Photoinduced Nonpersistent Radicals as Polarizing Agents for X-Nuclei Dissolution Dynamic Nuclear Polarization

Capozzi, Andrea; Hyacinthe, Jean-Noël; Tian, Chen; Eichhorn, Tim; Boero, Giovanni; Roussel, Christophe; Klink, J. J. van der; Comment, Arnaud

doi:10.1021/acs.jpcc.5b07315

Cited by 37 publications

(66 citation statements)

References 28 publications

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“…17,18,20,21,31,34,49 Trityl OX063, the stable organic radical used in this work, has a very narrow EPR linewidth that makes it ideal for polarizing low-γ nuclei such as 13 C. When using this free radical to polarize low-γ nuclei such as 13 C spins, DNP data at 3.35 T and temperatures close to 1 K have shown indications of thermal mixing (TM) as the predominant DNP mechanism. 24,[50][51][52][53] Other DNP data at similar conditions suggested that the mechanism could be a combination of the solid effect (SE) and cross effect (CE).…”

Section: Resultsmentioning

confidence: 99%

“…In dissolution DNP, organic free radicals including trityls and nitroxides are most commonly used as the polarizing agents. 16,17 Other radicals such as BDPA, 18 DPPH, 19 and galvinoxyl 20 have been used with some success as well as novel methods such as photoinduced radicals 21 and paramagnetic centers within nanoparticles. 22,23 Nitroxide free radicals have relatively wide EPR linewidths, which are better suited for DNP of high-γ nuclei such as 1 H spins and also provide decent polarization levels for low-γ nuclei such as 13 C. 24 This class of free radicals maintain their popularity by being comparatively inexpensive, highly water soluble, easily scavenged, and effective for cross polarization DNP.…”

Section: Introductionmentioning

confidence: 99%

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Influence of Dy3+ and Tb3+ doping on 13C dynamic nuclear polarization

Niedbalski

Parish

Kiswandhi

et al. 2017

The Journal of Chemical Physics

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Dynamic nuclear polarization (DNP) is a technique that uses a microwave-driven transfer of high spin alignment from electrons to nuclear spins. This is most effective at low temperature and high magnetic field, and with the invention of the dissolution method, the amplified nuclear magnetic resonance (NMR) signals in the frozen state in DNP can be harnessed in the liquid-state at physiologically acceptable temperature for in vitro and in vivo metabolic studies. A current optimization practice in dissolution DNP is to dope the sample with trace amounts of lanthanides such as Gd 3+ or Ho 3+ , which further improves the polarization. While Gd 3+ and Ho 3+ have been optimized for use in dissolution DNP, other lanthanides have not been exhaustively studied for use in 13 C DNP applications. In this work, two additional lanthanides with relatively high magnetic moments, Dy 3+ and Tb 3+ , were extensively optimized and tested as doping additives for 13 C DNP at 3.35 T and 1.2 K. We have found that both of these lanthanides are also beneficial additives, to a varying degree, for 13 C DNP. The optimal concentrations of Dy 3+ (1.5 mM) and Tb 3+ (0.25 mM) for 13 C DNP were found to be less than that of Gd 3+ (2 mM). W-band electron paramagnetic resonance shows that these enhancements due to Dy 3+ and Tb 3+ doping are accompanied by shortening of electron T 1 of trityl OX063 free radical. Furthermore, when dissolution was employed, Tb 3+ -doped samples were found to have similar liquid-state 13 C NMR signal enhancements compared to samples doped with Gd 3+ , and both Tb 3+ and Dy 3+ had a negligible liquid-state nuclear T 1 shortening effect which contrasts with the significant reduction in T 1 when using Gd 3+ . Our results show that Dy 3+ doping and Tb 3+ doping have a beneficial impact on 13 C DNP both in the solid and liquid states, and that Tb 3+ in particular could be used as a potential alternative to Gd 3+ in 13 C dissolution DNP experiments. Published by AIP Publishing.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Influence of Dy3+ and Tb3+ doping on 13C dynamic nuclear polarization

Niedbalski

Parish

Kiswandhi

et al. 2017

The Journal of Chemical Physics

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“…The maximum concentration was approximated by calibration with standard solutions of TEMPO in benzene under identical conditions (Figure S15). 10, 16 The number of radicals generated by 1 (4.5 mg) is similar to a 5.4 µM stock solution (0.1 mL), which is equivalent to a radical forming in ~0.01% of the macrocycles.…”

Section: Resultsmentioning

confidence: 99%

“…9,10 Instead, the quasi-stable, short-lived UV-induced radicals were shown to afford sizeable DNP enhancements at low temperatures. 9, 10 Larger DNP enhancements are possible in solution and have been observed in frozen media under constant irradiation (photochemically induced DNP). 11 With exogenous radicals, optimum concentration is key, as high radical concentration can result in excessive paramagnetic relaxation and line broadening.…”

Section: Introductionmentioning

confidence: 99%

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Persistent Radicals of Self‐assembled Benzophenone bis‐Urea Macrocycles: Characterization and Application as a Polarizing Agent for Solid‐state DNP MAS Spectroscopy

DeHaven

Tokarski

Korous

et al. 2017

Chemistry A European J

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UV-irradiation of a self-assembled benzophenone bis-urea macrocycle generates µM amounts of radicals that persist for weeks under ambient conditions. High-Field EPR and variable temperature X-band EPR studies suggest a resonance stabilized radical pair through H-abstraction. These endogenous radicals were applied as a polarizing agent for magic angle spinning (MAS) dynamic nuclear polarization (DNP) NMR enhancement. The field-stepped DNP enhancement profile exhibits a sharp peak with a maximum enhancement of εon/off = 4 superimposed on a nearly constant DNP enhancement of εon/off = 2 over a broad field range. This maximum coincides with the high field EPR absorption spectrum, consistent with an Overhauser effect mechanism. DNP enhancement was observed for both the host and guests, suggesting that even low levels of endogenous radicals can facilitate the study of host-guest relationships in the solid-state.

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Tailored Microstructured Hyperpolarizing Matrices for Optimal Magnetic Resonance Imaging

et al. 2018

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Tailoring the physical features and the porous network architecture of silica-based hyperpolarizing solids containing TEMPO radicals,k nowna sH YPSO (hybrid polarizing solids), enabled unprecedented performance of dissolution dynamic nuclear polarization (d-DNP). High polarization values up to P( 1 H) = 99 %w ere reached for samples impregnated with am ixture of H 2 O/D 2 Oa nd loaded in a6 .7 Tp olarizer at temperatures around 1.2 K. These HYPSO materials combine the best performance of homogeneous DNP formulations with the advantages of solid polarizing matrices,whichprovidehyperpolarized solutions free of any-potentially toxic-additives (radicals and glass-forming agents). The hyperpolarized solutions can be expelled from the porous solids,f iltered, and rapidly transferred either to an uclear magnetic resonance (NMR) spectrometer or to amagnetic resonance imaging (MRI) system.Supportinginformation and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.

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Photoinduced Nonpersistent Radicals as Polarizing Agents for X-Nuclei Dissolution Dynamic Nuclear Polarization

Cited by 37 publications

References 28 publications

Influence of Dy3+ and Tb3+ doping on 13C dynamic nuclear polarization

Influence of Dy3+ and Tb3+ doping on 13C dynamic nuclear polarization

Persistent Radicals of Self‐assembled Benzophenone bis‐Urea Macrocycles: Characterization and Application as a Polarizing Agent for Solid‐state DNP MAS Spectroscopy

Tailored Microstructured Hyperpolarizing Matrices for Optimal Magnetic Resonance Imaging

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