Derivate des Methylendioxybenzols, 7. Mitt.: Über die Einwirkung nucleophiler Reagenzien auf Myristicinabkömmlinge

Zusammenfassung In dieser Arbeit wird über die alkalische Verseifung des 2,6-Dinitro-myristicinsäuremethylesters berichtet, die zur Spaltung der Methylendioxygruppierung unter, Bildung von neuen Phenoläthern führt. Weiterhin werden Amino-myristicinsäuremethylester mit Alkyl-, Aryl- und heterocyclischen Säurechloriden acyliert und die entstehenden Acylaminoderivate durch Behandlung mit Hydrazinhydrat in die entsprechenden Aminochinazolone übergeführt. Additions-, Substitutions- und Abspaltungsreaktionen der N-ständigen Aminogruppe des 2-Methyl-3-amino-6,7-methylendioxy-8-methoxy-chinazolons-(4) waren schließlich Gegenstand unserer Untersuchungen.     

Comparison of silanization/hydrosilation and organosilanization modification procedures on etched capillaries for electrokinetic chromatography

Etched capillaries for use in open tubular electrochromatography are modified by silanization/hydrosilation and organosilanization. The migration behavior of both types of capillaries is evaluated with small basic molecules, peptides and proteins. Comparisons of peak symmetry and efficiency are used to measure the effectiveness of the two methods for modifying the etched surface. From this information, the suitability of each method for use with etched capillaries can be determined.     

Influence of reduction conditions on H2 adsorption in high-surface Rh/CeO2 catalysts as deduced by volumetry, calorimetry, and 1H NMR techniques

1H NMR spectra corresponding to H2 adsorption on high-surface Rh/CeO2 catalysts (S(BET) approximately 55 m2/g) are formed by two lines, attributed to hydrogen adsorbed on ceria (resonance line A) and rhodium-metal particles (upfield-shifted line B). The evolution of 1H NMR spectra as a function of temperature, time, and type of reduction (static or dynamic) allows the study of the progressive establishment of the strong metal-support interaction (SMSI) in Rh/CeO2 catalysts. As the reduction progresses, the mean adsorption heat and the amount of hydrogen adsorbed on the metal, deduced from volumetry, NMR, and calorimetry techniques, decrease considerably. As a consequence of the decrease in metal activity, the amount of hydrogen transferred to the support CeO2 is also reduced (spill-over processes). Outgassing of samples at 773 K eliminates hydrogen species retained at the metal-support surface, and oxidation treatments at 473 and 673 K eliminate the electronic effect and physical blocking of metal particles. The oxidation at 673 K recuperates the total adsorption capacity of metal particles. On the basis of these treatments, the contribution of different processes to the SMSI effect is analyzed. Electronic perturbation of rhodium particles is higher when reductions are performed in dynamic conditions; however, the importance of physical blocking of metal particles increases in static reductions. High reducibility of ceria strengthens electronic effects in Rh/CeO2 compared to those observed in Rh/TiO2 catalysts.     

Electron transfer in proteins: nonorthogonal projections onto donor-acceptor subspace of the Hilbert space

We develop nonorthogonal projectors, called L?wdin projectors, to construct an effective donor-acceptor system composed of localized donor (D) and acceptor (A) states of a long-distance electron transfer problem. When these states have a nonvanishing overlap with the bridge states these projectors are non-Hermitian and there are various possible effective two-level systems that can be built. We show how these can be constructed directly from the Schr?dinger or Dyson equation projected onto the D-A subspace of the Hilbert space and explore these equations to determine the connection between Hamiltonian and Green function partitioning. We illustrate the use of these effective two-level systems in estimating the electron transfer rate in the context of a simple electron transfer model.     

Nuclear magnetic resonance studies of sulfur inversion in bis(cyclopentadienyl)-molybdenum and -tungsten complexes with dithioethers

The metallocene thioether derivatives [Cp₂M(MeSCH₂CH₂SMe)][PF₆]₂ (1, M = MO; 2, M = W), [Cp₂Mo(SCH₂CH₂SMe)][PF₆] (3) and [Cp₂M(SCH₂CH₂S)] (4, M = Mo; 5, M = W) exhibit temperature-dependent fluxional behavior in solution, owing to the pyramidal sulfur inversion process. The activation energies for this process were determined from proton band-shape analysis in the cases of 1 (54.9 ± 2 kJ mol⁻¹), 2 (51.2 ± 4.6 kJ mol⁻¹) and 3 (30.0 ± 3.1 kJ mol⁻¹). Extended Hückel calculations on related model complexes suggest that local inversion at the sulfur atoms, rather that an inversion of the complete S---C---C---S chain, is responsible for the observed fluxional behaviour.     

