Solid-Phase Polarization Matrixes for Dynamic Nuclear Polarization from Homogeneously Distributed Radicals in Mesostructured Hybrid Silica Materials
2013
Gajan, David | Schwarzwälder, Martin | Conley, Matthew P. | Grüning, Wolfram R. | Rossini, Aaron J. | Zagdoun, Alexandre | Lelli, Moreno | Yulikov, Maxim | Jeschke, Gunnar | Sauvée, Claire | Ouari, Olivier | Tordo, Paul | Veyre, Laurent | Lesage, Anne | Thieuleux, Chloé | Emsley, Lyndon | Copéret, Christophe
Mesoporous hybrid silica–organic materials containing homogeneously distributed stable mono- or dinitroxide radicals covalently bound to the silica surface were developed as polarization matrixes for solid-state dynamic nuclear polarization (DNP) NMR experiments. For TEMPO-containing materials impregnated with water or 1,1,2,2-tetrachloroethane, enhancement factors of up to 36 were obtained at ∼100 K and 9.4 T without the need for a glass-forming additive. We show that the homogeneous radical distribution and the subtle balance between the concentration of radical in the material and the fraction of radicals at a sufficient inter-radical distance to promote the cross-effect are the main determinants for the DNP enhancements we obtain. The material, as well as an analogue containing the poorly soluble biradical bTUrea, is used as a polarizing matrix for DNP NMR experiments of solutions containing alanine and pyruvic acid. The analyte is separated from the polarization matrix by simple filtration.
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