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      Gd(III) and Mn(II) complexes for dynamic nuclear polarization: small molecular chelate polarizing agents and applications with site-directed spin labeling of proteins

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          Abstract

          We investigate complexes of two paramagnetic metal ions Gd 3+ and Mn 2+ to serve as polarizing agents for solid-state dynamic nuclear polarization (DNP) of 1H, 13C, and 15N at magnetic fields of 5, 9.4, and 14.1 T. Both ions are half-integer high-spin systems with a zero-field splitting and therefore exhibit a broadening of the m S = −½ ↔ +½ central transition which scales inversely with the external field strength. We investigate experimentally the influence of the chelator molecule, strong hyperfine coupling to the metal nucleus, and deuteration of the bulk matrix on DNP properties. At small Gd-DOTA concentrations the narrow central transition allows us to polarize nuclei with small gyromagnetic ratio such as 13C and even 15N via the solid effect. We demonstrate that enhancements observed are limited by the available microwave power and that large enhancement factors of >100 (for 1H) and on the order of 1000 (for 13C) can be achieved in the saturation limit even at 80 K. At larger Gd(III) concentrations (≥ 10 mM) where dipolar couplings between two neighboring Gd 3+ complexes become substantial a transition towards cross effect as dominating DNP mechanism is observed. Furthermore, the slow spin-diffusion between 13C and 15N, respectively, allows for temporally resolved observation of enhanced polarization spreading from nuclei close to the paramagnetic ion towards nuclei further removed. Subsequently, we present preliminary DNP experiments on ubiquitin by site-directed spin-labeling with Gd 3+ chelator tags. The results hold promise towards applications of such paramagnetically labeled proteins for DNP applications in biophysical chemistry and/or structural biology.

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          Author and article information

          Journal
          100888160
          32386
          Phys Chem Chem Phys
          Phys Chem Chem Phys
          Physical chemistry chemical physics : PCCP
          1463-9076
          1463-9084
          2 September 2016
          22 August 2016
          21 October 2016
          21 October 2017
          : 18
          : 39
          : 27205-27218
          Affiliations
          [1 ]Institute of Physical and Theoretical Chemistry and Institute of Biophysical Chemistry, Goethe University Frankfurt, Max-von-Laue-Str. 7-9, 60438 Frankfurt am Main, Germany
          [2 ]Center for Biomolecular Magnetic Resonance (BMRZ), Goethe University Frankfurt, Max-von-Laue-Str. 9, 60438 Frankfurt am Main, Germany
          [3 ]Francis Bitter Magnet Laboratory and Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA
          [4 ]Bruker Biospin Ltd., Billerica, Massachusetts 01821, United States
          [5 ]Institute of Organic Chemistry and Chemical Biology, Goethe University Frankfurt, Max-von-Laue-Str. 7, 60438 Frankfurt am Main, Germany
          Author notes
          [§]

          present address: Department of Chemical Physics, Weizmann Institute of Science, 76100 Rehovot, Israel

          [†]

          present address: Amgen, Inc., 360 Binney Street, Cambridge, Massachusetts 02142, United States

          [‡]

          present address: Department of Chemistry and Applied Biosciences, Laboratory of Physical Chemistry, ETH-Zürich, CH-8093 Zürich, Switzerland

          [* ]corresponding author: corzilius@ 123456em.uni-frankfurt.de
          Article
          PMC5053914 PMC5053914 5053914 nihpa812163
          10.1039/c6cp04623a
          5053914
          27545112
          9fa5eb33-684d-477c-a594-a36e40470bce
          History
          Categories
          Article

          polarizing agent,dynamic nuclear polarization,magic-angle spinning NMR,high-spin metal ion,site-directed spin-labeling

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