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Communication Dans Un Congrès Année : 2013

Dynamic nuclear polarization surface enhanced NMR spectroscopy: the design of new biradicals enables application to challenging materials

Résumé

NMR spectroscopy (often in conjunction with diffraction methods) is the method of choice for characterizing surfaces whenever possible, but the detection limit of NMR is far too low to allow many modern materials to be examined. Because it provides dramatic sensitivity enhancement, solid-state Dynamic Nuclear Polarization (DNP) NMR is currently emerging as a powerful tool to study samples previously inaccessible to NMR. We have recently shown how DNP could be used to selectively enhance the NMR signals from surfaces in a wide range of materials (DNP SENS). While signal enhancements of between 20 and 50 are routinely obtained at 9.4 T and 100 K (for 29Si, 13C, or 27Al nuclei after cross-polarization from protons), these enhancement factors are still far from the predicted maximum values. Much effort is currently devoted to the development of ever more efficient polarizing agents. We will present a series of bTbK derivatives suitable for high-field DNP enhanced solid-state NMR spectroscopy. These biradicals differ by the functional groups at the vicinal position of the two nitroxides. We establish clear relationships between the DNP efficiencies of these new radicals and (i) their molecular weight, (ii) the number of methyl groups and (iii) their electron spin relaxation rates. In particular, a new radical is introduced, that yields proton enhancement of over 200 at 9.4 T and 100 K in bulk solution as well as in mesoporous materials. The temperature and spinning speed dependence of the DNP enhancement factors is also discussed for this new family of polarizing agents. These new polarizing agents are demonstrated through the application of DNP SENS to the characterization of periodic mesoporous organosilicates (POM). The rapid acquisition of high quality natural abundance 1D 13C, 15N, and 29Si, and 2D 1H-13C and 1H-29Si DNP solid-state NMR spectra was essential to distinguish outer and inner layers in these porous materials and to monitor their surface functionalization.
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Dates et versions

hal-00980133 , version 1 (17-04-2014)

Identifiants

  • HAL Id : hal-00980133 , version 1

Citer

Alexandre Zagdoun, Gilles Casano, Aaron J. Rossini, Martin Schwarzwalder, Wolfram R Grüning, et al.. Dynamic nuclear polarization surface enhanced NMR spectroscopy: the design of new biradicals enables application to challenging materials. EUROMAR 2013, Jun 2013, Hersonissos, Greece. ⟨hal-00980133⟩
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