orals 5th Asia-Pacific NMR Symposium 2013

1H detected NMR at very fast MAS solid-state NMR (#91)

Yusuke Nishiyama 1
  1. JEOL RESONANCE Inc., tokyo, Japan

The recent advances in fast MAS technology achieve MAS above 110 kHz1 . Such an ultra-fast MAS is exclusively available by a tiny rotor with a limited sample volume; 0.75 mm O.D. (290 nL, 110 kHz MAS) and 1 mm O.D. (800 nL, 80 kHz MAS). Thus the limited sensitivity of NMR is very pronounced in these ultra-fast MAS experiments. Fortunately, 1H observation overcomes this problem due to its high gyromagnetic ratio and 100% natural abundance. 1H T2 relaxation time is significantly elongated, because the spinning frequency is then way faster than the 1H-1H dipolar interactions. This augments the sensitivity through the resolution enhancement and the increase of coherence lifetime. We present basic results and advanced applications using ulta-fast MAS with 1H detection. We demonstrate various 1H-1H DQ-SQ and SQ-SQ HOMCOR experiments, and 1H-{13C} and 1H-{14N} HETCOR experiments. In the 1H-{13C} HETCOR, the two-way magnetization transfer by two CP schemes is utilized. The high efficiency of DQ-CP brings about the sensitivity enhancement of HETCOR experiments even at ulta-fast MAS. Likewise, the long 1H coherence lifetime greatly enhances the sensitivity in HMQC experiments. This opens a way to indirect 14N observation2 . Internuclear distances can be easily obtained by CP with variable contact time (CP-VC) experiments at ulta-fast MAS3 . We also illustrate the great sensitivity enhancement of CP-VC with 1H detection. Finally, we introduce a novel method to facilitate rapid repetition in 1H NMR. At ultra-fast MAS of 110 kHz, the commonly believed assumption that all 1H nuclei in solid samples have uniform T1 due to spin diffusion is no longer true. Some 1H nuclei show very long T1, requiring very long recycle delays. This is especially troublesome in 2D experiments. We will show that RFDR during the repetition delay homogenizes 1H magnetization, enabling rapid polarization of all 1H nuclei.

  1. S. Parthasarathy, Y. Nishiyama, Y. Ishii, Acc. Chem. Res., in press.
  2. Z. Gan, J. Am. Chem. Soc. 128 (2006) 6040-6041; S. Cavadini, et al., J.Am. Chem. Soc. 128 (2006) 7706-7707; Y. Nishiyama et al., J. Magn. Reson. 208 (2011) 44-48.
  3. P. Paluch, et al., J. Magn. Reson. 233 (2013) 56-63.