Category Archives: 9 GHz ODNP

Heterogeneity of Network Structures and Water Dynamics in κ-Carrageenan Gels Probed by Nanoparticle Diffusometry #DNPNMR

Kort, Daan W. de, Erich Schuster, Freek J.M. Hoeben, Ryan Barnes, Meike Emondts, Henk M. Janssen, Niklas Lorén, Songi Han, Henk Van As, and John P.M. van Duynhoven. “Heterogeneity of Network Structures and Water Dynamics in κ-Carrageenan Gels Probed by Nanoparticle Diffusometry.” Langmuir 34, no. 37 (September 18, 2018): 11110–20.

A set of functionalized nanoparticles (PEGylated dendrimers, d = 2.8 – 9 nm) was used to probe the structural heterogeneity in Na+/K+ induced κ-carrageenan gels. The self-diffusion behavior of these nanoparticles as observed by 1H PFG NMR, FRAP and RICS revealed a fast and a slow component, pointing towards microstructural heterogeneity in the gel network. The self-diffusion behavior of the faster nanoparticles could be modelled with obstruction by a coarse network (average mesh size <100 nm), while the slower-diffusing nanoparticles are trapped in a dense network (lower mesh size limit of 4.6 nm). Overhauser DNP-enhanced NMR relaxometry revealed a reduced local solvent water diffusivity near TEMPO-labelled nanoparticles trapped in the dense network, showing that heterogeneity in the physical network is also reflected in heterogeneous self-diffusivity of water. The observed heterogeneity in mesh sizes and in water self-diffusivity is of interest for understanding and modelling of transport through and release of solutes from heterogeneous biopolymer gels.

Water Dynamics from the Surface to the Interior of a Supramolecular Nanostructure #DNPNMR #ODNP

Ortony, Julia H., Baofu Qiao, Christina J. Newcomb, Timothy J. Keller, Liam C. Palmer, Elad Deiss-Yehiely, Monica Olvera de la Cruz, Songi Han, and Samuel I. Stupp. “Water Dynamics from the Surface to the Interior of a Supramolecular Nanostructure.” Journal of the American Chemical Society 139, no. 26 (July 5, 2017): 8915–21.

Water within and surrounding the structure of a biological system adopts context-specific dynamics that mediate virtually all of the events involved in the inner workings of a cell. These events range from protein folding and molecular recognition to the formation of hierarchical structures. Water dynamics are mediated by the chemistry and geometry of interfaces where water and biomolecules meet. Here we investigate experimentally and computationally the translational dynamics of vicinal water molecules within the volume of a supramolecular peptide nanofiber measuring 6.7 nm in diameter. Using Overhauser dynamic nuclear polarization relaxometry, we show that drastic differences exist in water motion within a distance of about one nanometer from the surface, with rapid diffusion in the hydrophobic interior and immobilized water on the nanofiber surface. These results demonstrate that water associated with materials designed at the nanoscale is not simply a solvent, but rather an integral part of their structure and potential functions.

Perspective of Overhauser dynamic nuclear polarization for the study of soft materials #DNPNMR

Biller, Joshua R., Ryan Barnes, and Songi Han. “Perspective of Overhauser Dynamic Nuclear Polarization for the Study of Soft Materials.” Current Opinion in Colloid & Interface Science 33 (January 1, 2018): 72–85.

Solution state Overhauser dynamic nuclear polarization (ODNP) has been studied for 60years, but only in recent years has found applications of broad interest to biophysical sciences of hydration dynamics (HD-ODNP) around biomolecules and surfaces. In this review we describe state-of-the-art HD-ODNP methods and experiments, and identify technological and conceptual advances necessary to broadly disseminate HD-ODNP, as well as broaden its scope. Specifically, incomplete treatment of the saturation factor leads to the use of high microwave powers that induce temperature-dependent effects in HD-ODNP that can be detrimental to the stability and property of the sample and/or data interpretation, and thus must be corrected for. Furthermore, direct measurements of the electron spin relaxation times for the nitroxide radical-based spin labels used in HD-ODNP have recently caught up with the ambient solution conditions of relevance to HD-ODNP experiment, allowing us to envision an explicit treatment of the saturation factor. This would enable “single-shot” HD-ODNP at one or two concentrations and power levels, cutting down experimental times from the typical hours to minutes. With the development of a user-friendly and robust operation, the application of HD-ODNP experiments can be broadened for the study of biomolecules, biomaterials, soft polymer materials (i.e. hydrogels) and surfaces. In fact, any hydrated materials that can be viably spin labeled can yield information on local water dynamics and interfaces, and so guide the design of soft materials for medical and pharmaceutical uses. A brief introduction to spin-labeling, and exemplary applications to soft materials is discussed to serve as inspiration for future studies.

Electron spin resonance studies on deuterated nitroxyl spin probes used in Overhauser-enhanced magnetic resonance imaging #DNPNMR #ODNP

Jebaraj, D. David, Hideo Utsumi, and A. Milton Franklin Benial. “Electron Spin Resonance Studies on Deuterated Nitroxyl Spin Probes Used in Overhauser-Enhanced Magnetic Resonance Imaging.” Magnetic Resonance in Chemistry 55, no. 8 (2017): 700–705.

