Hyperpolarized NMR metabolomics

Boosting 1H and 13C NMR signals by orders of magnitude on a bench

Sensitivity is often the Achilles' heel of liquid-state nuclear magnetic resonance (NMR) experiments. This problem is perhaps most pressing at the lowest fields (e.g., 80-MHz 1H frequency), with rapidly increasing access to NMR through benchtop systems, but also sometimes for higher-field NMR systems from 300 MHz to 1.2 GHz. Hyperpolarization by dissolution dynamic nuclear polarization (dDNP) can address this sensitivity limitation. However, dDNP implies massive and complex cryogenic and high-field instrumentation, which cannot be installed on the bench. We introduce here a compact helium-free 1-T tabletop polarizer as a simple and low-cost alternative. After freezing and polarizing the frozen analyte solutions at 77 K, we demonstrate 1H signal enhancement factors of 100, with rapid 1-s buildup times. The high polarization is subsequently transferred by 1H→13C cross polarization (CP) to 13C spins. Such a simple benchtop polarizer, in combination with hyperpolarizing solid matrices (HYPSOs), may open the way to replenishable hyperpolarization throughout multiple liquid-state NMR experiments.

Full optimization of dynamic nuclear polarization on a 1 tesla benchtop polarizer with hyperpolarizing solids

Hyperpolarization by dissolution dynamic nuclear polarization (dDNP) provides the opportunity to dramatically increase the weak nuclear magnetic resonance (NMR) signal of liquid molecular targets using the high polarization of electron radicals. Unfortunately, the solution-state hyperpolarization can only be accessed once since freezing and melting of the hyperpolarized sample happen in an irreversible fashion. A way to expand the application horizon of dDNP can therefore be to find a recyclable DNP alternative. To pursue this ambitious goal, we recently introduced the concept of recyclable hyperpolarized flow (HypFlow) DNP where hyperpolarization happens in porous hyperpolarizing solids placed in a compact benchtop DNP polarizer at a magnetic field of 1 T and a temperature of 77 K. Here we aim to optimize the radical concentrations immobilized in hyperpolarizing solids with the objective of generating as much polarization as possible in a timeframe (<1 s) compatible with future recyclable DNP applications. To do so, the solid-state DNP enhancement factors, build-up rates and DNP spectra of different hyperpolarizing solids containing various nitroxide radical loadings (20-74 μmol cm-3) are compared against the DNP performance of varying nitroxide concentrations (10-100 mM) solvated in a glassy frozen solution. We demonstrate that in <1 s, polarization enhancement goes up to 56 and 102 with surface-bound and solvated radicals, respectively, under the optimized conditions. For the range of nitroxide concentrations used cross effect DNP seems to be the dominant mechanism under benchtop conditions. This was deduced from the electron paramagnetic resonance (EPR) lineshape of TEMPOL investigated using Q-band EPR measurements.

Hyperpolarizing Small Molecules using Parahydrogen and Solid-State Spin Diffusion

Parahydrogen-induced polarization (PHIP) is an inexpensive way to produce hyperpolarized molecules with polarization levels of >10 % in the solution-state, but is strongly limited in generality since it requires chemical reactions/ interactions with H2. Here we report a new method to widen the scope of PHIP hyperpolarization: a source molecule is produced via PHIP with high 13C polarization, and precipitated out of solution together with a target species. Spin diffusion within the solid carries the polarization onto 13C spins of the target, which can then be dissolved for solution-state applications. We name this method PHIP-SSD (PHIP with solid-state spin diffusion) and demonstrate it using PHIP-polarized [1-13C]-fumarate as the source molecule, to polarize different 13C-labelled target molecules. 13C polarizations of between 0.01 and 3 % were measured on [1-13C]-benzoic acid, depending on the molar ratio of fumarate:benzoate in the solid state. We also show that PHIP-SSD does not require specific co-crystallization conditions by grinding dry powders of target molecules together with solid fumarate crystals, and obtain 13C signal enhancements of between 100 and 200 on [13C,15N2]-urea, [1-13C]-pyruvate, and [1-13C]-benzoic acid. This approach appears to be a promising new strategy for facile hyperpolarization based on PHIP.

