Rapid chiral on-chip separation with simplified amperometric detection

The enantiomers of adrenaline, noradrenaline, ephedrine and pseudoephedrine were separated by capillary electrophoresis on a micromachined device. Detection was carried out with a new two-electrode amperometric detector, eliminating the need for individual counter and reference electrodes. Separation of the isomers was achieved by employing carboxymethyl-beta-cyclodextrin as chiral selector in the buffer, partly with the additional inclusion of the crown ether 18-crown-6. Plate numbers of up to 20,000, chiral resolutions of 2.5 and detection limits of the order of 10(-7) M were achieved. All separations were completed in less then 3 min.     

Dehydration of Alkanones by Bare FeO+ Involves the ω/(ω − 1) Positions: Exclusion of Iron Carbenes as Intermediates. Preliminary Communication

Fourier-transform ion-cyclotron-resonance (FTICR) mass spectrometry has been used to uncover the mechanisms by which FeO⁺ dehydrates heptan-4-one ( 5a ) and nonan-5-one ( 6a ) in the gas phase. The study of isotopomeric ketones provides evidence that H₂O loss is not due to a 1,1-elimination, thus ruling out the intermediacy of high-valent iron-carbene species. Rather, H₂O is generated in a formal 1,2-elimination involving the ω/ω ? 1 positions of the alkyl chain (‘remote C? H bond activation’). In the consecutive alkene/H₂O elimination, the olefins (ethylene from 5a and propene from 6a ) originate from the terminal part of one alkyl chain, and the H-atom is transferred to the FeO⁺ moiety in the course of this process, builds up together with an H-atom from the ω/ω-1 position of the other alkyl chain the H₂O molecule. In either case, the O-atom of H₂O is provided by the FeO⁺ species.     

Does ionized diacetylene have a positive proton affinity?

Singly and doubly charged C₄H₃^+/2+ ions generated upon electron ionization (EI) of the neutral precursors 1,3-butadiene, benzene, and exo-methylene cyclopropane, respectively, are examined by sector-field mass-spectrometry. Charge stripping of the mass-selected monocations affords the corresponding dications and charge exchange of the C₄H₃²⁺ dications allows for the reverse redox process. Refined analysis and additional MS/MS studies suggest that the monocations are mixtures of isomeric ions formed upon ionization, whereas only a single type of dication seems to be formed. As an average of energy-resolved measurements, a vertical ionization energy of IE_v(C₄H₃⁺)=16.5±0.4 eV is derived. In addition to the experimental work, density functional theory is used for a computational exploration of the mono- and dicationic species. The best theoretical estimates are IE_a(C₄H₃⁺)=16.33 eV and IE_v(C₄H₃⁺)=16.49 eV for the most stable isomer H₂C=C---CCH⁺. Combination of the experimental and theoretical findings leads to the conclusion that the diacetylene cation C₄H₂⁺ has indeed a positive proton affinity of PA(C₄H₂⁺)=1.50±0.42 eV.     

Definitive Proof for the Operation of Isotopically Sensitive Branching (‘Metabolic Switching’) in FeI-Mediated C?H Bond Activation in the Gas Phase Short Communication

Rigorous regio- and stereospecific labeling experiments are performed to demonstrate the operation of the previously suggested operation of ‘isotopically sensitive branching’ in Fe^I-mediated C? H bond activation. For the hexane-1,6-diol/Fe⁺-complex, it is shown that dehydrogenation involves specifically the central C(3)/C(4) position, and the study of the stereospecifically labeled D ,L - and meso-[3,4-D₂]-isotompomers 1e and 1f demonstrates that dehydrogenation proceedes via two competing pathways (i.e. ‘anti’- vs. ‘syn’-route). The contribution of these routes to the product formation is – due to a kinetic isotope effect – controlled by the relative configuration at the labeled positions C(3)/C(4). For the D ,L -form 1e , we estimate a ratio of 49:1 in favor of the ‘anti’-route; due to an isotope effect, this ratio drops to 4.3:1 for the meso-form 1f .     

Synthesen von Xyluron- und Riburonsäurederivaten

Zusammenfassung Durch acylierende Dehydratisierung von 1,2-Isopropyliden-d-xylo-und-d-ribo-pentodialdo-furanoseoxim bzw. aus Furanuronsäureestern und-amiden werden über eine Reihe von Zwischenstufen verschiedene 3-O-Acyl-pentofuranuronsäurenitrile synthetisiert und deren Reaktionen untersucht.

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Synthesis of xyluronic and riburonic acid derivatives

Various 3-O-acyl-pentofuranurononitrils were synthesized by acylating dehydration of 1,2-isopropylidene-d-xylo- andd-ribo-pentodialdo-furanose oximes, or pentofuranuronic acids via intermediates. Their reactions were investigated.

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Mit 1 Abbildung

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Aus den DissertationenH. W. Oberwalder (1970) undE. Wildschek (1967), Technische Hochschule in Graz.     

Explanation of the real stress-strain-behavior of elastomers

Summary The deviation from the statistical theory of rubberelasticity in the stress-strain-behavior of elastomers, which is described empirically by theRivlin-Mooney equation for the case of simple elongation, is explained by the cooperation of the short range order, which is to assume in amorphous polymers, and the chain length distribution and the occurrence of chain ends in crosslinked systems. This explanation is in qualitative agreement with all experimental results regarding the influence of swelling, preparation of the networks and type of deformation. The quantitative agreement is as good as one can expect from the underlying simple model. In particular the influence of the crosslinking density and the primary molecular weight is considered. In connection with this theory conclusions are drawn to the short range order and a remark is made concerning the problem of the crosslinking density.

