in order to reduce the computation time. Finally, the dynamical properties of the spin system have been characterized by pulsed EPR and ENDOR spectroscopy. The electron spin decoherence is driven by instantaneous and spectral diffusion. The nuclear dynamical properties have also been studied in order to determine the order of magnitude of nuclear spin relaxation and decoherence time.Le traitement quantique de l'information est un domaine très actif dont les enjeux sont importants tant d'un point de vue du savoir scientifique fondamental que des applications technologiques. Dans ce contexte le concept de bus de spin consiste à employer en tandem des spins électroniques et nucléaires. Les électrons célibataires servent de tête de lecture et d'écriture sur le registre de bits quantiques constitué par les spins nucléaires. Les électrons sont délocalisés sur un ensemble de spins nucléaires dont les temps de décohérences doivent être longs. Dans ce travail nous avons étudié un ion titane (III) dans l'oxyde de gallium dont nous avons synthétisé et étudié des monocristaux. Une étude approfondie par RPE et ENDOR en onde continue a montré que l'électron porté par le titane était en interaction avec huit noyaux de gallium qui constituent le registre de qubits potentiel. L'étude a également révélé un effet isotopique sur les interactions noyau-noyau véhiculées par l'électron. Lorsque les deux noyaux de gallium entourant le titane sont identiques (mêmes isotopes), cette interaction est d'un ordre de grandeur plus grande que dans le cas d'isotopes différents, un effet qui peut être employé afin de réduire la durée des opérations logiques. Enfin, la dynamique de cet ensemble de spin a été caractérisée par RPE et ENDOR en impulsions. Il s'avère que la décohérence électronique est dominée par des phénomènes de diffusion instantanée et de diffusion spectrale. La dynamique des spins nucléaires les expériences menées permettent de déterminer l'ordre de grandeur des temps de relaxation longitudinaux et de décohérence des spins nucléaires

Matériau paramagnétique pour l'information quantique (manipulations des spins électroniques et nucléaires dans b - Ga2O3 : Ti)

Le traitement quantique de l'information est un domaine très actif dont les enjeux sont importants tant d'un point de vue du savoir scientifique fondamental que des applications technologiques. Dans ce contexte le concept de bus de spin consiste à employer en tandem des spins électroniques et nucléaires. Les électrons célibataires servent de tête de lecture et d'écriture sur le registre de bits quantiques constitué par les spins nucléaires. Les électrons sont délocalisés sur un ensemble de spins nucléaires dont les temps de décohérences doivent être longs. Dans ce travail nous avons étudié un ion titane (III) dans l'oxyde de gallium dont nous avons synthétisé et étudié des monocristaux. Une étude approfondie par RPE et ENDOR en onde continue a montré que l'électron porté par le titane était en interaction avec huit noyaux de gallium qui constituent le registre de qubits potentiel. L'étude a également révélé un effet isotopique sur les interactions noyau-noyau véhiculées par l'électron. Lorsque les deux noyaux de gallium entourant le titane sont identiques (mêmes isotopes), cette interaction est d un ordre de grandeur plus grande que dans le cas d'isotopes différents, un effet qui peut être employé afin de réduire la durée des opérations logiques. Enfin, la dynamique de cet ensemble de spin a été caractérisée par RPE et ENDOR en impulsions. Il s'avère que la décohérence électronique est dominée par des phénomènes de diffusion instantanée et de diffusion spectrale. La dynamique des spins nucléaires les expériences menées permettent de déterminer l'ordre de grandeur des temps de relaxation longitudinaux et de décohérence des spins nucléairesPARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF

MAS-DNP Enhancements: Hyperpolarization, Depolarization, and Absolute Sensitivity

International audienceDynamic nuclear polarization at high magnetic fields has made significant progress over the last decades, and this hyperpolarizing technique is currently revolutionizing the impact of solid-state NMR for the study of complex systems in chemistry, material science, and biology. In this article, we emphasize the importance and difficulty in quantifying sensitivity from DNP under magic-angle spinning. To this end, we provide insight into the cross effect, the current main MAS-DNP mechanism. This includes a description of the microwave-induced hyperpolarization phenomenon but also of the reduction of the NMR signal prior to microwave irradiation for samples doped with polarizing agents (bleaching and depolarization effects). We highlight the importance of the nuclear hyperpolarization buildup time in the evaluation of MAS-DNP efficiency. Finally, we discuss other experimental parameters affecting sensitivity in DNP-enhanced spectra and propose a guideline for its proper characterization depending on the type of investigation

