Synthese von 3,3a-Dihydro-2H,5H-azeto[2,1-b]benzo[d]-1,3-oxazin-2,5-dionen,I

The thioformimidates4, which may be obtained by S-alkylation of the thioformamides3, react with chloroacetylchloride/triethylamine to yield the (3R, 4S/3S, 4R)-3-chloro-4-methylthio-2-azetidinones5. Dehalogenation of5 leads to6, which undergoes ring closure by the action of mercuric oxide. Treatment of8, which may be synthesized by chlorolysis of7, with triethylamine gives also the title compounds9.

     

Studies on the Chemistry of Thienoannelated O , N - and S , N -Containing Heterocycles, 28 [1]. Synthesis of Imidazo[1,5- d ]thieno[2,3- b ][1,4]thiazine Derivatives as GABA -Receptor Ligands

 GABA-receptor-ligands are still very interesting in drug-development. Usually benzodiazepines are used in the treatment but they have serious side-effects. Thus, a recently synthesized quioxaline derivative which showed reduced side-effects in an animal model was used as a model-substance. The cyclus was modified to optimize the pharmacological profile. Accordingly, a series of imidazo-thieno-thiazines was synthesized starting from 5-acetyl-2-chloro-3-nitrothiophene to yield 6-ethyl-2,3-dihydro-1H-thieno[2,3-b][1,4]thiazine-2-one. Reaction with potassium tert-butoxide and diethylchlorophosphate gave an intermediate, which resulted in the desired ring system after adding the corresponding isocyanides and potassium tert-butoxide.     

Effect of sequence length, sequence frequency, and data acquisition rate on the performance of a Hadamard transform time-of-flight mass spectrometer

Various factors influencing the performance of a Hadamard transform time-of-flight mass spectrometer (HT-TOFMS) have been investigated. Using a nitrogen corona discharge to produce an ion stream of N ₂ ⁺ , N ₃ ⁺ , and N ₄ ⁺ , it is found for spectra containing only N ₄ ⁺ that the signal-to-noise ratio (SNR) closely approaches the value calculated from the ion background by assuming that the ion background follows a Poisson distribution. In contrast, for a more intense beam containing N ₂ ⁺ , N ₃ ⁺ , and N ₄ ⁺ , the SNR is less than its theoretical value because of the appearance of discrete spikes in the mass spectrum caused by deviations in the actual modulation sequence from the ideal one. These spikes can be reduced, however, by decreasing the modulation voltage. Under these optimized conditions, the pseudo-random sequence length is varied to understand how it alters SNR, mass resolution, and scan speed. When the length of the pseudo-random sequence is doubled, the SNR increases by √2 while the time necessary to record a mass spectrum also doubles. Mass resolution can be varied between 500 and 1200 at m/z = 609 as the sequence length, modulation speed (10 MHz, 25 MHz), and acquisition rate (up to 50 MHz) are changed. Scan speeds of 6000 passes per s can be obtained using a sequence containing 4095 elements modulated at 25 MHz. The capability to tailor the HT-TOFMS to increase the scan speed and resolution with a constant 50% duty cycle makes the technique extremely appealing as a mass analyzer for measuring rapid changes in the composition of an ion stream.     

Computational study of the influence of solvent on (16)O/(18)O equilibrium isotope effects in phosphate deprotonation reactions

Results from theoretical calculations of (16)O/(18)O equilibrium isotope effects (EIEs) on deprotonation of phosphate and methyl phosphate monoanions as well as their deuterated counterparts are reported. The EIEs are calculated from the Bigeleisen equation using harmonic vibrational frequencies from several quantum mechanical methods (HF, DFT, MP2, and AM1). All methods correctly predict the qualitative trends in the EIEs related to the different isotope substitutions. However, the calculated gas-phase values are found to be systematically higher than those experimentally observed in aqueous solution. On the other hand, the addition of explicit solvent molecules (up to 24 waters) in the first solvation shells of the phosphate ion substantially improves the calculated EIE, which approaches the experimental value with increasing size of the water cluster. The large effects of surrounding water molecules on the phosphate deprotonation EIE can be explained by the strong solute-solvent interactions, which result in solvent coupled vibrational modes of the phosphate ions.     

Shifts in polystyrene particle surface charge upon adsorption of the Pluronic F108 surfactant

Electrical field-flow fractionation (ElFFF) and sedimentation field-flow fractionation (SdFFF) were used in combination to study the adsorption of the triblock polymeric surfactant, Pluronic F108 [(EO)129-(PO)56-(EO)129] to 200 nm polystyrene (PS) latex spheres. The SdFFF technique allowed an accurate determination of the mass of surfactant adsorbed on each particle from a solution of given concentration. To complement this isotherm study, we show that ElFFF can be used to measure fractional coverages of the formed electrically neutral surfactant layers on the charged PS particles. Through a combination of the two techniques it is possible to gain information about the structure of the adsorbate layer. Thus, when Pluronic F108 is taken up by the PS surface from solutions of low concentration, all three blocks appear to adhere to the surface as long as there is free space available. As the solution concentration increases and the fractional coverage reaches approximately 20%, the surface turns crowded enough to let the strongly adsorbing PPO blocks competitively displace the weakly adherent PEO blocks, which gradually rise to extend into the aqueous phase until the surface is fully saturated.     

