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JNM-ECZS Routine NMR

The ECZS NMR spectrometer (JNM-ECZS series) has functionality and performance of the high-end ECZR series, yet in a compact, space saving design. Through the combination of advanced software with highly reliable hardware, all routine measurements can be automated. Using high sensitivity auto tune probes, including the optional SuperCOOL probe which features cryogenically cooled technologies, JNM-ECZS affords the world’s best-in-class sensitivity. The high performance can be demonstrated in many application fields.

JNM-ECZR Research NMR

The JNM-ECZR NMR spectrometer (JNM-ECZR series), a member of the JNM-ECZ series of instruments, is a new research system that fully incorporates the latest digital and high frequency technologies. Highly reliable, yet in a more compact size made possible by incorporating advanced integrated circuits, it supports even greater expandability options than past models for multi-channel operation, high power amplifiers and other accessories. The bus line for control of attachments has been upgraded to even higher speed and enables highly accurate and rapid control.

Efficient symmetry-based γ-encoded DQ recoupling sequences for suppression of t1-noise in solid-state NMR spectroscopy at fast MAS

Solid-state NMR spectroscopy has played a significant role in elucidating the structure and dynamics of materials and biological solids at a molecular level for decades. In particular, the 1H double-quantum/single-quantum (DQ/SQ) chemical shift correlation experiment is widely used for probing the proximity of protons, rendering it a powerful tool for elucidating the hydrogen-bonding interactions and molecular packing of various complex molecular systems. Two factors, namely, the DQ filtering efficiency and t1-noise, dictate the quality of the 2D 1H DQ/SQ spectra. Experimentally different recoupling sequences show varied DQ filtering efficiencies and t1-noise. Herein, after a systematic search of symmetry-based DQ recoupling sequences, we report that the symmetry-based γ-encoded sequences show superior performance to other DQ recoupling sequences, which not only have a higher DQ recoupling efficiency but can also significantly reduce t1-noise. The origin of t1-noise is further discussed in detail via extensive numerical simulations. We envisage that such γ-encoded sequences are superior candidates for DQ recoupling in proton-based solid-state NMR spectroscopy due to its capability of efficiently exciting DQ coherences and suppressing t1-noise.

Selective 1H–1H recoupling via symmetry sequences in fully protonated samples at fast magic angle spinning

Proton-detected solid-state NMR at fast Magic Angle Spinning (MAS) is becoming the norm to characterize molecules. Routinely 1H–1H and 1H-X dipolar couplings are used to characterize the structure and dynamics of molecules. Selective proton recoupling techniques are emerging as a method for structural characterization via estimation of qualitative and quantitative distances. In the present study, we demonstrate through numerical simulations and experiments that the well-characterized CNvn sequences can also be tailored for selective recoupling of proton spins by employing C elements of the type (β)Φ(4β)Φ+π(3β)Φ. Herein, several CNvn sequences were examined through numerical simulations and experiments. C614 recoupling sequence with a modified POST-element ((β)Φ(4β)Φ+π(3β)Φ) shows selective polarization transfer efficiencies on the order of 40–50% between various proton spin pairs in fully protonated samples at rf amplitudes ranging from 0.3 to 0.8 times the MAS frequency. These selective recoupling sequences have been labeled as frequency-selective-CNvn sequences. The extent of selectivity, polarization transfer efficiency and the feasibility of experimentally measuring proton-proton distances in fully protonated samples are explored here. The development of efficient and robust selective 1H–1H recoupling experiments is required to structurally characterize molecules without artificial isotope enrichment or the need for diffracting crystals.

Selective detection of active pharmaceutical ingredients in tablet formulations using solid-state NMR spectroscopy

Highlights: • Selective detection of 1H signals of API in a tablet formulation is proposed. • 1H signals of excipients are suppressed. • 1H signals in the vicinity of nuclei (here 14N) which only appear in API are excited. • 1H{14N} magnetization is diffused to 1Hs in API crystals by RFDR recoupling.

Dynamic Transformation Between Covalent Organic Frameworks And Discrete Organic Cages

We propose a dynamic covalent chemistry (DCC)-induced linker exchange strategy for the structural transformation between covalent organic frameworks (COFs) and cages for the first time. Studies have shown that the COF-to-cage and cage-to-COF transformations were realized by using borate bonds and imine bonds, respectively, as linkages. Self-sorting experiments suggested that borate cages and imine COFs are thermodynamic minimum compounds. This research builds a bridge between discrete and polymeric organic scaffolds and broadens the knowledge of chemistry and materials for porous materials science.

Azoxystrobin amine: A novel azoxystrobin degradation product from Bacillus licheniformis strain TAB7

Azoxystrobin (AZ) is a broad-spectrum synthetic fungicide widely used in agriculture globally. However, there are concerns about its fate and effects in the environment. It is reportedly transformed into azoxystrobin acid as a major metabolite by environmental microorganisms. Bacillus licheniformis strain TAB7 is used as a compost deodorant in commercial compost and has been found to degrade some phenolic and agrochemicals compounds. In this article, we report its ability to degrade azoxystrobin by novel degradation pathway. Biotransformation analysis followed by identification by electrospray ionization-mass spectrometry (MS), high-resolution MS, and nuclear magnetic resonance spectroscopy identified methyl (E)-3-amino-2-(2-((6-(2-cyanophenoxy)pyrimidin-4-yl)oxy)phenyl)acrylate, or (E)-azoxystrobin amine in short, and (Z) isomers of AZ and azoxystrobin amine as the metabolites of (E)-AZ by TAB7. Bioassay testing using Magnaporthe oryzae showed that although 40 μg/mL of (E)-AZ inhibited 59.5 ± 3.5% of the electron transfer activity between mitochondrial Complexes I and III in M. oryzae, the same concentration of (E)-azoxystrobin amine inhibited only 36.7 ± 15.1% of the activity, and a concentration of 80 μg/mL was needed for an inhibition rate of 56.8 ± 7.4%, suggesting that (E)-azoxystrobin amine is less toxic than the parent compound. To our knowledge, this is the first study identifying azoxystrobin amine as a less-toxic metabolite from bacterial AZ degradation and reporting on the enzymatic isomerization of (E)-AZ to (Z)-AZ, to some extent, by TAB7. Although the fate of AZ in the soil microcosm supplemented with TAB7 will be needed, our findings broaden our knowledge of possible AZ biotransformation products.

Understanding hydrogen-bonding structures of molecular crystals via electron and NMR nanocrystallography

Understanding hydrogen-bonding networks in nanocrystals and microcrystals that are too small for X-ray diffractometry is a challenge. Although electron diffraction (ED) or electron 3D crystallography are applicable to determining the structures of such nanocrystals owing to their strong scattering power, these techniques still lead to ambiguities in the hydrogen atom positions and misassignments of atoms with similar atomic numbers such as carbon, nitrogen, and oxygen. Here, we propose a technique combining ED, solid-state NMR (SSNMR), and first-principles quantum calculations to overcome these limitations. The rotational ED method is first used to determine the positions of the non-hydrogen atoms, and SSNMR is then applied to ascertain the hydrogen atom positions and assign the carbon, nitrogen, and oxygen atoms via the NMR signals for 1H, 13C, 14N, and 15N with the aid of quantum computations. This approach elucidates the hydrogen-bonding networks in L-histidine and cimetidine form B whose structure was previously unknown.

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Corona - Glow Discharge (DART Ion Source)

February 22, 2020
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