Deprotonierte Dithiocarbaminsäureester als Thiolat-S-Donor-Liganden. Strukturen von Ph(H)NC(S)SMe,Co(PhNC(S)SMe)3 und Cu6(PhNC(S)SMe)6

Deprotonated Dithiocarbamic Acid Esters as Thiolate S-Donor Ligands. Structures of Ph(H)NC(S)SMe, Co(PhNC(S)SMe)₃, and Cu₆(PhNC(S)SMe)₆ The reaction of N-phenyl-S-methyldithiocarbamate, PhN(H)C(?S)SMe, ( 1 ) with cobalt(II) and copper(II) salts yields the monomeric compound Co^III(PhNC(S)SMe)₃ ( 2 ) and the hexameric compound Cu₆^I(PhNC(S)SMe)₆ ( 3 ). These complexes contain the negatively charged imino-thiolate ligand PhN?C(? S)SMe, which has been formed by deprotonation of 1 . The crystal structures of 1 – 3 have been determined. 1 forms centrosymmetrical dimers through N? H …? S bridge bonds, the conformation in the solid state and in solution is Z,E′. Co^III shows in 2 a trigonal-antiprismatic coordination, with the ligands acting as N,S-chelates. 3 contains an octahedral Cu₆-core with Cu …? Cu-distances ranging from 276.3(5) to 305.7(4) pm. Each copper center is trigonally coordinated to one nitrogen and two sulfur atoms of three different ligands. Crystal data: 1 , triclinic, space group P1 , a = 590.5(6), b = 869.0(1), c = 968.5(9) pm, α = 67.29(8), β = 78.44(8), γ = 81.64(9)°, Z = 2, 1 775 reflections, R(R_w) = 0.0317(0.032). 2 , orthorhombic, space group Pbca, a = 978.0(2), b = 1 842.9(4), c = 3 059.7(6) pm, Z = 8, 1 129 reflections, R(R_w) = 0.0997(0.0886). 3 , monoclinic, space group P2₁/c, a = 1 363.1(3), b = 1 342.8(3), c = 1 671.9(3) pm, β = 103.48°, Z = 2, 1 374 reflections, R(R_w) = 0.0708(0.0617).     

An improved method for the synthesis of cellulose membrane-bound peptides with free C termini is useful for PDZ domain binding studies

SPOT synthesis permits parallel synthesis and screening of thousands of cellulose membrane-bound peptides to study protein-protein interactions in a proteomic context. Recognition of C-terminal residues is one of the most common binding features of PDZ domains. Unfortunately, most solid support-bound peptide libraries lack a free C terminus due to C-terminal fixation on the solid support. To overcome this restriction, we developed a robust methodology based on our previous strategy for generating peptides with authentic C termini. To validate this improved method, we screened a human peptide library of 6223 C termini with the syntrophin PDZ domain. Furthermore, using the same library, new peptide ligands derived from membrane proteins and receptors were found for the ERBIN PDZ domain. Finally, we identified the protein kinase breakpoint cluster region, which is known as a negative regulator of cell proliferation and oncogenic transformation, as an ERBIN ligand.     

Destabilized carbenium ions: Secondary and tertiary α-carbomethoxybenzyl cations

The secondary α-carbomethoxybenzyl cations a and the tertiary α-carbomethoxybenzyl cations d have been generated by electron impact-induced fragmentation from appropriately α-substituted methyl phenylacetate and 2-phenylpropionates 1–4. The ions a and d are further examples of destabilized carbenium ions with a push–pull substitution at the carbenium ion centre. The characteristic reaction of these ions is a rearrangement by a 1,2-shift of the methoxy group concomitant to the elimination of CO. This rearrangement reaction is associated with a very large and non-statistical kinetic energy release (a : T ₅₀ = 570 meV; d : T ₅₀ = 760 meV), which is attributed to tight transition states along the reaction coordinates corresponding to the three-membered cyclic oxonium ions b and h, respectively. The tertiary ion d can be distinguished from its more stable isomers f and g by the mass-analysed ion kinetic energy and collisional activation spectra. The investigation of specifically deuterated analogues of ions d and g reveals an isomerization of d to g via a species protonated at the phenyl group but no equilibration between d and g. This isomerization exhibits a large isotope effect for the hydrogen transfer, indicating similar energy barriers for the isomerization and for the CO elimination of d.     

