Kongruenzsätze der affinen Differentialgeometrien

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Buchbesprechungen

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Zu einem Satz von G. Trautmann über den Rang gewisser kohärenter analytischer Moduln

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Dielectric spectroscopy on aqueous solutions of some zwitterionic amino acids

The complex (electric) permittivity of aqueous solutions of dipolar solutes has been measured as a function of frequency between 1 MHz and 40 GHz. Solutes are the isomers DL-2-aminobutyric acid, DL-3-aminobutyric acid, and 4-aminobutyric acid, and also 6-aminohexanoic acid. The measured dielectric spectra show two dispersion/dielectric loss regions, one due to the orientational diffusion of the solute molecules the other one due to the dielectric relaxation of the solvent water. A relaxation spectral function based on a model of the solutions has been fitted to the measured frequency dependence of the complex permittivity. The values for the electric dipole moment and reorientation time of the zwitterionic part of the solute particles derived by this analysis from the measurements fairly agree with theoretical predictions. Quite remarkably, the dipole moment in solution of 4-aminobutyric acid and 6-aminohexanoic acid up to remarkably high solute concentrations is nearly constant. A noteworthy result for the hydration water of the amino acids is, that its relaxation time is almost independent of the solute dipole moment.     

1,3-Dioxolium-, 1,3-dithiolium- und 1,3-diselenolium-ionen - aromatische strukturen oder durch heteroatome stabilisierte carbeniumionen?

Protonation of the bases 6, 7 and 8 with trifluoroacetic acid was investigated on the basis of ^1–3C-nmr measurements. Two models for the generated ions 1–3 are discussed. A decision is possible in favour of carbenium ions, which are stabilized by adjacent heteroatoms.