MULTIPLE-QUANTUM MAGIC-ANGLE-SPINNING AND DYNAMIC-ANGLE SPINNING NMR-SPECTROSCOPY OF QUADRUPOLAR NUCLEI

Several aspects of the Multiple-Quantum Magic-Angle Spinning (MQMAS) t echnique (L, Frydman and J,S, Harwood, J, Am, Chem, Sec., 117 (1995) 5 367) are compared with Dynamic-Angle Spinning (DAS), Examples of MQMAS spectra are shown for I = 3/2 nuclei with C-Q up to 3.6 MHz, and for: Al-27 (I = 5/2) with C-Q up to 10 MHz. The MQMAS linewidth is largely independent of the magnitude of the homonuclear dipolar interaction, while the spinning sideband manifold is similar to that observed in DA S experiments, MQMAS is technically simple and routinely useful for st udying nuclei with short spin-lattice relaxation times, but care must be taken in its use for quantitative studies as the excitation of the triple-quantum coherence is not uniform, In this regard, MQMAS is most useful for samples with small quadrupolar coupling constants, In the specific case of O-17, DAS would give spectra with excellent resolutio n in comparison to MQMAS, The different advantages of DAS and MQMAS ma ke them useful complementary techniques in many cases, Two additional methods are also presented for extracting the chemical shift anisotrop y (CSA) directly for quadrupolar nuclei using the multiple-quantum sch eme, (C) 1997 Elsevier Science B,V.