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

  • We investigate complexes of two paramagnetic metal ions Gd3+ and Mn2+ 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 mS = −1/2 ↔ +1/2 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 Gd3+ 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 Gd3+ 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:Monu Kaushik, Thorsten Bahrenberg, Thach V. Can, Marc A. Caporini, Robert Silvers, Jörg Heiliger, Albert A. Smith, Harald SchwalbeORCiDGND, Robert G. Griffin, Björn Corzilius
Pubmed Id:
Parent Title (English):Physical chemistry, chemical physics
Publisher:RSC Publ.
Place of publication:Cambridge
Document Type:Article
Date of Publication (online):2016/12/12
Date of first Publication:2016/08/12
Publishing Institution:Universitätsbibliothek Johann Christian Senckenberg
Release Date:2016/12/12
Page Number:15
First Page:27205
Last Page:27218
This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.
Institutes:Biochemie, Chemie und Pharmazie / Biochemie und Chemie
Exzellenzcluster / Exzellenzcluster Makromolekulare Komplexe
Wissenschaftliche Zentren und koordinierte Programme / Sonderforschungsbereiche / Forschungskollegs
Wissenschaftliche Zentren und koordinierte Programme / Zentrum für Biomolekulare Magnetische Resonanz (BMRZ)
Dewey Decimal Classification:5 Naturwissenschaften und Mathematik / 57 Biowissenschaften; Biologie / 570 Biowissenschaften; Biologie
Licence (German):License LogoCreative Commons - Namensnennung 3.0