Über neue olefin-dicarbonyl-isonitril-eisen(0)-komplexe

The reactions of [R₃O]BF₄ or R₃ECl (R = Me, Et; E = Si, Ge, Sn, Pb) with various olefincyanodicarbonyl ferrates(0) [olenFe(CO)₂CN]^?] (olen  C₄H₆, C₅H₈, C₆H₈, C₆H₁₀, C₇H₁₀, C₈H₈, C₈H₁₄), which can be easily synthesized from olenFe(CO)₃ and NaN(SiMe₃)₂, lead to the neutral isonitrile derivatives olenFe(CO)₂CNR or olenFe(CO)₂CNER₃. The 31 new complexes are characterized by their analyses, IR and ¹H NMR spectra.     

Zur Kinetik des durch Cu2+-Äthylendiamin katalysierten H2O2-Zerfalls: Metallionen und H2O2, 14. Mitteilung

Kinetic studies of the Cu²⁺-ethylenediamine catalysed decomposition of H₂O₂ show the initial rate v₀ of H₂O₂ decomposition to be proportional to [H+]^?1, [H₂O₂], and [Cu²⁺-en]². Maximal velocity is found at a ratio of [Cu²⁺]_tot:[en]_tot = 1:1,5. It is suggested that the active complex has a binuclear structure. This structure and probable mechanisms of the reaction are discussed. The kinetic measurements of the Cu²⁺-diethylenetriamine-H₂O₂ system are difficult to interprete because of degradation of the ligand by H₂O₂.     

Synthesis of nanosized BaSnO3 powders from metal isopropoxides

Nanocrystalline BaSnO₃ with a primary particle size of 40–60 nm was prepared through hydrolysis of a barium tin isopropoxide and following crystallization. The thermal decomposition, the crystallization and the microstructure of the obtained powders were investigated with the help of TG-DTA, IR, XRD, HRSEM and HRTEM. The organic rest groups in the as-prepared powder decompose thermally at 350°C, which is accompanied by the building of BaCO₃ that disappear again at 600°C. The crystallization of BaSnO₃ takes place at 500–600°C. Single-phase BaSnO₃ powders have been obtained at a temperature as low as 600°C. The amorphous as-prepared powder shows a cluster structure. Nucleation of BaSnO₃ beginning at 350°C was observed under HRTEM, and the spherical nano-particles of BaSnO₃ calcined at 760°C crystallize well and are strongly aggregated. The presented results indicate a heterogeneous nucleation and growth mechanism by the formation of BaSnO₃.     

The crystal and molecular structure of tris(ortho-aminobenzoato)aquoyttrium(III), Y(H2NC6H4COO)3 · H2O

Tris(ortho-aminobenzoato)aquoyttrium(III), Y(H₂NC₆H₄COO)₃ · H₂O, crystallizes in the monoclinic space group, $\text{C2}\text{c}$, with eight molecules in a unit cell of dimensions: a = 30.89(1) Å, b = 9.09(1) Å, c = 14.85(1) Å, and β = 109.3(1)°. The structure was determined using three-dimensional X-ray diffraction data gathered on multiple-film equi-inclination, integrated Weissenberg, and precession photographs taken about two crystal axes. The structure, excluding the hydrogen atoms, was solved from Patterson and electron density maps and refined by least-squares methods to a final R of 0.081. The coordination about the yttrium atom is sevenfold, best described by a capped trigonal prism. Each ortho-aminobenzoate ligand acts as a bridging bidentate ligand, resulting in six ortho-aminobenzoate residues coupled to each yttrium atom. The water molecule occupies the seventh position. This bonding configuration generates a structure in which each yttrium atom in (100) is attached to two other yttrium atoms via carboxylate bridges to give parallel sets of polymeric chains coincident with (100). It is suggested that this polymeric character accounts for the extreme insolubility of Y(H₂NC₆H₄COO)₃ · H₂O.     

Die Photoenolisierung,Autoxidation und Dimerisation von 2-Isobutyliden-1,3-indandion

The title compound,1, slowly decomposes in solution by autodixation, especially in daylight. The chemism of this photoinduced autoxidation has been investigated.Upon irradiation1 passes to the brick red isolable dienol2. The quantum yield is 0.3 at 313 nm in methanol. In solution an equilibrium is set up within several minutes between2 and the colorless deconjugated3. Unpolar or moderately polar solvents shift the equilibrium completely to3, whereas in highly polar solvents2 and3 coexist. In the dark the equilibrium12 (ca. 501 in methanol) is established very slowly.3 upon irradiation reacts further to dimer8. 2 instantaneously reacts with oxygen. With high oxygen concentrations, hydroperoxide9 is formed, with lower ones dehydrodimer10, inter alia.9 and10 may further form12, 14, and15. These reactions, together with ESR spectroscopy, point to a central role of the free radical13 both in the autoxidation and in the reaction1014.Basic catalysis sets up an equilibrium between1 and its dimer,17. The photoreaction12 has been investigated by sensitizing and quenching experiments.

