Dialyse

Ohne Zusammenfassung     

Zur Bestimmung des Atropins, Hyoszyamins und Strychnins

Ohne Zusammenfassung     

Zur Hochdruck-Flüssigkeits-Chromatographie von polycyclischen aromatischen Kohlenwasserstoffen

Two aspects of high-pressure liquid chromatography (HPLC) of polycyclic aromatic hydrocarbons (PAH) have been studied: The application of HPLC to the analysis of very highly condensed PAH, that cannot be analyzed by gas chromatography, and the application of u.v. spectroscopy to the identification of PAH, that have been separated by HPLC. A device, that allows the rapid scanning of u.v. spectra within the HPLC apparatus, is described.     

Tizanidine and tizanidine hydrochloride: on the correct tautomeric form of tizanidine

A crystallization series of tizanidine hydrochloride, used as a muscle relaxant for spasticity acting centrally as an α₂‐adrenergic agonist, yielded single crystals of the free base and the hydrochloride salt. The crystal structures of tizanidine [systematic name: 5‐chloro‐N‐(imidazolidin‐2‐ylidene)‐2,1,3‐benzothiadiazol‐4‐amine], C₉H₈ClN₅S, (I), and tizanidine hydrochloride {systematic name: 2‐[(5‐chloro‐2,1,3‐benzothiadiazol‐4‐yl)amino]imidazolidinium chloride}, C₉H₉ClN₅S⁺·Cl⁻, (II), have been determined. Tizanidine crystallizes with two almost identical molecules in the asymmetric unit (r.m.s. deviation = 0.179 Å for all non‐H atoms). The molecules are connected by N—H...N hydrogen bonds forming chains running along [21]. The present structure determination corrects the structure determination of tizanidine by John et al. [Acta Cryst. (2011), E 67 , o838–o839], which shows an incorrect tautomeric form. Tizanidine does not crystallize as the usually drawn 2‐amino–imidazoline tautomer, but as the 2‐imino–imidazolidine tautomer. This tautomer is present in solution as well, as shown by ¹H NMR analysis. In tizanidine hydrochloride, cations and anions are connected by N—H...Cl hydrogen bonds to form layers parallel to (100).     

HREELS of H/GaN(0001): evidence for Ga termination

Two issues relevant to the growth and processing of GaN are the termination of the GaN(0001) surface and its reaction with hydrogen. We have used high-resolution electron energy loss spectroscopy (HREELS), low-energy electron diffraction (LEED), and Auger electron spectroscopy (AES) to study the adsorption of hydrogen on MOCVD-grown GaN(0001). LEED of the sputtered and annealed surface shows evidence of facetting. No adsorbate vibrations are observed on the clean surface by HREELS, only Fuchs–Kliewer phonons at intervals of 700 cm⁻¹. Following exposure of the clean GaN surface to hydrogen atoms, HREEL spectra show adsorbate loss peaks at 2580, 3280, and 3980 cm⁻¹. The Ga–H stretching vibration at 1880 cm⁻¹ becomes evident when the HREEL spectrum is deconvoluted to remove the phonon multiple-loss peaks. We assign the 2580, 3280, and 3980 cm⁻¹ peaks to combination modes of the Ga–H stretch and phonon(s). Upon dosing with deuterium, the Ga–D bending mode is observed at 400 cm⁻¹. No vibrational peaks due to N–H (N–D) species are observed after H (D) exposure. We conclude that sputtered and annealed GaN(0001) is Ga-terminated.