Tuesday, October 21, 2008

Journal of Magnetic Resonance - Vol 195 Issue 1

Solid state water motions revealed by deuterium relaxation in 2H2O-synthesized kanemite and 2H2O-hydrated Na+-Zeolite A
Bernie O’Hare, Michael W. Grutzeck, Seong H. Kim, David B. Asay and Alan J. Benesi
Deuterium NMR relaxation experiments, low temperature deuterium NMR lineshape analysis, and FTIR spectra are consistent with a new model for solid state jump dynamics of water in 2H2O-synthesized kanemite and 2H2O-hydrated Na+-Zeolite A. Exchange occurs between two populations of water: one in which water molecules are directly coordinated to sodium ions and experience C2 symmetry jumps of their OH bonds, and a population of interstitial water molecules outside the sodium ion coordination sphere that experience tetrahedral jumps of their OH bonds. For both samples the C2 jump rate is much faster than the tetrahedral jump rate. 2H NMR relaxation experiments match well with the fast exchange regime of the model over a wide range of temperatures, including room temperature and above.

Coherence selection in double CP MAS NMR spectroscopy
Jen-Hsien Yang, Fang-Chieh Chou and Der-Lii M. Tzou
Applications of double cross-polarization (CP) magic-angle spinning (MAS) NMR spectroscopy, via 1H/15N and then 15N/13C coherence transfers, for 13C coherence selection are demonstrated on a 15N/13C-labeled N-acetyl-glucosamine (GlcNAc) compound. The 15N/13C coherence transfer is very sensitive to the settings of the experimental parameters. To resolve explicitly these parameter dependences, we have systematically monitored the 13C{15N/1H} signal as a function of the rf field strength and the MAS frequency. The data reveal that the zero-quantum coherence transfer, with which the 13C effective rf field is larger than that of the 15N by the spinning frequency, would give better signal sensitivity. We demonstrate in one- and two-dimensional double CP experiments that spectral editing can be achieved by tailoring the experimental parameters, such as the rf field strengths and/or the MAS frequency.

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