VNCl2(Pyridin)2 Synthese,IR-Spektrum und Kristallstruktur

VNCl₂(Pyridine)₂; Synthesis, I. R. Spectrum, and Crystal Structure VNCl₂(Pyridine)₂ is formed from the cyclothiazeno-vanadium(IV) complex [VCl(N₃S₂)(Pyridine)₂]₂ · 2 CH₂Cl₂ in boiling toluene in form of brown-red, hydrolysis sensitive crystal. It was characterized by its I.R. spectrum and an X-ray crystal structure determination. VNCl₂(Pyridine)₂crystallizes in the orthorhombic space group Pccn with four formula units per unit cell (668 observed independent reflexions, R = 0.055). Lattice constants: a = 1550, b = 924, c = 832 pm. Monomer molecules are situated on twofold rotation axes. They are stacked along the V?N axis to form columns V?N…V. The short VN bond of 160 pm corresponds to a triple bond, whereas the V…N distance of 256 pm indicates a weak interaction. The V? N(Pyridine) and V? Cl bond lengths are 213.0 and 233.5 pm, respectively.     

A Highly Stereoselective Synthesis of C(11)-Functionalized Aromatic Steroids by an Intramolecular Benzocyclobutene-Olefin -Cycloaddition. Preliminary Communication

The racemic cis-anti-trans-steroids 9 to 11 have been synthesized in a highly stereoselective manner starting from 4-methoxybenzocyclobutene carboxylic acid via the key step 8 → 9 . (cf. Scheme 2).     

Liquid chromatographic determination of 4,4'-dinitrocarbanilide, the active component of the infertility agent nicarbazin, in chicken, duck, goose, and snake eggs

4,4'-Dinitrocarbanilide (DNC) was extracted from chicken, duck, goose, and snake eggs and isolated by reversed-phase liquid chromatography. DNC was detected by ultraviolet absorbance at 347 nm and quantitated by comparison with a calibration standard. Recoveries of DNC from fortified control chicken, duck, goose, and snake egg samples were determined for DNC levels of 0.16, 10, and 16 microg/g. The mean recoveries from chicken, duck, goose, and snake eggs were 92 +/- 4, 88 +/- 9, 87 +/- 7, and 95 +/- 6%, respectively. The method limits of detection for DNC in chicken, duck, goose, and snake eggs ranged from 0.015 to 0.035 microg/g. The reported method is much simpler than and equally efficient as previous methods developed for the determination of DNC residues in egg contents.     

Ein v. Staudt-Clausenscher Satz für periodische Bernoullizahlen

Letk, n be relatively prime integers, 1k<n. The numbersB _k ^m =m(i/2) ^m cot^(m–1)(k/n),m2, belong to then-th cyclotomic field. They occur as values of certain simple Dirichlet series at integral arguments and have a natural interpretation as generalized Bernoulli numbers. Therefore the arithmetic properties of these numbers arouse some interest. Ifn is not a prime power,B _k ^m /m is an algebraic integer. In the other case, i.e.n=p ^e ,p prime, the fractional part ofB _k ^m /m resp.B _k ^m is determined in this paper. It is periodic modulop–1 and exhibits a connection between these Bernoulli numbers and the Stirling numbers of the second kind.     

Coordination compounds of disulphur dinitride

Summary Coordination compounds of the S₂N₂ molecule including methods for their preparation, reactivities, i.r. data, structures, and aspects of chemical bonding are reviewed. Methods of synthesis include reactions of S₂N₂, S₄N₄ or (NSCl)₃ with metal halides, metal complexes such as carbonyls, or even metals themselves. In all cases, the planar S₂N₂ ring is coordinated, usuallyvia both, of its nitrogen atoms so that S₂N₂ acts as a bridging ligand between two metal centres; short contact distances imply that halogen atoms linked to the metal atoms show some interaction with the sulphur atoms. The stability of S₂N₂ is greatly enhanced by coordination. In the i.r. spectra, two characteristic S₂N₂ vibrations assist identification of the S₂N₂ species, a ring stretching mode being observable atca. 850 cm^–1 and the out-of-plane deformation at 450–490 cm^–1.     

π-Bindungsbeitrag in Boranen, 2. Mitt.:Ab initio- und Kraftfeld-Rechnungen von Vinyldifluorboran

Ab initio calculations on vinyldifluoroborane yield a -contribution of 23 kJ/mol (5.5 kcal/mol) mainly due to the C=C bond and not to the lone pairs of the fluorine atoms. The rotational barrier was also determined. The force field calculations favour the interpretation of the bond structure derived from the theab initio results.