CARSA,a computer-assisted system for synthesis research in industry

Computer applications in chemical industry are outlined and the CARSA system (computer-assisted research in synthesis and application) is described. This modular system consists of the three main parts: WIFODATA (data base; substance and finding documentation), QSAR (programs for quantitative structure/activity relationships) and RDSS (reaction design by synthon substitution; program package for planning of syntheses). The vital RDSS component is discussed in more detail; the underlying philosophy is explained, and examples are given from practical work. Some future steps towards a real molecular-design system are outlined.     

Preparation of polycrystalline Ti-Al-O films by magnetron sputtering ion plating: constitution, structure and morphology

Ti-Al-O layers were deposited on Si-<100> wafers at 500 °C by means of reactive magnetron sputtering ion plating (R-MSIP). An Al-target was sputtered in rf-mode and a Ti-target in dc-mode simultaneously by an oxygen/argon plasma. The influence of the Al- and Ti-sputter powers on composition, structure, and morphology of the Ti-Al-O layers and the binding states of the components were investigated. The analysis with EPMA, XPS, AES and TEM yielded the following results: Ti-Al-O coatings with different Ti, Al, and O contents in the range of TiO₂ to Al₂O₃ were grown. TEM structure analysis revealed: the pure TiO₂ film consisted of the tetragonal phases rutile and anatase; the two structures were found in the titanium-rich Ti-Al-O film, too, but with significant smaller lattice constants. The aluminium-rich Ti-Al-O film displayed the same cubic structure of γ-Al₂O₃ as determined for the pure Al₂O₃ film, but the lattice constant is significant lower. Evaluation of the TEM pattern of the film with a Ti/Al ratio of 0.8 indicates a hexagonal structure with lattice constants similar to those of κ′-Al₂O₃. All films are nanocrystalline and not textured. Received: 24 June 1996 / Revised: 27 December 1996 / Accepted: 4 January 1997     

On hydrogen activation in the hydroformylation of olefins with Rh4(CO)12 or Co2(CO)8 as catalyst precursors

In the hydroformylation of ethylene with approximately equimolar H₂/D₂ mixtures and Rh₄(CO)₁₂ or Co₂(CO)₈ as the catalyst precursor about 50% of propionaldehyde-d₁ was formed. The propionaldehyde-d₀/d₂ ratio was ～ 3 for rhodium and ～ 2.6 for the cobalt catalyst. On the basis of the results and assuming that there is no rapid M(H)₂/M(D)₂ scrambling, activation of hydrogen through M(H)₂ or M(H)₂(olefin) complexes can be excluded.     

CHARGE TRANSFER ACROSS PIGMENTED BILAYER LIPID MEMBRANE AND ITS INTERFACES

Abstract— The technique of forming bilayer lipid membranes (BLM) has made it possible to study photoreactions of pigments in an environment that is much closer to those in photosynthetic and visual membranes. A pigmented BLM system with Mg²⁺-porphyrins as membrane-bound pigments and with ferricyanide and ferrocyanide as the aqueous electron acceptor and donor, respectively, was used to illustrate the photoelectric effects due to coupled interfacial charge transfer reactions.
The steady-state continuous photoresponse was studied by means of the voltage clamp method and a null current method. The independence of the pigment conductance channel and the ionic conductance channel was demonstrated. A tunable voltage clamp method was used to study the transient pulsed photoresponses. Such a measurement permits us to characterize the photosystem in terms of an equivalent circuit model which contains a novel chemical capacitance. Molecular interpretation of this equivalent circuit model was given.
A microscopic model based on the Gouy–Chapman theory and chemical kinetics calculation leads to an equivalent circuit which is also equivalent to the previous one. Generalization of this microscopic model further leads to a physical mechanism of the generation of the early receptor potential (ERP) in visual membranes. Relevance of pigmented BLM research to photosynthesis and other disciplines was also discussed.     

