Zur Bestimmung der Sulfit- und Thiosulfationen nebeneinander

Zusammenfassung Zur Bestimmung von Sulfit und Thiosulfat nebeneinander wird folgendes Verfahren beischrieben: In einem aliquoten Teil der zu untersuchenden Lösung wird mit elementarem Jod oxydiert, wobei die Sulfitionen zwei Äquivalente, die Thiosulfationen ein Äquivalent Jod je Mol verbrauchen. In einem zweiten aliquoten Teil der zu untersuchenden Lösung werden die Ionen mit — aus KBrO₃ + KBr hergestelltem — NaOBr oxydiert; die Sulfitionen verbrauchen dabei zwei Äquivalente, die Thiosulfationen acht Äquivalente Brom je Mol.     

A Preparatively Simple Access to Homochiral Heterocyclic α-Hydroxy Acids and their Derivatives

 The synthesis of homochiral heterocyclic α-hydroxy acids starting from (S)- and (R)-malic acid using hexafluoroacetone as protecting and activating agent is described. The new compounds are useful building blocks for peptide and depsipeptide modification.     

Die Kristallstruktur des Lithiumdigermanats Li2Ge2O5

The compound Li₂Ge₂O₅ has been prepared by annealing a glassy melt (500° C). The lattice parameters have been determined from single crystal photographs:a=5,99,b=15,19,c=4,97 Å and β=90,0°, space group C _S ⁴ :?Cc. Li₂Ge₂O₅ has a layer structure and is isostructural with Li₂Si₂O₅.     

Zur Biogenese der Betacyane: Versuche mit [2-14C]-Dopaxanthin

On the biogenesis of betacyanins. Expaiments with [2-¹⁴C]-dopaxanthine Labelled dopaxanthine is prepared from betanin by a double exchange procedure replacing first its cyclodopa part by diethylamine and effecting the second exchange with 2-[¹⁴C]-dopa on the purified intermediate ‘DEA-betalain’; the specific activity delivered with the dopa allowed accurate determination of ? in the electronic spectrum of dopaxanthine (λ_max 488 nm, ? = 41.800). The C(2)-labelled dopaxanthine is incubated into the fruits of Opuntia bergeriana. The incorporation rates into betanin are found to correspond approximately to those obtained in earlier experiments with labelled dopa alone: Only 1--5% of the label showed up in the cyclodopa moiety of the betanin (which is isolated as cyclodopa-glucoside) whereas 99--95% of the radioactivity was associated with the betalamic acid part (recovered in form of indicaxanthine).     

