The case of missing incommensurate smectic A phases

Two binary mixtures of polar liquid crystal materials were previously reported to exhibit three incommensurate smectic A phases predicted for such materials on the basis of phenomenological theory. Results of our recent high-resolution X-ray scattering experiments show that no incommensurate phases exist in the two systems. Wide coexistence regions are found at first order transitions between various frustrated smectic phases of these mixtures. These regions were previously identified as the incommensurate smectic A phases. The phase diagrams of the two systems determined with high-resolution X-ray technique are shown to be in excellent agreement with Baroisa-Prost-Lubensky theory.     

Activity evaluation of carbon paste electrodes loaded with pt nanoparticles prepared in different radiolytic conditions

Three Pt-based catalysts prepared in different radiolytic conditions and supported on graphite powder were packed into a carbon paste electrode configuration. They were compared to each other, to the commercial (Pt) deposited on activated carbon powder (Johnson Matthey) and to pure Vulcan XC-72 for their respective abilities toward the hydrogen evolution reaction (HER). The Tafel parameters were determined for all these electrodes. From the I–V curves and their quantitative treatment, the following order of activity emerged unambiguously and reads: (PtCO)₂ (fcc structure) > (PtCO)₁ (Chini cluster) > (Pt)_neat > (Pt)_JM (Johnson Matthey) ≫ (Vulcan XC-72). As expected, all the Pt-loaded electrodes were more efficient than Vulcan XC-72. The classification appears to be linked with the mean nanoparticle size, and for comparable sizes, with the surface morphology of the materials. The results and the stability of the electrodes suggest that the small particle sizes and the good dispersity on the carbon support were maintained during the HER.     

The synthesis of N-substituted ketimines from oxazirdines

N-Unsubstituted diaryl, alkyl aryl and dialkyl ketimines are prepared in good yield at ambient temperature by the reaction of KOBu^t on oxaziridines having an α-hydrogen atom on the N-alkyl substituent; the mechanism and stereochemistry of the reaction are discussed.     

Synthesis and characterisation of bis(pentafluorophenyl)antimony(V) cations, [(C6F5)2SbL3]

Pentacoordinate complex cations of the general formula [(C₆F₅)₂SbL₃]³⁺ stabilized as solid salts in combination with tetraphenylborate (BPh₄), tetrafluorobroate (BF₄) anions, where L=DMSO, Ph₃AsO, PyO, DMF, α-, β- and γ-picoline have been isolated. The newly formed complexes were characterized by elemental analysis, molar conductance measurements, solid-state IR and and NMR. From these results, a five-fold coordination around antimony was required.     

Potential cerebral perfusion agents. Synthesis and evaluation of berberine analogues

The synthesis and tissue distribution studies in rats of tetra[³H]-hydroberberine ([³H] 2 ) and 8-(p-[¹²⁵I]iodobenzyl)tetrahydroberberine ([¹²⁵I] 6 ) are described. Compound 2 was synthesized by sodium borohydride reduction of berberine hydrochloride ( 1 ). Treatment of berberine hydrochloride with p-bromo-benzylmagnesium bromide gave 8-(p-bromobenzyl)dihydroberberine ( 4 ) which after sodium borohydride reduction and iodine-125 bromine exchange gave [¹²⁵I] 6 . The unsubstituted tetrahydro compound [³H] 2 showed significantly higher brain uptake (2.2% dose/gm after 5 minutes) as compared to the corresponding 8-substituted derivative [¹²⁵I] 6 . Both radiolabeled compounds washed out from the brain relatively quickly.     

Stereoselective reductase-catalysed deoxygenation of sulfoxides in aerobic and anaerobic bacteria

Direct and indirect evidence, of unexpected stereoselective reductase-catalysed deoxygenations of sulfoxides, was found. The deoxygenations proceeded simultaneously, with the expected dioxygenase-catalysed asymmetric sulfoxidation of sulfides, during some biotransformations with the aerobic bacterium Pseudomonas putida UV4. Stereoselective reductase-catalysed asymmetric deoxygenation of racemic alkylaryl, dialkyl and phenolic sulfoxides was observed, without evidence of the reverse sulfoxidation reaction, using anaerobic bacterial strains. A purified dimethyl sulfoxide reductase, obtained from the intact cells of the anaerobic bacterium Citrobacter braakii DMSO 11, yielded, from the corresponding racemates, enantiopure alkylaryl sulfoxide and thiosulfinate samples.     

Liesegang rings — Part I

Summary The conditions for the formation of revert type ofLiesegang rings have been studied here. Various systems of rhythmic precipitations of silver chromate are produced in a mixtures of agar and gelatin gels under different environmental conditions. Ring systems of silver, copper and other ferricyanides have also been studied in gelatin gel. The observations show that the cause of the revert systems ofLiesegang rings is the high peptizability of the precipitating matter in the media containing gel and the unreacted ions.

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Zusammenfassung Die Bedingungen der Bildung des „umgekehrten“ Types vonLiesegang-Ringen wurden untersucht. Verschiedene Systeme rhythmischer F?llung von Silberchromat wurden in einer Mischung von Agar und Gelatinegelen unter verschiedenen Umgebungsbedingungen erzeugt. Ringsysteme von Kupfer, Silber und anderen Ferricyaniden in Gelatine wurden untersucht. Die Beobachtungen zeigen, da? die Ursache für die „umgekehrten“Liesegang-Ringe in der hohen Peptisierbarkeit der Füllsubstanz im gelhaltigen Medium und den noch nicht reagierten Ionen liegt.

     

Über die Eigenschaften hydratisierten Chromoxydes. Teil V

Ohne ZusammenfassungÜbersetzt von Dr. K. Jäckel, Marburg/L.Wir danken Herrn Prof. N. R. Dhar D.Sc. (London und Paris), F.R.I.C., F.N.I., I.E.S. (Eetd) Direktor Shila Dhar Institut für Bodenkunde und Vorstand der Chemischen Abteilung, Universität Allahabad, für sein lebhaftes Interesse und seine Ratschläge für die Arbeit.