A High-Conversion-Factor, Double-Resonance Structure for High-Field Dynamic Nuclear Polarization

Annino, G.; Villanueva-Garibay, J. A.; Bentum, P.J.M. van; Klaassen, A. A. K.; Kentgens, A.P.M.

doi:10.1007/s00723-009-0091-6

Cited by 24 publications

(25 citation statements)

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“…In comparison, EPR and ENDOR resonators are able to achieve much higher average B 1 S values per W 1/2 and improved homogeneity. Specifically, by using low order metallic resonant structures and sample volumes that occupy a small fraction of the resonator, B 1 S values on the order of 1 mT/W 1/2 have been reported [51, 52, 53]. However, to optimize S/N in MAS DNP experiments, large sample volumes are required.…”

Section: Discussionmentioning

confidence: 99%

Microwave field distribution in a magic angle spinning dynamic nuclear polarization NMR probe

Nanni

Barnes

Matsuki

et al. 2011

Journal of Magnetic Resonance

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We present a calculation of the microwave field distribution in a magic angle spinning (MAS) probe utilized in dynamic nuclear polarization (DNP) experiments. The microwave magnetic field (B 1S ) profile was obtained from simulations performed with the High Frequency Structure Simulator (HFSS) software suite, using a model that includes the launching antenna, the outer Kel-F stator housing coated with Ag, the RF coil, and the 4 mm diameter sapphire rotor containing the sample. The predicted average B 1S field is 13µT/W 1/2 , where S denotes the electron spin. For a routinely achievable input power of 5 W the corresponding value is γ SB 1S = 0.84 MHz. The calculations provide insights into the coupling of the microwave power to the sample, including reflections from the RF coil and diffraction of the power transmitted through the coil. The variation of enhancement with rotor wall thickness was also successfully simulated. A second, simplified calculation was performed using a single pass model based on Gaussian beam propagation and Fresnel diffraction. This model provided additional physical insight and was in good agreement with the full HFSS simulation. These calculations indicate approaches to increasing the coupling of the microwave power to the sample, including the use of a converging lens and fine adjustment of the spacing of the windings of the RF coil. The present results should prove useful in optimizing the coupling of microwave power to the sample in future DNP experiments. Finally, the results of the simulation were used to predict the cross effect DNP enhancement (ε) vs. ω 1S /(2π) for a sample of 13 C-urea dissolved in a 60:40 glycerol/water mixture containing the polarizing agent TOTAPOL; very good agreement was obtained between theory and experiment.

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Section: Discussionmentioning

confidence: 99%

Microwave field distribution in a magic angle spinning dynamic nuclear polarization NMR probe

Nanni

Barnes

Matsuki

et al. 2011

Journal of Magnetic Resonance

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“…[36]. The novel non-radiative microwave resonator design presented by Annino et al [37, 38] provides very high ESR performance at 95 GHz, easily integrates DNP functionality, and can be fabricated from commonly available materials. Researchers have also employed ODNP hyperpolarization to enhance perfusion imaging, where the first proof of principle application by Han et al [39] was followed by further development and applications at 10 GHz (ESR) [40–43], an extension to higher frequencies (35 GHz ESR) by Krummenacher et al [44], and a recent in vivo study demonstrating enhanced visualization of brain perfusion in a live rat [45].…”

Section: Reviewmentioning

confidence: 99%

Quantitative cw Overhauser effect dynamic nuclear polarization for the analysis of local water dynamics