Die durch Silberionen katalysierte Umlagerung von Propargyl-phenyläther

It is known that propargyl-phenylethers rearrange at about 200° to 2 H-chromenes [1–4]. It is shown that this rearrangement occurs in benzene or chloroform at lower temperatures (20–80°) in the presence of silver-tetrafluoroborate (or-trifluoracetate). The ethers examined are presented in Scheme 1. Thus in chloroform at 61° in the presence of AgBF₄, phenyl-propargylether ( 3 ) yields 2 H-chromene ( 13 ). With 0.78 molar equivalents AgBF₄ in benzene at 80° the same ether 3 yields a 3:1 mixture of 2-methyl-cumaron ( 14 ) and 2 H-chromene ( 13 ). From 1′-methylpropargyl-phenylether ( 4 ) and 2′-butinyl-3,5-dimethylphenylether ( 5 ) under similar conditions the corresponding chromenes 16 and 17 resp. are obtained. Rearrangement of propargyl- and 2′-butinyl-1-methyl-2-naphthylether ( 6 and 7 resp.) in benzene at 80° in the presence of AgBF₄ gives the corresponding allenyl-naphthalenones 18 and 19 resp. Treatment of propargyl- and 2′-butinyl-mesityl-ether ( 8 and 9 resp.), and propargyl- and l′-methylpropargyl- 2 , 6 -dimethyl-phenylether ( 10 and 11 resp.) in benzene at 80° with AgRF, yields as the only product the corresponding 3 -allenyl-phenols 21 , 22 , 24 and 25 (Scheme 3). It is shown that in the presence of μ-dichlor-dirhodiuni (1)-tetracarbonyl in benzene a t 80° the ether 4 rearranges to 2-methyl-2H-chromene (16). However with this catalyst the predominant reaction is a cleavage to phenol. No reaction was observed when ethers 3 and 12 , (Scheme 7 ) were treated with the tris-(trimethylsily1)-ester of vanadic acid in benzene a t 80° (see also [8]). By analogy with the known mechanism for thc silver catalysis of the reversible propargylesterl/allenylester rearrangement [S], the silver (1)ion is assumed to form a pre-equilibrium π-complex with the C, C-triplebond of the substrate. This complex then undergoes a [3s, 3s]-sigmatropic rearrangement (Scheme 2). In the case of the others 6 , 7 and 12 the resulting allenyldienones were isolated. The 2,G-dimethyl substituted ethers 8 , 9 , 10 and 11 resp. first give the usual allenyl- dienones (Scheme 3). These then undergo a novel silver catalysed dienon-phenol-rearrangement (Sclzenzu4) to give the 3-allenylphenols 21 , 22 , 24 and 25 . Thc others 3 , 4 and 5 with free ortho positions presumably rearrange first to the non-isolated 2-allenyl-phenols 15 , 42 and 43 resp.(Scheme 7). These then rearrange, either thermally or by silver (1)ion catalysis to the 2H-chromenes 13 , 16 and 17 resp. The rate of the rearrangement of 2-allenylphenol ( 15 ) to 13 at room temperature in benzene or chloroform is approximately doubled when silver ions are present as catalyst.     

Linear low density polyethylene: Microstructure and sealing properties correlation

The microstructures of four commercial linear low density polyethylenes (LLDPE) were evaluated and correlated with their sealing properties. Atomic Force Microscopy (AFM), Temperature Rising Elution Fractionation (TREF), Differential Scanning Calorimetry (DSC) and Crystallization Analysis Fractionation (CRYSTAF) experiments revealed that the comonomer distribution is one of the main factors that influence the sealing properties. The superior sealing performance showed by metallocene LLDPE samples in comparison to Ziegler-Natta LLDPE samples can be attributed to their well balanced chemical composition distribution.     

Negative electrorheological responses of micro-polar fluids in the finite spin viscosity small spin velocity limit. I. Couette flow geometries

Negative electrorheological responses induced by micro-particle electrorotation in two-dimensional Couette flow geometries are analyzed by a set of continuum modeling field equations originating from anti-symmetric/couple stress theories in the finite spin viscosity small spin velocity (FSV) limit. Analytical solutions are obtained for the first time to express the spin velocity, linear velocity, and effective viscosity in terms of the electric field strength, driving shear rate, boundary condition selection parameter, and spin viscosity. Good agreement is achieved between the FSV theoretical predictions presented herein and the experimental measurements reported in recent literature for the effective viscosity for low driving shear rates.     

The conserved protein kinase-A target motif in synapsin of Drosophila is effectively modified by pre-mRNA editing

Background  

Synapsins are abundant synaptic vesicle associated phosphoproteins that are involved in the fine regulation of neurotransmitter release. The Drosophila member of this protein family contains three conserved domains (A, C, and E) and is expressed in most or all synaptic terminals. Similar to mouse mutants, synapsin knock-out flies show no obvious structural defects but are disturbed in complex behaviour, notably learning and memory.     

Time-dependent density functional theory molecular dynamics simulation of doubly charged uracil in gas phase

We use time-dependent density functional theory and Born-Oppenheimer molecular dynamics methods to investigate the fragmentation of doubly ionized uracil in gas phase. Different initial electronic excited states of the dication are obtained by removing electrons from different inner-shell orbitals of the neutral species. We show that shape-equivalent orbitals lead to very different fragmentation patterns revealing the importance of the intramolecular chemical environment. The results are in good agreement with ionion coincidence measurements of uracil collision with 100 keV protons.