Quasiparticle bandstructures of covalent semiconductors and their surfaces

The exchange-correlation self-energies and quasiparticle shifts are calculated for band states of covalent materials (diamond, silicon) and their (001) 2×1 surface in order to solve the bulk and surface band-gap problem of the LDA. The screening properties are described by a model dielectric function taking into account the spatial nonlocality in the surface case assuming specular electron reflection. The wave functions are expanded in terms of localized orbitals. The quasiparticle bandstructures obtained are in reasonable agreement with experimental results.     

Alkyl-Diol Silica (ADS): restricted access precolumn packings for direct injection and coupled-column chromatography of biofluids

The direct and repetitive injection of untreated biological fluids (e.g., hemolyzed blood, plasma, serum, cell culture and tissue homogenates) onto an HPLC-system and the subsequent analysis of low-molecular weight compounds (e.g. drugs, xenobiotics, metabolites) is rendered possible by a coupled-column configuration and special precolumn packings. For this purpose a new family of chemically and enzymatically tailored reversed-phase packing materials have been prepared. The LC-integrated sample clean-up with these restricted access (bimodal) phases is based on the complete nonadsorptive size exclusion of macromolecules (e.g. proteins) and on the simultaneous dynamic partitioning of the target molecules. The bonded phase which exclusively covers the internal pore surface of a glyceryl-modified silica is a butyryl-(C-4), capryloyl-(C-8) or stearoyl-(C-18) moiety. These ligands allow a classical reversed-phase or ion-pair chromatography during the sample work-up step. The capacity of the n-alkyl phase is comparable with conventional silica based RP-materials. The broad hydrophobic retentive capability of these packings allows the extraction of a wide variety of compounds of biomedical interest. The electroneutral and hydrophilic particle exterior (glyceryl-residues) was generated using either soluble or immobilized enzymes (lipase, esterase) which cleave the fatty acid esters exclusively at the outer surface. Unwanted macromolecular components of a sample (e.g. proteins) are quantitatively eluted in the void volume due to the restricted access given by the pore size (6 nm) and the nonadsorptive external diol coverage. The lifetime of a precolumn (25 × 4 mm I.D.) packed with these novel bimodal, i.e. RP-SEC phases exceeds more than 200 injections of 500 l plasma. In addition to the synthesis, this paper describes an application of each of these Alkyl-Diol Silica (ADS) precolumn packings in fully automated coupled-column HPLC systems for the analysis of drugs and endogenous compounds in different biological matrices.Dedicated to Professor Dr. Dr. h.c. mult. J.F.K. Huber on the occasion of his 70th birthday     

Cyclic esters of aliphatic diacids with pyrocatechol and hydroquinone

Cyclic esters of adipic acid, suberic acid and sebacic acid were prepared by reaction of the acid dichlorides and pyrocatechol or hydroquinone in benzene under high dilution conditions. While only the cyclic dimers could be obtained from hydroquinone, pyrocatechol formed cyclic monomers as well as cyclic dimers (and also a cyclic dimer with succinic acid). The structure of all compounds was confirmed by¹H-NMR- and mass spectra. The crystal structures of the pyrocatechol esters were determined by single crystal X-ray analysis.

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Cyclische Ester aliphatischer Dicarbonsäuren mit Brenzcatechin und Hydrochinon

Zusammenfassung Es wurden cyclische Ester von Adipinsäure, Korksäure und Sebacinsäure durch Reaktion der entsprechenden Säure-Dichloride mit Brenzcatechin oder Hydrochinon bei hoher Verdünnung hergestellt. Während mit Hydrochinon lediglich die cyclischen Dimeren erhalten werden konnten, wurden mit Brenzcatechin sowohl cyclische Monomere als auch cyclische Dimere erhalten (ebenfalls das cyclische Dimer mit Bernsteinsäure). Die Strukturen wurden mittels¹H-NMR und Massenspektren gesichert. Die Kristallstrukturen der Brenzcatechin-Ester wurden mittels Röntgenstrukturanalyse bestimmt.

     

1H-NMR-spektroskopische Analyse von 2-Chlor-1.3.2-dioxarsolan

The¹H-NMR-spectral data of 2-chloro-1.3.2-dioxarsolane are presented and discussed. The protons of the methylene groups form in concentrated solutions by rapide chlorine exchange anAAAA spin system. In dilute solutions the protons form anAABB spin system, which is changed to anAAAA system by addition of chlorine ions.The vicinal H–C–C–H-coupling constants indicate a twist-envelope conformation.

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Many body effects in the electronic and optical properties of the (1 1 1) surface of diamond

The (1 1 1) face is the cleavage surface of diamond. Understanding its properties is very important for the growing technological interest on the chemistry of diamond surfaces. Within DFT the most stable reconstruction is the Pandey chain model, the atoms on the chain being neither buckled nor dimerised. However this geometry gives rise to a semi metallic band structure in contrast with experimental findings that show the presence of a gap ranging from 0.5 to 2 eV. Here we show that the same equilibrium geometry and thus the same metallic band structure is found relaxing the surface using screened exchange (sX) or Hartree-Fock (HF) functionals. We will discuss in detail how breaking the equivalence of the atoms on the chain affects the band structure and we will show that a buckling would yield a semiconducting surface, but is energetically unfavorable. A semiconducting character can be restored, within the equilibrium geometry, if quasiparticle corrections are carefully included within an iterative GW scheme. The result of the theoretical reflectance anisotropy spectra (RAS) at a DFT-RPA level are also presented and discussed. As expected, a strong anisotropy signal is found at low energies due to transitions between surface states inside the fundamental gap.