Recherches sur la synthese totale des alcaloides appartenant a la serie de la carpaine et de la cassine—V : Synthese totale de l'acide (±) carpamique

The total synthesis is described of (±) 6-(7-carboxy hept-1-yl) 3-hydroxy 2-methyl piperidine [(±) carpamic acid] in five steps from 1-ethoxycarbonyl 6-methyl hept-5-en-2-one.     

Amperometric detection of hydrazine by cyclic voltammetry and flow injection analysis using ruthenium modified glassy carbon electrodes

Glassy carbon electrodes modified with (5-amino-1,10-phenanthroline)bis(bipyridine)ruthium(II) chloride hydrate, [(bpy)₂Ru(5-phenNH₂)]Cl₂·H₂O, are shown to oxidize hydrazine with excellent sensitivity. The presence of an amine group on the ruthenium complex facilitates electropolymerization onto the electrode surface. Using cyclic voltammetry, a large catalytic current is observed upon oxidation of hydrazine in phosphate buffer (pH 5.0), compared to the current obtained from the ruthenium-modified electrode with no hydrazine present. The sensitivity of cyclic voltammetry is sufficient for obtaining a linear calibration curve for hydrazine over the range of 10⁻⁵ to 10⁻² M. Hydrodynamic amperometry was used to determine the working potential for flow injection analysis. The limit of detection for hydrazine was determined to be 8.5 μM using FIA. The thickness of these films was shown to increase linearly with the number of electropolymerization cycles, in the range of 1000-2500 nm for 5-20 cycles, respectively, using Rutherford backscattering spectrometry (RBS). RBS analysis also suggests that the film is multilayered with the outermost layers containing a high ruthenium concentration, followed by layers where the concentration of ruthenium decreases linearly and approaches zero at the electrode surface.     

Electron binding energies of aqueous alkali and halide ions: EUV photoelectron spectroscopy of liquid solutions and combined ab initio and molecular dynamics calculations

Photoelectron spectroscopy combined with the liquid microjet technique enables the direct probing of the electronic structure of aqueous solutions. We report measured and calculated lowest vertical electron binding energies of aqueous alkali cations and halide anions. In some cases, ejection from deeper electronic levels of the solute could be observed. Electron binding energies of a given aqueous ion are found to be independent of the counterion and the salt concentration. The experimental results are complemented by ab initio calculations, at the MP2 and CCSD(T) level, of the ionization energies of these prototype ions in the aqueous phase. The solvent effect was accounted for in the electronic structure calculations in two ways. An explicit inclusion of discrete water molecules using a set of snapshots from an equilibrium classical molecular dynamics simulations and a fractional charge representation of solvent molecules give good results for halide ions. The electron binding energies of alkali cations computed with this approach tend to be overestimated. On the other hand, the polarizable continuum model, which strictly provides adiabatic binding energies, performs well for the alkali cations but fails for the halides. Photon energies in the experiment were in the EUV region (typically 100 eV) for which the technique is probing the top layers of the liquid sample. Hence, the reported energies of aqueous ions are closely connected with both structures and chemical reactivity at the liquid interface, for example, in atmospheric aerosol particles, as well as fundamental bulk solvation properties.     

Rhodopsin reconstituted into a planar-supported lipid bilayer retains photoactivity after cross-linking polymerization of lipid monomers

Transmembrane proteins (TMPs), particularly ion channels and receptors, play key roles in transport and signal transduction. Many of these proteins are pharmacologically important and therefore targets for drug discovery. TMPs can be reconstituted in planar-supported lipid bilayers (PSLBs), which has led to development of TMP-based biosensors and biochips. However, PSLBs composed of natural lipids lack the high stability desired for many technological applications. One strategy is to use synthetic lipid monomers that can be polymerized to form robust bilayers. A key question is how lipid polymerization affects TMP structure and activity. In this study, we have examined the effects of UV polymerization of bis-Sorbylphosphatidylcholine (bis-SorbPC) on the photoactivation of reconstituted bovine rhodopsin (Rho), a model G-protein-coupled receptor. Plasmon-waveguide resonance spectroscopy (PWR) was used to compare the degree of Rho incorporation and activation in fluid and poly(lipid) PSLBs. The results show that reconstitution of Rho into a supported lipid bilayer composed only of bis-SorbPC, followed by photoinduced lipid cross-linking, does not measurably diminish protein function.     

