Nuclear Cross-Effect NMR.

Solid Effect DNP in a Rapid-melt setup

The inherently low sensitivity of nuclear magnetic resonance(NMR)spectroscopy is the major limiting factor for its application to elucidatestructure and dynamics in solids. In the solid state, nuclear spinhyperpolarization methods based on microwave-induced dynamic nuclearpolarization (DNP) provide a versatile platform to enhance the bulkNMR signal of many different sample formulations, leading to significantsensitivity improvements. Here we show that 1H NMR hyperpolarizationcan also be generated in solids at high magnetic fields by opticalirradiation of the sample. We achieved this by exploiting a donor–chromophore–acceptormolecule with an excited state electron–electron interactionsimilar to the nuclear Larmor frequency, enabling solid-state 1H photochemically induced DNP (photo-CIDNP) at high magneticfields. Through hyperpolarization relay, we obtained bulk NMR signalenhancements εH by factors of ∼100 at both9.4 and 21.1 T for the 1H signal of o-terphenylin magic angle spinning (MAS) NMR experiments at 100 K. These findingsopen a pathway toward a general light-induced hyperpolarization approachfor dye-sensitized high-field NMR in solids.

Nuclear magnetic resonance (NMR) has been broadly investigated and applied in many industries (e.g., medical treatment, food safety and materials) as a powerful approach to explore the internal structure and composition of substances. However, the need for more sensitivity has been one of the most severe problems hindering the practical application of NMR. This paper suggests various approaches to deal with this defect, from adjusting factors based on the theoretical principle to the progressive hyperpolarization method. Classified by polarization sources, several representative sub-fields of hyperpolarization are further interpreted and analyzed, including Dynamic Nuclear Polarization (DNP), Optical Pumping (OP) and Parahydrogen Induced Polarization (PHIP). Based on the analysis and prospect of the aforementioned feasible methods, the main factors that restrict the sensitivity of NMR will be identified. Moreover, the prospects and new technologies brought by the methods based on different theoretical foundations have been considered to improve these factors and make NMR apply to a broader range of fields. Overall, these results not only indicate the current research status but also shed light on guiding further exploration of methods of enhancing NMR sensitivity and usability.

Dynamic nuclear polarization (DNP) has become a very important hyperpolarization method because it can dramatically increase the sensitivity of nuclear magnetic resonance (NMR) of various molecules. Liquid-state DNP based on Overhauser effect is capable of directly enhancing polarization of all kinds of nuclei in the system. The combination of simultaneous Overhauser multi-nuclei enhancements with the multi-nuclei parallel acquisitions provides a variety of important applications in both MR spectroscopy (MRS) and image (MRI). Here we present two simple illustrative examples for simultaneously enhanced multi-nuclear spectra and images to demonstrate the principle and superiority. We have observed very large simultaneous DNP enhancements for different nuclei, such as 1H and 23Na, 1H and 31P, 19F and 31P, especially for the first time to report sodium ion enhancement in liquid. We have also obtained the simultaneous images of 19H and 31P, 19F and 31P at low field by solution-state DNP for the first time.

Dynamic nuclear polarisation (DNP) is a process that transfers electron spin polarisation to nuclei by applying resonant microwave radiation, and has been widely used to improve the sensitivity of nuclear magnetic resonance (NMR). Here we demonstrate new levels of performance for static cross-effect proton DNP using high peak power chirped inversion pulses at 94 GHz to create a strong polarisation gradient across the inhomogeneously broadened line of the mono-radical 4-amino TEMPO. Enhancements of up to 340 are achieved at an average power of a few hundred mW, with fast build-up times (3 s). Experiments are performed using a home-built wideband kW pulsed electron paramagnetic resonance (EPR) spectrometer operating at 94 GHz, integrated with an NMR detection system. Simultaneous DNP and EPR characterisation of other mono-radicals and biradicals, as a function of temperature, leads to additional insights into limiting relaxation mechanisms and give further motivation for the development of wideband pulsed amplifiers for DNP at higher frequencies.

