Polar effect in the reaction of CH3O with HBr

The discharge flow method with laser induced fluorescence detection of CH₃O was applied to determine the rate constant, k ₁, for the reaction CH₃O + HBr → products (1) k ₁ (298 K) = (8.41 ± 0.80(1σ)) 10¹¹ cm³ mol^-1 s^-1. The unusually large k ₁ value was explained by the polar nature of the transition state of the reaction. This revised version was published online in June 2006 with corrections to the Cover Date.     

Through-space electrostatic control in a novel regiospecific ring transformation of 1,3,4-trisubstituted maleimides

Ring transformation of 1-ethoxycarbonyl-3,4-disubstituted maleimide in alkaline solution yielded exclusively 1,5-disubstituted orotic acid. No hydantoin derivatives were detected. These findings can be best explained by assuming that the initial attack of the hydroxylate anion occurs at C2 and not at C5. X-ray diffraction and quantum chemical investigations indicate that stereospecificity is mainly due to through-space electrostatic effects.     

Influence of fadA G203R and ΔflbA mutations on morphology and physiology of submerged Aspergillus nidulans cultures

Morphologic and physiologic changes taking place in carbon-limited submerged cultures of Aspergillus nidulans ΔflbA and fadA ^G203R strains were studied. Loss-of-function mutation of the flbA gene resulted in an altered germination with unusually thick germination tubes, “fluffy” pellet morphology, as well as a reduced fragmentation rate of hyphae during autolysis. In the fadA ^G203R mutant strain, conidiophores formed in the stationary phase of growth, and the size of pellets shrank considerably. There were no significant differences in the generation of reactive oxygen species (ROS) and in the specific catalase and superoxide dismutase activities by the tested mutants and the appropriate parental strains. Therefore, the participation of ROS or antioxidative enzymes in FadA/FlbA signaling pathways seems to be unlikely in submerged cultures. On the other hand, earlier increases in the extracellular protease and ammonia production were recorded with the ΔflbA strain, whereas the protease and ammonia production of the fadA ^G203R mutant lagged behind those of the wild-type strains. Similar changes in the time courses of the induction of γ-glutamyltranspeptidase and the degradation of glutathione were observed. These results suggest that FadA/FlbA signaling may be involved in the mobilization of protein and peptide reserves as energy sources during carbon starvation.     

Über ein kristallisiertes Reaktionsprodukt des Formisobutyraldols mit Ammoniak

Ohne Zusammenfassung     

Infrarot- und ultraviolettspektroskopische Untersuchungen des Primycins

Ohne ZusammenfassungDem Gedächtnis an Prof. Dr.Ernst Späth ehrfurchtsvoll gewidmet.     

A simplified multidimensional integral

We present a simplified integral of functions of several variables. Although less general than the Riemann integral, most functions of practical interest are still integrable. On the other hand, the basic integral theorems can be obtained more quickly. We also give a characterization of the integrable functions and their primitives.     

Self‐association promoted conformational transition of (3R,4S,8R,9R)‐9‐[(3,5‐bis(trifluoromethyl)phenyl))‐thiourea](9‐deoxy)‐epi‐cinchonine

The conformational diversity of the (3R,4S,8R,9R)‐9‐[(3,5‐bis(trifluoromethyl)phenyl))‐thiourea](9‐deoxy)‐epi‐cinchonine organocatalyst is discussed. Low‐temperature NMR experiments confirmed a self‐association process, which promotes the quinoline rotation between two intramolecularly hydrogen‐bonded monomeric conformers of the catalyst. The balanced population of the coexisting monomeric and dimeric species allowed us to conduct a structural study of a rather complex conformational dynamics of the pure catalyst. The study is extended by a comparison with other members of the bifunctional amine‐thiourea organocatalyst family. Changes in the molecular structure of the catalysts influence the interplay between intra‐ and intermolecular hydrogen bonding, and yield different extent of catalyst self‐association. By assessing the conformation of the individual states, we established the thermodynamic model of a self‐association promoted conformational transition. Copyright © 2009 John Wiley & Sons, Ltd.     

Generalized Monotone Operators on Dense Sets

In the present work we show that the local generalized monotonicity of a lower semicontinuous set-valued operator on some certain type of dense sets ensures the global generalized monotonicity of that operator. We achieve this goal gradually by showing at first that the lower semicontinuous set-valued functions of one real variable, which are locally generalized monotone on a dense subsets of their domain are globally generalized monotone. Then, these results are extended to the case of set-valued operators on arbitrary Banach spaces. We close this work with a section on the global generalized convexity of a real valued function, which is obtained out of its local counterpart on some dense sets.     

The effect of K+ ion exchange on the structure and thermal reduction of hexagonal ammonium tungsten bronze

This paper discusses the changes in the structure and thermal reduction of nanosize hexagonal ammonium tungsten bronze (HATB), (NH₄)_0.33−xWO_3−y, which were caused by K⁺ ion exchange (doping) and studied by XRD, XPS, ¹H-MAS NMR, FTIR, SEM and TG/DTA-MS. Comparison of the cell parameters of undoped and doped HATB revealed that both a and c cell parameters decreased after the ion exchange reaction, which showed that smaller K⁺ ions partly replaced the larger NH₄⁺ ions in the hexagonal channels of HATB. After the reaction, from the hexagonal channels less NH₃ evolved, which also supported the incorporation of K⁺ ions into the hexagonal channels.     

Novel tert-butyl-tris(3-hydrocarbylpyrazol-1-yl)borate ligands: synthesis, spectroscopic studies, and coordination chemistry

The lithium (1) and thallium (2) salts of five new tert-butyl-tris(3-hydrocarbylpyrazol-1-yl)borate ligands [t-BuTp(R)]- (R = H, a; Me, b; i-Pr, c; t-Bu, d; Ph, e) have been synthesized and characterized. Because of steric congestion at B, the reaction between t-BuBH3Li x 0.5 Et2O and excess 2,5-dimethylpyrazole Hpz(Me2) afforded the bis-pz(Me2) derivative, Tl[t-BuBH(3,5-Me2pz)2] (3) after metathesis with TlNO3. The compounds were characterized by elemental analysis and NMR spectroscopy. The Li salts 1a and 1c exhibit fluxional behavior on the NMR time scale in solution at room temperature. The solid-state 7Li and 11B NMR spectra of 1c suggest that this salt exists as a mixture of axial and equatorial isomers. The partial hydrolysis of 1d afforded the dimeric Li complex {Li[t-BuB(pz(t-Bu))2(mu-OH)]}2 (4). The crystal structure of 4 shows two Li cations encapsulated by the heteroscorpionate [t-BuB(OH)(3-t-Bupz)2]- ligands. A salt elimination reaction between FeCl2(THF)1.5 and 2 equiv of Li[t-BuTp(R)] (R = H, Me) followed by an in situ one-electron oxidation produced good yields of the homoleptic, paramagnetic low-spin iron(III) complexes [Fe(t-BuTp)2]PF6 (5) and [Fe(t-BuTp(Me))2]PF6 (6) that were characterized by elemental analyses, magnetic susceptibility measurements in solution and the solid phase, 1H NMR, high-resolution mass spectrometry, M?ssbauer spectroscopy, and single-crystal X-ray diffraction. The crystals are composed of discrete molecular units with the central Fe(III) ion in an almost perfectly octahedral coordination to six nitrogen atoms. Compound 5 has the shortest Fe-N bond lengths ever reported for [Fe(RTp(R)')2]+-type compounds.