Antisymmetric exchange in [2Fe-2S]1+ clusters: EPR of the Rieske protein from Thermus thermophilus at pH 14

[2Fe-2S] clusters found in the xanthine oxidase family of proteins exhibit an S = 1/2 EPR feature, called signal II, for which one g-value is significantly above g = 2.0. The g-values of signal II cannot be explained with the standard spin coupling model that has been so successful in describing the g = 1.94 signals of [2Fe-2S] ferredoxins. We have studied the EPR spectra of the Rieske protein from Thermus thermophilus at pH 14 and observed a signal II-type EPR spectrum, with g-values at 1.81, 1.94, and 2.14. It is shown that the g-values of signal II can be explained by including an antisymmetric exchange term, d.S1xS2, in the spin Hamiltonian. The presence of this term is sensed by EPR if the isotropic exchange coupling constant J is sufficiently small. For the Rieske protein we determined J = 43 cm-1 which is at least 4 times smaller than the J values reported for [2Fe-2S] clusters that yield standard g = 1.94 signals.     

A convenient synthesis of 2-amino-6-methoxy-1-methyl (and 1,4-dimethyl)carbazole derivatives and their 6-aza analogues

2,6-Diaminotoluene ( 3a ) and 2,6-diamino-p-xylene ( 3c ) led to 2-methyl (and 2,5-dimethyl)-3-acetylamino-phenylhydrazines 5a,b. Fischer indolization of their hydrazones 6a,b and 7a,b derived from 4-methoxycy-clohexanone and 4-piperidone, and subsequent aromatization of intermediate tetrahydrocarbazole derivatives 8a,b and 9a,b allowed us to work out a convenient route to the title compounds.     

Furannes et pyrroles disubstitués en 2,3. XVI synthèse de furo[3,2-c]pyranones-4 et nouvelle voie d'accès aux furo[3,2-c]pyridines

Treatment of 4-hydroxy-6-methylpyran-2-one with chloracetalhyde in basic aqueous medium gave 6-methylfuro[3,2-c]pyran-4-one. This compound reacted with ammonium hydroxide and some primary amines to form the corresponding N-substituted furo[3,2-c]pyrid-4-ones which may also be obtained from 4-hydroxy-α-pyridones. Furo[3,2-c]pyran-4-one was acylated at the 2 position and 4-chloro-6-methylfuro[3,2-c]pyridine easily gave 4-substituted derivatives by displacement of the halogen atom.     

Synthèse de 5H-isoquino[6, 7-b][1, 6]naphtyridones-12 substituées sur leur sommet 10

Starting from 4-chloronicotinic and derivatives and 6-amino-5-methyl-2H-isoquinolin-1-one, subsequent cyclization of intermediates by sulfuric acid or trifluoromethanesulfonic acid and chlorination by phosphorus oxychloride gave 10-chloro-6-methyl-5H-isoquino[6,6-b][1,6]naphthyridin-12-ones. Cytotoxicity of the corresponding 10-(diethylamino-3)propylamino-6-methyl-5H-isoquino[6,7-b][1,6]naphthyridinh12-ones, compared to that of related 9-azaellipticine derivatives, showed that replacement of pyrrole by a pyridin-4-one nucleus resulted in loss of biological activity.     

Über den Mechanismus des teilweisen Verschwindens des Phosphors beim Veraschen organischer Substanzen

Analytical and Bioanalytical Chemistry -     

Sur un théorème relatif aux surfaces pour lesquelles les coordonnées d'un point quelconque s'expriment par des louctions abéliennes de deux paramètres

Sans résumé     

Synthesis and biological evaluation of gramicidin S dimers

The design and synthesis of analogues of the cyclic beta-sheet gramicidin S (GS), having additional functionalities in their turn regions, is reported. The monomeric GS analogues were transformed into dimers and their activities towards biological membranes, through antimicriobial and hemolytic assays, were evaluated. Finally, conductivity measurements have been performed to elucidate ion channel forming properties.     

Détermination d'un champ de forces de valence pour le thiazole et ses dérivés deutériés: Étude du méthyl-2 et chloro-2 thiazole

The vibrational frequencies of thiazole and its deuterated derivatives have been used in valence force field calculations. The transferability of the force field is verified by the study of 2-chloro- and 2-methyl-thiazole. Previous assignments are discussed.     

Transformation thermique des β-(méthyl-2 furyl)-3 acryloylazides: Nouveau mode de formation de certaines pyrimidines

In boiling diphenyl ether, P-3-(2-methylfuryl)acryloylazides were not transformed to the expected furo[3,4-c]pyridones according to the Eloy and Deryckere reaction but 5-substituted pyrimidine-2,4-dioncs, generated by dimerization of vinyl isocyanates issued from the Curtius rearrangement of the starting material, were obtained.     

Etude en Spectrometrie de Masse. VIII—Fragmentation de Qulques Benzalacetophenones et Benzalacetones Diversement Substituees sur le Cycle Aromatique

A comparative mass spectrometric study of the behaviour of variously substituted 1,3-diphenylpropenones (or benzylacetophenones) and 4-phenylbuta-2-ones (or benzylacetones) is reported. These compounds are very stable under electron impact owing to the extensive conjugation, which covers practically all of the molecule. The presence of a substituent on the aromatic ring gives characteristic fragments whose significance is discussed.