Polarizing agents for efficient high field DNP solid-state NMR spectroscopy under magic-angle spinning: from design principles to formulation strategies

Menzildjian, Georges; Schlagnitweit, Judith; Casano, Gilles; Ouari, Olivier; Gajan, David; Lesage, Anne

doi:10.1039/d3sc01079a

“…Sample preparation is the first difficulty, where the polymer has to be intimately mixed with a low amount of DNP polarizing agent to enable the occurrence of polarization transfer between electrons and nuclei, typically protons, under continuous microwave irradiation . Thus, the polarizing agent needs to be carefully designed and chosen for obtaining remarkable signal enhancement, depending on the external static magnetic field, MAS frequency, experimental temperature, and DNP mechanism. − In addition, the DNP experiments are usually performed at a cryogenic temperature as low as 100 K. Such a low temperature is typically necessary in order to reduce the proton and electron spin–lattice relaxation ( T 1 ) rate and thus to improve the electron–proton polarization transfer efficiency. , In the meantime, the increased proton T 1 at a low temperature can facilitate relaying the enhanced proton polarization (obtained from electrons) to remote protons via spin diffusion over large length scale, leading to uniform signal enhancement of all protons. Nevertheless, for polymers containing methyl groups, the C 3 rotation motions of methyl groups even at the very low temperature may result in the reduction of proton T 1 , leading to insufficient spin diffusion, nonuniform signal enhancement, and significant reduction of DNP signal enhancement .…”

Section: Sensitivity-enhanced Ssnmr Techniquesmentioning

confidence: 99%

Elucidations of Structure and Molecular Dynamics of Complex Polymers by State-of-the-Art Solid-State NMR Spectroscopy

Zhang,

Chen,

Miyoshi

2024

Macromolecules

1

0

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Solid-state nuclear magnetic resonance (ssNMR) has been playing an indispensable role in revealing the interplay of structure and molecular dynamics in polymers at different states. In this Perspective, we first provide an overview about the fundamental spin interactions in ssNMR and then highlight some recent progress on sensitivity-enhanced ssNMR spectroscopy and in situ NMR. Moreover, we highlight ssNMR applications in the field of polymer crystallization, molecular dynamics, chemical reactions, supramolecular polymers, energy materials, and so on. Finally, our personal perspective is given on the future development at the crossroad of ssNMR and polymer science.

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“…[1,8] The structural and electronic nature of the bridge results in a varying degree of interaction between the two unpaired electrons relevant for the usage as polarizing agents in DNP (Dynamic Nuclear Polarization) NMR spectroscopy. [4,[9][10][11] Here we want to report on a novel phosphorus-centered disbiradical and its electronic and chemical properties.…”

mentioning

confidence: 99%

Rational Design of a Phosphorus‐Centered Disbiradical

Rosenboom,

Taube,

Teichmeier

et al. 2024

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Phosphorus‐centered disbiradicals, in which the radical sites exist as individual spin doublets with weak spin‐spin interaction have not been known so far. Starting from monoradicals of the type [•P(μ‐NTer)2P–R], we have now succeeded in linking two such monoradical phosphorus centers by appropriate choice of a linker. To this end, biradical [•P(μ‑NTer)2P•] (1) was treated with 1,6‐dibromohexane, affording the brominated species {Br[P(μ‐NTer)]2}2C6H12 (3). Subsequent reduction with KC8 led to the formation of the disbiradical {•[P(μ‐NTer)]2}2C6H12 (4) featuring a large distance between the radical phosphorus sites in the solid state and formally the highest biradical character observed in a P‐centered biradical so far, approaching 100%. EPR spectroscopy revealed a three‐line signal in solution with a considerably larger exchange interaction than would be expected from the molecular structure of the single crystal. Quantum chemical calculations revealed a highly dynamic conformational space; thus, the two radical sites can approach each other with a much smaller distance in solution. Further reduction of 4 resulted in the formation of a potassium salt featuring the first structurally characterized P‐centered distonic radical anion (5–). Moreover, 4 could be used in small molecule activation.

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“…[1,8] Die strukturelle und elektronische Natur der Brücke führt zu einem unterschiedlichen Grad an Wechselwirkung zwischen den beiden ungepaarten Elektronen, die für die Verwendung als polarisierende Reagenzien in der DNP-(Dynamic Nuclear Polarization) NMR-Spektroskopie relevant sind. [4,[9][10][11] Hier wollen wir über ein neuartiges phosphor-zentriertes Disbiradikal und seine elektronischen und chemischen Eigenschaften berichten.…”

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Design eines Phosphor‐zentrierten Disbiradikals

Rosenboom,

Taube,

Teichmeier

et al. 2024

Angewandte Chemie

0

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Phosphorus‐centered disbiradicals, in which the radical sites exist as individual spin doublets with weak spin‐spin interaction have not been known so far. Starting from monoradicals of the type [•P(μ‐NTer)2P–R], we have now succeeded in linking two such monoradical phosphorus centers by appropriate choice of a linker. To this end, biradical [•P(μ‑NTer)2P•] (1) was treated with 1,6‐dibromohexane, affording the brominated species {Br[P(μ‐NTer)]2}2C6H12 (3). Subsequent reduction with KC8 led to the formation of the disbiradical {•[P(μ‐NTer)]2}2C6H12 (4) featuring a large distance between the radical phosphorus sites in the solid state and formally the highest biradical character observed in a P‐centered biradical so far, approaching 100%. EPR spectroscopy revealed a three‐line signal in solution with a considerably larger exchange interaction than would be expected from the molecular structure of the single crystal. Quantum chemical calculations revealed a highly dynamic conformational space; thus, the two radical sites can approach each other with a much smaller distance in solution. Further reduction of 4 resulted in the formation of a potassium salt featuring the first structurally characterized P‐centered distonic radical anion (5–). Moreover, 4 could be used in small molecule activation.

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Polarizing agents for efficient high field DNP solid-state NMR spectroscopy under magic-angle spinning: from design principles to formulation strategies

Abstract: Dynamic Nuclear Polarization (DNP) has recently emerged as a cornerstone approach to enhance the sensitivity of solid-state NMR spectroscopy under Magic Angle Spinning (MAS), opening unprecedented analytical opportunities in chemistry...

Cited by 15 publications

References 195 publications

Elucidations of Structure and Molecular Dynamics of Complex Polymers by State-of-the-Art Solid-State NMR Spectroscopy

Elucidations of Structure and Molecular Dynamics of Complex Polymers by State-of-the-Art Solid-State NMR Spectroscopy

Rational Design of a Phosphorus‐Centered Disbiradical

Design eines Phosphor‐zentrierten Disbiradikals

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