Bulk Hyperpolarization of Inorganic Materials

Solid-state NMR spectroscopy is a well-established method to obtain atomic-level information about the structure of inorganic materials, but its use is often limited by low sensitivity. We review how solvent generated dynamic nuclear polarization can be used to increase sensitivity in solid-state NMR of inorganic materials, with emphasis on our recent method for hyperpolarization of proton-free bulk. We use selected examples to show how overall gains in sensitivity can be observed in both the surface and bulk spectra of inorganic compounds such as lithium titanate. The hyperpolarization methods reviewed here can be used to improve NMR sensitivity for a range of inorganic materials

Syntheses of Biradicals for Surface Studies by DNP ssNMR

Dynamic nuclear polarization (DNP) is a method that can be used to increase signal intensities in nuclear magnetic resonance (NMR) spectroscopy. This is usually attained by doping the sample of interest with a paramagnetic polarizing agent, such as a stable organic radical. The high electron polarization of the radical is then transferred to the nuclei of the sample by irradiating electron-nuclear transitions, resulting in increased NMR signal intensities. In this work, two different types of biradical nitroxide spin labels for solid-state DNP NMR experiments are introduced. A novel sulfhydryl-specific spin label for proteins was developed, synthesized and covalently attached to proteins. Four biradicals for immobilization on surfaces of materials have also been prepared. These radicals have different functional groups and the various methods used for coupling them to different surfaces are described. Finally, radicals that might be useful for studying surfaces of nanoparticles are reported. Evaluation of the DNP properties of all radicals is in progress.Mögnun á kjarnskautun (dynamic nuclear polarization, DNP) er tækni sem hægt er að nota til að magna upp merki í kjarnsegulgreiningu (nuclear magnetic resonance, NMR). Lága næmni NMR má rekja til lágrar skautunar segulvirkra kjarna, en næmnina er hægt að auka með því að nýta háa skautun stakra (óparaðra) rafeinda. Þetta er oft gert með því að bæta stöðugri lífrænni stakeind í sýnið sem á að rannsaka og geisla það með örbylgjum. Þannig er há skautun stakeindarinnar færð yfir á kjarnann sem verið er að mæla, sem leiðir til sterkari merkja í NMR. Í þessari ritgerð eru tvær mismunandi gerðir af tvístakeindum fyrir DNP í föstum efnum kynntar. Hönnun og smíði á cysteine-sértæku spunamerki fyrir prótein eru gerð skil, sem og festingu þess á tvö mismunandi prótein. Fjórar mismunandi tvístakeindir sem hægt er að tjóðra við yfirborð efna voru smíðaðar. Þessar stakeindir hafa mismunandi virknihópa og eru festar á yfirborð með mismunandi aðferðum. Tvístakeind sem gæti nýst við rannsóknir á yfirborðum nanóagna var líka smíðuð. Greiningar á eiginleikum tvístakeindanna til mögnunar á kjarnskautun standa ný yfir

A Computational Investigation of the Catalytic Activity of an MoS2 Compound for the Conversion of CN- to SCN-

In this study, density functional theory (DFT) was used to develop a suitable computational model for a molybdenum sulfur compound. The PBE0 hybrid functional, a def2-TZVPD basis set for all atoms and ECPs for the molybdenum atoms was used. Solvent and dispersion effects were accounted for to obtain more reliable reaction energies

Control and Manipulation of Microwave Polarization and Power of a Frequency-Agile 198 GHz Gyrotron for Magnetic Resonance