Direct versus resonances mediated F+OH collisions on a new 3A" potential energy surface

A theoretical study of the F(2P) + OH(2Pi) --> HF(1Sigma+) + O(3P) reactive collisions is carried out on a new global potential energy surface (PES) of the ground 3A" adiabatic electronic state. The ab initio calculations are based on multireference configuration interaction calculations, using the aug-cc-pVTZ extended basis sets of Dunning et al. A functional representation of the PES shows no nominal barrier to reaction, contrary to previous results by others. Wave packet and quasiclassical trajectory calculations have been performed for this PES to study the F + OH(v = 0,j) reactive collision. The comparison was performed at fixed and constant values of the total angular momentum from 0 to 110 and relative translational energy up to 0.8 eV. The reaction presents a dynamical barrier, essentially due to the zero-point energy for the bending vibration near the saddle point. This determines two different reaction mechanisms. At energies higher than approximately 0.125 eV the reaction is direct, while below that value it is indirect and mediated by heavy-light-heavy resonances. Such resonances, also found in the simulations of the photodetachment spectrum of the triatomic anion, manifest themselves in the quasiclassical simulations, too, where they are associated to periodic orbits.     

Anion-pi interactions in cyanuric acids: a combined crystallographic and computational study

Several structures of pi complexes of isocyanuric acid and of several thio derivatives with anions have been computed by using high level ab initio calculations. The nature of the complexes has been studied by means of the method of molecular interaction potential with polarization (MIPp) and Bader's theory of atoms-in-molecules. These molecules form favorable complexes with anions and can be used as binding units for building receptors for the molecular recognition of anions. In several cases, the anion-pi interaction has been demonstrated experimentally by means of X-ray crystallography.     

Untersuchungen an Kristallhydraten anorganischer Salze, 8. Mitt. Interpretation der Schwingungsspektren vonM(BF4)2·6H2O fürM=Fe2+, Co2+, Ni2+

The infrared and Raman spectra were recorded in the range 4000–160 cm^–1 forM(BF₄)₂·6 H₂O whereM=Fe²⁺, Co²⁺, Ni²⁺. The spectroscopic data support the X-ray structural data in showing that in the crystal hydrates studied two kinds of hydrogen bonds are present: H₂O...H₂O and OH₂... F₄B^–. The energies and molecular force constants (f _OH and fH₂O) andr _OH for OH₂...F₄B^– were calculated for the three crystal hydrates. It was found that the bond OH₂... F₄B^– is comparatively weak, with mean energy 3.7–3.3 kcal/mol. Two types of water molecule with different structures are existing as the first are participating in H₂O...H–O–H...F₄B^– and the second in BF₄ ^–...H–O–H...F₄B^–.     

Effect of film thickness on the electro-reduction of molecular oxygen on electropolymerized cobalt tetra-aminophthalocyanine films

We studied the electrocatalytic activity of cobalt tetra-aminophthalocyanine (CoTAPc) for the reduction of molecular oxygen (O₂) on adsorbed monomeric and on electropolymerized films of different thicknesses on glassy carbon (GC) electrode. The polymeric films, denoted poly-CoTAPc, were first characterized by electrochemical impedance spectroscopy and it appears that the types of phenomena revealed to be occurring depend less on the film thickness in basic than in acid media. For O₂ reduction, the results showed that poly-CoTAPc is more active than the monomeric CoTAPc adsorbed on GC. Indeed, rotating ring-disk electrode data showed that polymeric CoTAPc promotes the four-electron reduction of O₂ to water in parallel to a two-electron reduction to give peroxide. On monomeric and thin films of poly-CoTAPc, a two-electron reduction mechanism predominates. In basic media the activity increases very slightly with thickness, whereas in acid media this increase is more pronounced. This parallels the observed behavior revealed by electrochemical impedance spectroscopy.