@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 {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.} } @article {452, title = {Solid-State O-17 Magic-Angle and Dynamic-Angle Spinning Nmr-Study of the Sio2 Polymorph Coesite}, journal = {Journal of Physical Chemistry}, volume = {99}, year = {1995}, note = {J Phys Chem-UsRn706Times Cited:95Cited References Count:41}, month = {Aug 10}, pages = {12341-12348}, abstract = {

Five distinctly resolved O-17 solid-state NMR resonances in room temperature coesite, an SiO2 polymorph, have been observed and assigned using dynamic-angle spinning (DAS) at 11.7 T along with magic-angle spinning (MAS) spectra at 9.4 and 11.7 T. The O-17 quadrupolar parameters for each of the five oxygen environments in coesite are correlated with the Si-O-Si bridging bond angles determined by diffraction experiments. The sign of e(2)qQ/h along with the orientation of the electric field gradient for oxygen in the Si-O-Si linkage were determined from a Townes-Dailey analysis of the data.

}, keywords = {oxygen}, isbn = {0022-3654}, doi = {Doi 10.1021/J100032a045}, url = {://WOS:A1995RN70600045}, author = {Grandinetti, P. J. and Baltisberger, J. H. and Farnan, I. and Stebbins, J. F. and Werner, U. and Pines, A.} } @article {469, title = {Cross-Polarization Dynamic-Angle Spinning Nuclear-Magnetic-Resonance of Quadrupolar Nuclei}, journal = {Molecular Physics}, volume = {81}, year = {1994}, note = {Mol PhysNe628Times Cited:21Cited References Count:29}, month = {Apr 10}, pages = {1109-1124}, abstract = {

The use of variable-angle spinning (VAS) with cross-polarization (CP) for quadrupolar nuclei has been evaluated both experimentally and theoretically. It is known that under normal spinning speeds the best VAS angle for performing CP is 0-degrees (parallel to the magnetic field). We show that, with the use of dynamic-angle spinning (DAS) probes, CP may be done at 0-degrees and detection in a one-dimensional VAS experiment may be performed at any angle in a zero-polarized VAS (ZPVAS) experiment. Finally, the combination of CP with k = 5 DAS (where the sample is spun first at 0-degrees followed by 63.43-degrees) provides both the highest resolution and the greatest sensitivity under normal conditions.

}, keywords = {probe}, isbn = {0026-8976}, doi = {Doi 10.1080/00268979400100741}, url = {://WOS:A1994NE62800007}, author = {Baltisberger, J. H. and Gann, S. L. and Grandinetti, P. J. and Pines, A.} } @article {479, title = {Dynamic-Angle Spinning without Side-Band}, journal = {Chemical Physics Letters}, volume = {210}, year = {1993}, note = {Chem Phys LettLp038Times Cited:18Cited References Count:16}, month = {Jul 30}, pages = {405-410}, abstract = {

By means of rotor-synchronized pi-pulses, it is possible to eliminate the spinning sidebands (while retaining their full intensity in the isotropic centerband) that usually arise in dynamic-angle spinning (DAS) NMR. The theory of this approach, dynamic-angle hopping (DAH-180), is described and illustrated with experimental results on quadrupolar nuclei. A magic-angle hopping (MAH-180) version of magic-angle spinning is also possible and can be used in a two-dimensional NMR experiment to produce sideband-free isotropic-anisotropic correlation spectra for spin-1/2 nuclei.

}, keywords = {resolution}, isbn = {0009-2614}, doi = {Doi 10.1016/0009-2614(93)87045-5}, url = {://WOS:A1993LP03800018}, author = {Gann, S. L. and Baltisberger, J. H. and Pines, A.} } @article {478, title = {Pure-Absorption-Mode Lineshapes and Sensitivity in 2-Dimensional Dynamic-Angle Spinning Nmr}, journal = {Journal of Magnetic Resonance Series A}, volume = {103}, year = {1993}, note = {J Magn Reson Ser ALj625Times Cited:98Cited References Count:20}, month = {Jun 1}, pages = {72-81}, keywords = {nuclei}, isbn = {1064-1858}, doi = {Doi 10.1006/Jmra.1993.1132}, url = {://WOS:A1993LJ62500010}, author = {Grandinetti, P. J. and Baltisberger, J. H. and Llor, A. and Lee, Y. K. and Werner, U. and Eastman, M. A. and Pines, A.} } @article {477, title = {Side-Band Patterns in Dynamic-Angle-Spinning Nmr}, journal = {Journal of Magnetic Resonance Series A}, volume = {102}, year = {1993}, note = {J Magn Reson Ser AKz480Times Cited:19Cited References Count:26}, month = {Apr}, pages = {195-204}, keywords = {samples}, isbn = {1064-1858}, doi = {Doi 10.1006/Jmra.1993.1091}, url = {://WOS:A1993KZ48000011}, author = {Grandinetti, P. J. and Lee, Y. K. and Baltisberger, J. H. and Sun, B. Q. and Pines, A.} } @article {492, title = {Isotropic Chemical-Shifts and Quadrupolar Parameters for O-17 Using Dynamic-Angle Spinning Nmr}, journal = {Journal of Physical Chemistry}, volume = {96}, year = {1992}, note = {J Phys Chem-UsJk807Times Cited:66Cited References Count:48}, month = {Aug 20}, pages = {7001-7004}, abstract = {