The measurement and manipulation of the microwave polarization emitted from a frequency-agile 198 GHz gyrotron for dynamic nuclear polarization (DNP) are demonstrated. In general, gyrotrons emit linearly polarized radiation, yet in this case elliptical polarization is observed from the 198 GHz gyrotron window. Indeed, half of the microwave power is circularly polarized while the other half is linearly polarized with a polarization of 60(circle) with respect to the horizontal plane. For optimal use of microwave power for DNP experiments, the elliptical polarization from the gyrotron is converted into circular polarization with a Martin-Puplett interferometer (MPI). The dependence of the DNP enhancement on the microwave polarization was investigated by modifying the microwave polarization with the MPI. In addition, the MPI can generate a linearly polarized beam, which holds promise for future development of induction-mode electron spin detected experiments.ISSN:1866-6892ISSN:1866-690

Solid-state NMR spectra of protons and quadrupolar nuclei at 28.2 T: resolving signatures of surface sites with fast magic angle spinning

Advances in solid-state nuclear magnetic resonance (NMR) methods and hardware offer expanding opportunities for analysis of materials, interfaces, and surfaces. Here, we demonstrate the application of a very high magnetic field strength of 28.2 T and fast magic-angle-spinning rates (MAS, >40 kHz) to surface species relevant to catalysis. Specifically, we present as case studies the 1D and 2D solid-state NMR spectra of important catalyst and support materials, ranging from a well-defined silica-supported organometallic catalyst to dehydroxylated γ-alumina and zeolite solid acids. The high field and fast-MAS measurement conditions substantially improve spectral resolution and narrow NMR signals, which is particularly beneficial for solid-state 1D and 2D NMR analysis of 1H and quadrupolar nuclei such as 27Al at surfaces

Solid-state NMR spectra of protons and quadrupolar nuclei at 28.2 T: Resolving signatures of surface sites with fast magic angle spinning

Advances in solid-state nuclear magnetic resonance (NMR) methods and hardware offer expanding opportunities for analysis of materials, interfaces, and surfaces. Here, we demonstrate the application of a very high magnetic field strength of 28.2 T and fast magic-angle-spinning rates (MAS, >40 kHz) to surface species relevant to catalysis. Specifically, we present as case studies the 1D and 2D solid-state NMR spectra of important catalyst and support materials, ranging from a well-defined silica-supported organometallic catalyst to dehydroxylated γ-alumina and zeolite solid acids. The high field and fast-MAS measurement conditions substantially improve spectral resolution and narrow NMR signals, which is particularly beneficial for solid-state 1D and 2D NMR analysis of 1H and quadrupolar nuclei such as 27Al at surfaces.ISSN:2691-370

High Sensitivity Detection of a Solubility Limiting Surface Transformation of Drug Particles by DNP SENS

We investigate the presence of a surface species for the active pharmaceutical ingredient (API) AZD9496 with dynamic nuclear polarization surface enhanced nuclear spectroscopy (DNP SENS). We show that using DNP we can elucidate the presence of an amorphous form of the API at the surface of crystalline particles of the salt form. The amorphous form of the API has distinguishable 13C chemical shifts when compared to the salt form under various acidic conditions. The predominant form in frozen particles of AZD9496 is the salt, and we provide evidence to suggest that the amorphous layer at the surface is mainly made up of the dissociated free form

Molecularly defined lubricant hydrocarbons from olefin metathesis

Hydrocarbon-based lubricants are ubiquitous in industrial applications but are typically complex mixtures of branched molecules that are challenging to characterize and to relate to their macroscopic properties. Consequently, lubricants are typically optimized empirically for specific applications by blending base oils and organic or inorganic additives. Here, we report the synthesis and characterization of molecularly defined lubricants via metathesis of branched terminal olefins followed by hydrogenation of the internal olefin products. The resulting saturated hydrocarbons are characterized by ultra-high-field (28.2 T) 1H and 13C NMR spectroscopies to establish their molecular structures and resolve different stereoisomers, showing the utility of state-of-the-art spectroscopic tools for resolving structures of branched alkanes. Furthermore, the molecular-level diffusion and bulk viscosity properties compare favorably to classical synthetic lubricants based on hydrogenated polyalphaolefin blends, establishing olefin metathesis as a selective and scalable route to high-performance lubricant oils with defined molecular structures

