Zero-field NMR J-Spectroscopy of Organophosphorus Compounds

In this paper, we report the results of theoretical and experimental studies on basic organophosphorus compounds using zero-field NMR, where spin dynamics are investigated in the absence of a magnetic field with the dominant heteronuclear J-coupling. We demonstrate that the zero-field NMR enables distinguishing the chemicals owing to their unique electronic environment even for identical spin systems. Such information can be obtained just in a single measurement, while amplitudes and widths of observed low-field NMR resonances enable to study of processes affecting spin dynamics. An excellent agreement between simulations and measurements of the spectra, particularly in the largest frequency J-couplings range ever reported in zero-field NMR is demonstrated

Zero- to Low-field Relaxometry of Chemical and Biological Fluids

NMR relaxometry is an analytical method that provides information about the molecular environment, including even NMR “silent” molecules (spin-0), by analyzing the properties of NMR signals versus the magnitude of the longitudinal field. Conventionally, this technique has been performed at fields much higher than Earth’s magnetic field, but in this work, we present NMR relaxometry at zero and ultra-low magnetic fields (ZULFs). Operation under ZULFs allows us to investigate many slow (bio)chemical processes, whose timescale (milliseconds-seconds) coincides with a timescale of spin evolution. ZULFs regime also limits the detrimental role of T2 dephasing, which, in heterogeneous samples, is induced by magnetic susceptibility and often leads to line broadening, hence low-resolution spectra. Finally, in contrast to their high-field NMR, ZULF NMR measurements can be performed with inexpensive, portable/small-size sensors (atomic magnetometers). Here, we use ZULF NMR relaxometry in the analysis of (bio)chemical compounds containing 1H 13C, 1H-15N, and 1H-31P spin pairs. We also detected high-quality ULF NMR spectra of human whole blood at 0.8 μT, despite a shortening of spin relaxation by blood proteomes (e.g., hemoglobin). Information on relaxation times of blood, a potential early biomarker of inflammation, can be obtained in less than a minute and without the need for a sophisticated apparatus

Zero-field J-Spectroscopy of Urea: Spin-Topology Engineering by Chemical-Exchange

Well-resolved and information-rich J-spectra are the foundation for chemical analysis based on zero-field NMR. Yet, even in relatively small molecules, the spectra may gain complexity, hindering the analysis. To address this problem, we investigate an example biomolecule characterized with a complex J-coupling network -- urea, a key metabolite in protein catabolism -- and demonstrate ways of simplifying its zero-field spectra by modifying spin topology. This goal is achieved by controlling pH-dependent chemical-exchange rates of 1H nuclei and varying the composition of the D2O/H2O mixture used as a solvent. Specifically, we demonstrate that by increasing hydrogen chemical-exchange rate in [13C, 15N2]-urea solution, the molecule, being an effective spin system XAB2A\u27B\u272, behaves as a much simpler XA2 system (where X = 13C, A = 15N, B = 1H), manifesting through a single narrow spectral peak. Additionally, we show that introducing spin-1 nuclei into the molecule and investigating J-spectra of 1H/D isotopologues of [15N2]-urea allows to study various isolated spin subsystems: XA2, (XA)B, and XB2 (here X = 15N, A = 1H, B = D), again greatly simplifying spectra analysis. The influence of the chemical exchange process on zero-field $J$-spectra for each urea solution is elucidated by theoretical studies, demonstrating solid agreement between results and simulations. This study shows the applicability of zero-field NMR to detect complex biomolecules in aqueous solutions, and it opens the means for future in vivo/in vitro biochemical investigations, particularly in biofluids with a high concentration of water

13C and 15N NMR Detection of Metabolites via Relayed Hyperpolarization at 1 T and 1.4 T

