Cleavage of different ether bonds in butyl glycidyl ether and allyl glycidyl ether by K, K(15-crown-5)2

The kind of substituent in alkyl glycidyl ethers affects the course of their reaction with K⁻, K⁺(15-crown-5)₂. The cyclic oxirane ring is exclusively cleaved in the case of butyl glycidyl ether whereas the presence of the unsaturated allyl group in the glycidyl ether molecule unexpectedly prefers the scission of the linear ether bond. In both the systems organometallic intermediates are formed. They react with crown ether causing its ring opening. Allylpotassium formed from allyl glycidyl ether reacts also with another glycidyl ether molecule; the oxirane ring is opened in this case.     

Das Gleichgewicht zwischen oktaedrisch und tetraedrisch koordiniertem Kobalt(II) in N,N-Dimethylacetamid

Zusammenfassung In Lösung von [Co(DMA)₆](ClO₄)₂ in wasserfr. N,N-Dimethylacetamid (DMA) wird spektrophotometrisch ein Gleichgewicht zwischen tetraedrisch und oktaedrisch koordiniertem Co²⁺ festgestellt. Die GleichgewichtskonstanteK=[Co _tetr ²⁺ ]/[Co _oct ²⁺ ] wurde bei 25°C zu 0,028 und bei 70°C zu 0,19 bestimmt. Bei –8°C zeigen die Elektronenspektren keinen meßbaren Anteil der tetraedrischen Species. Für den oktaedrischen Komplex ergibt sichD _q =805 cm^–1,B=834 cm^–1.

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The equilibrium between octahedral and tetrahedral coordinated cobalt(II) in N,N-dimethylacetamide

Spectrophotometric results establish an equilibrium between tetrahedral and octahedral coordinated cobalt(II) in anhydrous N,N-dimethylacetamide (DMA). The equilibrium constantK=[Co _tetr ²⁺ ]/[Co _okt ²⁺ ] has been found to be 0,028 at 25°C and 0,19 at 70°C. Electronic spectra indicate no measurable amount of the tetrahedral species at –8°C. For the octahedral complexD _q =805 cm^–1 andB=834 cm^–1.

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Mit 4 Abbildungen     

Effect of poly(arylene ether ketone)s of different chemical constitutions on adhesion properties of epoxyamine binder

The adhesive strength at the bipolymer blend/fiber interface was determined by the pull-out method. Epoxy resin blends with heat-resistant linear thermoplastics, poly(arylene ether ketone)s of different molecular masses and chemical compositions, were used as adhesives, and a steel wire of 150 μm diameter was used as a substrate. It was found that the addition of 5–20 wt % poly(arylene ether ketone) to epoxy resin results in a 10–20% increase in the adhesive strength; a sharp gain in the adhesive strength (by 50–80%) is observed at a modifier content of 30%. The introduction of nanoparticles (Na⁺-montmorillonite) into the epoxy resin-poly(arylene ether ketone) blend increases the strength of adhesive bonding to steel wire. Possible reasons for the observed changes in the adhesive strength are discussed.     

Dimerisierung von benzocyclobuten zu 1-ethyl-9,10-dihydrophenanthren unter dem einfluss von natrium-kalium-legierung in tetrahydrofuran

Benzocyclobutene is cleaved by sodium-potassium alloy in THF at a C_aryl-CH₂ bond whereby in contrast to the corresponding reaction with lithium a dimeric product, 1-ethyl-9,10-dihydrophenanthrene, is formed.     

