Amperometric titration of boron with fructose

Aqueous solutions of boratei can be titrated amperometrically with standard fi uctose solutions This procedure may be used to determine the boron content of various types of samples after conversion of the boron to the borate form The methode is based upon the observation that the polarographic wave of fructose. in a o I M LiCl, 001 N'LiOH solution is deprcssed by the presence of borate ions Under the prescribed conditions the methode is sensitive to a few hundredths of a milligram of boron The few comnonly occurring intcrferenes can be conveniently removed prior to the titration     

UV-blocking property of dumbbell-shaped ZnO crystallites on cotton fabrics

A facile process to prepare uniform dumbbell-shaped ZnO crystallites was presented. The evidence in this Article discovered a unique morphological effect on the UV-blocking property. The as-prepared ZnO crystallites were characterized by XRD, HRTEM, FESEM, UV-blocking, and Raman scattering spectra. Our tentative investigation created a breakthrough to both the ultrahigh "Ultraviolet protection factor" (UPF) and the overall-range of complete UV-radiation blocking. Therefore, the as-prepared structural material demonstrated a significant advance in protective functional treatment and provided a potential commercialization.     

E-olefin dipeptide isostere incorporation into a polypeptide backbone enables hydrogen bond perturbation: probing the requirements for Alzheimer's amyloidogenesis

Herein, we report a stereospecific E-olefin dipeptide isostere synthesis that can be used to make gram quantities of the Phe-Phe isostere desired for eliminating a specific backbone H-bond donor and acceptor in the Alzheimer's disease related Abeta peptide. The Phe19-Phe20 E-olefin analogue of Abeta(1-40) was prepared by solid-phase peptide synthesis and was subjected to amyloidogenesis conditions. This analogue can aggregate into spherical morphologies but does not progress on to form protofibrils or fibrils as is the case for the all-amide sequence, providing insight into the structural requirements for amyloidogenesis.     

Synthesis of diterpene glycosides

Summary Mono-, di-, and linear triglycosides of a diterpene alcohol, derived from abietic acid and glucose have been synthesized employing peracetylbromo--D-glucose (4) and maltose derivatives5 and8 as glycosyl donors. The triglycoside14 exhibits slight haemolytic activity.

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Synthese von Diterpenglycosiden

Zusammenfassung Es wird die Synthese von Mono-, Di-, und linearen Triglycosiden aus einem von Abietinsäure abgeleiteten Diterpenalkohol beschrieben. Als Glycosyldonoren wurden neben Peracetobrom--D-glucose (4) die Maltosederivate5 und8 verwendet. Das Triglycosid14 zeigt schwache hämolytische Aktivität.

     

One-Pot Formation of Carbonates from the Reactions of Carbonyl Compounds with Samarium Diiodide and Methyl Chloroformate

Treatment of carbonyl compounds with SmI₂ and methyl chloroformate in the presence of molecular sieves provides the cyclic carbonates or biscarbonates of pinacols. This one-pot reaction proceeds rapidly even with aliphatic ketones. The stereochemistry obtained by this procedure is different from that of conventional pinacolic couplings.     

Phytoecdysteroids of plants of the genusSilene XIV. Brahuisterone fromSilene brahuica

A new ecdysteroid with the composition C₂₇H₄₄O₆ which has been called brahuisterone has been isolated from the epigeal part of the plantSilene brahuica Boiss. Its chemical and complete spatial structures have been established by spectral studies and the x-ray structural method (diffractometer, Cu-K radiations, 996 reflections, direct method, R=0.119).Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbekistan Republic, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 553–558, July–August, 1993.     

An investigation of catalytic activity in mixed metal oxide nanophase materials

We present preliminary evidence for catalytic activity by unsupported mixed metal oxide nanocrystalline materials. The results of this study show that a nanophase form of Li-MgO has begun to exhibit catalytic activity by 300 °C. This is at least 200 degrees below the temperature at which conventional Li-MgO catalysts exhibit comparable activity. Furthermore, at higher temperatures, the same nanophase composition shows enhanced activities and somewhat improved hydrocarbon selectivities over conventional Li-MgO catalysts.     

Darstellung,Struktur und magnetisches Verhalten von Alkali-metallmanganchalkogeniden A6MnX4 mit A Na oder K und X S,Se oder Te

Inhaltsübersicht. Die Verbindungen Na₆MnS₄, Na₆MnSe₄, Na₆MnTe₄, K₆MnS₄, K₆MnSe₄ und K₆MnTe₄ wurden durch Umsetzungen von Alkalimetallcarbonaten mit Chalkogen und Mangan bzw. Mangancarbonat in einem mit Chalkogen beladenen Wasserstoffstrom erhalten. Röntgenstrukturuntersuchungen an Einkristallen ergaben, daß alle sechs Verbindungen isotyp kristallisieren (Na₆ZnO₄-Typ, Raumgruppe P6₃mc). Als charakteristische Baugruppen treten “isolierte” tetraedrische [MnX₄]-Einheiten auf. Die Temperaturabhängigkeiten der magnetischen Suszeptibilitäten führen zu einem Curie-WeissVerhalten. Erst bei tiefen Temperaturen treten offensichtlich antiferromagnetische Kopplungen auf. Dabei sind die Wechselwirkungen in den Tellurverbindungen stärker als in den Schwefelverbindungen und in den Kaliumverbindungen stärker als in den Natriumverbindungen ausgeprägt. Synthesis, Structure, and Magnetic Properties of Alkali Metal Manganese Chalcogenides A₆MnX₄ with A Na or K and X S, Se or Te The compounds Na₆MnS₄, Na₆MnSe₄, Na₆MnTe₄, K₆MnS₄, K₆MnSe₄ and K₆MnTe₄ were synthesized by the reaction of alkali metal carbonates with chalcogen and Mn or MnCO₃ in a stream of hydrogen charged with chalcogen. Structural investigations on single crystals show that all six compounds crystallize in isotypic atomic arrangements (Na₆ZnO₄-type, space group P6₃mc), which are characterized by isolated [MnX₄] tetrahedra. The magnetic susceptibilities show Curie-Weiss behaviour. At low temperatures there are obviously antiferromagnetic interactions increasing from the sulfides to the tellurides and from the sodium compounds to the potassium compounds.     

Synthesis and properties of benzyl-substituted thiiranes

The reaction of phenyl- and p-tolylmagnesium bromides, as well as di, tri, and tetramethylbenzene, with epichlorohydrin was used to synthesize the corresponding chlorohydrins, which were then converted to various benzyl-substituted oxiranes and thiiranes.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 598–602, May, 1988.     

Synthesis and stereochemical studies of 6-substituted 1H,3H,6H,7aH-3,3-dimethylimidazo-[1,5-c]thiazol-5-one-7-thiones

The reaction of (4S)-5,5-dimethyl-4-thiazolidine-carboxylic acid 1 with alkyl and aryl isothiocyanates 2 gave bicyclic thiohydantoins 3 . The (2R,4S)- and (2S,4S)-mixtures of 2-substituted 5,5-dimethyl-4-thiazolidine-carboxylic acids 4 and 8 containing two centers of chirality in the analogous reaction afforded thiohydantoins 7 and 10 , respectively, with (1R)-configuration. In some cases we managed to isolate the thioureido acid intermediates 6 and 9 or their triethylamine salts which afforded the corresponding bicycles 7 and 10 under thermal cyclization or acidification. The stereochemistry has been elucidated by high resolution ram studies, optical rotation measurements and X-ray crystallography.