Reactions of powdered silicon with some pyrotechnic oxidants

Thermogravimetry (TG) and differential scanning calorimetry (DSC) have been used to examine the thermal behaviour, in N₂ and in air, of the Si/Sb₂O₃, Si/KNO₃, Si/Fe₂O₃ and Si/SnO₂ pyrotechnic systems, in relation to the behaviour of the individual constituents.TG curves for Si powder, heated alone in air, showed that limited oxidation of Si occurred above 700°. In N₂, Sb₂O₃ sublimed completely between 500 and 900° and, in air, sublimation was accompanied by oxidation to Sb₂O₄. The Sb₂O₄ decomposed at higher temperatures. DSC curves for KNO₃ heated in N₂ showed the usual crystalline transition and melting endotherms followed by endothermic decomposition between 400 and 950°. DSC and TG curves of SnO₂and Fe₂O₃ revealed no thermal events when samples were heated to 1000° in either N₂ or air.For the Si/Sb₂O₃ system, the oxidation of Si by Sb₂O₃ between 590 and 700°, was complicated by sublimation of Sb₂O₃ in N₂ and also by the oxidation of Sb₂O₃ in air. No thermal events were observed for the Si/SnO₂and Si/Fe₂O₃ systems when heated under a variety of conditions in either N2 or in air, although these systems do sustain combustion on suitable ignition. In the Si/KNO₃ system, oxidation of Si occurs in a KNO₃ melt at temperatures above 560° in nitrogen and in air.

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Zusammenfassung Mittels TG und DSC wurde das thermische Verhalten der pyrotechnischen Systeme Si/Sb₂O₃, Si/KNO₃, Si/Fe₂O₃ und Si/SnO₂in N₂ und in Luft im Vergleich zum Verhalten der einzelnen Komponenten untersucht.TG-Aufnahmen über das Erhitzen von Si-Pulver in Luft zeigten eine begrenzte Oxidation von Silizium oberhalb 700°C. Sb₂O₃ sublimiert in Stickstoff vollständig zwischen 500 und 900°C, in Luft wird die Sublimation durch Oxidation zu Sb₂O₄ begleitet. Sb₂O₄ zersetzt sich bei höheren Temperaturen. DSC-Aufnahmen für KNO₃ in N₂ zeigen die gewohnten Umwandlungs- und Schmelzendothermen, gefolgt von einer endothermen Zersetzung zwischen 400 und 950°C. Die DSC- und TG-Kurven für SnO₂und Fe₂O₃ zeigen bei Erhitzen bis 1000°C weder in N₂ noch in Luft den Verlauf thermische Prozesse an.Bei dem System Si/Sb₂O₃ spielt sich neben der Oxidation von Si durch Sb₂O₃ zwischen 590 und 700°C auch eine Sublimation von Sb₂O₃ in N₂ sowie eine Oxidation von Sb₂O₃ in Luft ab. Für die Systeme Si/SnO₂und Si/Fe₂O₃ konnten durch Erhitzen unter einer Reihe von Bedingungen weder in Luft noch in N₂ Thermoprozesse nachgewiesen werden, obwohl diese Systeme nach geeigneter Zündung den Brennvorgang aufrechterhalten. Im System Si/KNO₃ erfolgt sowohl in N₂ als auch in Luft oberhalb 560°C die Oxidation von Si in der KNO₃-Schmelze.

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Dedicated to Professor Dr. H. J. Seifert on the occasion of his 60^th birthday     

The chemistry of chromyl fluoride III. Reactions with inorganic systems

Reactions of CrO₂F₂ with MF or MF₂ gave the corresponding M₂CrO₂F₄ and MCrO₂F₄ fluorochromates. With the Lewis Acids (SO₃, TaF₅, SbF₅) and (CF₃CO)₂O known and new chromyl compounds [CrO₂(CF₃COO)₂, CrO₂(SO₃F)₂, CrO₂FTaF₆, CrO₂FSbF₆, CrO₂FSb₂F₁₁] were produced. Chromyl fluoride and inorganic salts (CF₃COONa and NaNO₃) produced the following complexes - Na₂CrO₂F₂(CF₃COO)₂ and Na₂CrO₂F₂(NO₃)₂. Unusual solid products were obtained with CrO₂F₂ and NO, NO₂, SO₂.A new method of preparing CrO₂F₂ is also presented.     

Novel approaches to the analysis of the Maillard reaction of proteins

The Maillard reaction comprises a complex network of reactions which has proven to be of great importance in both food science and medicine. The majority of methods developed for studying the Maillard reaction in food have focused on model systems containing amino acids and monosaccharides. In this study, a number of electrophoretic techniques, including two-dimensional gel electrophoresis and capillary electrophoresis, are presented. These have been developed specifically for the analysis of the Maillard reaction of food proteins, and are giving important insights into this complex process.     

