540 Chemie und zugeordnete Wissenschaften
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Nuclear magnetic resonance (NMR) spectroscopy is a powerful and popular technique for probing the molecular structures, dynamics and chemical properties. However the conventional NMR spectroscopy is bottlenecked by its low sensitivity. Dynamic nuclear polarization (DNP) boosts NMR sensitivity by orders of magnitude and resolves this limitation. In liquid-state this revolutionizing technique has been restricted to a few specific non-biological model molecules in organic solvents. Here we show that the carbon polarization in small biological molecules, including carbohydrates and amino acids, can be enhanced sizably by in situ Overhauser DNP (ODNP) in water at room temperature and at high magnetic field. An observed connection between ODNP 13C enhancement factor and paramagnetic 13C NMR shift has led to the exploration of biologically relevant heterocyclic compound indole. The QM/MM MD simulation underscores the dynamics of intermolecular hydrogen bonds as the driving force for the scalar ODNP in a long-living radical-substrate complex. Our work reconciles results obtained by DNP spectroscopy, paramagnetic NMR and computational chemistry and provides new mechanistic insights into the high-field scalar ODNP.
Wir untersuchen eine neuartige Gruppe von Polarisationsmitteln – gemischtvalente Verbindungen – mittels theoretischer und experimenteller Methoden und demonstrieren ihre Leistungsfähigkeit in NMR-Experimenten mit Hochfeld-DNP (DNP=Dynamic Nuclear Polarization, dynamische Kernpolarisation) im festen Zustand. Diese gemischtvalenten Verbindungen stellen eine Gruppe von Molekülen dar, bei denen die molekulare Mobilität auch in Festkörpern erhalten bleibt. Folglich können solche Polarisationsmittel unter günstigen Bedingungen für die dynamische Kernpolarisationsbildung bei ultrahohen Magnetfeldern verwendet werden, um Overhauser-DNP-Experimente im Festkörper durchzuführen.
Mixed-valence compounds as polarizing agents for overhauser dynamic nuclear polarization in solids
(2021)
Herein, we investigate a novel set of polarizing agents—mixed-valence compounds—by theoretical and experimental methods and demonstrate their performance in high-field dynamic nuclear polarization (DNP) NMR experiments in the solid state. Mixed-valence compounds constitute a group of molecules in which molecular mobility persists even in solids. Consequently, such polarizing agents can be used to perform Overhauser-DNP experiments in the solid state, with favorable conditions for dynamic nuclear polarization formation at ultra-high magnetic fields.