QUantitative Cross-Polarization at magic-angle spinning frequency of about 20 kHz |
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Authors: | Takeda Kazuyuki Noda Yasuto Takegoshi K Lafon Olivier Trébosc Julien Amoureux Jean-Paul |
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Affiliation: | Division of Chemistry, Graduate School of Science, Kyoto University, 606-8502 Kyoto, Japan. takezo@kuchem.kyoto-u.ac.jp |
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Abstract: | We study the QUantitative Cross-Polarization (QU-CP) method proposed by Hou et al. (Chem. Phys. Lett. 421 (2006) 356) under the moderate MAS speed of 23 kHz, re-examining its two building blocks, namely, the CP polarization transfer from (1)H to (13)C, and the thermal equalization of the (13)C magnetizations. We show that the nuclear-integrated cross-polarization (NI-CP) scheme is conveniently used for (1)H-(13)C polarization transfer, because of its simplicity, robustness to rf-mismatch, and compatibility with fast sample spinning. In the mixing part, in addition to dipolar-assisted rotational-resonance (DARR) recoupling, we examine the Phase-Alternated Recoupling Irradiation Schemes (PARIS and PARIS(xy)), and Second-order Hamiltonian among Analogous Nuclei Generated by Hetero-nuclear Assistance Irradiation (SHANGHAI) sequences, and show that SHANGHAI gives the best performances in equalizing the (13)C magnetizations. |
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