Nuclear-spin hyperpolarization allows various magnetic-resonance applications in chemistry and medicine that are unattainable by standard methods. For such applications, parahydrogen-based hyperpolarization approaches are particularly attractive because of their technical simplicity, low cost, and ability to quickly (in seconds) produce large volumes of hyperpolarized material. Although many parahydrogen-based techniques have emerged, some of them remain unexplored due to the lack of careful optimization studies. In this work, we investigate and optimize a novel parahydrogen-induced polarization (PHIP) technique that relies on proton exchange referred to below as PHIP-relay. An INEPT (insensitive nuclei enhanced by polarization transfer) sequence is employed to transfer polarization from hyperpolarized protons to heteronuclei (15N and 13C) and nuclear signals are detected using benchtop NMR spectrometers (1 T and 1.4 T, respectively). We demonstrate the applicability of the PHIP-relay technique for hyperpolarization of a wide range of biochemicals by examining such key metabolites as urea, ammonium, glucose, amino acid glycine, and a drug precursor benzamide. By optimizing chemical and NMR parameters of the PHIP-relay, we achieve a 17,100-fold enhancement of 15N signal of [13C, 15N2]-urea compared to the thermal signal measured at 1 T. We also show that repeated measurements with shorter exposure to parahydrogen provide a higher effective signal-to-noise ratio compared to longer parahydrogen bubbling

Zero- to low-field relaxometry of chemical and biological fluids

Abstract Nuclear magnetic resonance (NMR) relaxometry is an analytical method that provides information about molecular environments, even for NMR “silent” molecules (spin-0), by analyzing the properties of NMR signals versus the magnitude of the longitudinal field. Conventionally, this technique is performed at fields much higher than Earth’s magnetic field, but our work focuses on NMR relaxometry at zero and ultra-low magnetic fields (ZULFs). Operating under such conditions allows us to investigate slow (bio)chemical processes occurring on a timescale from milliseconds to seconds, which coincide with spin evolution. ZULFs also minimize T 2 line broadening in heterogeneous samples resulting from magnetic susceptibility. Here, we use ZULF NMR relaxometry to analyze (bio)chemical compounds containing 1H-13C, 1H-15N, and 1H-31P spin pairs. We also detected high-quality ULF NMR spectra of human whole-blood at 0.8 μT, despite a shortening of spin relaxation by blood proteomes (e.g., hemoglobin). Information on proton relaxation times of blood, a potential early biomarker of inflammation, can be acquired in under a minute using inexpensive, portable/small-size NMR spectrometers based on atomic magnetometers

Detection of Pyridine Derivatives by SABRE Hyperpolarization at Zero Field

Zero-field nuclear magnetic resonance (NMR) recently emerged as an interesting new analytical modality. While zero-field NMR provides new capabilities, it also suffers from some limitations associated, to a great degree, with low signal amplitude. In this context, parahydrogen-induced polarization naturally complements zero-field NMR, as this hyperpolarization is active even at zero magnetic field. In turn, the efficient production of large non-equilibrium polarization is possible in zero field, boosting the signal amplitude and enabling realization of the concept of "NMR without magnets\u27\u27. In this work, we present zero-field NMR studies of various hyperpolarized pyridine derivatives where the 15N isotope is present at a natural abundance (0.36%). By comparing the signals of these pyridine derivatives, which include vitamin B3, as a function of their substituents, we demonstrate unique zero-field NMR spectra, consequently establishing how chemical analysis is possible even in zero field. We also study the effect of the parahydrogen-polarization-transfer catalyst activation on the resulting hyperpolarization dynamics. All of these measurements were made using apparatus designed to allow repeated in situ hyperpolarization of these samples without affecting their composition

Detection of pyridine derivatives by SABRE hyperpolarization at zero field

Abstract Nuclear magnetic resonance (NMR) spectroscopy is a powerful analytical tool used in modern science and technology. Its novel incarnation, based on measurements of NMR signals without external magnetic fields, provides direct access to intramolecular interactions based on heteronuclear scalar J-coupling. The uniqueness of these interactions makes each zero-field NMR spectrum distinct and useful in chemical fingerprinting. However, the necessity of heteronuclear coupling often results in weak signals due to the low abundance of certain nuclei (e.g., 15N). Hyperpolarization of such compounds may solve the problem. In this work, we investigate molecules with natural isotopic abundance that are polarized using non-hydrogenative parahydrogen-induced polarization. We demonstrate that spectra of hyperpolarized naturally abundant pyridine derivatives can be observed and uniquely identified whether the same substituent is placed at a different position of the pyridine ring or different constituents are placed at the same position. To do so, we constructed an experimental system using a home-built nitrogen vapor condenser, which allows for consistent long-term measurements, crucial for identifying naturally abundant hyperpolarized molecules at a concentration level of ~1 mM. This opens avenues for future chemical detection of naturally abundant compounds using zero-field NMR