Category Archives: ODNP

Overhauser Dynamic Nuclear Polarization: A Tool for Building Maps of Hydration Water #DNPNMR #ODNP #Review

Franck, John M. “Overhauser Dynamic Nuclear Polarization: A Tool for Building Maps of Hydration Water.” Biophysical Journal 118, no. 3, Supplement 1 (February 7, 2020): 487a.

https://doi.org/10.1016/j.bpj.2019.11.2695

Coating the surface of every macromolecule or macromolecular assembly, one finds a hydration layer composed of water molecules that move typically between 3× and 10× slower than water molecules in bulk water. The interaction between the water molecules in the hydration layer and the macromolecules contributes to the structural stability and sometimes the function of, e.g., proteins and lipid bilayers. Overhauser Dynamic Nuclear Polarization (ODNP) is an emerging electron-spin nuclear-spin (EPR-NMR) double-resonance tool that has demonstrated a capability of measuring the translational dynamics of water in the hydration layer. Here we discuss our efforts on two fronts: First, we design a scheme for measuring the thickness of the hydration layer and the effect of confinement on translational dynamics, as measured by ODNP, with controlled, appropriately labeled reverse micelle systems. Second, we describe the development of an a priori technique for converting ODNP measurements into a 3D “map” of hydration layer properties in dynamic room temperature samples that explore an ensemble of structures. This latter effort focuses on transmembrane model systems and utilizes the modern structure-prediction tool Rosetta in a fashion analogous to successful efforts to predict NMR order parameters. Particular focus is given to improving the quality and automation of the ODNP measurement, as well as validating predicted ensemble structures against both continuous wave EPR and NMR Paramagnetic Relaxation Enhancement (PRE) data.

A compact X-Band ODNP spectrometer towards hyperpolarized 1H spectroscopy #DNPNMR #ODNP

Überrück, Till, Michael Adams, Josef Granwehr, and Bernhard Blümich. “A Compact X-Band ODNP Spectrometer towards Hyperpolarized 1H Spectroscopy.” Journal of Magnetic Resonance, April 2020, 106724.

https://doi.org/10.1016/j.jmr.2020.106724

The demand for compact benchtop NMR systems that can resolve chemical shift differences in the ppm to sub-ppm range is growing. However due to material and size restrictions these magnets are limited in field strength and thus in signal intensity and quality. The implementation of standard hyperpolarization techniques is a next step in an effort to boost the signal. Here we present a compact Overhauser Dynamic Nuclear Polarization (ODNP) setup with a permanent magnet that can resolve 1H chemical shift differences in the ppm range. The assembly of the setup and its components are described in detail, and the functionality of the setup is demonstrated experimentally with ODNP enhanced relaxation measurements yielding a maximal enhancement of -140 for an aqueous 4Hydroxy-TEMPO solution. Additionally, 1H spectroscopic resolution and significant enhancements are demonstrated on acetic acid as a solvent.

Motional Dynamics of Halogen‐Bonded Complexes Probed by Low‐Field NMR Relaxometry and Overhauser Dynamic Nuclear Polarization #DNPNMR #ODNP

Banerjee, Abhishek, Arnab Dey, and N. Chandrakumar. “Motional Dynamics of Halogen‐Bonded Complexes Probed by Low‐Field NMR Relaxometry and Overhauser Dynamic Nuclear Polarization.” Chemistry – An Asian Journal, July 9, 2019, asia.201900754.

https://doi.org/10.1002/asia.201900754

Halogen bonding is a subject of considerable interest owing to wide-ranging chemical, materials and biological applications. The motional dynamics of halogenbonded complexes play a pivotal role in comprehending the nature of the halogen-bonding interaction. However, not many attempts appear to have been made to shed light on the dynamical characteristics of halogen-bonded species. For the first time, we demonstrate here that the combination of low-field NMR relaxometry and Overhauser dynamic nuclear polarization (ODNP) makes it possible to obtain a cogent picture of the motional dynamics of halogen-bonded species. We discuss here the advantages of this combined approach. Low-field relaxometry allows us to infer the hydrodynamic radius and rotational correlation time, whereas ODNP probes the molecular translational correlation times (involving the substrate as well as the organic radical) with high sensitivity at low field.

