Oxygen-17 dynamic nuclear polarisation enhanced solid-state NMR spectroscopy at 18.8 T

We report O-17 dynamic nuclear polarisation (DNP) enhanced solid-state NMR experiments at 18.8 T. Several formulations were investigated on the Mg(OH)(2) compound. A signal enhancement factor of 17 could be obtained when the solid particles were incorporated into a glassy o-terphenyl matrix doped with BDPA using the Overhauser polarisation transfer scheme whilst the cross effect mechanism enabled by TEKPol yielded a slightly lower enhancement but more time efficient data acquisition

Iridium(I)/N-Heterocyclic Carbene Hybrid Materials: Surface Stabilization of Low-Valent Iridium Species for High Catalytic Hydrogenation Performance

An Ir-I(NHC)-based hybrid material was prepared using a methodology which allowed the precise positioning and isolation of the Ir centers along the pore channels of a silica framework. The full characterization of the material by solid-state NMR spectroscopy showed that the supported Ir sites were stabilized by the silica surface, as low-coordinated single-site complexes. The material is extremely efficient for the hydrogenation of functional alkenes. The catalytic performance (TOF and TON) is one to two orders of magnitude higher than those of their molecular Ir analogues, and could be related to the prevention of the bimolecular deactivation of Ir complexes observed under homogeneous conditions

Off-the-Shelf Gd(NO3)(3) as an Efficient High-Spin Metal Ion Polarizing Agent for Magic Angle Spinning Dynamic Nuclear Polarization

[Image: see text] Magic angle spinning nuclear magnetic resonance spectroscopy experiments are widely employed in the characterization of solid media. The approach is incredibly versatile but deleteriously suffers from low sensitivity, which may be alleviated by adopting dynamic nuclear polarization methods, resulting in large signal enhancements. Paramagnetic metal ions such as Gd(3+) have recently shown promising results as polarizing agents for (1)H, (13)C, and (15)N nuclear spins. We demonstrate that the widely available and inexpensive chemical agent Gd(NO(3))(3) achieves significant signal enhancements for the (13)C and (15)N nuclear sites of [2-(13)C,(15)N]glycine at 9.4 T and ∼105 K. Analysis of the signal enhancement profiles at two magnetic fields, in conjunction with electron paramagnetic resonance data, reveals the solid effect to be the dominant signal enhancement mechanism. The signal amplification obtained paves the way for efficient dynamic nuclear polarization without the need for challenging synthesis of Gd(3+) polarizing agents

Hybrid polarizing solids for pure hyperpolarized liquids through dissolution dynamic nuclear polarization

Hyperpolarization of substrates for magnetic resonance spectroscopy (MRS) and imaging (MRI) by dissolution dynamic nuclear polarization (D-DNP) usually involves saturating the ESR transitions of polarizing agents (PAs; e.g., persistent radicals embedded in frozen glassy matrices). This approach has shown enormous potential to achieve greatly enhanced nuclear spin polarization, but the presence of PAs and/or glassing agents in the sample after dissolution can raise concerns for in vivo MRI applications, such as perturbing molecular interactions, and may induce the erosion of hyperpolarization in spectroscopy and MRI. We show that D-DNP can be performed efficiently with hybrid polarizing solids (HYPSOs) with 2,2,6,6-tetramethyl-piperidine-1-oxyl radicals incorporated in a mesostructured silica material and homogeneously distributed along its pore channels. The powder is wetted with a solution containing molecules of interest (for example, metabolites for MRS or MRI) to fill the pore channels (incipient wetness impregnation), and DNP is performed at low temperatures in a very efficient manner. This approach allows high polarization without the need for glass-forming agents and is applicable to a broad range of substrates, including peptides and metabolites. During dissolution, HYPSO is physically retained by simple filtration in the cryostat of the DNP polarizer, and a pure hyperpolarized solution is collected within a few seconds. The resulting solution contains the pure substrate, is free from any paramagnetic or other pollutants, and is ready for in vivo infusion

Three-Dimensional Structure Determination of Organometallic Catalysts by DNP Enhanced Solid-state NMR Spectroscopy

