Electronic properties of kekulene

The fluorescence and phosphorescence of kekulene in a host matrix of polycrystalline tetrachlorobenzene are investigated, together with the triplet zero field splitting parameters |D| and |E| obtained by ODMR in zero field. The D value is also calculated within a semi-empirical π-theory and compared with experiment. It could be shown that the triplet state energies of a number of different sites of kekulene in the host matrix and the zero field splitting parameters are related, in first order, by spin orbit interaction.     

Application of high-performance liquid chromatography coupled to nuclear magnetic resonance spectrometry, mass spectrometry and bioassay for the determination of active saponins from Bacopa monniera Wettst.

Reversed-phase high-performance liquid chromatographic separation coupled to (structurally informative) spectroscopic methods like NMR and MS and an efficient bioassay have been used to determine the active compounds from a crude fraction of Bacopa monniera. The fraction containing a mixture of saponins with closely related structures was found to show a significant anthelmintic activity against Caenorhabditis elegans (used as a model test organism for determining anthelmintic activity). The activity was correlated to two dammarane type triterpenoidal saponins containing at least three sugar units. The optimization of separation for 1 mg of the crude sample on column and the sensitivity of on-flow one- and two-dimensional NMR experiments to the high-molecular-mass compounds (M(r) 890-930) has been demonstrated.     

Acoustically Enhanced Ganglia Dissolution and Mobilization in a Monolayer of Glass Beads

A pore network consisting of a monolayer of glass beads was constructed for experimental investigation of the effects of acoustic waves on the dissolution and mobilization of perchloroethylene (PCE) ganglia. Dissolution experiments were conducted with acoustic wave frequencies ranging from 75 to 225 Hz at a constant pressure amplitude of 3.68 kPa applied to the inlet of the monolayer. Ganglia mobilization experiments were conducted with a constant acoustic wave frequency of 125 Hz and acoustic pressure amplitudes ranging from 0 to 39.07 kPa. Effluent dissolved PCE concentrations were observed to increase in the presence of acoustic waves with the greatest increase (over 300%) occurring at the lowest frequency employed (75 Hz). Acoustic waves were also observed to mobilize otherwise immobile PCE ganglia, break them apart, and further enhance dissolution.     

Near-infrared laser based cavity ringdown spectroscopy for applications in petrochemical industry

A simple, economic diode laser based cavity ringdown system for trace-gas applications in the petrochemical industry is presented. As acetylene (C₂H₂) is sometimes present as an interfering contaminant in the gas flow of ethylene (ethene, C₂H₄) in a polyethylene production process, an on-line monitoring of such traces is essential. We investigated C₂H₂–C₂H₄ mixtures in a gas-flow configuration in real time. The experimental setup consists of a near-infrared external cavity diode laser with an output power of a few mW, standard telecommunication fibers and a home-made gas cell providing a user-friendly cavity alignment. A noise-equivalent detection sensitivity of 4.5×10^-8 cm^-1 Hz^-1/2 was achieved, corresponding to a detection limit of 20 ppbV C₂H₂ in synthetic air at 100 mbar. In an actual C₂H₂–C₂H₄ gas-flow measurement the minimum detectable concentration of C₂H₂ added to the C₂H₄ gas stream (which may already contain an unknown C₂H₂ contamination) increased to 160 ppbV. Moreover, stepwise C₂H₂ concentration increments of 500 ppbV were resolved with a 1-min time resolution and an excellent linear relationship between the absorption coefficient and the concentration was found. PACS 07.07.Df; 42.62.Fi; 82.80.Gk     

Synthesis, characterization and spectroscopic properties of 1,2-diiminetricarbonylrhenium(I)chloride complexes with o-benzoquinone diimines as ligands

The novel organometallic complexes Re(BQDI---R)(CO)₃Cl with BQDI---R=4,5-substituted o-benzoquinone diimines (R=H, Me, OMe, Cl) have been prepared and characterized by elemental analysis, IR, MS and ¹H-NMR spectroscopic methods. Their electronic spectra display a long-wavelength absorption band which can be ascribed to a metal-to-ligand charge transfer (MLCT) transition from Re(I) to the low-lying π*-orbitals of the o-benzoquinone diimine ligand, even though a significant degree of metal–ligand orbital mixing is occurring. The energy of this absorption band correlates very well with the nature of the substituents R in the 4,5-position of BQDI---R. In solvent series of decreasing polarity, the MLCT absorption maximum is shifted to longer wavelengths (negative solvatochromism). None of the Re(BQDI---R)(CO)₃Cl complexes studied is photoluminescent at 298 or 77 K.     

Optical metal-to-ligand charge-transfer of 2,2′-bipyridyl complexes of antimony(III) and bismuth(III)

The complexes [M(2,2′-bipyridyl)X₃], with M = Sb, Bi and X = Cl, Br, I, are characterized by long-wavelength metal-to-ligand charge-transfer (MLCT) bands which determine the colours of these compounds in the solid state. The energy of the MLCT bands depends on the reducing strength of the metal and the extent of sp mixing of the lone electron pair at the metal.