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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.

Terpenes are a classification of aromatic compounds that are nearly ubiquitous throughout nature. Terpenes are primarily found in plants, but can also be observed in marine organisms, insects, and, to a lesser extent, higher-order animals. They are present in cannabis in significant concentrations and are one of the most interesting and diverse aspects of cannabis. They provide the unique aroma of the plant and are critical to the cannabis experience; however, understanding the role that they play in the psychoactive experience of cannabis consumption is still not well understood. Terpenes themselves are built from repeating five-carbon units called isoprene. Their classification as a monoterpene, diterpene, etc., is dependent on the number of isoprene units in their structure. Terpene content in cannabis is typically not regulated, but can provide unique insights into the “flavor profile” of the cannabis flower. Demand for terpene testing has increased significantly in the past few years as consumers become increasingly interested in the terpene profiles of the cannabis strains they consume. Cannabis has a high abundance of mono- and sesquiterpenes, and the majority of terpenes present in the flower fall into these classifications. This study presents a comprehensive gas chromatography- mass spectrometry (GC-MS) method for the analysis of 22 terpenes in cannabis flower, with a focus on developing a rapid and robust method for the analysis of terpenes in a commercial laboratory.

Gas chromatography combined with high-resolution time-of-flight mass spectrometry (GC-HRTOFMS) is a powerful tool for the analysis of complex mixtures. The AccuTOF GC-Alpha (JMS-T2000GC) mass spectrom-eter is fast, accurate and sensitive with high mass-resolving power and high mass accuracy.

The composition of volatiles from freshly ground roasted coffee is complex, with hundreds of chemical compounds contributing to the aroma. Headspace solid-phase microextraction was used to sample volatiles from five different coffees for analysis by GC-MS. Chemometric analysis revealed specific differences between coffees from different origins and different preparations.

The power flow process mediated by spin current in the bilayer device consisting of ferromagnetic metal (FM) and nonmagnetic metal (NM) layers is examined by realizing experimental evaluations for each process from the microwave absorption to electromotive force (EMF) output. The absorption power by ferromagnetic resonance (FMR) of the thin FM layer during the EMF output is directly measured in operando using an antenna probe system. The transfer efficiency of the absorption power into the NM layer by spin pumping is estimated from strict linewidth evaluation of EMF spectra. The maximum transfer efficiency of the spin pumping power to the external load via the inverse spin Hall effect is determined to be 4.2 × 10–8 under 162 mW microwave irradiation using an analysis model assuming a parallel circuit. The main factors reducing the efficiency are found to be low resistivity of the NM layer and the interface loss. These quantifications are important as a first step to consider the efficient transfer of spin energy mediated by spin currents.

Non-targeted analysis of complex mixtures by GC-HRMS should make use of all of the available data to identify unknowns. An automated data analysis software package combining chromatographic deconvolution with integrated analysis of high-resolution mass spectra for electron ionization (EI) and soft ionization measurements is applied to the identification of trace impurities in a fine chemical (triphenylphosphine).

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.

This experimental approach allows direct correlation of JCC values with specific molecular conformations since, in crystalline samples, molecular conformation is essentially static and can be determined by X-ray crystallography.

A collaborative paper was published in Tetrahedron. The INADEQUATE spectrum discussed in this research was obtained using a cryogenic probe (UltraCOOL probe) in liquid helium in a JEOL 800 MHz spectrometer (JNM-ECZ800R).

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.

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    Corona - Glow Discharge (DART Ion Source)

    January 28, 2022
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