Developing DNP/Solid-State NMR Spectroscopy of Oriented Membranes
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Dynamic nuclear polarization (DNP)/solid-state nuclear magnetic resonance (NMR) spectroscopy bears great potential for the investigation of membrane-associated polypeptides which can often be produced only in small amounts and which need to be ‘diluted’ in lipid bilayer environments to adopt or maintain their functional structure. Here we present investigations using biradicals, such as TOTAPOL and bTbK, for solid-state NMR signal enhancement using DNP in the context of lipid membranes. By transferring polarization from electron to nuclear spins using microwave irradiation signal enhancement factors of up to 13 are obtained with TOTAPOL and up to 17 with bTbK. The possible reasons why these factors are below those obtained in glassy samples of bulk solvents (40–60 under similar conditions) are evaluated and discussed. In order to further ameliorate the enhancement factors the physico-chemical characteristics of TEMPOL, TOTAPOL, bTbK, and bCTbK, such as their partitioning between hydrophilic and hydrophobic solvents or their stability under different environmental conditions are presented. Finally, having provided proof-of-concept that DNP/solid-state NMR measurements can be performed with oriented membrane samples work in progress is presented on the development of a flat-coil probe for DNP/solid-state NMR experiments on oriented membranes.
KeywordsNuclear Magnetic Resonance Nuclear Magnetic Resonance Spectroscopy Dynamic Nuclear Polarization Magic Angle Spin Nuclear Magnetic Resonance Experiment
We are grateful to Ralph Weber from Bruker BioSpin for acquiring EPR spectra and the EPR service of the University of Strasbourg for access to their spectrometers. The discussions with Fabien Aussenac and Werner Maas have provided valuable insight and helped us to advance with this work. We acknowledge the Bio-NMR European Commission’s Program 7 (FP7), project number 261863, BIO-NMR 00060 for access to DNP/solid-state NMR instrumentation in Berlin. The financial support by the CNRS (grant to support H.S.), the RTRA Foundation International Center for Frontier Research in Chemistry, Strasbourg and the University of Strasbourg (PPF RMN) is gratefully acknowledged. The Bechinger laboratory is grateful to the Institute of Supramolecular Chemistry for hosting the team.
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