Studies on decarboxylation reactions. Part 6 . Kinetic study of decarboxylation of 5-amino-1,3,4-oxadiazole-2-carboxylic acid and its N-phenyl derivatives at high hydrochloric acid concentrations

The dissociation constants (K₁) of both acids 4a-c and esters 5a-c and the rate constants of the decarboxylation reaction of acids 4a-c have been measured at various high concentrations of hydrochloric acid (0.5-8.0 M range). The results obtained have enabled us to suggest the probable structure of the zwitterion which undergoes decarboxylation.     

Dimethyl carbonate as a novel methylating reagent for fatty acids in analytical pyrolysis

Dimethyl carbonate (DMC) was investigated as a mild, harmless and odorless reagent for pyrolytic methylation of fatty acids. Soybean oil was selected as test material for its high content of (poly)unsaturated fatty acids. Pyrolyses were performed at 500, 700 and 900 degrees C by means of a heated platinum filament pyrolyser on-line and off-line to the GC-MS apparatus. Methyl esters of palmitic, linoleic, oleic and stearic acid were formed as prominent products from off-line pyrolysis of soybean oil in the presence of DMC and zeolite 13X. Fatty acid methyl esters (FAMEs) were not observed at important levels in the absence of zeolite, while on-line Py-GC-MS experiments resulted principally in the formation of free fatty acids and hydrocarbons. The FAME profiles obtained from the DMC/zeolite off-line pyrolysis were compared to those resulting from tetramethylammonium hydroxide (TMAH) thermochemolysis and BF3-methanol procedure. The observed differences between pyrolysis and methanolysis methods were principally attributed to the thermal degradation of unsaturated fatty acids. The effectiveness of the DMC/zeolite pyrolytic methylation was further demonstrated by the analysis of tripalmitine and soybean seeds.     

On the “projective” magnetohydrodynamics

In the projective relativity based on the de Sitter universe, Maxwell's generalized theory gives us the magnetohydrodynamics, valid on a cosmic scale, for hyperdense matter and high energies. From the new theory can be deduced as limiting cases the hydrodynamics and thermohydrodynamics, the ideal magnetohydrodynamics, the electromagnetism, and the electrohydrodynamics, invariants for the projective Fantappié group.     

Azobenzene complexes of dicyclopentadienyltitanium and dicyclopentadienylvanadium

Reactions of azobenzene with dicarbonyldicyclopentadienyltitanium(II), Ti(π-C₅H₅)₂(CO)₂, and dicyclopentadienylvanadium(II), V(π-C₅H₅)₂, have yielded the corresponding dicyclopentadienylmetal-azobenzene complexes.     

The relative permittivity of 1,2-dimethoxyethane and N,N-dimethylformamide mixtures from −10 to 40°C

Binary solutions of N,N-dimethylformamide and 1,2-dimethoxyethane have been investigated by means of dielectric measurements at temperatures ranging from –10 to +40°C, and for nine mixtures covering the whole miscibility field expressed by the mole fraction of one component (0X₁1). The experimental data were used to study the dependence of on T and X₁, of the type = (T), = (X₁), and = (T,X₁). Further, the excess mixing function _E has been evaluated in order to identify particular patterns of interaction between unlike molecules and any other factor that could modify such patterns. The minimum in the _E vs. composition plots suggests the formation of an adduct of stoichiometric ratio DMFDME=11 at all the investigated temperatures.     

Stereoselective total synthesis of (S)-Virol C and (S)-1-dehydroxyvirol A

A stereoselective total synthesis of (S)-Virol C and (S)-1-dehydroxyvirol A has been developed, based upon the selective and sequential substitution of the two trimethylsilyl groups of readily available 1,4-bis(trimethylsilyl)-1,3-butadiyne.     

ASV determination of cadmium complexation in seawater. Methodology evaluation

The methodology for using DPASV to study cadmium complexation in seawater is evaluated using EDTA as a model ligand and by analysing natural samples. The results show that the methodology gives an accurate evaluation of metal complexation when inert complexes are studied, both as regards the ligand concentration and the conditional stability constant; the error for both the parameters is lower than 10% at a ligand concentration of about 10(-8) M and a conditional stability constant of 10(9) M-1. Cadmium complexes with ligands present in natural seawater show an evident kinetic lability that may lead to underestimation of the conditional stability constant when a working electrode characterised by a very thick diffusion layer is used. The conditional stability constant in one water sample of the Adriatic coast ranged between 0.14 and 1.4 l/nmol using a rotating disk electrode at rotation rates of 300 and 6000 rpm. The results of cadmium complexation obtained for samples collected in coastal seawater show that the ligands present low specificity for the metal.     

ENERGY TRANSFER FROM ENZYME-GENERATED TRIPLET CARBONYLS TO THYLAKOID MEMBRANE FRACTIONS ENRICHED IN PHOTOSYSTEMS I and II

Abstract— Enzyme-generated triplet species transfer energy very efficiently to thylakoid membrane fractions enriched in either photosystem-I or photosystem-II. Independent of the nature of the triplet donor, the emission is always more intense with photosystem-I. Since the fluorescence quantum yield of chlorophyll in PS-I is lower and the rate of energy transfer usually smaller than to chlorophyll in PS-II, the yield of ¹S chlorophylls in PS-I is substantially higher. This is tentatively attributed to more favorable reverse intersystem crossing from an upper triplet state in PS-I.     

Hydrierung prochiraler Olefine mit Rhodium-Komplexen von optisch aktiven Amidinen

[RhCl(C₈H₁₄)₂]₂ together with the optically active amidines C₆H₅C(=NR)NHCH(CH₃) (C₆H₅) I–V or their Li derivatives after activation with molecular hydrogen gives catalysts which at room temperature and 1.1 bar H₂-pressure hydrogenate the prochiral substrates (Z)-[N-acetylamino]-cinnamic acid, itaconic acid, -methylcinnamic acid, -methylcinnamic aldehyde, and -methylcinnamic alcohol as well as cyclohexene, benzene and toluene. Good hydrogenation activity of the new catalysts is in contrast to low optical induction which only in the hydrogenation of -methylcinnamic alcohol with 1.5 to 2% leads to values different from zero.

3. Mitt.:H. Brunner undW. Pieronczyk, J. Chem. Res., im Druck.     

CHEMILUMINESCENT DIPHENYLACETALDEHYDE OXIDATION BY MITOCHONDRIA IS PROMOTED BY CYTOCHROMES and LEADS TO OXIDATIVE INJURY OF THE ORGANELLE

Plant and animal mitochondria promote the aerobic oxidation of diphenylacetaldehyde (DPAA). This process is accompanied by chemiluminescence and rotenone-insensitive oxygen uptake. Tn rat liver and potato tubers, mitochondrial swelling is concurrently detected. Light emission and oxygen consumption decreased (about 50%) in cytochrome c-depleted mitochondria. A model system–cytochrome c or b5/dihexadecylphosphate liposomes–was also able to oxidize DPAA with parallel reduction of the cytochrome. Reduction of respiratory complex I or I plus II by addition of rotenone or antimycin A, respectively, did not prevent DPAA oxidation. However, when all cytochrome was reduced by addition of cyanide, aldehyde oxidation was completely suppressed. Altogether these data indicate that respiratory cytochromes are responsible for DPAA oxidation with production of excited species and consequent mitochondrial permeabilization.