34. Mitteilung:J. Bitter, J. Leitich, H. Partale, O. E. Polansky, W. Riemer, U, Ritter-Thomas, B. Schlamann undB. Stilkerieg, Chem. Ber., im Druck.     

Homodromic hydrogen bonds in low-energy conformations of single molecule cyclodextrins

Low-energy conformations of β-cyclodextrin under anhydrous conditions in the gas phase were investigated by DFT calculations. In these conformations, two homodromic hydrogen bond rings are formed with very short hydrogen bonds at the narrow side of the cyclodextrin ring and a second one at the wider side. These hypothetical conformations are not comparable to those conformations, which have been studied experimentally, forming inclusion complexes with small and medium-sized guest molecules, but their energy is significantly lower than the open conformations (ΔE = 10 kcal/mol).     

The influence of additives on the X-ray induced aggregation of malate synthase monitoring of the aggregation processin situ by time-resolved small-angle X-ray scattering

The X-ray induced aggregation of the sulfhydryl enzyme malate synthase in aqueous solution was monitoredin situ by time-resolved small-angle X-ray scattering. Experiments were performed in the absence/presence of various additives: formate, superoxide dismutase, catalase, NaCl, acetyl-CoA, glyoxylate, malate, pyruvate, -ketobutyrate, oxaloacetate, glycollate, lactate. The scattering curves were measured as a function of the time of irradiation and were analysed in terms of radii of gyration, degrees of aggregation, distance distribution functions, and parameters derived therefrom. Irradiation in the absence of additives resulted in a strong aggregation of enzyme particles. Each of the additives impeded aggregation, however to a different extent. The OH scavenger formate reduced aggregation efficiently; less pronounced effects were registered for superoxide dismutase and/or catalase (the scavengers for and H₂O₂), and for NaCl. Very pronounced diminutions of the aggregation phenomena were provided by substrates or analogues; the efficiency of these substances as radioprotectors may be explained by their action as both scavengers and specific ligands. Based on these results some implications for the performance of conventional small-angle X-ray scattering experiments on biopolymers are derived.

---

Der Einfluß von Zusätzen auf die röntgeninduzierte Aggregation der Malatsynthase. Registrierung des Aggregationsvorganges in situ mittels zeitaufgelöster Röntgenkleinwinkelstreuung

Zusammenfassung Die röntgeninduzierte Aggregation des Sulfhydrylenzyms Malatsynthase in wäßriger Lösung wurdein situ mittels zeitaufgelöster Röntgenkleinwinkelstreuung messend verfolgt. Streuexperimente wurden in An- bzw. Abwesenheit verschiedener Zusätze durchgeführt: Formiat, Superoxiddismutase, Catalase, NaCl, Acetyl-CoA, Glyoxylat, Malat, Pyruvat, -Ketobutyrat, Oxalacetat, Glycolat, Lactat. Die Streukurven wurden als Funktion der Bestrahlungsdauer registriert. Die Auswertung lieferte Streumassenradien, Aggregationsgrade, Abstandsverteilungsfunktionen, und daraus abgeleitete Parameter. Die Bestrahlung in Abwesenheit von Zusätzen verursachte eine starke Aggregation der Enzymteilchen. Jeder der Zusätze verminderte die Aggregation, wenn auch in unterschiedlichem Ausmaß. Der OH Fänger Formiat verringerte die Aggregation wirksam; weniger stark ausgeprägte Effekte ergaben sich für die bzw. H₂O₂ Fänger Superoxiddismutase bzw. Catalase und für NaCl. Substrate und Substratanaloge reduzierten das Ausmaß der Aggregation besonders wirkungsvoll; der Schutzeffekt dieser Substanzen kann durch ihre zweifache Wirkung als Fänger bzw. spezifische Liganden erklärt werden. Ausgehend von diesen Ergebnissen werden einige Schlußfolgerungen für die Durchführung üblicher Röntgenkleinwinkelexperimente an Biopolymeren abgeleitet.