Recovery time reduction to decrease experimental duration (R2D2): A simple and universal method to accelerate NMR experiments

Acceleration techniques for one dimensional Nuclear Magnetic Resonance (1D NMR) are very useful, both for NMR enthusiasts and for chemists that use NMR for structural elucidation. To the latter, such techniques need to be straightforward. Recovery time Reduction to Decrease the experimental Duration (R2D2) relies on the incremental reduction of a pulse sequence's Recycle Time (TR). A pseudo-2D spectrum is acquired and after two Fourier transform, extraction and addition of the central rows, a 1D spectrum is obtained. Not only can it be applied to any pulse sequence that contains a TR, but it also requires only a list of recovery times and 2D processes to operate. With this method, we were able to easily reduce the experimental time by a factor of 2 and up to 4 using single-pulse, APT and DEPT 13C sequences. Moreover, R2D2 has the potential to be used on other low abundance nuclei (such as 15N or 2H) and numerous other pulse sequences.

Twenty Years of 1H NMR Plant Metabolomics: A Way Forward toward Assessment of Plant Metabolites for Constitutive and Inducible Defenses to Biotic Stress

Metabolomics has become an important tool in elucidating the complex relationship between a plant genotype and phenotype. For over 20 years, nuclear magnetic resonance (NMR) spectroscopy has been known for its robustness, quantitative capabilities, simplicity, and cost-efficiency. 1H NMR is the method of choice for analyzing a broad range of relatively abundant metabolites, which can be used for both capturing the plant chemical profile at one point in time and understanding the pathways that underpin plant defense. This systematic Review explores how 1H NMR-based plant metabolomics has contributed to understanding the role of various compounds in plant responses to biotic stress, focusing on both primary and secondary metabolites. It clarifies the challenges and advantages of using 1H NMR in plant metabolomics, interprets common trends observed, and suggests guidelines for method development and establishing standard procedures.

The experimental approach for the interleaved joint modulation of PHIP and NMR

Nuclear spin hyperpolarization derived from parahydrogen is a technique for enhancing nuclear magnetic resonance (NMR) sensitivity. The key to hyperpolarization experiments is to achieve rapid transfer and detection to minimize relaxation losses, while also avoiding bubbles or turbulence to guarantee high spectral resolution. In this article, we describe an experimental approach for the interleaved joint modulation of parahydrogen-induced polarization and NMR. We provide schematic diagrams of parahydrogen-based polarizer with in situ high-pressure detection capability and low-field polarization transfer. This approach can help to control the experimental process and acquire experimental information, one example of which is the attainment of the highest hyperpolarization signal intensity at 3.6 s after closing the valve. The polarizer demonstrates in situ detection capability, allowing sample to be restabilized within 0.3 ± 0.1 s and high-resolution NMR sampling under a pressure of 3 bars. Moreover, it can transfer polarized samples from the polarization transfer field to the detection region of NMR within 1 ± 0.3 s for completing signal amplification by reversible exchange experiments.

Recent Advances and Perspectives in Relation to the Metabolomics-Based Study of Diabetic Retinopathy

Diabetic retinopathy (DR), a prevalent microvascular complication of diabetes, is a major cause of acquired blindness in adults. Currently, a clinical diagnosis of DR primarily relies on fundus fluorescein angiography, with a limited availability of effective biomarkers. Metabolomics, a discipline dedicated to scrutinizing the response of various metabolites within living organisms, has shown noteworthy advancements in uncovering metabolic disorders and identifying key metabolites associated with DR in recent years. Consequently, this review aims to present the latest advancements in metabolomics techniques and comprehensively discuss the principal metabolic outcomes derived from analyzing blood, vitreous humor, aqueous humor, urine, and fecal samples.