Polysulfonylamine. LXXIII [1]. Metall(II)-dimesylamid-Tetrahydrate: Das Dimesylamid-Anion als einzähniger O-Ligand und tetrafunktioneller Wasserstoffbrücken-Akzeptor in den isotypen Komplexen [M(H2O)4 {(CH3SO2)2N}2] mit M = Magnesium,Nickel, Kupfer und Zink

Polysulfonyl Amines. LXXIII. Metal(II) Dimesylamide Tetrahydrates: The Dimesylamide Anion as a Monodentate O-Ligand and a Tetrafunctional Hydrogen Bond Acceptor in the Isotypic Complexes [M(H₂O)₄{(CH₃SO₂)₂N}₂], where M = Magnesium, Nickel, Copper, or Zinc By treating aqueous HN(SO₂CH₃)₂ solutions with the appropriate metal hydroxides, oxides, or carbonates, the crystalline tetrahydrates M[(CH₃SO₂)₂N]₂ · 4 H₂O (M = Mg, Ca, Mn, Co, Ni, Cu, Zn, Cd) were obtained and analytically characterized. The crystal structures of the Mg, Ni, Cu and Zn compounds, as determined by single-crystal X-ray diffraction at low temperatures, reveal an isotypic series (triclinic, space group P1 , Z = 1). The structures consist of centrosymmetric trans-octahedral [M(H₂O)₄{(CH₃SO₂)₂N}₂] molecules in which the anionic ligand acts as a monodentate O-donor. For the Mg, Ni and Zn complexes, the M? OH₂ and M? O(anion) distances lie in the ranges 203–206 pm and 209–214 pm, respectively. The copper compound features a marked Jahn-Teller distortion with Cu? OH₂ = 195.8 and 197.7 pm and Cu? O(anion) = 232.5 pm. The cis-angles O? M? O of the four molecules do not deviate appreciably from 90°. The complex units are associated through a highly organized three-dimensional hydrogen bond network in which all the water protons act as donors and the non-coordinating oxygen atoms and the nitrogen atom of the anionic ligand are involved as acceptors. The H-bond pattern is subjected to a graph-theoretical analysis at the first and second levels.     

Stereoselective synthesis of chiral, non-racemic 1,2,3-tri- and 1,3-disubstituted ferrocene derivatives

Chiral, non-racemic 1,2,3-trisubstituted ferrocene derivatives are accessible from monosubstituted ferrocenes through two sequential ortho-deprotonation reactions; removal of the central substituent gives 1,3-disubstituted ferrocenes.     

Elementorganische Amin/Imin-Verbindungen,XXXI. Cyclometallierung bei N-tert-Butyl-Phosphor-Stickstoff-Iridiumkomplexen

Element-Organic Amine/Imine Compounds, XXXI. - Cyclometallation with N-tert-Butyl-Phosphorus-Nitrogen Iridium Complexes The interaction of R¹R²N–PNR³ ( 1 ) (R¹  SiMe₃, tBu, iC₃H₇; R²  R³  SiMe₃, tBu) with [M(COD)(μ-Cl)]₂ ( 2 ), M  Rh, Ir, affords the amino(imino)phosphane complexes 3 , whose PN bond adds methanol with formation of the diamidophosphite complexes 4 . Already below 0°C the iridium compounds of 4 undergo cyclometallation of a tBu methyl group (R²) with formation of the hydrido-iridium metallaheterocycles 5 . The structures of 4b and 5a are elucidated by X-ray analyses.     

Mass transfer characteristics of plasmids in monoliths

The hydrodynamic properties and pore-structure of monoliths based on functionalized poly(glycidyl methacrylate-ethylene dimethacrylate) were characterised by pulse response experiments using different probes representing a wide range of molecular mass. On a small scale, band spreading was found to be caused to the extent of more than 90% by extra-column effects. These monoliths have large channel diameters, providing a suitable chromatography adsorbent for processing of large molecules. Dynamic and static binding capacity for plasmid DNA was investigated. For our model plasmid, consisting of 4.9 kbp, a capacity of 7 mg/mL was observed in comparison to 0.3 mg/mL for a conventional medium designed for protein separation. When plasmids were loaded on the monolith a gradual increase in pressure drop was observed. The channels filled up and the cross-sectional area available for liquid flow decreased. Therefore, a higher pressure drop was observed during elution. This is caused by (i) shrinking of the channels as effect of the high salt concentration, (ii) high viscosity of the mobile phase due to high concentration of plasmids, and (iii) an increase of the hydrodynamic radius of the plasmid with salt concentration from 45 nm at 150 mM to 70 nm at 2 M NaCl, as measured by dynamic light scattering. These types of monoliths are considered to be the preferred adsorbents for plasmid separation.