Mixed dialkyltin(IV) trifluoroacetates

Mixed dialkytin(IV) trifluoroacetates,Me EtSn(O₂CCF₃)₂,Et Pr ⁿ Sn(O₂CCF₃)₂ andPr ⁿ Bu ⁿ Sn(O₂CCF₃)₂ have been prepared by metathetical reactions of the corresponding dialkyltin(IV) chlorides with silver trifluoroacetate in CH₂Cl₂. They are monomeric in benzene and nonconducting inMeNO₂ andMeCN. Bidentate trifluoroacetate groups are indicated by their IR spectra.Mössbauer spectra confirmtrans-arrangement of theR-Sn-R moiety.¹H,¹⁹F NMR and mass spectra are also discussed.

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Gemischte Dialkylzinn(IV)-trifluoracetate

Zusammenfassung Die gemischten Dialkylzinn(IV)-trifluoroacetateMe EtSn(O₂CCF₃)₂,Et Pr ⁿ Sn(O₂CCF₃)₂ undPr ⁿ Bu ⁿ Sn(O₂CCF₃)₂ wurden über Metathese-Reaktionen der entsprechenden Dialkylzinn(IV)-chloride mit Silbertrifluoracetat in CH₂Cl₂ dargestellt. Sie sind monomer in Benzol und nichtleitend inMeNO₂ undMeCN. Die IR-Spektren zeigen zweizähnige Trifluoracetat-Gruppen an. DieMössbauer-Spektren bestätigen dietrans-Anordnung derR-Sn-R-Einheit. Die¹H-,¹⁹F-NMR und die Massenspektren werden ebenfalls diskutiert.

     

Stoichiometric and catalytic oxygen activation by trimesityliridium(III)

Trimesityliridium(III) (mesityl = 2,4,6-trimethylphenyl) reacts with O(2) to form oxotrimesityliridium(V), (mes)(3)Ir=O, in a reaction that is cleanly second order in iridium. In contrast to initial reports by Wilkinson, there is no evidence for substantial accumulation of an intermediate in this reaction. The oxo complex (mes)(3)Ir=O oxidizes triphenylphosphine to triphenylphosphine oxide in a second-order reaction with DeltaH++ = 10.04 +/- 0.16 kcal/mol and DeltaS++ = -21.6 +/- 0.5 cal/(mol.K) in 1,2-dichloroethane. Triphenylarsine is also oxidized, though over an order of magnitude more slowly. Ir(mes)(3) binds PPh(3) reversibly (K(assoc) = 84 +/- 3 M(-1) in toluene at 20 degrees C) to form an unsymmetrical, sawhorse-shaped four-coordinate complex, whose temperature-dependent NMR spectra reveal a variety of dynamic processes. Oxygen atom transfer from (mes)(3)Ir=O and dioxygen activation by (mes)(3)Ir can be combined to allow catalytic aerobic oxidations of triphenylphosphine at room temperature and atmospheric pressure with overall activity (approximately 60 turnovers/h) comparable to the fastest reported catalysts. A kinetic model that uses the rates measured for dioxygen activation, atom transfer, and phosphine binding describes the observed catalytic behavior well. Oxotrimesityliridium does not react with sulfides, sulfoxides, alcohols, or alkenes, apparently for kinetic reasons.     

Purine N-oxides—XLI : The 3-acyloxypurine 8-substitution reaction: On the mechanism of the reaction

The 3-acyloxypurine 8-substitution reaction involves elimination of the 3-acyloxy group and nucleophilic substitution at C-8 to yield 8-substituted xanthines or guanines. In aqueous solutions the reaction of 3-acetoxyxanthine proceeds slowly below pH 2, but is greatly accelerated with an increase of the pH from 3 to 7. It is proposed that the slow reaction involves heterolytic cleavage of the 3-acetoxy moiety from 3-acetoxyxanthine to yield a nitrenium ion at N-3 followed by intermolecular nucleophilic substitution of the incipient carbonium ion at the allylic C-8 position, also the most probable mechanism in polar aprotic solvents. The beginning of the fast reaction coincides with the beginning of ionization of the imidazole hydrogen of 3-acetoxyxanthine. It is proposed that this ionization induces a similar but more rapid departure of the 3-acetoxy group from the anion of 3-acetoxyxanthine to produce dehydroxanthine. The latter, upon protonation, yields the same reactive carbonium ion at C-8 that is formed in the slow reaction. Some reduction of 3-acetoxyxanthine to xanthine accompanies the fast reaction. That reduction has the characteristics of a free-radical mediated reaction. It is proposed that reduction results from a homolytic cleavage of the NO bond in the 3-acetoxyxanthine anion to produce a radical-anion, which abstracts hydrogen from water to yield xanthine. These reaction mechanisms and possible alternatives are evaluated.