Synthesen und Reaktionen von Pyridazinderivaten, 11. Mitt.: 5-Acyl-4-pyridazincarbonsäurrester als „key intermediates” für 4-Acylpyridazine und 4-Alkyl-bzw. 4-Arylpyridazino[4,5-d]pyridazin-1 (2H) one

A convenient general method of preparing 4-acylpyridazines (4) is reported. It involves homolytic acylation of ethyl-4-pyridazinecarboxylate yielding ethyl-5-acyl-4-pyridazinecarboxylates (2) which easily can be converted to4 by alkaline hydrolysis followed by decarboxylation. The hitherto unknown pyridazino[4,5-d]pyridazine-1 (2H) ones bearing an alkyl- or arylsubstituent on C-4 (5a-g) were prepared in quantitative yields by reaction of2 with hydrazine.

10. Mitt.:G. Heinisch, A. Jentzsch undI. Kirchner, Tetrahedron Lett.1978, 619.     

An improved nicotinic pharmacophore and a stereoselective CoMFA-model for nicotinic agonists acting at the central nicotinic acetylcholine receptors labelled by [3H]-N-methylcarbamylcholine

A study of a series of compounds with agonistic effect at the alpha4beta2 nicotinic acetylcholine receptors resulted in an improved pharmacophore model as well as a CoMFA model. The pharmacophore was composed of three pharmacophoric elements: (1) a site point (a) corresponding to a protonated nitrogen atom, (2) a site point (b) corresponding to an electronegative atom capable of forming a hydrogen bond, and (3) the centre of a heteroaromatic ring or a C=O bond (c). The pharmacophoric elements were related by the following parameters: (a-b) 7.3-8.0 A, (a-c) 6.5-7.4 A, and the angle between the two distance vectors (delta bac) 30.4-35.8 degrees. In addition to this, a stereoselective CoMFA model was developed, which showed good predictability even for compound classes not present in the training set.     

(Z)-1-[2-(Triarylstannyl)vinyl]-1-cycloheptanols: Synthesis, characterization, halodemetallation and crystal structures

The synthesis and characterization by ¹H, ¹³C, ¹¹⁹Sn NMR and ¹¹⁹Sn Mössbauer spectroscopy of (Z)-1-[2-(triphenylstannyl)vinyl]-1-cycloheptanol,

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(1), and (Z)-1-[2-tri-p-tolylstannyl)vinyl-1-cycloheptanol,

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(2), are described, together with their halodemetallation by I₂, Br₂ and ICIl to yield derivatives of the types

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(Ar = phenyl or p-tolyl, N = 1, 2; X = I, Br, Cl, respectively). The solid-state structures of four compounds have been determined by X-ray diffraction analysis. In the crystals of

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(1) and

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(2) the Sn atom has a tetrahedral geometry distorted towards trigonal bipyramid as a consequence of a close intramolecular contact with the hydroxyl O(1) atom of 2.742(3) Å and 2.768(3) Å, respectively. A trigonal bipyramidal geometry is found in

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(12) and

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(4), in which significant Sn---O(1) interactions are noted [2.437(8) Å and 2.407(8) Å, respectively].     

Quantitative analysis of the low molecular weight serum proteome using 18O stable isotope labeling in a lung tumor xenograft mouse model

With advancements in the analytical technologies and methodologies in proteomics, there is great interest in biomarker discovery in biofluids such as serum and plasma. Current hypotheses suggest that the low molecular weight (LMW) serum proteome possesses an archive of clipped and cleaved protein fragments that may provide insight into disease development. Though these biofluids represent attractive samples from which new and more accurate disease biomarkers may be found, the intrinsic person-to-person variability in these samples complicates their discovery. Mice are one of the most extensively used animal models for studying human disease because they represent a highly controllable experimental model system. In this study, the LMW serum proteome was compared between xenografted tumor-bearing mice and control mice by differential labeling utilizing trypsin-mediated incorporation of the stable isotope of oxygen, 18O. The digestates were combined, fractionated by strong cation exchange chromatography, and analyzed by nanoflow reversed-phase liquid chromatography coupled online with tandem mass spectrometry, resulting in the identification of 6003 proteins identified by at least a single, fully tryptic peptide. Almost 1650 proteins were identified and quantitated by two or more fully tryptic peptides. The methodology adopted in this work provides the means for future quantitative measurements in comparative animal models of disease and in human disease cohorts.     

One electron molecules with relativistic kinetic energy: Properties of the discrete spectrum

We discuss the discrete spectrum of the operator $$H_K (c) = \left[ { - \hbar ^2 c^2 \Delta + m^2 c^4 } \right]^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} - \sum\limits_{k = 1}^K {Z_k e^2 \left| {x - R_k } \right|^{ - 1} } $$ . More specifically, we study 1) the behaviour of the eigenvalues when the internuclear distances contract, 2) the existence of ac-independent lower bound forH _K (c)?mc ², 3) the nonrelativistic limit of the eigenvalues ofH _K (c)?mc ².     

