L?slichkeit des Kalium-, Rubidium- und C?sium-Platinchlorids

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Kleiner spectralapparat zum gebrauch in laboratorien

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Molecular dynamics of cryptophane and its complexes with tetramethylammonium and neopentane using a continuum solvent model

Time scales currently obtainable in explicit–solvent molecular dynamics simulations are inadequate for the study of many biologically important processes. This has led to increased interest in the use of continuum solvent models. For such models to be used effectively, it is important that their behavior relative to explicit simulation be clearly understood. Accordingly, 5 ns stochastic dynamics simulations of a derivative of cryptophane-E alone, and complexed with tetramethylammonium and neopentane were carried out. Solvation electrostatics were accounted for via solutions to the Poisson equation. Nonelectrostatic aspects of solvation were incorporated using a surface area-dependent energy term. Comparison of the trajectories to those from previously reported 25 ns explicit–solvent simulations shows that use of a continuum solvent model results in enhanced sampling. Use of the continuum solvent model also results in a considerable increase in computational efficiency. The continuum solvent model is found to predict qualitative structural characteristics that are similar to those observed in explicit solvent. However, some differences are significant, and optimization of the continuum parameterization will be required for this method to become an efficient alternative to explicit–solvent simulation. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 956–970, 1999     

Thiolato-technetium complexes. 4(1): Synthesis,characterization and electrochemical properties of bis(1,2-bis(dimethylphosphino)-ethane)technetium(III) complexes with arene-thiolato ligands

Summary The reaction of trans-[Tc^v(OH)(O)(DMPE)₂]²⁺ (DMPE = 1,2-bis(dimethylphosphino)ethane) with a series of arenethiols in base produces the novel complexes cis-[Tc^III-(SC₆H₄X-p)₂ (DMPE)₂]⁺ for X = H, Cl, Me, OMe, t-Bu. One of the complexes has been characterized by X-ray crystallography: cis-[Tc(SPh)₂(DMPE)₂]PF₆, chemical formula Tc₁S₂P₅F₆C₂₄H₄₂, crystallizes in the orthorhombic space group P2₁nb with Z = 4 and lattice parameters a = 9.311(1) Å, b=11.190(2) Å, c = 31.936(4) Å, Vol = 3327.3(8) ų. The final weighted R-value was 0.033. Averaged structural parameters are Tc—S = 2.29(2) Å, Tc—P (trans to P) = 2.42(1) Å, Tc—P (trans to S) = 2.49(3) Å, Tc—S—C = 118.5(5)°. The complexes have been characterized by FAB mass spectrometry and u.v.-vis. spectroscopy. The visible region charge transfer bands are diagnostic for cis geometry in the [Tc(SR)₂(DMPE)₂]⁺ complexes. Electrochemical and spectroelectrochemical measurements show reversible Tc^III/II redox couples in the range -0.19V to -0.38V versus Ag/AgCl (3 M NaCl). Irreversible couples are exhibited at ca. -1.1 V to -1.2 V for Tc^II/I and +0.7V to +0.9V for Tc^IV/III. Variation in redox potential is discussed in terms of sulphur nucleophilicity.On leave from the Department of Chemistry, The University of Tsukuba, Tsukuba, Ibaraki 305, Japan.On leave from Dipartimento di Chimica dell'Universita' di Sassari, Via Vienna, 2-Sassari, Italy.     

Boronic acids: new coupling partners in room-temperature Suzuki reactions of alkyl bromides. Crystallographic characterization of an oxidative-addition adduct generated under remarkably mild conditions

The Suzuki reaction is an exceptionally useful cross-coupling process that has been widely applied in synthetic chemistry, and boronic acids are, by far, the most commonly employed coupling partner. To date, however, no versatile method has been developed for cross-coupling boronic acids with unactivated alkyl (as opposed to aryl or vinyl) electrophiles. This report describes a catalyst system that achieves this objective at room temperature. On the mechanistic side, this study demonstrates that Pd(P(t-Bu)2Me)2 undergoes oxidative addition under surprisingly mild conditions (0 degrees C). The resulting adduct is sufficiently stable toward beta-hydride elimination that it can be structurally characterized, and it is a chemically competent intermediate in the cross-coupling process.     

A Novel Hydrazine Linker Resin and Its Application for the Solid-Phase Synthesis of alpha-Branched Primary Amines

A novel hydrazine linker resin for solid-phase organic synthesis has been developed. Starting from Merrifield resin, the new N-butyl-N-methylpolystyrene-hydrazine linker is prepared in three steps. Polymer-supported hydrazones, readily prepared from aldehydes and the hydrazine resin, react with alkyl- and arylorganolithium reagents under 1,2-addition to the C-N double bond to afford the corresponding hydrazines. Release from solid support was achieved by reductive N-N bond cleavage using the borane-tetrahydrofuran complex. The resulting alpha-branched primary amines were protected as their amides or carbamates, respectively, and, after purification, were obtained in good overall yields and in high purity (12 examples).     

Evaluation of the inhibition of choline uptake in synaptosomes by capillary electrophoresis with electrochemical detection

A direct method for evaluating choline uptake by the high-affinity choline transport system in synaptosomes was developed using capillary electrophoresis (CE) with electrochemical (EC) detection. On-column EC detection of choline and the internal standard, butyrylcholine, was accomplished with a 25 microm platinum electrode modified with the enzymes, choline oxidase and acetylcholinesterase. Choline uptake was evaluated as a function of choline concentration and a KM value of 1.7 microM was determined. The method was also used to evaluate a new class of redox affinity inhibitors of choline transport. In particular, the effectiveness of 3-[(trimethylammonio)methyl]catechol (TMC) as an inhibitor of choline uptake was examined independently and relative to the inhibition of the well-known inhibitor of choline transport, hemicholinium-3. The IC50 and KI for TMC were determined to be 30 microM and 14 microM, respectively. The combination of the selectivity and sensitivity afforded by CEEC provides a relatively straightforward approach for monitoring choline transport in synaptosomes.     

Spectral-analyse

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Spectral-analyse

     

Untersuchung des Kalkstickstoffs

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