Deterioration of western redcedar (Thuja plicata Donn ex D. Don) seeds: protein oxidation and in vivo NMR monitoring of storage oils

Deterioration of conifer seeds during prolonged storage has a negative impact on reforestation and gene conservation efforts. Western redcedar (Thuja plicata Donn ex D. Don) is a species of tremendous value to the forest industry. The seeds of this species are particularly prone to viability losses during long-term storage. Reliable tools to assess losses in seed viability during storage and their underlying causes, as well as the development of methods to prevent storage-related deterioration of seeds are needed by the forest industry. In this work, various imaging methods and biochemical analyses were applied to study deterioration of western redcedar seeds. Seedlots that exhibited poor germination performance, i.e. those that had experienced the greatest losses of viability during prolonged storage, exhibited greater abundance of oxidized proteins, detected by protein oxidation assays, and more pronounced changes in their in vivo (13)C NMR spectra, most likely due to storage oil oxidation. The proportion of oxidized proteins also increased when seeds were subjected to accelerated ageing treatments. Detection of oxidized oils and proteins may constitute a reliable and useful tool for the forest industry

Welcoming gallium- and indium-fumarate MOFs to the family:synthesis, comprehensive characterization, observation of porous hydrophobicity, and CO₂ dynamics

The properties and applications of metal–organic frameworks (MOFs) are strongly dependent on the nature of the metals and linkers, along with the specific conditions employed during synthesis. Al-fumarate, trademarked as Basolite A520, is a porous MOF that incorporates aluminum centers along with fumarate linkers and is a promising material for applications involving adsorption of gases such as CO2. In this work, the solvothermal synthesis and detailed characterization of the gallium- and indium-fumarate MOFs (Ga-fumarate, In-fumarate) are described. Using a combination of powder X-ray diffraction, Rietveld refinements, solid-state NMR spectroscopy, IR spectroscopy, and thermogravimetric analysis, the topologies of Ga-fumarate and In-fumarate are revealed to be analogous to Al-fumarate. Ultra-wideline 69Ga, 71Ga, and 115In NMR experiments at 21.1 T strongly support our refined structure. Adsorption isotherms show that the Al-, Ga-, and In-fumarate MOFs all exhibit an affinity for CO2, with Al-fumarate being the superior adsorbent at 1 bar and 273 K. Static direct excitation and cross-polarized 13C NMR experiments permit investigation of CO2 adsorption locations, binding strengths, motional rates, and motional angles that are critical to increasing adsorption capacity and selectivity in these materials. Conducting the synthesis of the indium-based framework in methanol demonstrates a simple route to introduce porous hydrophobicity into a MIL-53-type framework by incorporation of metal-bridging −OCH3 groups in the MOF pores

Quadrupolar metal NMR of oxide materials including catalysts

In this work, we review the basic methodology and recent applications of quadrupolar metal solid-state NMR spectroscopy in oxide systems with emphasis on materials science and catalysis. Three typical quadrupolar metal nuclei, 51V, 93Nb, and 95Mo, are discussed in detail to illustrate the complex interplay between the quadrupolar and chemical shielding interactions in oxides. In the first part, a systematic overview is given of the metal coordination environments in oxides and their corresponding NMR parameters. The importance of quantum chemical calculations in correlating experimental NMR results with a molecular level oxide structure is highlighted. In the second part, we present examples of quadrupolar metal NMR in materials science, including paramagnetic oxide systems, layered materials, ferroelectrics, silicates, and glasses. The final section is dedicated to the latest applications of NMR in heterogeneous oxide catalysis.Peer reviewed: YesNRC publication: Ye

A natural abundance 33S solid-state NMR study of layered transition metal disulfides at ultrahigh magnetic field

Using a series of layered transition metal disulfides we demonstrate that the wide-line natural abundance solid-state NMR spectra of 33S in a less symmetric environment can readily be obtained at ultrahigh magnetic field of 21.1 T and that surprisingly these closely related materials display a wide range of 33S quadrupole coupling constant and chemical shift anisotropy values.Peer reviewed: NoNRC publication: Ye

Perspectives of fast magic-angle spinning 87^{87}Rb NMR of organic solids at high magnetic fields

See also:Erratum: "Perspectives of fast magic-angle spinning 87 Rb NMR of organic solids at high magnetic fields".Wu G., Terskikh V., Wong A., in : Magn. Reson. Chem. 2021 Sep;59(9-10):1101. doi: 10.1002/mrc.5198.International audienceWe report solid-state $^{87}$Rb NMR spectra from two Rb-ionophore complexes obtained with fast magic-angle spinning (MAS) (up to 60 kHz) at 21.1 T. These Rb-ionophore complexes containing macrocycles such as benzo-15-crown-5 and cryptand [2.2.2] are typical of organic Rb salts that exhibit very large $^{87}$Rb quadrupole coupling constants (close to 20 MHz). We have also obtained static $^{87}$Rb NMR spectra for these two compounds and determined both $^{87}$Rb quadrupole coupling and chemical shift tensors. The experimental 87Rb NMR tensor parameters are compared with those obtained by quantum chemical computations. Our results demonstrate that the combination of fast MAS (60 kHz or higher) and a high magnetic field (21.1 T or higher) is sufficient to produce high-quality solid-state $^{87}$Rb NMR spectra for organic Rb solids at the natural abundance level. We anticipate that, with additional $^{87}$Rb isotope enrichment (up to 99%), the sensitivity of solid-state $^{87}$Rb NMR will be 400 times higher than $^{39}$K NMR, which makes the former an attractive surrogate probe for studying K$^+$ ion binding in biological systems

Application of Solid-State 209Bi NMR to the Structural Characterization of Bismuth-Containing Materials