No-Insulation All- GdBCO Double Pancake Magnets in Liquid Helium

The no-insulation (NI) high temperature superconductor (HTS) winding technique enables the fabrication of highly compact magnets with self-quench protection. NI pancake coils are implemented to develop a 28 T HTS magnet for the operation of a 792 GHz gyrotron, which is a microwave source for dynamic nuclear polarization nuclear magnetic resonance. To this end, three NI all-GdBCO double pancake (DP) magnets were fabricated using different winding diameters and procedures. The objective was to explore different mechanical coil protection mechanisms at high magnetic fields, including clamping, overband, and solder impregnation. Experiments in liquid helium using magnets with winding diameters of 18 mm, 25 mm, and 66 mm yielded a center field of 14.4 T, 11.2 T, and 8.1 T, respectively. The maximum currents applied to the DP magnets ranged from 780 A to 1000 A. Both the 18 mm and 66 mm DP coils contained 400 m (2 × 200 m) HTS tape, while the 25 mm seamless DP coil consisted of only one continuous 200 m HTS tape. The 25 mm magnet with solder impregnation showed the best repeatability, although the current density was reduced owing to the solder thickness between the coil windings. Critical to the implementation of such coils in liquid helium is to effectively transfer high currents to the magnet, while not compromising the helium boil-off. Furthermore, the design of hybrid copper-HTS current leads capable of carrying current larger than 1000 A from room temperature to the HTS magnet at 4.2 K is presented. The implementation of liquid nitrogen-cooled hybrid copper-HTS current leads reduced the helium boil-off and permitted independent temperature control of the current leads. </p

Active Site Descriptors from 95Mo NMR Signatures of Silica-supported Mo-based Olefin Metathesis Catalysts

The catalytic activity of silica-supported molybdenum oxides for olefin metathesis depends strongly on the metal loading and preparation conditions indicating that the nature and/or amounts of the active sites vary across catalysts. This is illustrated by comparing Mo-based (pre)catalysts prepared by impregnation with different metal loadings (2.5-15.6 wt% Mo) and a well-defined model material (2.3 wt% Mo) prepared via a surface organometallic chemistry (SOMC) synthetic approach. Analyses of FTIR, UV-vis, and Mo K-edge X-ray absorption spectra provide strong evidence that all the (pre)catalysts are composed predominantly of similar isolated Mo dioxo sites; however, they exhibit very different proportions of reducible surface sites and catalytic reaction properties. Specifically, the SOMC-derived catalyst is more active for liquid and gas-phase olefin metathesis conditions than a classical catalyst of similar Mo loading by a factor of 1.5-1.9, depending on precise reaction conditions. Most notably, solid-state 95Mo NMR spectra of these catalysts show distinct features, particularly evident under state-of-the-art high-field (28.2 T) measurement conditions where at least four distinct types of surface Mo dioxo sites are resolved, the distribution of which depends on the preparation methods. In particular, the presence of Mo sites with a specific deshielded 95Mo NMR signal correlates with the catalysts reducibility and metathesis activity; such sites are most prominent in the SOMC-derived catalyst. First-principles calculations show that the 95Mo NMR parameters, specifically the isotropic chemical shift and quadrupolar coupling constant, are good descriptors for local strain and coordination environment: acute (SiO-Mo(O)2-OSi) angles and low coordination numbers at the Mo sites leads to highly deshielded iso chemical shifts and small CQ values, respectively. Orbital and natural chemical shift analyses indicate that the deshielded 95Mo iso values of strained species are directly related to low LUMO energies, consistent with their higher reducibility and corresponding reactivity. Overall, this study shows that solid-state NMR is particularly powerful for the identification of distinct supported Mo dioxo species and that their 95Mo chemical shifts are related to their specific local electronic structures, providing a powerful descriptor for the propensity of Mo sites towards reduction and the formation of active sites