Overhauser dynamic nuclear polarization (ODNP) in solutions of various paramagnetic complexes has been studied for 60 years, but only in recent years has found applications of broad interest to biophysical and biomedical sciences, for the investigation of soft materials and biomolecules. Relatively few aplications are focused on the ODNP in petroleum dispersed systems (PDS) like oils, bitumen, their fractions and solutions. This work present a short review of the ODNP studies of PDS with aim to introduce the basic concepts and key values for the effective petroleum ODNP in low and high magnetic fields. Experimental results obtained in our Laboratory by using home-made spectrometer are included. The study can be used for designing ODNP spectrometers, proton precession magnetometers for geological and geophysical exploration, investigation of supramolecular organisation of PDS and their components.

Solid-state MAS NMR at ultra low temperature of hydrated alanine doped with DNP radicals

Low-field nuclear magnetic resonance (NMR) instruments are an indispensable tool in industrial research and quality control. However, the intrinsically low spin polarization at low magnetic fields severely limits their detection sensitivity and measurement throughput, preventing their widespread use in biomedical analysis. Overhauser dynamic nuclear polarization (ODNP) effectively addresses this problem by transferring the spin polarization from free electrons to protons, significantly enhancing sensitivity. In this paper, we explore the potential of using ODNP for signal enhancement in a custom-designed portable chip-based DNP-enhanced NMR platform, which is centered around a miniaturized microwave (MW) transmitter, a custom-designed NMR-on-a-chip transceiver, and two application-specific ODNP probes. The MW transmitter provides frequency synthesis, signal modulation, and power amplification, providing sufficient output power for efficient polarization transfer. The NMR-on-a-chip transceiver combines a radio frequency (RF) transmitter with a fully differential quadrature receiver, providing pulsed excitation and NMR signal down-conversion and amplification. Two custom-designed ODNP probes are used for proof-of-concept DNP-enhanced NMR relaxometry and spectroscopy measurements. The presented chip-based ODNP platform achieves a maximum MW output power of , resulting in a signal enhancement of using the relaxometry ODNP probe with of non-degassed TEMPOL solution, and an enhancement of with the spectroscopy ODNP probe using of the same solution. The proton polarization was increased from to at a low field of . Proof-of-concept measurements on radical-doped tattoo inks and acetic acid verify the potential of our chip-based ODNP platform for the analysis of biologically and medically relevant parameters such as relaxation times, chemical shifts, and hyperfine interactions.

Dynamic nuclear polarization with photo-excited triplet electrons (triplet-DNP) has the potential to enhance the sensitivity of nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) at a moderate temperature. While many efforts have been devoted to achieving a large nuclear polarization based on triplet-DNP, the application of triplet-DNP has been limited to nuclear physics experiments. The recent introduction of materials chemistry into the field of triplet-DNP has achieved air-stable and water-soluble polarizing agents as well as the hyperpolarization of nanomaterials with a large surface area such as nanoporous metal-organic frameworks (MOFs) and nanocrystal dispersion in water. This Feature Article overviews the recently-emerged materials chemistry of triplet-DNP that paves new paths towards unprecedented biological and medical applications.

Gyrotrons have been developed as terahertz wave sources in dynamic nuclear polarisation (DNP) system to increase the sensitivity of nuclear magnetic resonance (NMR) in the high-magnetic field regime. However, the transmission of the Gaussian beam from the gyrotron output window to the NMR system proves to be a critical challenge. In this study, a terahertz transmission system, composed of a rectangular corrugated waveguide and a back-to-back rectangular corrugated horn for Gaussian mode filtering, is proposed. The attenuation in the optimised 0.33 THz corrugated waveguide remains lower than 0.01 dB/m in a broad frequency range from 280 GHz to 450 GHz. Besides, the coupling coefficient from the electric field in the 0.33 THz mode-filtering horn to the fundamental HE11 mode in the rectangular corrugated waveguide is obtained nearly 99.5%. This terahertz transmission system is potential to be applied in DNP-NMR spectrometer based on continuous wave gyrotrons.

