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Bis‐Gadolinium Complexes for Solid Effect and Cross Effect Dynamic Nuclear Polarization

Abstract

High‐spin complexes act as polarizing agents (PAs) for dynamic nuclear polarization (DNP) in solid‐state NMR spectroscopy and feature promising aspects towards biomolecular DNP. We present a study on bis(Gd‐chelate)s which enable cross effect (CE) DNP owing to spatial confinement of two dipolar‐coupled electron spins. Their well‐defined Gd⋅⋅⋅Gd distances in the range of 1.2–3.4 nm allowed us to elucidate the Gd⋅⋅⋅Gd distance dependence of the DNP mechanism and NMR signal enhancement. We found that Gd⋅⋅⋅Gd distances above 2.1 nm result in solid effect DNP while distances between 1.2 and 2.1 nm enable CE for 1H, 13C, and 15N nuclear spins. We compare 263 GHz electron paramagnetic resonance (EPR) spectra with the obtained DNP field profiles and discuss possible CE matching conditions within the high‐spin system and the influence of dipolar broadening of the EPR signal. Our findings foster the understanding of the CE mechanism and the design of high‐spin PAs for specific applications of DNP.

Bis‐Gd‐Komplexe wurden als Polarisationsmittel für die dynamische Kernpolarisation (DNP) untersucht. Bei Verkleinerung des Abstandes zwischen den beiden GdIII‐Ionen wird ein Übergang vom „Solid‐Effect”‐ zum „Cross‐Effect”‐DNP‐Mechanismus beobachtet. Die Analyse der NMR‐Signalverstärkungen für 1H, 13C und 15N gibt Aufschluss über die Abstandsabhängigkeit zwischen zwei Elektronenspins für den Kreuzeffekt.

Authors:   Monu Kaushik, Mian Qi, Adelheid Godt, Björn Corzilius
Journal:   Angewandte Chemie
Volume:   129
edition:   15
Year:   2017
Pages:   4359
DOI:   10.1002/ange.201612388
Publication date:   20-Mar-2017
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