Effective charge in the II–VI and III–V compounds with zincblende or wurtzite type structure

The effective charge in the II–VI and III–V compounds was analyzed by using a linear chain model. On the assumption that the ionic lattice is immersed in a cloud of valence electrons with the dielectric constant of ?(∞) = n²?₀ (n: refractive index, ?₀ = 8·85 × 10^?12f/m), the effective charge on an ion is equal to 2e in the II–VI compounds and to e in the III–V compounds (e: electronic charge), respectively. These values of the effective charge are just n times the Szigeti charge.Although direct connection between neighboring atoms is the main part of the binding force, the fact can not be neglected that the second nearest neighbor atoms are connected by sharing some of valence electrons between them. The electrons in valence bonds contribute to the refractive index and are estimated to be e and 2e per atom in the II–VI and III–V compounds, respectively.     

Syntheses of helical polymers through the combination of axially dissymmetric segments

Wholly aromatic polymers with various helical structures were prepared through the combination of two axially dissymmetric bifunctional compounds. The palladium-catalyzed condensation of (R)-2,2-diethoxy-6,6′-dibromo-1,1′-binaphthyl with (R)-1,1′-binaphthyl-2,2′-diamine and the reaction of (S)-2,2-diethoxy-6,6′-dibromo-1,1′-binaphthyl with (S)-1,1′-binaphthyl-2,2′-diamine produced helical polyamines, and the chiral conformation was confirmed by their circular dichroism spectra and large specific rotations. The combination of (R)-2,2-diethoxy-6,6′-dibromo-1,1′-binaphthyl and (S)-1,1′-binaphthyl-2,2′-diamine afforded polyamines with a zigzag conformation. The condensation of (R)-2,2′-dimethylbiphenyl-6,6′-dicarbonyl chloride with (R)-2,2′-diamino-6,6′-dimethylbiphenyl and the reaction of (S)-2,2′-dimethylbiphenyl-6,6′-dicarbonyl chloride with (S)-2,2′-diamino-6,6′-dimethylbiphenyl predominantly yielded cyclic dimers and tetramers because of the steric proximity of the reactive groups of the propagating species. The experimental results indicated that the structures of the obtained polymers depended on the combination of the chirality of the bifunctional atropisomeric compounds and the position of the functional groups on the aromatic rings. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4607–4620, 2004     

Electrospray mass spectrometry of pentacosasaccharides of blood group I-activity and related compounds

The structural characterization of large synthetic oligosaccharides and related glycoconjugates performed by the use of electrospray ionization mass spectrometry (ESIMS) is described. The largest molecules described here are unprotected and protected pentaantennary pentacosasaccharides 2 and 5 with average molecular masses of 4441 and 9416, respectively. The straight-chain neutral ceramide decasaccharide (d18:1/c24:0) 6 and the disialoganglioside GD2 (d18:1/c24:0) 7 were also successfully analyzed by ESIMS. In addition to exact mass determination, collision-induced dissociation (CID) spectrometry of these compounds provided saccharide chain sequence information.     

A synthetic approach to seven-membered lactones by the microbial transformation of ynones having a trifluoromethyl group

Studies on the microbial transformations of a number of ynones bearing a trifluoromethyl group prepared by the reaction of ethyl trifluoroacetate with a variety of lithium alkynates, have been undertaken. The major products were the corresponding carbinols but microbial carbon-carbon bond degradation and formation occurred also, which proceeded to novel fluorinated seven-membered lactones as significant products.     

Synthesis of Block Copolymers and Asymmetric Star-Branched Polymers Comprised of Polyacetylene and Polystyrene Segments via Ionic Bond Formation

Novel ion-bonded AB diblock copolymers and three-arm AB₂ asymmetric star-branched polymers comprised of polyacetylene (A) and polystyrene (B) segments have been synthesized by the stoichiometric reaction of tert-amine-chain-end-functionalized poly(phenyl vinyl sulfoxide)s with either chain-end- or in-chain-carboxylated polystyrenes to link the two polymer segments via ionic bond, followed by thermal treatment to convert their poly(phenyl vinyl sulfoxide)s to polyacetylene segments. Periodic lamellar morphologies were observed in the cast films of such polymers by TEM measurement. The isolation of the nano-size sheet consisting of polyacetylene lamellar layers was attempted.     

Preparation and regioselective reactions of novel gem-difluorinated vinyloxiranes with some organometallic reagents

Hitherto unknown, relatively labile gem-difluorinated vinyloxiranes were prepared by difluoro-Wittig reactions with alpha,beta-epoxyketones; for these vinyloxiranes alkyl groups were delivered at the fluorine-attached terminal carbon atom in an SN2' manner by RLi, while Me3Al and MeMgBr-CuCl (3: 1) introduced the Me group at the allylic epoxy carbon with retention and inversion of the original stereochemistry, respectively.     

Stannylative cycloaddition of enynes catalyzed by palladium-iminophosphine

Palladium-iminophosphine complex catalyzes stannylative cycloaddition of conjugated enynes using hexabutyldistannoxane as a stannylating agent to afford highly substituted 3-alkenylphenylstannanes regioselectively. Stannylative cross-cycloaddition reactions between different enynes or between enynes and diynes are also achieved. The reaction is successfully applied to a concise synthesis of alcyopterosin N, which has been isolated recently from sub-Antarctic soft coral, Alcyonium paessleri.     

Contortisiliosides A–G: Isolation of Seven New Triterpene Bisdesmosides from Enterolobium contortisiliquum and Their Cytotoxic Activity

Seven new bisdesmosidic triterpene saponins, with up to eight monosaccharides, which were given the trivial names contortisiliosides A–G ( 1 – 7 ), were isolated from Enterolobium contortisiliquum. The structures of the new saponins were determined on the basis of extensive spectroscopic and chromatographic analyses of both intact and acid‐hydrolyzed compounds. The isolated saponins were evaluated for their cytotoxic activities against BAC1.2F5 mouse macrophages, EL‐4 mouse lymphoma cells, and L‐929 mouse fibroblasts. Whereas contortisiliosides A ( 1 ) and C ( 3 ) were moderately cytotoxic to both BAC1.2F5 macrophages and EL‐4 cells, and contortisiliosides D–G ( 4 – 7 ) did not show any apparent cytotoxic activities against the three cell lines, contortisilioside B ( 2 ) exhibited selective cytotoxic activity against BAC1.2F5 mouse macrophages, with an IC₅₀ value of 3.4 μM . The macrophage death caused by 2 was shown to be neither necrotic nor apoptosis‐inducing based on the unique morphological change of the killed cells, whose cytosols were transformed into large vacuoles, and according to the TUNEL assay.     

An efficient method for cyclopentene annulation onto alpha,beta-unsaturated ketones: W(CO)(5)(L)-catalyzed 5-endo-dig cyclization of 6-siloxy-5-en-1-ynes

[reaction: see text] A highly efficient method for the cyclopentene annulation onto alpha,beta-unsaturated ketones is described. Indium-mediated 1,4-propargylation onto alpha,beta-unsaturated ketones in the presence of tert-butyldimethylsilyl triflate and dimethyl sulfide gives the 6-siloxy-5-en-1-yne derivatives, which undergo W(CO)(5)(L)-catalyzed 5-endo-dig cyclization to give the corresponding cyclopentene derivatives in good yield.