@article {406, title = {Multiple-quantum magic-angle spinning and dynamic-angle spinning NMR spectroscopy of quadrupolar nuclei}, journal = {Solid State Nuclear Magnetic Resonance}, volume = {8}, year = {1997}, note = {Solid State Nucl MagWy629Times Cited:60Cited References Count:40}, month = {Mar}, pages = {1-16}, abstract = {

Several aspects of the Multiple-Quantum Magic-Angle Spinning (MQMAS) technique (L, Frydman and J,S, Harwood, J, Am, Chem, Sec., 117 (1995) 5367) 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 DAS experiments, MQMAS is technically simple and routinely useful for studying 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 resolution in comparison to MQMAS, The different advantages of DAS and MQMAS make them useful complementary techniques in many cases,Two additional methods are also presented for extracting the chemical shift anisotropy (CSA) directly for quadrupolar nuclei using the multiple-quantum scheme, (C) 1997 Elsevier Science B,V.

}, keywords = {rb-87}, isbn = {0926-2040}, doi = {Doi 10.1016/S0926-2040(96)01277-5}, url = {://WOS:A1997WY62900001}, author = {Wang, S. H. and Xu, Z. and Baltisberger, J. H. and Bull, L. M. and Stebbins, J. F. and Pines, A.} } @article {422, title = {Determination of quadrupolar and chemical shielding tensors using solid-state two-dimensional NMR spectroscopy}, journal = {Journal of Chemical Physics}, volume = {105}, year = {1996}, note = {J Chem PhysVv625Times Cited:18Cited References Count:40}, month = {Dec 1}, pages = {9412-9420}, abstract = {

The quadrupolar and chemical shift tensors, as well as the relative orientation of the two principle axis systems, are accurately determined using a two-dimensional nuclear magnetic resonance technique. Good agreement between experimental and simulated two-dimensional spectra is obtained for a series of rubidium and sodium compounds at multiple magnetic field strengths. Extension of this technique to correlate the quadrupolar and dipolar interactions, as well as the incorporation of a purely isotropic dimension resulting in a three-dimensional experiment is also discussed. (C) 1996 American Institute of Physics.

}, keywords = {line-shapes}, isbn = {0021-9606}, doi = {Doi 10.1063/1.472776}, url = {://WOS:A1996VV62500003}, author = {Shore, J. S. and Wang, S. H. and Taylor, R. E. and Bell, A. T. and Pines, A.} } @article {435, title = {Triple-quantum two-dimensional Al-27 magic-angle spinning nuclear magnetic resonance spectroscopic study of aluminosilicate and aluminate crystals and glasses}, journal = {Journal of the American Chemical Society}, volume = {118}, year = {1996}, note = {J Am Chem SocVa026Times Cited:139Cited References Count:31}, month = {Jul 31}, pages = {7209-7214}, abstract = {

A new two-dimensional magic-angle spinning NMR experiment(1,2) using multiple-quantum coherences of half-integer quadrupolar nuclei was used to study Al-27 sites in crystalline samples of leucite (KAlSi2O6), anorthite (CaAl2Si2O8), and kyanite (Al2SiO5), as well as CaAl2Si2O8 glass and a magnesium aluminoborate glass. In the crystals, multiple sites are partially resolved and new results for isotropic chemical shifts and quadrupolar parameters are derived, using data collected at a single magnetic field. Data for both leucite and anorthite are consistent with previous results that correlate chemical shifts with mean intertetrahedral bond angle. Signal can be obtained from sites with quadrupolar coupling constants as large as 9 MHz, but intensities are reduced. In the aluminoborate glass, peaks for sites with different Al coordination numbers are well separated. The lack of such features in CaAl2Si2O8 glass rules out the presence of significant quantities of AlO5 and AlO6 groups.

}, keywords = {anorthite}, isbn = {0002-7863}, doi = {Doi 10.1021/Ja9606586}, url = {://WOS:A1996VA02600027}, author = {Baltisberger, J. H. and Xu, Z. and Stebbins, J. F. and Wang, S. H. and Pines, A.} }