The electron spin resonance studies were carried out for 2 mm concentration of 14N-labeled and 15N-labeled 3-carbamoyl-2,2,5,5-tetramethyl-pyrrolidine-1-oxyl, 3-carboxy-2,2,5,5-tetramethyl-pyrrolidine-1-oxyl, 3-methoxycarbonyl-2,2,5,5-tetramethyl-pyrrolidine-1-oxyl and their deuterated nitroxyl radicals using X-band electron spin resonance spectrometer. The electron spin resonance line shape analysis was carried out. The electron spin resonance parameters such as linewidth, Lorentzian component, signal intensity ratio, rotational correlation time, hyperfine coupling constant and g-factor were estimated. The deuterated nitroxyl radicals have narrow linewidth and an increase in Lorentzian component, compared with undeuterated nitroxyl radicals. The dynamic nuclear polarization factor was observed for all nitroxyl radicals. Upon 2H labeling, about 70% and 40% increase in dynamic nuclear polarization factor were observed for 14N-labeled and 15N-labeled nitroxyl radicals, respectively. The signal intensity ratio and g-value indicate the isotropic nature of the nitroxyl radicals in pure water. Therefore, the deuterated nitroxyl radicals are suitable spin probes for in vivo/in vitro electron spin resonance and Overhauser-enhanced magnetic resonance imaging modalities. Copyright © 2017 John Wiley & Sons, Ltd.

A table-top PXI based low-field spectrometer for solution dynamic nuclear polarization #DNPNMR #ODNP

Biller, Joshua R., Karl F. Stupic, and J. Moreland. “A Table-Top PXI Based Low-Field Spectrometer for Solution Dynamic Nuclear Polarization.” Magnetic Resonance in Chemistry 56, no. 3 (2017): 153–63.

We present the development of a portable dynamic nuclear polarization (DNP) instrument based on the PCI eXtensions for Instrumentation platform. The main purpose of the instrument is for study of 1H polarization enhancements in solution through the Overhauser mechanism at low magnetic fields. A DNP probe set was constructed for use at 6.7 mT, using a modified Alderman–Grant resonator at 241 MHz for saturation of the electron transition. The solenoid for detection of the enhanced 1H signal at 288 kHz was constructed with Litz wire. The largest observed 1H enhancements (ε) at 6.7 mT for 14N-CTPO radical in air saturated aqueous solution was ε 65. A concentration dependence of the enhancement is observed, with maximum ε at 5.5 mM. A low resonator efficiency for saturation of the electron paramagnetic resonance transition results in a decrease in ε for the 10.3 mM sample. At high incident powers (42 W) and long pump times, capacitor heating effects can also decrease the enhancement. The core unit and program described here could be easily adopted for multi-frequency DNP work, depending on available main magnets and selection of the “plug and play” arbitrary waveform generator, digitizer, and radiofrequency synthesizer PCI eXtensions for Instrumentatione cards.

DNP sensitivity of 19F-NMR signals in hexafluorobenzene depending on polarizing agent type #DNPNMR #ODNP

Peksoz, Ahmet. “DNP Sensitivity of 19F-NMR Signals in Hexafluorobenzene Depending on Polarizing Agent Type.” Magnetic Resonance in Chemistry 54, no. 9 (2016): 748–52.

Low field dynamic nuclear polarization or low field magnetic double resonance technique enables enhanced nuclear magnetic resonance signals to be detected without increasing the strength of the polarizing field. The study reports that the dynamic nuclear polarization of 19F nuclei in hexafluorobenzene solutions doped with nitroxide, BDPA, MC800 asphaltene and MC30 asphaltene free radicals at 15 G. The 19F nuclei in all solutions gave positive DNP enhancements changing between 3.42 and 189.54, corresponding to predominantly scalar interactions with the unpaired electrons in the radicals. DNP sensitivity of 19F nuclei in hexafluorobenzene was observed to be changed significantly depending on the radical type. Nitroxide was found to have the best DNP performance among the polarizing agents. Copyright © 2016 John Wiley & Sons, Ltd.

Nuclear-Electron Overhauser Effect in MC800 Liquid Asphalt Solutions

Yet another application (although not new) for Overhauser DNP at 9 GHz. 

Firat, Y.E., H. Yildirim, and A. Peksoz, Nuclear-Electron Overhauser Effect in MC800 Liquid Asphalt Solutions. Journal of Dispersion Science and Technology, 2015. 37(9): p. 1349-1359.

Experimental results on the extrapolated ultimate enhancement factors of o-, m-, and p-xylene protons at 1.53 mT are obtained for MC800 asphalt solutions. The ultimate enhancement factors are found such as ?26.9, ?25.7, and ?11.7 for o-, m-, and p-xylene, respectively. These results show that the solvent proton Overhauser effect cannot reach the extrapolated enhancement of ?330 in the extreme narrowing case because of occurrence of small scalar interactions in addition to the dipole?dipole interactions between solvent protons and asphalt electrons. The ortho, meta, and para positions of the ?CH3 group change the nature of the interactions. The nuclear magnetic resonance (NMR) signal enhancements exhibit a sensitive behavior depending on the chemical environment differing from isomer to isomer. The solvation or association of asphalt in xylene isomers at room temperature is revealed. Quantum chemical calculations for the xylene isomers with the electronic and optical properties; absorption wavelengths, excitation energy, atomic charges, dipole moment and frontier molecular orbital energies, molecular electrostatic potential; are carried out using the density functional theory (DFT) method (B3LYP) with the 6-311G(d,p) basis set by the standard Gaussian 09 software package program. The relative importance of scalar and translational dipolar interaction parameters determined in dynamic nuclear polarization experiments is explained by the electronic structure of HOMO?LUMO of the xylene isomers.

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.

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