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1. Zero-Field J-spectroscopy of Quadrupolar Nuclei

   Barskiy, Danila ; Blanchard, John ; Reh, Moritz ; Sjoelander, Tobias ; Pines, Alexander ; Budker, Dmitry ( November 2020 , ArXivorg)

   null (Ed.)

   Zero- to ultralow-field (ZULF) nuclear magnetic resonance (NMR) is a version of NMR that allows studying molecules and their transformations in the regime dominated by intrinsic spin-spin interactions. While spin dynamics at zero magnetic field can be probed indirectly, J-spectra can also be measured at zero field by using non-inductive sensors, for example, optically-pumped magnetometers (OPMs). A J-spectrum can be detected when a molecule contains at least two different types of magnetic nuclei (i.e., nuclei with different gyromagnetic ratios) that are coupled via J-coupling. Up to date, no pure J-spectra of molecules featuring the coupling to quadrupolar nuclei were reported. Here we show that zero-field J-spectra can be collected from molecules containing quadrupolar nuclei with I = 1 and demonstrate this for solutions containing various isotopologues of ammonium cations. Lower ZULF NMR signals are observed for molecules containing larger numbers of deuterons compared to protons; this is attributed to less overall magnetization and not to the scalar relaxation of the second kind. We analyze the energy structure and allowed transitions for the studied molecular cations in detail using perturbation theory and demonstrate that in the studied systems, different lines in J-spectra have different dependencies on the magnetic pulse length allowing for unique on-demand zero-field spectral editing. Precise values for the 15N-1H, 14N-1H, and D-1H coupling constants are extracted from the spectra and the difference in the reduced coupling constants is explained by the secondary isotope effect. Simple symmetric cations such as ammonium do not require expensive isotopic labeling for the observation of J-spectra and, thus, may expand the applicability of ZULF NMR spectroscopy in biomedicine and energy storage. 

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2. Challenges and advances in measuring sap flow in agriculture and agroforestry: A review with focus on nuclear magnetic resonance

   https://doi.org/10.3389/fpls.2022.1036078  

   Kumar, Ritesh ; Hosseinzadehtaher, Mohsen ; Hein, Nathan ; Shadmand, Mohammad ; Jagadish, S. V. ; Ghanbarian, Behzad ( November 2022 , Frontiers in Plant Science)

   Sap flow measurement is one of the most effective methods for quantifying plant water use.A better understanding of sap flow dynamics can aid in more efficient water and crop management, particularly under unpredictable rainfall patterns and water scarcity resulting from climate change. In addition to detecting infected plants, sap flow measurement helps select plant species that could better cope with hotter and drier conditions. There exist multiple methods to measure sap flow including heat balance, dyes and radiolabeled tracers. Heat sensor-based techniques are the most popular and commercially available to study plant hydraulics, even though most of them are invasive and associated with multiple kinds of errors. Heat-based methods are prone to errors due to misalignment of probes and wounding, despite all the advances in this technology. Among existing methods for measuring sap flow, nuclear magnetic resonance (NMR) is an appropriate non-invasive approach. However, there are challenges associated with applications of NMR to measure sap flow in trees or field crops, such as producing homogeneous magnetic field, bulkiness and poor portable nature of the instruments, and operational complexity. Nonetheless, various advances have been recently made that allow the manufacture of portable NMR tools for measuring sap flow in plants. The basic concept of the portal NMR tool is based on an external magnetic field to measure the sap flow and hence advances in magnet types and magnet arrangements (e.g., C-type, U-type, and Halbach magnets) are critical components of NMR-based sap flow measuring tools. Developing a non-invasive, portable and inexpensive NMR tool that can be easily used under field conditions would significantly improve our ability to monitor vegetation responses to environmental change. 

