Category Archives: X-Band ODNP

Electrochemical Overhauser dynamic nuclear polarization #DNPNMR #ODNP

Tamski, Mika, Jonas Milani, Christophe Roussel, and Jean-Philippe Ansermet. “Electrochemical Overhauser Dynamic Nuclear Polarization.” Physical Chemistry Chemical Physics 22, no. 32 (2020): 17769–76.

Nuclear Magnetic Resonance (NMR) spectroscopy suffers from low sensitivity due to the low nuclear spin polarization obtained within practically achievable external magnetic fields. Dynamic Nuclear Polarization (DNP) refers to the techniques that increases NMR signal intensity by transferring spin polarization from electrons to the nuclei.

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.

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.

Overhauser DNP FFC study of block copolymer diluted solution #DNPNMR

Gizatullin, Bulat, Carlos Mattea, and Siegfried Stapf. “Overhauser DNP FFC Study of Block Copolymer Diluted Solution.” Magnetic Resonance Imaging 56 (February 2019): 96–102.

Overhauser dynamic nuclear polarization (DNP) is the dominating hyperpolarization technique to increasing the nuclear magnetic resonance signal in liquids and diluted systems. The enhancement obtained depends on the overall mobility of the radical-carrying molecule but also on its specific interaction with the host molecules. Information about the nature of molecular and radical dynamics can be identified from determining the nuclear T1 as a function of Larmor frequency by Fast Field Cycling (FFC) relaxometry. In this work, DNP and FFC methods were combined for a detailed study of 1H Overhauser DNP enhancements at 340 mT (X-band) and 73 mT (S-band) for diluted solutions of a block-copolymer with and without the addition of TEMPO radicals. NMR relaxation dispersions of these solutions are measured at thermal polarization and DNP conditions in the Xband, and the obtained DNP data were analyzed by a model of electron-nucleus interactions modulated by translational diffusion. The coupling factors for the two different blocks of the copolymer are obtained independently from DNP and NMRD experiments. An additional contribution from scalar interactions was found for polystyrene blocks.

Surface chemical heterogeneity modulates silica surface hydration #DNPNMR #ODNP

Schrader, Alex M., Jacob I. Monroe, Ryan Sheil, Howard A. Dobbs, Timothy J. Keller, Yuanxin Li, Sheetal Jain, M. Scott Shell, Jacob N. Israelachvili, and Songi Han. “Surface Chemical Heterogeneity Modulates Silica Surface Hydration.” Proceedings of the National Academy of Sciences 115, no. 12 (March 20, 2018): 2890–95.

An in-depth knowledge of the interaction of water with amorphous silica is critical to fundamental studies of interfacial hydration water, as well as to industrial processes such as catalysis, nanofabrication, and chromatography. Silica has a tunable surface comprising hydrophilic silanol groups and moderately hydrophobic siloxane groups that can be interchanged through thermal and chemical treatments. Despite extensive studies of silica surfaces, the influence of surface hydrophilicity and chemical topology on the molecular properties of interfacial water is not well understood. In this work, we controllably altered the surface silanol density, and measured surface water diffusivity using Overhauser dynamic nuclear polarization (ODNP) and complementary silica–silica interaction forces acrosswater using a surface forces apparatus (SFA). The results show that increased silanol density generally leads to slower water diffusivity and stronger silica– silica repulsion at short aqueous separations (less than ∼4 nm). Both techniques show sharp changes in hydration properties at intermediate silanol densities (2.0–2.9 nm−2). Molecular dynamics simulations of model silica–water interfaces corroborate the increase in water diffusivity with silanol density, and furthermore show that even on a smooth and crystalline surface at a fixed silanol density, adjusting the spatial distribution of silanols results in a range of surface water diffusivities spanning ∼10%. We speculate that a critical silanol cluster size or connectivity parameter could explain the sharp transition in our results, and can modulate wettability, colloidal interactions, and surface reactions, and thus is a phenomenon worth further investigation on silica and chemically heterogeneous surfaces.