Herein, we report the first detailed study of 209Bi solid-state NMR (SSNMR) spectroscopy of extremely broad central transition powder patterns. 209Bi ultrawideline SSNMR spectra of several bismuth-containing materials (bismuth oxyhalides, bismuth nitrate pentahydrate, nonaaquabismuth triflate, and bismuth acetate) were acquired at field strengths of 9.4 and 21.1 T using frequency-stepped techniques. The 209Bi SSNMR experiments at 9.4 T yield powder patterns with breadths ranging from 0.9 to 14.6 MHz, from which quadrupolar coupling constants, CQ(209Bi), between 78 and 256 MHz, were extracted via analytical simulations. The breadths of the quadrupolar-dominated spectra and overall experimental times are greatly reduced for experiments conducted at 21.1 T, which yield high signal-to-noise spectra in which the smaller effects of bismuth chemical shift anisotropy can be clearly observed. The 209Bi electric field gradient (EFG) and chemical shift (CS) tensor parameters extracted from these spectra are correlated to the molecular structures at the bismuth sites, via first principles calculations of 209Bi EFG and CS tensors performed using CASTEP for periodic solids and Gaussian 03 for molecular clusters. The rapidity with which 209Bi SSNMR spectra can be acquired at ultrahigh fields, the sensitivity of the 209Bi NMR parameters to the bismuth environment, and the predictive power of theoretically calculated NMR interaction tensors suggest that 209Bi SSNMR may be useful for the characterization of a variety of Bi-containing materials and compounds.Peer reviewed: YesNRC publication: Ye

Distinguishing surface versus buried cation sites in aluminosilicate mesoporous materials

Mesoporous MCM-41 aluminosilicates were prepared through direct synthesis and surface grafting resulting in the incorporation of aluminum into the pore walls and onto the wall surface, respectively. 7Li and 23Na NMR studies of ion-exchanged Li and Na-Al-MCM-41 were able to distinguish between cations in the surface region and those buried deeper in the pore walls. Thus it was demonstrated that most of the cations in the grafted Al-MCM-41 locate in the surface region, whereas the cations in the synthesized Al-MCM-41 are distributed throughout the pore walls. The NMR spectra of dehydrated Li- and Na-MCM-41 resemble those of glassy materials, reflecting the amorphous nature of this class of mesoporous materials. 7Li NMR studies of dehydrated Li-Al-MCM-41 prepared from direct synthesis in the presence of oxygen showed that most of the Li+ cations are not accessible to O2, while the Li+ cations in Al-grafted Li-Al-MCM-41 are accessible, which also confirms their locations. This study provides valuable insights for the understanding of the structure and properties of aluminosilicate mesoporous materials.NRC publication: Ye

²⁵Mg Solid-State NMR: A Sensitive Probe of Adsorbing Guest Molecules on a Metal Center in Metal–Organic Framework CPO-27-Mg

Metal–organic frameworks (MOFs) have excellent adsorption capability. To understand their adsorptive properties requires detailed information on the host–guest interaction. The information on MOF desolvation (or activation) is also crucial because the very first step of many applications requires removal of the solvent molecules occluded inside of the pores. Unfortunately, such information is not always available from powder XRD data. Solid-state NMR is an excellent complementary technique to XRD. CPO-27-Mg is a MOF with unusual adsorption ability. The adsorption involves a direct interaction between Mg and guest species. Herein, we present, for the first time, a natural abundance ²⁵Mg solid-state NMR study of CPO-27-Mg at an ultrahigh magnetic field of 21.1 T. The results provide new physical insights into the effects of dehydration/rehydration and adsorption of guest species on the Mg local environment

Spin–Spin Coupling between Quadrupolar Nuclei in Solids: ¹¹B–⁷⁵As Spin Pairs in Lewis Acid–Base Adducts

Solid-state ¹¹B NMR measurements of Lewis acid–base adducts of the form R₃AsBR′₃ (R = Me, Et, Ph; R′ = H, Ph, C₆F₅) were carried out at several magnetic field strengths (e.g., <i>B</i>₀ = 21.14, 11.75, and 7.05 T). The ¹¹B NMR spectra of these adducts exhibit residual dipolar coupling under MAS conditions, allowing for the determination of effective dipolar coupling constants, <i>R</i>_eff(⁷⁵As,¹¹B), as well as the sign of the ⁷⁵As nuclear quadrupolar coupling constants. Values of <i>R</i>_eff(⁷⁵As,¹¹B) range from 500 to 700 Hz. Small isotropic <i>J</i>-couplings are resolved in some cases, and the sign of ¹<i>J</i>(⁷⁵As,¹¹B) is determined. Values of <i>C</i>_Q(⁷⁵As) measured at <i>B</i>₀ = 21.14 T for these triarylborane Lewis acid–base adducts range from −82 ± 2 MHz for Et₃AsB­(C₆F₅)₃ to −146 ± 1 MHz for Ph₃AsBPh₃. For Ph₃AsBH₃, two crystallographically nonequivalent sites are identified with <i>C</i>_Q(⁷⁵As) values of −153 and −151 ± 1 MHz. For the uncoordinated Lewis base, Ph₃As, four ⁷⁵As sites with <i>C</i>_Q(⁷⁵As) values ranging from 193.5 to 194.4 ± 2 MHz are identified. At these applied magnetic field strengths, the ⁷⁵As quadrupolar interaction does not satisfy high-field approximation criteria, and thus, an exact treatment was used to describe this interaction in ¹¹B and ⁷⁵As NMR spectral simulations. NMR parameters calculated using the ADF and CASTEP program packages support the experimentally derived parameters in both magnitude and sign. These experiments add to the limited body of literature on solid-state ⁷⁵As NMR spectroscopy and serve as examples of spin–spin-coupled quadrupolar spin pairs, which are also rarely treated in the literature