Nitroxide Derivatives for Dynamic Nuclear Polarization in Liquids: The Role of Rotational Diffusion #DNPNMR

Levien, M., M. Hiller, I. Tkach, M. Bennati, and T. Orlando. “Nitroxide Derivatives for Dynamic Nuclear Polarization in Liquids: The Role of Rotational Diffusion.” The Journal of Physical Chemistry Letters 11, no. 5 (March 5, 2020): 1629–35.

https://doi.org/10.1021/acs.jpclett.0c00270

Polarization transfer efficiency in liquid-state dynamic nuclear polarization (DNP) depends on the interaction between polarizing agents (PAs) and target nuclei modulated by molecular motions. We show how translational and rotational diffusion differently affect the DNP efficiency. These contributions were disentangled by measuring 1HDNP enhancements of toluene and chloroform doped with nitroxide derivatives at 0.34 T as a function of either the temperature or the size of the PA. The results were employed to analyze 13C-DNP data at higher fields, where the polarization transfer is also driven by the Fermi contact interaction. In this case, bulky nitroxide PAs perform better than the small TEMPONE radical due to structural fluctuations of the ring conformation. These findings will help in designing PAs with features specifically optimized for liquid-state DNP at various magnetic fields.

Characterizing oils in oil-water mixtures inside porous media by Overhauser dynamic nuclear polarization #DNPNMR #ODNP

Chen, Junfei, Jiwen Feng, Fang Chen, Zhen Zhang, Li Chen, Zhekai Zhang, Rugang Liao, Maili Liu, and Chaoyang Liu. “Characterizing Oils in Oil-Water Mixtures inside Porous Media by Overhauser Dynamic Nuclear Polarization.” Fuel 257 (December 2019): 116107.

https://doi.org/10.1016/j.fuel.2019.116107

We present a method to identify and sort the oils in oil-water mixtures based on the Overhauser dynamic nuclear polarization (ODNP) enhancement at low field. Through combining two types of radicals, e.g. ODNP enhancer TEMPO and relaxation reagent Mn2+, we can selectively enhance the 1H NMR signal of oil in oil-water mixture infiltrated in porous media. More importantly, we have found that the enhancements of light oils in porous materials are inversely dependent of their viscosities but independent of pore size approximately above 10 μm. This allows us to roughly sort oils according to their ODNP enhancement values. The verification experiments in sandstones saturated with several oil and water mixtures show that the method is useful for oils identification and classification in porous media, especially for reservoir assessment or development.

High-Resolution Overhauser Dynamic Nuclear Polarization Enhanced Proton NMR Spectroscopy at Low Magnetic Fields #DNPNMR #Bridge12

Overhauser DNP spectroscopy at X-Band is mostly used to study hydration dynamics. However, using a hybrid magnet (permanent magnet in combination with sweep coils) with active shimming it is possible to record high-resolution NMR spectra with chemical shift resolution. This is an example of the research and development activities performed at Bridge12.

Keller, Timothy J., Alexander J. Laut, Jagadishwar Sirigiri, and Thorsten Maly. “High-Resolution Overhauser Dynamic Nuclear Polarization Enhanced Proton NMR Spectroscopy at Low Magnetic Fields.” Journal of Magnetic Resonance, March 2020, 106719. 

https://doi.org/10.1016/j.jmr.2020.106719.

Dynamic nuclear polarization (DNP) has gained large interest due to its ability to increase signal intensities in nuclear magnetic resonance (NMR) experiments by several orders of magnitude. Currently, DNP is typically used to enhance high-field, solid-state NMR experiments. However, the method is also capable of dramatically increasing the observed signal intensities in solution-state NMR spectroscopy. In this work, we demonstrate the application of Overhauser dynamic nuclear polarization (ODNP) spectroscopy at an NMR frequency of 14.5 MHz (0.35 T) to observe DNP-enhanced highresolution NMR spectra of small molecules in solutions. Using a compact hybrid magnet with integrated shim coils to improve the magnetic field homogeneity we are able to routinely obtain proton linewidths of less than 4 Hz and enhancement factors > 30. The excellent field resolution allows us to perform chemical-shift resolved ODNP experiments on ethyl crotonate to observe proton J-coupling. Furthermore, recording high-resolution ODNP-enhanced NMR spectra of ethylene glycol allows us to characterize the microwave induced sample heating in-situ, by measuring the separation of the OH and CH2 proton peaks.

New limits of sensitivity of site-directed spin labeling electron paramagnetic resonance for membrane proteins #DNPNMR

A nice overview how spinlabels can be used for structural biology studies. This includes pulsed EPR techniques such as PELDOR (DEER) and ODNP spectroscopy.

