title: Large molecular weight nitroxide biradicals providing efficient dynamic nuclear polarization at temperatures up to 200 K.
abstract: A series of seven functionalized nitroxide biradicals (the bTbK biradical and six derivatives) are investigated as exogenous polarization sources for dynamic nuclear polarization (DNP) solid-state NMR at 9.4 T and with ca. 100 K sample temperatures. The impact of electron relaxation times on the DNP enhancement (ε) is examined, and we observe that longer inversion recovery and phase memory relaxation times provide larger ε. All radicals are tested in both bulk 1,1,2,2-tetrachloroethane solutions and in mesoporous materials, and the difference in ε between the two cases is discussed. The impact of the sample temperature and magic angle spinning frequency on ε is investigated for several radicals each characterized by a range of electron relaxation times. In particular, TEKPol, a bulky derivative of bTbK with a molecular weight of 905 g·mol(-1), is presented. Its high-saturation factor makes it a very efficient polarizing agent for DNP, yielding unprecedented proton enhancements of over 200 in both bulk and materials samples at 9.4 T and 100 K. TEKPol also yields encouraging enhancements of 33 at 180 K and 12 at 200 K, suggesting that with the continued improvement of radicals large ε may be obtained at higher temperatures.
authors: Centre de RMN à Très Hauts Champs, Institut de Sciences Analytiques, Université de Lyon (CNRS/ENS Lyon/UCB Lyon 1), 69100 Villeurbanne, France.
authors: Alexandre
authors: A
authors: Zagdoun
authors: Gilles
authors: G
authors: Casano
authors: Olivier
authors: O
authors: Ouari
authors: Martin
authors: M
authors: Schwarzwälder
authors: Aaron J
authors: AJ
authors: Rossini
authors: Fabien
authors: F
authors: Aussenac
authors: Maxim
authors: M
authors: Yulikov
authors: Gunnar
authors: G
authors: Jeschke
authors: Christophe
authors: C
authors: Copéret
authors: Anne
authors: A
authors: Lesage
authors: Paul
authors: P
authors: Tordo
authors: Lyndon
authors: L
authors: Emsley
mesh_terms: D005609:Free Radicals / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D008970:Molecular Weight; D009589:Nitrogen Oxides / Q000737:chemistry*; D013696:Temperature
chemical_list: D005609:Free Radicals; D009589:Nitrogen Oxides