Molecular dynamics-based selectivity for Fast-Field-Cycling relaxometry by Overhauser and solid effect dynamic nuclear polarization #DNPNMR

Neudert, O., C. Mattea, and S. Stapf, Molecular dynamics-based selectivity for Fast-Field-Cycling relaxometry by Overhauser and solid effect dynamic nuclear polarization. J. Magn. Reson., 2017. 276: p. 113-121.

In the last decade nuclear spin hyperpolarization methods, especially Dynamic Nuclear Polarization (DNP), have provided unprecedented possibilities for various NMR techniques by increasing the sensitivity by several orders of magnitude. Recently, in-situ DNP-enhanced Fast Field Cycling (FFC) relaxometry was shown to provide appreciable NMR signal enhancements in liquids and viscous systems. In this work, a measurement protocol for DNP-enhanced NMR studies is introduced which enables the selective detection of nuclear spin hyperpolarized by either Overhauser effect or solid effect DNP. Based on field-cycled DNP and relaxation studies it is shown that these methods allow for the independent measurement of polymer and solvent nuclear spins in a concentrated solution of high molecular weight polybutadiene in benzene doped with α,γ-bisdiphenylene-β-phenylallyl radical. Appreciable NMR signal enhancements of about 10-fold were obtained for both constituents. Moreover, qualitative information about the dynamics of the radical and solvent was obtained. Selective DNP-enhanced FFC relaxometry is applied for the measurement of the 1H nuclear magnetic relaxation dispersion of both constituents with improved precision. The introduced method is expected to greatly facilitate NMR studies of complex systems with multiple overlapping signal contributions that cannot be distinguished by standard methods.

Field‐frequency locked X‐band Overhauser effect spectrometer #DNPNMR

This article is already a bit older. However, it nicely illustrates that DNP, specifically ODNP has been around for a while already, and gives some interesting specifics on the instrumentation that are still valid today.

Chandrakumar, N. and P.T. Narasimhan, Field‐frequency locked X‐band Overhauser effect spectrometer. Review of Scientific Instruments, 1981. 52(4): p. 533-538.

The design and construction of an Overhauser Effect Spectrometer operating at X band is described. The ESR section is a Varian V-4502 spectrometer equipped with a 9-in. electromagnet and a shim coil assembly. NMR detection is based on a broadband rf hybrid juction feeding a coil in an X-band quartz dielectric cavity. Signal processing is carried out at a constant intermediate frequency of 25.1 MHz with a Varian V -4311 fixed frequency rf unit. The mixing scheme employed to translate the NMR information to 25.1 MHz is described. Medium resolution performance (resolution _10-6 ) for the NMR is achieved under field-frequency locked conditions. The lock is based on a Super-Regenerative Oscillator (SRO) housing a control sample, and operating as a field-tracking frequency source. This SRO injects into an oscillator which excites the analytical sample resonance and also serves as a local oscillator, thereby making the locked spectrometer multinuclear in capability. Typical Overhauser effect recordings of protons and fluorines are presented.

Quantitative analysis of molecular transport across liposomal bilayer by J-mediated 13C Overhauser dynamic nuclear polarization

Cheng, C.Y., O.J. Goor, and S. Han, Quantitative analysis of molecular transport across liposomal bilayer by J-mediated 13C Overhauser dynamic nuclear polarization. Anal Chem, 2012. 84(21): p. 8936-40.

