Solid-state 29Si, 113Cd, 119Sn, and 31P NMR studies of II-IV-P2 semiconductors.

Solid-state 29Si, 113Cd, 119Sn, and 31P MAS NMR spectra are reported on a series of II-IV-P2 compounds. In favorable cases (e.g., high degree of crystallinity, low concentration of unpaired electrons), well-defined spectra, with sharp lines for each specific nearest-neighbor configuration, are observed; in such cases, expected J coupling patterns are also seen. High-resolution solid-state NMR studies of this type provide useful information on structure (disorder), doping, and electron-mediated coupling in semiconductor systems.

13C NMR lineshapes of acetone adsorbed on silica.

13C NMR data, obtained as a function of temperature with magic-angle spinning (MAS) and either cross polarization or direct polarization, are reported on acetone and a sample of acetone (an approximately equal mixture with 13C labels at C-1 or C-2) adsorbed on dry silica gel. Various contributions to the observed linewidths and T2C values are considered in terms of a previously established model of the acetone/SiO2 system; in that model, acetone species are in equilibrium between a physisorbed-acetone (non-hydrogen-bonded) state and a state consisting of acetone units that are hydrogen bonded to silanol moieties on the silica surface. Spin dynamics simulations are useful in interpreting the effects of variations of experimental parameters. It is concluded that the main linewidth contributions, which increase at lower temperatures, are: (a) a dispersion of chemical shifts in the hydrogen-bonded state, associated with the inhomogeneous character of the silica surface; (b) the interference between MAS averaging of the chemical shift anisotropy (especially for the carbonyl carbon) and molecular motion and/or chemical exchange; and (c) chemical exchange broadening. Prominence of the last of these contributions is most consistent with data obtained as a function of magnetic field strength, MAS speed, and temperature.

NMR of samples containing metal foils.

By using spool configurations of a sample containing aluminum foil, in which the axis of the spool is collinear with the RF coil axis, one can obtain high-quality 13C NMR spectra of static samples of organic material attached to the aluminum foil. By combining such a spool configuration (or, alternatively, analogous samples containing equivalent amounts of fine aluminum powder) with the magic-angle hopping (MAH) technique, one can achieve a high degree of isotropic averaging of the 13C spectrum. This opens to NMR techniques the study of a variety of samples containing macroscopic pieces of metal foils, e.g., thin films deposited on metal foils and electrochemical systems with species adsorbed on metal-foil electrodes.

Investigation of germination and aging in Moravian III barley grain by nuclear magnetic resonance.

High-resolution, solid-state 1H nuclear magnetic resonance (NMR) techniques are used for the first time to study germination in imbibed Moravian III barley grains. Whereas magic-angle spinning 1H NMR spectra reveal the water and lipid components in barley grains, combined rotation and multiple-pulse spectroscopy techniques provide 1H NMR spectra of grains that reveal the protein and carbohydrate as well as the water and lipid components. Spectra of grains are compared with spectra of model compounds to verify assignments. 1H T1 and T2 measurements using magic-angle spinning only and combined rotation and multiple-pulse spectroscopy techniques provide information about molecular mobility within the grains during inhibition. Some grains were subjected to artificial aging conditions. 1H NMR spectral comparisons are made between normal, viable grains and artificially aged grains.

High-resolution nuclear magnetic resonance of solids.

The development of line-narrowing techniques, such as magic-angle spinning (MAS) and high-power decoupling, has led to powerful high-resolution nuclear magnetic resonance approaches for solid samples. In favorable cases (for instance, where high abundances of protons are present) cross polarization (CP) provides a means of circumventing the time bottleneck caused by inefficient spinlattice relaxation in many solids. The combined CP-MAS approach for carbon-13 with proton decoupling has become a popular and routine experiment for organic solids. For many nuclides with spin quantum number /> (1/2) the central nuclear magnetic resonance transition can be employed in high-resolution experiments that involve rapid sample spinning. A continuing stream of advances holds great promise for the use of high-resolution techniques for the characterization of solids by a wide range of nuclides.

Organic matter in a coal ball: peat or coal?

Chemical analyses of morphologically preserved organic matter in a Carboniferous coal ball reveal that the material is coalified to a rank approximately equal to that of the surrounding coal. Hence, the plant tissues in the coal ball were chemically altered by coalification processes and were not preserved as peat.