     

Artificial multiple criticality and phase equilibria: an investigation of the PC-SAFT approach

The perturbed-chain statistical associating fluid theory (PC-SAFT) is studied for a wide range of temperature, T, pressure, p, and (effective) chain length, m, to establish the generic phase diagram of polymers according to this theory. In addition to the expected gas-liquid coexistence, two additional phase separations are found, termed "gas-gas" equilibrium (at very low densities) and "liquid-liquid" equilibrium (at densities where the system is expected to be solid already). These phase separations imply that in one-component polymer systems three critical points occur, as well as equilibria of three fluid phases at triple points. However, Monte Carlo simulations of the corresponding system yield no trace of the gas-gas and liquid-liquid equilibria, and we conclude that the latter are just artefacts of the PC-SAFT approach. Using PC-SAFT to correlate data for polybutadiene melts, we suggest that discrepancies in modelling the polymer density at ambient temperature and high pressure can be related to the presumably artificial liquid-liquid phase separation at lower temperatures. Thus, particular care is needed in engineering applications of the PC-SAFT theory that aims at predicting properties of macromolecular materials.     

Synthesis, characterization, and reactivity of half-sandwich Ru(II) complexes containing phosphine, arsine, stibine, and bismutine ligands

The synthesis and some reactions of the Ru(II) and Ru(IV) half-sandwich complexes [RuCp(EPh₃)(CH₃CN)₂]⁺ (E=P, As, Sb, Bi) and [RuCp(EPh₃)(η³-C₃H₅)Br]⁺ have been investigated. The chemistry of this class of compounds is characterized by a competitive coordination of EPh₃ either via a RuE or a η⁶-arene bond, where the latter is favored when the former is weaker, that is in going down the series. Thus in the case of Bi, the starting material [RuCp(CH₃CN)₃]⁺ does not react with BiPh₃ to give [RuCp(BiPh₃)(CH₃CN)₂]⁺ but instead gives only the η⁶-arene species [RuCp(η⁶-PhBiPh₂)]⁺ and [(RuCp)₂(μ-η⁶,η⁶-Ph₂BiPh)]²⁺. Similarly, the EPh₃ ligand can be replaced by an aromatic solvent or an arene substrate. Thus, the catalytic performance of [RuCp(EPh₃)(CH₃CN)₂]⁺ for the isomerization of allyl-phenyl ethers to the corresponding 1-propenyl ethers is best with E=P, while the conversion drops significantly using the As and Sb derivatives. By the same token, only [RuCp(PPh₃)(CH₃CN)₂]⁺ is stable in a non-aromatic solvent, whereas both [RuCp(AsPh₃)(CH₃CN)₂]⁺ and [RuCp(SbPh₃)(CH₃CN)₂]⁺ rearrange upon warming to [RuCp(η⁶-PhEPh₂)]⁺ and related compounds. In addition, the potential of [RuCp(EPh₃)(CH₃CN)₂]⁺ as precatalysts for the transfer hydrogenation of acetophenone and cyclohexanone has been investigated. Again aromatic substrates are clearly less suited than non-aromatic ones due to facile η⁶-arene coordination leading to catalyst's deactivation.     

EFFECTS OF BOUND MONOCLONAL ANTIBODIES ON THE DECAY OF THE PHOTOTRANSFORMATION INTERMEDIATES I1,21700 FROM NATIVE Avena PHYTOCHROME*

Abstract–Thc kinetics of the microsecond phototransformation intermediates of 124 kDa Avena phytochrome (1700^1,2) were studied in the prcsence of bound monoclonal antibodies at various temperatures. A global analysis was applied to the decays at all wavelengths at each temperature in order to derive the rate constants and the decay-associated spectra of the three decay components. Monoclonal antibodies bound to specific epitopes altered the Arrhenius parameters of both 1700^1,2 decay components. The strongest influence on these parameters was observed with OAT 8 (epitope between residues 624 and 686), which decreased by more than 50% the activation parameters of both components. This decrease is interpreted to result from an increased flexibility induced by this antibody in the ground state or in the transition state of bonds changing during the decay of both 1700 transients. Thus, the OAT 8 cpitope appears to be functionally important during the decay of the 1700^1,2 intermediates. For the case of 1100¹ bound OAT 23 and OAT 25 (epitopes between residues 1 and 66) reduced even further the relatively small flexibility of these bonds in the red light-absorbing form of phytochrome (P1) without antibodies, as reflected by the high preex-ponential factors for its decay. This resulted also in higher activation energies for this decay in the presence of the antibodies. Thus, the amino-terminus should act as a rigid spacer of the chromophore cavity without affecting it during the microsecond transformation, because the Arrhenius parameters for these decays are similar to those for small phytochrome. The possible implications of the influence of the various antibodies on the bleaching remaining after the decay of 1700^1,2 are discussed.