We introduce a new NMR technique to dramatically enhance the solution-state (13)C NMR sensitivity and contrast at 0.35 T and at room temperature by actively transferring the spin polarization from Overhauser dynamic nuclear polarization (ODNP)-enhanced (1)H to (13)C nuclei through scalar (J) coupling, a method that we term J-mediated (13)C ODNP. We demonstrate the capability of this technique by quantifying the permeability of glycine across negatively charged liposomal bilayers composed of dipalmitoylphosphatidylcholine (DPPC) and dipalmitoylphosphatidylglycerol (DPPG). The permeability coefficient of glycine across this DPPC/DPPG bilayer is measured to be (1.8 +/- 0.1) x 10(-11)m/s, in agreement with the literature value. We further observed that the presence of 20 mol % cholesterol within the DPPC/DPPG lipid membrane significantly retards the permeability of glycine by a factor of 4. These findings demonstrate that the high sensitivity and contrast of J-mediated (13)C ODNP affords the measurement of the permeation kinetics of small hydrophilic molecules across lipid bilayers, a quantity that is difficult to accurately measure with existing techniques.

Chemical-shift-resolved (1)(9)F NMR spectroscopy between 13.5 and 135 MHz: Overhauser-DNP-enhanced diagonal suppressed correlation spectroscopy

George, C. and N. Chandrakumar, Chemical-shift-resolved (1)(9)F NMR spectroscopy between 13.5 and 135 MHz: Overhauser-DNP-enhanced diagonal suppressed correlation spectroscopy. Angew Chem Int Ed Engl, 2014. 53(32): p. 8441-4.

Overhauser-DNP-enhanced homonuclear 2D (19)F correlation spectroscopy with diagonal suppression is presented for small molecules in the solution state at moderate fields. Multi-frequency, multi-radical studies demonstrate that these relatively low-field experiments may be operated with sensitivity rivalling that of standard 200-1000 MHz NMR spectroscopy. Structural information is accessible without a sensitivity penalty, and diagonal suppressed 2D NMR correlations emerge despite the general lack of multiplet resolution in the 1D ODNP spectra. This powerful general approach avoids the rather stiff excitation, detection, and other special requirements of high-field (19)F NMR spectroscopy.

Chapter Sixteen – Overhauser Dynamic Nuclear Polarization Studies on Local Water Dynamics #DNPNMR

Kaminker, I., R. Barnes, and S. Han, Chapter Sixteen – Overhauser Dynamic Nuclear Polarization Studies on Local Water Dynamics, in Methods in Enzymology, Z.Q. Peter and W. Kurt, Editors. 2015, Academic Press. p. 457-483.

Abstract Overhauser dynamic nuclear polarization (ODNP) is an emerging technique for quantifying translational water dynamics in the vicinity (1 nm) of stable radicals that can be chemically attached to macromolecules of interest. This has led to many in-depth and enlightening studies of hydration water of biomolecules, revolving around the role of solvent dynamics in the structure and function of proteins, nucleic acids, and lipid bilayer membranes. Still to date, a complete and fully automated ODNP instrument is not commercialized. The purpose of this chapter is to share the technical know-how of the hardware, theory, measurement, and data analysis method needed to successfully utilize and disseminate the ODNP technique.

Theoretical treatment of pulsed Overhauser dynamic nuclear polarization: Consideration of a general periodic pulse sequence #DNPNMR

Nasibulov, E.A., et al., Theoretical treatment of pulsed Overhauser dynamic nuclear polarization: Consideration of a general periodic pulse sequence. JETP Letters, 2016. 103(9): p. 582-587.

A general theoretical approach to pulsed Overhauser-type dynamic nuclear polarization (DNP) is presented. Dynamic nuclear polarization is a powerful method to create non-thermal polarization of nuclear spins, thereby enhancing their nuclear magnetic resonance signals. The theory presented can treat pulsed microwave irradiation of electron paramagnetic resonance transitions for periodic pulse sequences of general composition. Dynamic nuclear polarization enhancement is analyzed in detail as a function of the microwave pulse length for rectangular pulses and pulses with finite rise time. Characteristic oscillations of the DNP enhancement are found when the pulse-length is stepwise increased, originating from coherent motion of the electron spins driven by the pulses. Experimental low-field DNP data are in very good agreement with this theoretical approach.

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