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Zusammenfassung Die Abweichung von der statistischen Theorie der Kautschukelastizität im Spannungs-Dehnungs-Verhalten von Elastomeren, die im Falle der uniaxialen Dehnung durch dieRivlin-Mooney-Gleichung beschrieben wird, wird erklärt durch das Zusammenwirken der Nahordnung, die in amorphen Polymeren anzunehmen ist, und der Kettenlängenverteilung sowie das Vorhandensein von freien Kettenenden in vernetzten Systemen. Die gegebene Erklärung stimmt qualitativ mit allen experimentellen Ergebnissen überein bezüglich des Einflusses der Quellung, der Herstellung der Netzwerke und der Art der Deformation. Die quantitative Übereinstimmung ist so gut, wie man es nach dem zugrunde liegenden einfachen Modell erwarten kann. Insbesondere wird der Einfluß der Vernetzungsdichte und des Molekulargewichts vor der Vernetzung betrachtet. Im Zusammenhang mit dieser Theorie werden Folgerungen bezüglich der Nahordnung gezogen und eine Betrachtung zum Problem der Vernetzungsdichte angestellt.

     

Synthese und Struktur von [(Ph3PAu)3NPPh3][PF6]2, einem Gold(I)‐phosphoraniminato‐Komplex

Synthesis and Crystal Structure of [(Ph₃PAu)₃NPPh₃][PF₆]₂, a Gold(I) Phosphoraneiminato Complex The photolytic reaction of Ph₃PAuN₃ with Cr(CO)₆ in THF yields the phosphoraneiminato complex [(Ph₃PAu)₃NPPh₃]²⁺ in low yield as well as the cluster cation [(Ph₃PAu)₈]²⁺ as the main product. The phosphoraneiminato complex crystallizes from CH₂Cl₂ with [PF₆]^? ions as [(Ph₃PAu)₃NPPh₃][PF₆]₂·CH₂Cl₂ in the triclinic space group with a = 1200.8(1), b = 1495.6(2), 2053.5(5), α = 86.97(2)°, β = 82.79(1)°, γ = 81.87(2)°, and Z = 2. The phosphoraneiminato ligand bridges through its N atom three Au atoms, which itself are connected to each other by weak aurophilic interactions.     

UVA-INDUCED AUTOCRINE STIMULATION OF FIBROBLAST-DERIVED COLLAGENASE/MMP-1 BY INTERRELATED LOOPS OFINTERLEUKIN–1 andINTERLEUKIN–6

Abstract— Previous work has shown that fibroblast-derived collagenase/matrix-metalloproteinase-1(MMP–1), responsible for the breakdown of dermal interstitial collagen, was dose-dependently induced in vitro and in vivo by UVA irradiation and this induction was at least partly mediated byinterleukin–6(IL–6). We here provide evidence that UVA-inducedIL–1α andIL–1β play a central role in the induction of the synthesis both ofIL–6 and collagenase/MMP–1. In contrast to the late increase ofIL–1α andIL–1β mRNA levels at 6 h postirradiation, bioactivity ofIL–1 is already detectable at 1 h postirradiation. This early peak ofIL–1 bioactivity appears to be responsible for the induction ofIL–6 synthesis and together withIL–6 lead to an increase of the steady-state mRNA level of collagenase/MMP–1 as deduced from studies usingIL–1α andIL–1β antisense oligonucleotides or neutralizing antibodies againstIL–1α andIL–1β Besides the early posttranslationally controlled release of intracellularIL–1, a latter pretranslationally controlled synthesis and release ofIL–1 perpetuates the UV response. From these data we suggest a UV-induced cytokine network consisting ofIL–1α,IL–1β andIL–6, which via interrelated autocrine loops induce collagenase/MMP–1 and thus may contribute to the loss of interstitial collagen in cutaneous photoaging.     

exo/endo-Selectivity in the Reaction of ‘Bare’ FeO+ with Bicyclo[2.2.1]heptane (Norbornane)

‘Bare’ FeO⁺ reacts in the gas phase with norbornane with collision efficiency, and the most prominent cationic products correspond to [FeC₅H₆]⁺ (32%), [FeC₇H₈]⁺ (19%), [FeC₃H₆O]⁺ (19%) and [FeC₆H₆]⁺ (14%), which are structurally characterized by ligand exchange as well as collision-induced dissociation experiments. Circumstantial evidence is provided which indicates that the complexes [FeC₅H₆]⁺, [FeC₇H₈]⁺, and [FeC₆H₆]⁺ originate from an Fe(norbornene)⁺ intermediate which itself is formed by elimination of H₂O from the [FeO(norbornane)]⁺ encounter complex. Although the reactions are preceded and/or accompanied by partial H/D exchange, the isotope distribution in the productions clearly points to a preferential endo-attack of bare FeO⁺, with an endo/exo-ratio of ca. 10.3 and kinetic isotope effects k_H/k_D for the endo-abstraction of 2.4 and of 7.7 for approaching an exo-C? H bond. The preferred endo-approach of bicyclo[2.2.1]heptane by ‘bare’ FeO⁺ is in distinct contrast to the P-450-mediated or the iron(III)porphyrin-catalyzed hydroxylation of this substrate which favor reactions at the exo-face.