Two-dimensional multiple-quantum MAS NMR of quadrupolar nuclei: a comparison of methods

Brown, S.P. and Wimperis, S. (1997) Two-dimensional multiple-quantum MAS NMR of quadrupolar nuclei: a comparison of methods. Journal of Magnetic Resonance, 128(1), pp. 42-61. (doi: 10.1006/jmre.1997.1217)

Abstract

Multiple-quantum magic-angle-spinning (MQMAS) NMR experiments have recently been used to remove second-order broadening from the central transition of half-integer quadrupolar nuclei. In this paper, the various methods that have been proposed for obtaining pure absorption-mode lineshapes in MQMAS experiments are described and compared. The methods can be classified according to whether the data are amplitude- or phase-modulated as a function of the evolution period,<i>t</i>₁. Both classes of experiment are usually performed in such a way that the inhomogeneous quadrupolar broadening is spread out along a ridge which, for spinsI= 3/2 and 5/2, respectively, has a slope of −7/9 or 19/12 with respect to the<i>F</i>₂axis. This paper shows, however, that there are disadvantages associated with recording the data in this fashion and demonstrates, in particular, that a shearing transformation of the final two-dimensional spectrum can lead to distorted lineshapes. Novel amplitude- and phase-modulated “split-<i>t</i>₁” MQMAS experiments are introduced which fully refocus the second-order broadening during the evolution period,t1, thereby avoiding the need for a shearing transformation. The considerable practical advantages of these split-<i>t</i>₁experiments are discussed, particularly with regard to ease of implementation and processing. In general, the sensitivities achievable using the split-<i>t</i>₁MQMAS experiments are predicted to be similar to those obtainable with other methods and, in the special case of the spin<i>I</i>= 3/2 phase-modulated experiments, are even shown to be slightly superior.

• Item Type: Articles
• Glasgow Author(s) Enlighten ID: Wimperis, Professor Stephen
• Authors: Brown, S.P., and Wimperis, S.
• College/School: College of Science and Engineering > School of Chemistry
• Journal Name: Journal of Magnetic Resonance
• Publisher: Academic Press
• ISSN: 1090-7807
• ISSN (Online): 1096-0856
• Published Online: 15 April 2002