Photochemische synthese von H2Fe3-komplexen und ihre aktivität bei der photokatalytischen hydrierung von olefinen und dienen

The photochemical reaction of the trinuclear complex Fe₃(CO)₁₀NSi(CH₃)₃ under hydrogen leads to substitution of the bridging carbonyl group by two hydrogens. The resulting complex H₂Fe₃(CO)₉NSi(CH₃)₃ acts as a catalyst in the photochemical hydrogenation of olefins and dienes.     

Electrodeposition on copper powder as a means of separation for trace analysis of noble metals in activation analysis: A tracer study

Studies are reported to illustrate surface adsorption of¹⁴⁴Ce,⁵⁹Fe,²³⁴Th,²³³U,²³⁷Np,²³⁹Pu and²⁴¹Am on a dextran gel made by crosslinkage of the polysaccharide dextran (Sephadex). Fixation of such elements was studied from aqueous solution and was found to depend on pH, age of the tracer solution, hydrolytic behaviour of the adsorbed species, concentration and the valency of the adsorbed element.     

Carbazole compounds as host materials for triplet emitters in organic light-emitting diodes: polymer hosts for high-efficiency light-emitting diodes

A carbazole homopolymer and carbazole copolymers based on 9,9'-dialkyl-[3,3']-bicarbazolyl, 2,5-diphenyl-[1,3,4]-oxadiazole and 9,9-bis(4-[3,7-dimethyloctyloxy]phenyl)fluorene were synthesized and their electrical and photophysical properties were characterized with respect to their application as host in phosphorescent polymer light-emitting diodes. It is shown that the triplet energy of a polymer depends on the specific connections between its building blocks. Without changing the composition of the polymer, its triplet energy can be increased from 2.3 to 2.6 eV by changing the way in which the different building blocks are coupled together. For poly(9-vinylcarbazole) (PVK), a carbazole polymer often used as host for high-energy triplet emitters in polymer light-emitting diodes, a large hole-injection barrier of about 1 eV exists due to the low-lying HOMO level of PVK. For all carbazole polymers presented here, the HOMO levels are much closer to the Fermi level of a commonly used anode such as ITO and/or a commonly used hole-injection layer such as PEDOT:PSS. This makes high current densities and consequently high luminance levels possible at moderate applied voltages in polymer light-emitting diodes. A double-layer polymer light-emitting diode is constructed comprising a PEDOT:PSS layer as hole-injection layer and a carbazole-oxadiazole copolymer doped with a green triplet emitter as emissive layer that shows an efficacy of 23 cd/A independent of current density and light output.     

Capillary zone electrophoresis in non-aqueous solutions: pH of the background electrolyte

Although the establishment of a pH scale and the determination of the pH in water is not problematic, it is not a straightforward task in non-aqueous solvents. As capillary zone electrophoresis (CZE) in organic solvents has gained increasing interest, it seems to be valuable to re-discuss the concept of the pH in such media, especially pointing to those aspects, which make pH measurement uncertain in non-aqueous solvents. In this review, the relevant aspects when dealing with primary standard (PS) and secondary standard (SS) as recommended by the International Union of Pure and Applied Chemistry (IUPAC), and the usage of the operational pH are discussed with special emphasis to non-aqueous solvents. Here, different liquid junction potentials, incomplete dissociation of the electrolytes (especially in solvents with low or moderate relative permittivity) and the occurrence of homo- and heteroconjugation must be taken into account. Problems arising in capillary zone electrophoresis practice are addressed, e.g. when the background electrolyte (BGE) consists of organic solvents, but the measuring electrode (normally the glass electrode) is calibrated with aqueous buffers, and the liquid junction potentials between the solvents do not cancel each other. The alternative concept of establishing a certain pH is described, using mixtures of reference acids or bases with known pKa in the organic solvent, and their respective salts, at a certain concentration ratio, relying to the Henderson-Hasselbalch equation. Special discussion is directed to those organic solvents most common in capillary zone electrophoresis, methanol (MeOH) and acetonitrile (ACN), but other solvents are included as well. The potential significance of small amounts of water present in the organic solvent on changes in pKa values, and thus on the pH of the buffering components is pointed out.     

An efficient and highly flexible synthesis of (α),β-unsaturated γ-oxoesters

Siloxy substituted methyl cyclopropanecar?ylates are cleaved by bromine to afford α-bromo-γ-oxoester and, after treatment with triethylamine, good yields of α,β-unsaturated γ-oxoesters.