Development of DNPEnhanced HighResolution Solid

Authors: Fumitaka Horii Toshitaka Idehara Yutaka Fujii Isamu Ogawa Akifumi Horii George Entzminger F David Doty

Publish Date: 2012/02/01

Volume: 33, Issue: 7, Pages: 756-765

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Abstract

A dynamic nuclear polarization DNPenhanced crosspolarization/magicangle spinning DNP/CP/MAS NMR system has been developed by combining a 200 MHz Chemagnetics CMX200 spectrometer operating at 47 T with a highpower 1315 GHz Gyrotron FU CW IV The 30 W subTHz wave generated in a long pulse TE 411 mode with a frequency of 5 Hz was successfully transmitted to the modified Doty Scientific lowtemperature CP/MAS probe through copper smoothwall circular waveguides Since serious RF noises on NMR signals by arcing in the electric circuit of the probe and undesired sample heating were induced by the continuous subTHz wave pulse irradiation with higher powers the onoff subTHz wave pulse irradiation synchronized with the NMR detection was developed and the appropriate setting of the irradiation time and the cooling time corresponding to the nonirradiation time was found to be very effective for the suppression of the arcing and the sample heating The attainable maximum DNP enhancement was more than 30 folds for C1 13 Cenriched Dglucose dissolved in the frozen medium containing monoradical 4aminoTEMPO The first DNP/CP/MAS 13 C NMR spectra of polymethyl methacrylate PMMA submicron particles were obtained at the dispersed state in the same frozen medium indicating that DNPenhanced 1H spins effectively diffuse from the medium to the PMMA particles through their surface and are detected as highresolution 13 C spectra in the surficial region to which the 1H spins reach On the basis of these results the possibility of the DNP/CP/MAS NMR characterization of the surface structure of nanomaterials including polymer materials was discussed

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