Several oxygen-17-enriched silicates were studied using dynamic-angle spinning (DAS) NMR spectroscopy at two magnetic field strengths. The DAS method averages second-order quadrupolar interactions by reorienting a sample about a time-dependent axis, thereby yielding high-resolution spectra for half-odd integer spin quadrupolar nuclei such as oxygen-17. A narrow spectral line is observed for each distinct oxygen site in a powdered sample at the sum of the isotropic chemical shift and the field-dependent isotropic second-order quadrupolar shift. Using equations for the total shift observed at two field strengths, the chemical shift is uniquely determined together with a product of the quadrupolar coupling constant (C(Q) = e2qQ/h) and the quadrupolar asymmetry parameter (eta). For one silicate, we demonstrate aa computer program that uses the isotropic shifts and quadrupolar products as constraints and provides simulations of overlapped magic-angle spinning line shapes. In this way the quadrupolar parameters, C(Q) and eta, are determined separately for each crystallographic site. The silicates studied include the discrete orthosilicates larnite (Ca2SiO4) and forsterite (Mg2SiO4), as well as diopside (CaMgSi2O6), wollastonite (CaSiO3), and clinoenstatite (MgSiO3), which are minerals composed of chains of silicon-oxygen tetrahedra.

}, keywords = {zeolites}, isbn = {0022-3654}, doi = {Doi 10.1021/J100196a028}, url = {://WOS:A1992JK80700028}, author = {Mueller, K. T. and Baltisberger, J. H. and Wooten, E. W. and Pines, A.} } @article {498, title = {Quantification of the Disorder in Network-Modified Silicate-Glasses}, journal = {Nature}, volume = {358}, year = {1992}, note = {NatureJb341Times Cited:169Cited References Count:32}, month = {Jul 2}, pages = {31-35}, abstract = {

Local order in silicate glasses has been observed by many experimental techniques to be similar to that in crystalline materials. Details of the intermediate-range order are more elusive, but essential for understanding the lack of long-range symmetry in glasses and the effect of composition on glass structure. Two-dimensional O-17 dynamic-angle-spinning nuclear magnetic resonance experiments reveal intermediate-range order in the distribution of inter-tetrahedral (Si-O-Si) bond angles and a high degree of order in the disposition of oxygen atoms around the network-modifying cations.

}, keywords = {time}, isbn = {0028-0836}, doi = {Doi 10.1038/358031a0}, url = {://WOS:A1992JB34100043}, author = {Farnan, I. and Grandinetti, P. J. and Baltisberger, J. H. and Stebbins, J. F. and Werner, U. and Eastman, M. A. and Pines, A.} } @article {500, title = {Rb-87 Dynamic-Angle Spinning Nmr-Spectroscopy of Inorganic Rubidium Salts}, journal = {Journal of the American Chemical Society}, volume = {114}, year = {1992}, note = {J Am Chem SocJm979Times Cited:39Cited References Count:28}, month = {Sep 9}, pages = {7489-7493}, abstract = {

Five inorganic rubidium salts, RbCl, RbClO4, Rb2SO4, Rb2CrO4, and RbNO3, were examined using Rb-87 NMR spectroscopy. Significant line narrowing occurs under dynamic-angle spinning (DAS) compared to magic-angle spinning (MAS) or variable-angle spinning (VAS). From DAS spectra acquired at various magnetic field strengths, isotropic chemical shifts and isotropic second-order quadrupolar shifts were obtained. By simulations of single-site line shapes obtained from MAS-detected DAS experiments, complete chemical shift and quadrupolar parameters were determined for each of the three crystallographically distinct rubidium sites in RbNO3.

}, keywords = {cesium}, isbn = {0002-7863}, doi = {Doi 10.1021/Ja00045a023}, url = {://WOS:A1992JM97900023}, author = {Baltisberger, J. H. and Gann, S. L. and Wooten, E. W. and Chang, T. H. and Mueller, K. T. and Pines, A.} } @article {485, title = {Sidebands in dynamic angle spinning (DAS) and double rotation (DOR) NMR}, journal = {Solid State Nuclear Magnetic Resonance}, volume = {1}, year = {1992}, note = {Solid State Nucl MagV26htTimes Cited:63Cited References Count:29}, month = {Dec}, pages = {267-295}, abstract = {

A theory of dynamic angle spinning (DAS) and double rotation (DOR) NMR is described using average Hamiltonian and irreducible tensor methods. Sideband intensities in DAS and DOR spectra are analyzed by both the moment and Bessel function methods, and general formulae are derived. Results show that the DAS moments depend on the relative rotor phase between the first and the second evolution periods, whereas the second and third DOR moments are independent of the relative phase between the inner and outer rotors. Sideband intensities in DAS spectra also depend on the relative rotor phases between evolution at the first and second angles, as well as on the ratio of time spent at each angle. Sideband intensities and phases in DOR spectra are related to the relative rotor phases between the inner and outer rotors, and the sideband pattern is determined by the ratio of the inner and outer rotor spinning speeds. An inversion symmetry of the odd numbered DOR sidebands at the relative rotor phase gamma(r) = 0 degrees. 180 degrees permits the elimination of these sidebands. Finally, numerical simulations are implemented and shown to agree with experimental results. Quadrupolar parameters can therefore be recovered either by calculating the second and third moments or by simulating the sideband intensities and phases.

}, keywords = {central transition}, isbn = {0926-2040}, doi = {Doi 10.1016/0926-2040(92)90047-D}, url = {://WOS:000208537400006}, author = {Sun, B. Q. and Baltisberger, J. H. and Wu, Y. and Samoson, A. and Pines, A.} }