Powder pattern recoupling at 10 kHz spinning speed applied to cellulose.

Effective powder pattern recoupling by pi-pulses at spinning speeds up to 10kHz has been introduced. In a 2D experiment, the static chemical shift spectra of the indirect dimension were separated by the isotropic values of the direct dimension. Sufficient high spinning speeds ensured optimal exploitation of spectral intensities. This experiment was used to extract the 13C chemical shift tensor values of native Cellulose I and regenerated Cellulose II.

Distribution of principal values of the 31P NMR chemical shift tensor in phosphate glasses.

The static line shapes of the powder pattern of the 31P nuclear magnetic resonance (NMR) chemical shift (CS) tensor in phosphate glasses can only be explained by using individual distributions parameters for the principal axes. A model is discussed, which assumes a linear dependency of such distributions from the principal values themselves. Furthermore, the influence of such distributions on magic angle spinning (MAS) spectra is investigated.

New Semi-empirical Approach for the Calculation of 13C Chemical-Shift Tensors

The semi-empirical bond polarization theory is applied to the calculation of 13C chemical-shift tensors. This method allows prediction of shift tensors with deviations from experiment comparable to the errors of the ab initio methods. In contrast to ab initio calculations, a set of empirical parameters is needed, which can be estimated from experimental chemical-shift tensors solving a set of linear equations. The coefficients of this overdetermined set of equations are bond polarization energies that must be calculated within the framework of this theory. The parameters for C-C, C-H, and C-O bonds of sp3 and sp2 hybridized carbons and C-N bonds of sp3 carbons were obtained from 606 equations formed from experimental data from 20 substances taken from the literature. The substances include sugars, aromatic compounds, amino acids, and organic acids. The mean deviation of calculated from experimental 13C chemical-shift tensor components is 9 ppm.

A randomized study comparing fluconazole with amphotericin B/5-flucytosine for the treatment of systemic Candida infections in intensive care patients.

In this prospective, randomized study fluconazole and amphotericin B/5-flucytosine were compared in the treatment of systemic candidiasis. Seventy-two non-neutropenic intensive care patients with systemic Candida infections were enrolled. Thirty-six patients were randomly assigned to receive fluconazole (400 mg on the first day then 200 mg) and 36 were randomized to amphotericin B/5-flucytosine (1.0-1.5 mg/kg body weight every other day and 3 x 2.5 g flucytosine/day) for 14 days following the diagnosis. There was no statistically significant difference in clinical outcome in regard to the treatment of pneumonia and sepsis: 18/28 of the patients were treated successfully with fluconazole and 17/27 with amphotericin B/5-flucytosine. For the treatment of peritonitis, however, amphotericin B/5-flucytosine was more effective than fluconazole (55% vs. 25%). Furthermore, amphotericin B/5-flucytosine was found to be superior to fluconazole with regard to pathogen eradication (86% vs. 50%). Fluconazole was associated with less toxicity than amphotericin B/5-flucytosine.

The bond angle dependence of the asymmetry parameter of the oxygen-17 electric field gradient tensor.

From primarily geometric starting points, simple formulae for the bond angle dependence of the 17O quadrupolar asymmetry parameter eta were derived. Expressions for the bond angle dependence of the components of the electric field gradient (EFG) were first derived by Vega. Poplett used these expressions to discuss the 17O NQR results obtained for the water molecule. The formulae presented in this paper were derived essentially from other starting points and contain only the bond angle of a A- 17O-A oxygen bridge and all details concerning the electron distribution within the bonds will cancel out. Since no assumptions concerning the p-orbital occupancies had to be invoked, these geometric eta formulae are valid for most bridging oxygens. A necessary prerequisite of the eta formulae was that the electron distribution around the oxygen atom under study should exhibit C2v or D2 symmetry. The formulae were applied to explain the data of water molecules in the gaseous state, of various ice polymorphs and of crystal water. As supposed, the theory worked best for the free water molecule because of its perfect C2v symmetry. The differences between experiment and theory for water in solid compounds were mostly smaller than 6%. In the case of silicates and zeolites it was demonstrated that the eta formulae correctly described the experimental trends of the 17O NMR measurements of these substances. It could be demonstrated that reliable A-O-A-bond angles could be obtained from an eta measurement independent of the bond partner A. Comparing calculated eta values with ab initio calculations of this parameter, the largest difference was observed in the case of a Si-O-Si bond angle near 90 degrees. The eta formulae gave slightly lower eta values than ab initio calculations but the general trends were correctly reflected.