Metal Exchange in the Interprotein ZnII-Binding Site of the Rad50 Hook Domain: Structural Insights into CdII-Induced DNA-Repair Inhibition

Cd^II is a major genotoxic agent that readily displaces Zn^II in a multitude of zinc proteins, abrogates redox homeostasis, and deregulates cellular metalloproteome. To date, this displacement has been described mostly for cysteine(Cys)-rich intraprotein binding sites in certain zinc finger domains and metallothioneins. To visualize how a Zn^II-to-Cd^II swap can affect the target protein's status and thus understand the molecular basis of Cd^II-induced genotoxicity an intermolecular Zn^II-binding site from the crucial DNA repair protein Rad50 and its zinc hook domain were examined. By using a length-varied peptide base, Zn^II-to-Cd^II displacement in Rad50’s hook domain is demonstrated to alter it in a bimodal fashion: 1) Cd^II induces around a two-orders-of-magnitude stabilization effect (log =20.8 vs. log =22.7), which defines an extremely high affinity of a peptide towards a metal ion, and 2) the displacement disrupts the overall assembly of the domain, as shown by NMR spectroscopic and anisotropy decay data. Based on the results, a new model explaining the molecular mechanism of Cd^II genotoxicity that underlines Cd^II’s impact on Rad50’s dimer stability and quaternary structure that could potentially result in abrogation of the major DNA damage response pathway is proposed.     

A low-spin alkylperoxo-iron(III) complex with weak Fe-O and O-O bonds: implications for the mechanism of superoxide reductase

The synthesis of a mononuclear, five-coordinate ferrous complex [([15]aneN4)FeII(SPh)](BF4) (1) is reported. This complex is a new model of the reduced active site of the enzyme superoxide reductase (SOR), which is comprised of a [(NHis)4(Scys)FeII] center. Complex 1 reacts with alkylhydroperoxides (tBuOOH, cumenylOOH) at low temperature to give a metastable, dark red intermediate (2a: R = tBu; 2b: R = cumenyl) that has been characterized by UV-vis, EPR, and resonance Raman spectroscopy. The UV-vis spectrum (-80 degrees C) reveals a 526 nm absorbance (epsilon = 2150 M-1 cm-1) for 2a and a 527 nm absorbance (epsilon = 1650 M-1 cm-1) for 2b, indicative of alkylperoxo-to-iron(III) LMCT transitions, and the EPR data (77 K) show that both intermediates are low-spin iron(III) complexes (g = 2.20 and 1.97). Definitive identification of the Fe(III)-OOR species comes from RR spectra, which give nu(Fe-O) = 612 (2a) and 615 (2b) cm-1, and nu(O-O) = 803 (2a) and 795 (2b) cm-1. The assignments for 2a were confirmed by 18O substitution (tBu18O18OH), resulting in a 28 cm-1 downshift for nu(Fe-18O), and a 46 cm-1 downshift for nu(18O-18O). These data show that 2a and 2b are low-spin FeIII-OOR species with weak Fe-O bonds and suggest that a low-spin intermediate may occur in SOR, as opposed to previous proposals invoking high-spin intermediates.     

The mechanism of photoinsertion of haloalkenes into Fe---C bonds of dieneiron tricarbonyls

1,1-Dichloro-2,2-difluoroethylene (like other fluoroalkenes) and dieneiron tricarbonyls react photochemically to give products in which the haloalkene has inserted into the Fe---C(1) bond of the diene complex. The reaction is regiospecific with respect to both diene and haloalkene. The reaction is shown to occur by (a) photodissociation of a CO ligand from iron; (b) π-complexation of haloalkene; (c) π → σ ligand rearrangements accompanied by CO reattachment. The adducts undergo hydrolysis on silica gel chromatography, to give substituted 2-chlorocyclohexadienoneiron tricarbonyls.     

Kristallstruktur von Caesiumacetat,Cs(CH3COO)

Crystal Structure of Cesium Acetate, Cs(CH₃COO) . The crystal structure of cesium acetate, Cs(CH₃COO), was determined from single crystal fourcirclediffractometer data: hexagonal crystal system, P6/m (No. 175), Z = 6, a = 1 488.0(2), c = 397.65(5) pm, V_m = 76.54(2) cm³/mol, R = 0.045, R_w = 0.030. The structure consists of flat layers of acetate anions parallel (001) that are separated by layers of cesium cations. There is a close relationship with the CaF₂ type according to CsO₂(CCH₃): each cesium cation has eight oxygen atoms as nearest neighbours. They form a heavily distorted cube with trapezoidal basal faces. In contrast to CaF₂, these polyhedra are linked via three faces and two edges to a three-dimensional network.