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3. Zero-field nuclear magnetic resonance of chemically exchanging systems

   https://doi.org/10.1038/s41467-019-10787-9  

   Barskiy, Danila A. ; Tayler, Michael C. D. ; Marco-Rius, Irene ; Kurhanewicz, John ; Vigneron, Daniel B. ; Cikrikci, Sevil ; Aydogdu, Ayca ; Reh, Moritz ; Pravdivtsev, Andrey N. ; Hövener, Jan-Bernd ; et al ( July 2019 , Nature Communications)

   Zero- to ultralow-field (ZULF) nuclear magnetic resonance (NMR) is an emerging tool for precision chemical analysis. In this work, we study dynamic processes and investigate the influence of chemical exchange on ZULF NMRJ-spectra. We develop a computational approach that allows quantitative calculation ofJ-spectra in the presence of chemical exchange and apply it to study aqueous solutions of [¹⁵N]ammonium (¹⁵N$${\mathrm{H}}_4^ +$$$H_4^{+}$) as a model system. We show that pH-dependent chemical exchange substantially affects theJ-spectra and, in some cases, can lead to degradation and complete disappearance of the spectral features. To demonstrate potential applications of ZULF NMR for chemistry and biomedicine, we show a ZULF NMR spectrum of [2-¹³C]pyruvic acid hyperpolarized via dissolution dynamic nuclear polarization (dDNP). We foresee applications of affordable and scalable ZULF NMR coupled with hyperpolarization to study chemical exchange phenomena in vivo and in situations where high-field NMR detection is not possible to implement.

    

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4. Low‐field 1 H NMR spectroscopy: Factors impacting signal‐to‐noise ratio and experimental time in the context of mixed microstructure polyisoprenes

   https://doi.org/10.1002/mrc.5022  

   Minkler, Jr, Michael J. ; Kim, Jung Min ; Shinde, Vinita V. ; Beckingham, Bryan S. ( April 2020 , Magnetic Resonance in Chemistry)

   Low‐cost, high‐accuracy characterization of polymeric materials is critical for satisfying societal demand for high‐quality materials with ultra‐specific requirements. Low‐field nuclear magnetic resonance (NMR) spectroscopy presents an opportunity to replace costlier or destructive methods while utilizing nondeuterated solvents. Many factors play key roles in the ability of low‐field NMR spectroscopy to accurately analyze polymer systems. Sample characteristics such as polymer concentration, composition, and molecular weight all directly affect the capability of low‐field spectrometers to accurately determine polymer microstructure compositions. In addition to inherent sample properties affecting instrumental accuracy, many choices concerning instrumental parameters (including number of scans, relaxation delay, spectral width, and points per scan) must be made that impact the quality of the resulting NMR spectra. In this work, we benchmark the capability of a 60‐MHz low‐field NMR spectrometer for analyzing polymer materials using mixed microstructure polyisoprenes as a model polymer system of interest. The aforementioned critical sample and instrumental variables are varied, and we report on the ability to quantitatively characterize polyisoprene microstructure to within 1–2% of a higher field NMR spectrometer (400 MHz). We anticipate our findings to be generally applicable to other low‐field spectrometers of similar field strength and other polymer systems.

    

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5. Synthesis and Self-Assembling Properties of Peracetylated β-1-Triazolyl Alkyl D-Glucosides and D-Galactosides

   https://doi.org/10.3390/chemistry3030068  

   Sharma, Pooja ; Chen, Anji ; Wang, Dan ; Wang, Guijun ( September 2021 , Chemistry)

   Carbohydrate-based low-molecular-weight gelators (LMWGs) are useful classes of compounds due to their numerous applications. Among sugar-based LMWGs, certain peracetylated sugar beta-triazole derivatives were found to be effective organogelators and showed interesting self-assembling properties. To further understand the structural influence towards molecular assemblies and obtain new functional materials with interesting properties, we designed and synthesized a library of tetraacetyl beta-1-triazolyl alkyl-D-glucosides and D-galactosides, in which a two or three carbon spacer is inserted between the anomeric position and the triazole moiety. A series of 16 glucose derivatives and 14 galactose derivatives were synthesized and analyzed. The self-assembling properties of these new triazole containing glycoconjugates in different solvents were analyzed. Several glucose derivatives were found to be effective LMWGs, with compound 7a forming gels in a variety of organic solvents as well as in the presence of metal ions in aqueous solutions. The organogels formed by several compounds were characterized using optical microscopy, atomic force microscopy (AFM) and UV-vis spectroscopy, etc. The co-gels formed by compound 7a with the Fmoc derivative 7i showed interesting fluorescence enhancement upon gelation. Several gelators were also characterized using powder X-ray diffraction and FT-IR spectroscopy. The potential applications of these sugar-based gelators for drug delivery and dye removal were also studied. 

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