Solid-state nmr and dnp investigations of carbohydrates and cell-wall biomaterials

© 2020 John Wiley & Sons, Ltd. The cell walls in plants and microbes serve as a central source for biorenewable energy and biomaterials, as well as the target for novel antibiotics and antifungals. They are biocomposites abundant in complex carbohydrates, a class of biologically important but underinvestigated molecules. Solid-state nuclear magnetic resonance (ssNMR) of carbohydrate materials and cell walls has made significant progress over the past 10 years. This article summarizes the recent ssNMR studies that have elucidated the polymorphic structure and heterogeneous dynamics of polysaccharides and other biomolecules, such as proteins, lignin, and pigment, in the intact cell walls or biofilms of 11 species across plants, fungi, bacteria, and algae. We also highlight the assistance of magic-angle spinning dynamic nuclear polarization (MAS-DNP) in the enhanced detection of the interaction interface involving lowly populated biopolymers and summarize the recent applications of natural-abundance MAS-DNP in cell-wall research, which could substantially broaden the scope of biomolecular NMR by skipping isotope labeling

Terahertz EPR spectroscopy using a 36-tesla high-homogeneity series-connected hybrid magnet

Electron Paramagnetic Resonance (EPR) is a powerful technique to study materials and biological samples on an atomic scale. High-field EPR in particular enables extracting very small g-anisotropies in organic radicals and half-filled 3d and 4f metal ions such as MnII (3d5) or GdIII (4f7), and resolving EPR signals from unpaired spins with very close g-values, both of which provide high-resolution details of the local atomic environment. Before the recent commissioning of the high-homogeneity Series Connected Hybrid magnet (SCH, superconducting + resistive) at the National High Magnetic Field Laboratory (NHMFL), the highest-field, high-resolution EPR spectrometer available was limited to 25 T using a purely resistive “Keck” magnet at the NHMFL. Herein, we report the first EPR experiments performed using the SCH magnet capable of reaching the field of 36 T, corresponding to an EPR frequency of 1 THz for g = 2. The magnet’s intrinsic homogeneity (25 ppm, that is 0.9 mT at 36 T over 1 cm diameter, 1 cm length cylinder) was previously established by NMR. We characterized the magnet’s temporal stability (5 ppm, which is 0.2 mT at 36 T over one-minute, the typical acquisition time) using 2,2-diphenyl-1-picrylhydrazyl (DPPH). This high resolution enables resolving the weak g-anisotropy of 1,3-bis(diphenylene)-2-phenylallyl (BDPA), Δg = 2.5 × 10–4 obtained from measurements at 932 GHz and 33 T. Subsequently, we recorded EPR spectra at multiple frequencies for two GdIII complexes with potential applications as spin labels. We demonstrated a significant reduction in line broadening in Gd[DTPA], attributed to second order zero field splitting, and a resolution enhancement of g-tensor anisotropy for Gd[sTPATCN]-SL

PyrroTriPol: a semi-rigid trityl-nitroxide for high field dynamic nuclear polarization

International audienceA semi-rigid trityl-nitroxide polarizing agent is introduced for magic angle spinning (MAS) dynamic nuclear polarization (DNP), which significantly broadened the scope of solid-state NMR to study biomolecular systems and materials.Magic angle spinning (MAS) dynamic nuclear polarization (DNP) has significantly broadened the scope ofsolid-state NMR to study biomolecular systems and materials. In recent years, the advent of very highfield DNP combined with fast MAS has brought new challenges in the design of polarizing agents (PA)used to enhance nuclear spin polarization. Here, we present a trityl-nitroxide PA family based ona piperazine linker, named PyrroTriPol, for both aqueous and organic solutions. These new radicals havesimilar properties to that of TEMTriPol-I and can be readily synthesized, and purified in large quantitiesthereby ensuring widespread application. The family relies on a rigid bridge connecting the trityl and thenitroxide offering a better control of the electron spin–spin interactions thus providing improvedperformance across a broad range of magnetic fields and MAS frequencies while requiring reducedmicrowave power compared to bis-nitroxides. We demonstrate the efficiency of the PyrroTriPol familyunder a magnetic field of 9.4, 14.1 and 18.8 T with respect to TEMTriPol-I. In particular, the superiority ofPyrroTriPol was demonstrated on g-Al2O3 nanoparticles which enabled the acquisition of a high signalto-noise surface-selective 27Al multiple-quantum MAS experiment at 18.8 T and 40 kHz MAS frequency