Bordignon, Enrica, and Stephanie Bleicken. “New Limits of Sensitivity of Site-Directed Spin Labeling Electron Paramagnetic Resonance for Membrane Proteins.” Biochimica et Biophysica Acta (BBA) – Biomembranes 1860, no. 4 (April 2018): 841–53. https://doi.org/10.1016/j.bbamem.2017.12.009

Site-directed spin labeling electron paramagnetic resonance is a biophysical technique based on the specific introduction of spin labels to one or more sites in diamagnetic proteins, which allows monitoring dynamics and water accessibility of the spin-labeled side chains, as well as nanometer distances between two (or more) labels. Key advantages of this technique to study membrane proteins are addressed, with focus on the recent developments which will expand the range of applicability. Comparison with other biophysical methods is provided to highlight the strength of EPR as complementary tool for structural biology. This article is part of a Special Issue entitled: Beyond the Structure-Function Horizon of Membrane Proteins edited by Ute Hellmich, Rupak Doshi and Benjamin McIlwain.

Optically-generated Overhauser dynamic nuclear polarization: A numerical analysis #ODNP #DNPNMR

Cheney, Daniel J., and Christopher J. Wedge. “Optically-Generated Overhauser Dynamic Nuclear Polarization: A Numerical Analysis.” The Journal of Chemical Physics 152, no. 3 (January 21, 2020): 034202.

https://doi.org/10.1063/1.5133408

Recently, an alternative approach to dynamic nuclear polarization (DNP) in the liquid state was introduced using optical illumination instead of microwave pumping. By exciting a suitable dye to the triplet state which undergoes a diffusive encounter with a persistent radical forming a quartet-doublet pair in the encounter complex, dynamic electron polarization (DEP) is generated via the radical-triplet pair mechanism. Subsequent cross-relaxation generates nuclear polarization without the need for microwave saturation of the electronic transitions. Here, we present a theoretical justification for the initial experimental results by means of numerical simulations. These allow investigation of the effects of various experimental parameters, such as radical and dye concentrations, sample geometry, and laser power, on the DNP enhancement factors, providing targets for experimental optimization. It is predicted that reducing the sample volume will result in larger enhancements by permitting a higher concentration of triplets in a sample of increased optical density. We also explore the effects of the pulsed laser rather than continuous-wave illumination, rationalizing the failure to observe the optical DNP effect under illumination conditions common to DEP experiments. Examining the influence of the illumination duty cycle, the conditions necessary to permit the use of pulsed illumination without compromising signal enhancement are determined, which may reduce undesirable laser heating effects. This first simulation of the optical DNP method therefore underpins the further development of the technology.

Large volume liquid state scalar Overhauser dynamic nuclear polarization at high magnetic field #DNPNMR

Dubroca, Thierry, Sungsool Wi, Johan van Tol, Lucio Frydman, and Stephen Hill. “Large Volume Liquid State Scalar Overhauser Dynamic Nuclear Polarization at High Magnetic Field.” Physical Chemistry Chemical Physics 21, no. 38 (2019): 21200–204.

https://doi.org/10.1039/C9CP02997D

Dynamic Nuclear Polarization (DNP) can increase the sensitivity of Nuclear Magnetic Resonance (NMR), but it is challenging in the liquid state at high magnetic fields. In this study we demonstrate significant enhancements of NMR signals (up to 70 on 13C) in the liquid state by scalar Overhauser DNP at 14.1 T, with high resolution (∼0.1 ppm) and relatively large sample volume (∼100 μL).

Understanding Overhauser Dynamic Nuclear Polarisation through NMR relaxometry #DNPNMR

Parigi, Giacomo, Enrico Ravera, Marina Bennati, and Claudio Luchinat. “Understanding Overhauser Dynamic Nuclear Polarisation through NMR Relaxometry.” Molecular Physics 117, no. 7–8 (April 18, 2019): 888–97.

https://doi.org/10.1080/00268976.2018.1527409

Overhauser dynamic nuclear polarisation (DNP) represents a potentially outstanding tool to increase the sensitivity of solution and solid state NMR experiments, as well as of magnetic resonance imaging. DNP signal enhancements are strongly linked to the spin relaxation properties of the system under investigation, which must contain a paramagnetic molecule used as DNP polariser. In turn, nuclear spin relaxation can be monitored through NMR relaxometry, which reports on the field dependence of the nuclear relaxation rates, opening a route to understand the physical processes at the origin of the Overhauser DNP in solution. The contributions of dipole–dipole and Fermi-contact interactions to paramagnetic relaxation are here described and shown to be responsible to both the relaxometry profiles and the DNP enhancements, so that the experimental access to the former can allow for predictions of the latter.

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