Rapid measurement of multidimensional 1H solid-state NMR spectra at ultra-fast MAS frequencies.

A novel method to realize rapid repetition of (1)H NMR experiments at ultra-fast MAS frequencies is demonstrated. The ultra-fast MAS at 110kHz slows the (1)H-(1)H spin diffusion, leading to variations of (1)H T1 relaxation times from atom to atom within a molecule. The different relaxation behavior is averaged by applying (1)H-(1)H recoupling during relaxation delay even at ultra-fast MAS, reducing the optimal relaxation delay to maximize the signal to noise ratio. The way to determine optimal relaxation delay for arbitrary relaxation curve is shown. The reduction of optimal relaxation delay by radio-frequency driven recoupling (RFDR) was demonstrated on powder samples of glycine and ethenzamide with one and multi-dimensional NMR measurements.