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Surface sites of complex systems : single sites, supported nanoparticles vs. hybrid materials : structure, reactivity and formation mechanism : a NMR point of view

Afin d’optimiser par une approche moléculaire des catalyseurs hétérogènes, qu’ils soient dits sites uniques ou des particules supportées, il est nécessaire d’accéder à une compréhension détaillée de leur structure et de leur processus de formation. Dans ce but, les techniques classiques de caractérisation (adsorption, IR, EXAFS, TEM…) ont été combinées à la RMN solide, pour accéder à la structure fine et à la dynamique des espèces présentes en surface. Dans ce cadre, nous avons tout d’abord montré que la formation d’espèces Au(I) (densité de surface de 0.35/nm2) entouré de fragments hydrophobes (OSiMe3) par greffage contrôlé de {AuN(SiMe3)2}4 sur silice se transforment en particules d’or de ca. 1.8nm supportées sur silice passivée par réduction ménagée sous H2 à 300°C. Ce système a démontré des propriétés particulières en oxydation et hydrogénation, et permet d’affiner les mécanismes d’activation de l’O2 sur les nanoparticules d’or. Cette approche a aussi été utilisée pour la préparation et la caractérisation de particules de ruthénium supportées. La réactivité de ces particules d’or et ruthénium vis-à-vis de petites molécules (H2, phosphines, éthylène et CO) a été étudiée, en particulier par RMN. Toutefois, la faible densité d’espèces de surface sur ces particules constitue un des problèmes majeurs pour obtenir des spectres RMN de bonne qualité. Ainsi, nous avons développé une méthode basée sur l’augmentation du signal RMN des espèces de surface de matériaux par polarisation dynamique nucléaire (DNP). Cette approche, très prometteuse, d’abord appliquée à des matériaux hybrides (inorganique-organiques), devrait lever un des freins majeurs de la caractérisation des sites de surface des matériaux et en particulier des catalyseurs hétérogènesIn order to optimize heterogeneous catalysts through a molecular approach, whether based on single-sites or supported nanoparticles, it is necessary to access to a detailed understanding of its structures and formation mechanism. To reach this goal, classical characterization techniques (adsorption, IR, EXAFS, TEM…) have been combined with solid state NMR in order to access to the detailed structure and the dynamics of surface species. Here, we showed that the formation of well-dispersed Au(I) surface species (0.35/nm2) surrounded by hydrophobic groups (OSiMe3) by the controlled grafting of {AuN(SiMe3)2}4 and its conversion into 1.8nm gold nanoparticles supported on fully passivated silica upon a mild reduction under H2 (300°C). This system displays good activity and selectivity in air oxidation and hydrogenation reactions and provides new information on the activation of O2 on gold nanoparticles. By a similar approach, supported ruthenium nanoparticles have been prepared and characterized. Reactivity of Au and Ru nanoparticles with probe molecules (H2, phosphines, ethylene and CO) has been studied, in particular by NMR. However, the low density of these surface species, especially for supported nanoparticles is still one of the main problems, making difficult to obtain high quality NMR spectra in a reasonable time. Therefore, we have developed a method based on the enhancement of NMR signals of surface species via dipolar nuclear polarization (DNP). This very promising approach has first been applied very successfully to hybrid materials and silica; this opens new avenues in the characterization of surface species of materials and particularly heterogeneous catalyst

BDPA-Nitroxide Biradicals for Efficient Dynamic Nuclear Polarization Enhanced Solid-State NMR at Magnetic Fields up to 21.1 T

International audienc

Research Data Supporting N. J. Brownbill et al."Oxygen-17 Dynamic Nuclear Polarisation Enhanced Solid-State NMR Spectroscopy at 18.8 T", Chemical Communications, DOI: 10.1039/C6CC09743J

This includes all the FIDs and processed NMR data published in the paper "Oxygen-17 Dynamic Nuclear Polarisation Enhanced Solid-State NMR Spectroscopy at 18.8 T", Chemical Communications, 2017. All the NMR data were acquired and processed with Topspin 3.2. Please see the paper for more details. All attached files are referenced in the paper, and a guide can be found in the README spreadsheet