title: Gd(iii) and Mn(ii) complexes for dynamic nuclear polarization: small molecular chelate polarizing agents and applications with site-directed spin labeling of proteins.
abstract: We investigate complexes of two paramagnetic metal ions Gd3+and Mn2+to serve as polarizing agents for solid-state dynamic nuclear polarization (DNP) of1H,13C, and15N 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 as13C and even15N via the solid effect. We demonstrate that enhancements observed are limited by the available microwave power and that large enhancement factors of >100 (for1H) and on the order of 1000 (for13C) 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 between13C and15N, 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.
authors.affiliation: 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. corzilius@em.uni-frankfurt.de.
authors.forename: Monu
authors.initials: M
authors.lastname: Kaushik
authors.forename: Thorsten
authors.initials: T
authors.lastname: Bahrenberg
authors.forename: Thach V
authors.initials: TV
authors.lastname: Can
authors.forename: Marc A
authors.initials: MA
authors.lastname: Caporini
authors.forename: Robert
authors.initials: R
authors.lastname: Silvers
authors.forename: Jörg
authors.initials: J
authors.lastname: Heiliger
authors.forename: Albert A
authors.initials: AA
authors.lastname: Smith
authors.forename: Harald
authors.initials: H
authors.lastname: Schwalbe
authors.forename: Robert G
authors.initials: RG
authors.lastname: Griffin
authors.forename: Björn
authors.initials: B
authors.lastname: Corzilius
mesh_terms: D002614:Chelating Agents / Q000737:chemistry*; D005682:Gadolinium / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008345:Manganese / Q000737:chemistry; D009942:Organometallic Compounds / Q000737:chemistry*; D011506:Proteins / Q000737:chemistry*; D011789:Quantum Theory; D054852:Small Molecule Libraries / Q000737:chemistry*
chemical_list: D002614:Chelating Agents; D009942:Organometallic Compounds; D011506:Proteins; D054852:Small Molecule Libraries; D008345:Manganese; D005682:Gadolinium