The atomic description of glycosylated proteins is essential for gaining an understanding of the physiological roles of protein glycosylation. X-ray crystallographic and cryo-EM analyses currently play a central role in the 3D structural determination of biological macromolecules. 3D structural information of glycosylated proteins remains limited due to the weak or absent electron densities of the glycan parts. Solution nuclear magnetic resonance (NMR) analysis is unique in that the conformation and dynamics of the glycan part can be obtained experimentally at atomic resolution. The sensitivity of NMR can be greatly enhanced through 13C isotope labeling of the glycoprotein glycan, and such labeling provides a new dimension in the NMR spectra. Specifically, signal assignment of the glycoprotein glycan can be attained unambiguously through scalar and nuclear Overhauser effect (NOE) connectivities. To this end, efficient and cost-effective 13C-labeling methodology is needed, through good yields in glycoprotein expression and purification. Here we introduce our method for the preparation of a 13C-labeled immunoglobulin A (IgA) Fc fragment using a transient mammalian expression system.

High magnetic fields significantly improve the resolution and sensitivity of nuclear magnetic resonance (NMR) spectroscopy measurements, which presents exciting research opportunities in areas of chemistry, biology, and material science. Powered magnets can provide much higher magnetic fields than persistent mode superconducting magnets but suffer from temporal magnetic field fluctuations due to power supply ripple and variations in cooling water temperature and flow rate which make powered magnets non-viable for high resolution NMR experiments. Previous work has demonstrated that a multi-rate sampled data cascade control system may be used to improve the resolution of NMR experiments in powered magnets. Despite these advances in reducing temporal magnetic field fluctuations, the field regulation design does not accommodate the use of pulsed field gradients, which are necessary in many NMR experiments. This work presents a control topology which accommodates the use of pulsed field gradient signals with the field regulation system. This control approach is verified using NMR measurements.

Nuclear Magnetic Resonance (NMR) spectroscopy would be a method of choice to follow biochemical events in cells because it can analyze molecules in complex environments. However, the intrinsically low sensitivity of NMR makes in-cell measurements challenging. Dynamic Nuclear Polarization (DNP) has emerged as a method to circumvent this limitation, but most polarizing agents developed for DNP are unstable in reducing cellular environments. Here, we introduce the use of Gd(III)-based DNP polarizing agents for in-cell NMR spectroscopy. Specifically, we show their persistent stability in cellular formulations, and we investigate the DNP performance of the Gd(III)-based complex [Gd(tpatcn)] in human embryonic kidney cell lysates and intact cells. For cell lysates, DNP enhancements up to -27 are obtained on the cellular signals, reproducible even after storage at room temperature for days. Mixing the [Gd(tpatcn)] solution with intact cells enables the observation of cellular signals with DNP, and DNP enhancement factors of about -40 are achieved.

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Benchtop 13C NMR spectroscopy is highly attractive for reaction and process monitoring. However, insufficient premagnetization and low signal intensities largely prevent its application to flowing liquids. We show that hyperpolarization by Overhauser dynamic nuclear polarization (ODNP) can be used to overcome these problems, as ODNP operates on short time scales and results in strong 13C signal enhancements. Benchtop 13C NMR spectra with ODNP enhancement acquired in continuous-flow are reported here for the first time. We have investigated two ODNP approaches: direct ODNP, which transfers the polarization of unpaired electrons to 13C nuclei via direct hyperfine coupling, and indirect ODNP, in which the electron polarization is first transferred to 1H nuclei before a polarization transfer pulse sequence finally transfers the polarization to the 13C nuclei. Experiments were carried out for three pure solvents and a mixture for different flow rates. The results show significant 13C signal enhancements for both approaches. However, their performance varies for different substances, depending on the strength and type of the hyperfine interaction as well as on the relaxation properties, but by selecting a suitable approach, good single-scan 13C NMR spectra can be obtained with benchtop NMR, even at high flow rates.