Overhauser effects in non-conducting solids at 1.2 K

Recently, it was observed that protons in non-conducting solids doped with 1,3-bisdiphenylene-2-phenylallyl (BDPA) or its sulfonated derivative (SA-BDPA) can be polarized through Overhauser effects via resonant microwave irradiation. These effects were present under magic angle spinning conditions in magnetic fields between 5 and 18.8 T and at temperatures near 100 K. This communication reports similar effects in static samples at 6.7 T and, more importantly, at temperatures as low as 1.2 K, in a different dynamic regime than in the previous study. Our results provide new information towards understanding the mechanism of the Overhauser effect in non-conducting solids. We discuss possible origins of the fluctuations that can give rise to an Overhauser effect at such low temperatures.US National Institute of Biomedical Imaging and Bioengineering (grant nos. EB-002804 and EB-002026

Efficient cross-effect dynamic nuclear polarization without depolarization in high-resolution MAS NMR

Dynamic nuclear polarization (DNP) has the potential to enhance the sensitivity of magic-angle spinning (MAS) NMR by many orders of magnitude and therefore to revolutionize atomic resolution structural analysis. Currently, the most widely used approach to DNP for studies of chemical, material, and biological systems involves the cross-effect (CE) mechanism, which relies on biradicals as polarizing agents. However, at high magnetic fields (≥5 T), the best biradicals used for CE MAS-DNP are still far from optimal, primarily because of the nuclear depolarization effects they induce. In the presence of bisnitroxide biradicals, magic-angle rotation results in a reverse CE that can deplete the initial proton Boltzmann polarization by more than a factor of 2. In this paper we show that these depolarization losses can be avoided by using a polarizing agent composed of a narrow-line trityl radical tethered to a broad-line TEMPO. Consequently, we show that a biocompatible trityl-nitroxide biradical, TEMTriPol-1, provides the highest MAS NMR sensitivity at ≥10 T, and its relative efficiency increases with the magnetic field strength. We use numerical simulations to explain the absence of depolarization for TEMTriPol-1 and its high efficiency, paving the way for the next generation of polarizing agents for DNP. We demonstrate the superior sensitivity enhancement using TEMTriPol-1 by recording the first solid-state 2D¹³ C- ¹³ C correlation spectrum at natural isotopic abundance at a magnetic field of 18.8 T

17O solid state NMR as a valuable tool for deciphering reaction mechanisms in mechanochemistry: the case study on the 17 O-enrichment of hydrated Ca-pyrophosphate biominerals

International audienceThe possibility of enriching in 17O the water molecules within hydrated biominerals belonging to the Ca-pyrophosphate family was investigated, using liquid assisted grinding (LAG) in the presence of 17O-labelled water. Two phases with different hydration levels, namely triclinic calcium pyrophosphate dihydrate (Ca2P2O7·2H2O, denoted t-CPPD) and monoclinic calcium pyrophosphate tetrahydrate (Ca2P2O7·4H2O, denoted m-CPPT β) were enriched in 17O using a “post-enrichment” strategy, in which the non-labelled precursors were ground under gentle milling conditions in the presence of stoichiometric quantities of 17O-enriched water (introduced here in very small volumes ∼10 μL). Using high-resolution 17O solid-state NMR (ssNMR) analyses at multiple magnetic fields, and dynamic nuclear polarisation (DNP)-enhanced 17O NMR, it was possible to show that the labelled water molecules are mainly located at the core of the crystal structures, but that they can enter the lattice in different ways, namely by dissolution/recrystallisation or by diffusion. Overall, this work sheds light on the importance of high-resolution 17O NMR to help decipher the different roles that water can play as a liquid-assisted grinding agent and as a reagent for 17O-isotopic enrichment