Franck

Pavlova

Scott

et al. 2013

Progress in Nuclear Magnetic Resonance Spectroscopy

118

237

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Liquid state Overhauser Effect Dynamic Nuclear Polarization (ODNP) has experienced a recent resurgence of interest. The ODNP technique described here relies on the double resonance of electron spin resonance (ESR) at the most common, i.e. X-band (~ 10 GHz), frequency and 1H nuclear magnetic resonance (NMR) at ~ 15 MHz. It requires only a standard continuous wave (cw) ESR spectrometer with an NMR probe inserted or built into an X-band cavity. Our focus lies on reviewing a new and powerful manifestation of ODNP as a high frequency NMR relaxometry tool that probes dipolar cross relaxation between the electron spins and the 1H nuclear spins at X-band frequencies. This technique selectively measures the translational mobility of water within a volume extending 0.5–1.5 nm outward from a nitroxide radical spin probe that is attached to a targeted site of a macromolecule. This method has been applied to study the dynamics of water that hydrates or permeates the surface or interior of proteins, polymers, and lipid membrane vesicles. We begin by reviewing the recent advances that have helped develop ODNP into a tool for mapping the dynamic landscape of hydration water with sub-nanometer locality. In order to bind this work coherently together, and to place it in the context of the extensive body of research in the field of NMR relaxometry, we then rephrase the analytical model and extend the description of the ODNP-derived NMR signal enhancements. This extended model highlights several aspects of ODNP data analysis, including the importance of considering all possible effects of microwave sample heating, the need to consider the error associated with various relaxation rates, and the unique ability of ODNP to probe the electron–1H cross-relaxation process, which is uniquely sensitive to fast (tens of ps) dynamical processes. By implementing the relevant corrections in a stepwise fashion, this paper draws a consensus result from previous ODNP procedures, and then shows how such data can be further corrected to yield clear and reproducible saturation of the NMR hyperpolarization process. Finally, drawing on these results, we broadly survey the previous ODNP dynamics literature. We find that the vast number of published, empirical hydration dynamics data can be reproducibly classified into regimes of surface, interfacial, vs buried water dynamics.

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“…It is noteworthy to know that DNP can occur in the liquid state at high magnetic fields (3–9 T) [55; 56; 57]. For example, OE DNP enhancements with factors of > 100 at 5 T and room temperatures were observed in a low-dielectric solvent with solutes undergoing transient contacts with BDPA that modulate the scalar electron-nuclear interactions [58*].…”

Section: Introductionmentioning

confidence: 99%

Polarizing agents and mechanisms for high-field dynamic nuclear polarization of frozen dielectric solids

2011

Solid State Nuclear Magnetic Resonance

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This article provides an overview of polarizing mechanisms involved in high-frequency dynamic nuclear polarization (DNP) of frozen biological samples at temperatures maintained using liquid nitrogen, compatible with contemporary magic-angle spinning (MAS) nuclear magnetic resonance (NMR). Typical DNP experiments require unpaired electrons that are usually exogenous in samples via paramagnetic doping with polarizing agents. Thus, the resulting nuclear polarization mechanism depends on the electron and nuclear spin interactions induced by the paramagnetic species. The Overhauser Effect (OE) DNP, which relies on time-dependent spin-spin interactions, is excluded from our discussion due the lack of conducting electrons in frozen aqueous solutions containing biological entities. DNP of particular interest to us relies primarily on time-independent, spin interactions for significant electron-nucleus polarization transfer through mechanisms such as the Solid Effect (SE), the Cross Effect (CE) or Thermal Mixing (TM), involving one, two or multiple electron spins, respectively. Derived from monomeric radicals initially used in DNP experiments, bi- or multiple-radical polarizing agents facilitate CE/TM to generate significant NMR signal enhancements in dielectric solids at low temperatures (< 100 K). For example, large DNP enhancements (~300 times at 5 T) from a biologically compatible biradical, 1-(TEMPO-4-oxy)-3-(TEMPO-4-amino)propan-2-ol (TOTAPOL), have enabled high-resolution MAS NMR in sample systems existing in submicron domains or embedded in larger biomolecular complexes. The scope of this review is focused on recently developed DNP polarizing agents for high-field applications and leads up to future developments per the CE DNP mechanism. Because DNP experiments are feasible with a solid-state microwave source when performed at <20 K, nuclear polarization using lower microwave power (< 100 mW) is possible by forcing a high proportion of biradicals to fulfill the frequency matching condition of CE (two EPR frequencies separated by the NMR frequency) using the strategies involving hetero-radical moieties and/or molecular alignment. In addition, the combination of an excited triplet and a stable radical might provide alternative DNP mechanisms without the microwave requirement.

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A High-Conversion-Factor, Double-Resonance Structure for High-Field Dynamic Nuclear Polarization

Cited by 24 publications

References 50 publications

Microwave field distribution in a magic angle spinning dynamic nuclear polarization NMR probe

Microwave field distribution in a magic angle spinning dynamic nuclear polarization NMR probe

Quantitative cw Overhauser effect dynamic nuclear polarization for the analysis of local water dynamics

Polarizing agents and mechanisms for high-field dynamic nuclear polarization of frozen dielectric solids

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