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Solid-Phase Polarization Matrixes for Dynamic Nuclear Polarization from Homogeneously Distributed Radicals in Mesostructured Hybrid Silica Materials

2013; American Chemical Society; Volume: 135; Issue: 41 Linguagem: Inglês

10.1021/ja405822h

1943-2984

David Gajan, Martin Schwarzwälder, Matthew P. Conley, W Grüning, Aaron J. Rossini, Alexandre Zagdoun, Moreno Lelli, Maxim Yulikov, Gunnar Jeschke, Claire Sauvée, Olivier Ouari, Paul Tordo, Laurent Veyre, Anne Lesage, Chloé Thieuleux, Lyndon Emsley, Christophe Copéret,

Electron Spin Resonance Studies

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.