Sensitivity enhancements in MQ-MAS NMR of spin-5/2 nuclei using modulated rf mixing pulses

An X-(X) over bar pulse train with stepped modulation frequency was employe d to enhance the multiple-quantum to single-quantum coherence transfer in t he mixing period of the multiple-quantum magic-angle spinning (MQ-MAS) expe riment for spin I = 5/2 nuclei. Two MQ-MAS pulse sequences employing this m ixing scheme for the triple-to-single and quintuple-to-single quantum coher ence transfers have been designed and their performance is demonstrated for Al-27 on samples of NaSi3AlO8 and 9Al(2)O(3) . 2B(2)O(3). Compared to the standard single-pulse mixing sequences, the sensitivity is approximately do ubled in the present experiments. (C) 2000 Elsevier Science B.V. All rights reserved.