Formation of Zn(1-x)MnxS nanowires within mesoporous silica of different pore sizes

Arrays of highly ordered Zn(1-x)MnxS quantum wires with x ranging from 0.01 to 0.3 and with lateral dimensions of 3, 6, and 9 nm were synthesized within mesoporous SiO2 host structures of the MCM-41 and SBA-15 type. The hexagonal symmetry of these arrays (space group p6m) and the high degree of order was confirmed by X-ray diffraction and transmission electron microscopy (TEM) studies. Physisorption measurements show the progressive filling of the pores of the SiO2 host structures, while TEM and Raman studies reveal the wire-like character of the incorporated Zn(1-x)MnxS nanostructures. X-ray absorption near-edge structure, extended X-ray absorption fine structure, photoluminescence excitation (PLE), and electron paramagnetic resonance studies confirm the good crystalline quality of the incorporated Zn(1-x)MnxS guest species and, in particular, that the Mn2+ ions are randomly distributed and are situated on tetrahedrally coordinated cation sites of the Zn(1-x)MnxS wires for all x up to 0.3. The amount of Mn2+ ions loosely bound to the surface of the Zn(1-x)MnxS nanowires is less than 4% of the total Mn content even for the 3 nm nanostructures up to the highest Mn content of x = 0.3. The effects of the reduction of the lateral dimensions on electronic properties of the diluted magnetic semiconductor were studied by PLE spectroscopy. Due to the quantum confinement of the excitons in the wires an increase of the direct band gap with decreasing particle size is observed.     

Microstructure and electrical properties of BaTiO<Subscript>3</Subscript> and (Ba,Sr)TiO<Subscript>3</Subscript> ferroelectric thin films on nickel electrodes

Nickel thin films have been sputtered on standard Si/SiO₂ substrates with TiO₂ as an adhesive layer. The thermal stability of these substrates was analyzed. SEM images show an increase in grain size with annealing temperature. They were found to be stable till 800°C, beyond which the nickel layer disintegrated. These substrates were used for deposition of BaTiO₃ and (Ba,Sr)TiO₃ dielectric thin films under a reducing atmosphere. The dielectric thin films were processed with various pyrolysis and annealing temperatures in order to optimize the dielectric properties. Increased pyrolysis temperatures showed an increase in the grain size. Results on these nickelised substrates were finally compared with dielectric films deposited on platinized silicon substrates under identical conditions but crystallized in an oxygen atmosphere.     

Kinetic dehydroxylation of nontronite,estimated from isothermal and nonisothermal thermogravimetry

Dehydroxylation of an American nontronite (Manito) was followed via records of isothermal and dynamic thermogravimetry. Analysis of the isothermal weight-change curves (673-753 K). was performed with the procedure suggested by Hancock and Sharp. A fourteen-kinetic equation procedure was employed for analysis of the non-isothermal weight change in the range 623–1023 K. (A second-order decomposition equation seems to fit the dehydroxylation better under these conditions). The activation energies associated with the isothermal and nonisothermal processes are 118.8 and 136.8 kJ/mol^–1, respectively.

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Zusammenfassung Anhand isothermer und herkömmlicher Thermogravimetrie wurde die Dehydroxylierung eines amerikanischen Nontronites (Manito) verfolgt. Die isothermen TG-Kurven (673–753 K) wurden mittels der von Hancock und Sharp (1972). Ein kinetisches Vierzehngleichungsverfahren wurde zur Analyse der nichtisothermen TG-Kurven im Bereich 623–1023 K angestellt. Einer Dehydroxylierung unter diesen Bedingungen scheint eine Zersetzungsgleichung zweiter Ordnung besser zu entsprechen. Die Aktivierungsenefgie für die isothermen bzw. nichtisothermen Prozesse beträgt 118,8 bzw. 136,8 kJ/mol.

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(). (673–753 ) . , 623–1023, . . , , 118,8 136,8 /.