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.     

Free-standing and vertically aligned InP nanowires grown by metalorganic vapor phase epitaxy

Metalorganic vapor phase epitaxial technique has been used to grow surface mounted vertical and uniform cross-sectional InP nanowires on a wafer scale basis. The growth was carried out under the vapor–liquid–solid mechanism using Au colloidal nanoparticles of nominal diameters of 10 and 20 nm, and their properties were compared. The effect of the pre-growth anneals and growth temperatures on the stability of the nanowires were studied in detail. Scanning electron microscopy and transmission electron microscopic studies showed average diameter of the nanowires in the range of 20–35 nm, and of length 700 nm with growth direction of 1 1 1. Room temperature photoluminescence measurements of the nanowires grown on 10 and 20 nm Au particles showed strong peaks, which were blue shifted by 25 and 32 meV, respectively, compared to bulk InP.     

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     

Highly active CoMo HDS catalyst for the production of clean diesel fuels

HY–Al₂O₃-supported CoMo catalysts with a chelating agent and phosphorus for the hydrodesulfurization (HDS) of diesel fractions were prepared. The activity measurements with the prepared catalysts were carried out with straight-run light gas oil feedstocks in a pilot plant under industrial hydrotreating conditions. As a result, Cosmo Oil Co., Ltd. developed a new CoMoP/HY–Al₂O₃ catalyst, C-606A, which had three times higher HDS activity than the conventional CoMoP/Al₂O₃ catalyst. Commercial operations to produce ultra-low sulfur diesel (ULSD) with C-606A have successfully demonstrated its high performance and high stability. This catalyst has an extremely high activity, which enables to achieve <10-ppm sulfur in products in diesel hydrotreater designed to produce 500-ppm sulfur diesel fuels. Mo K-edge EXAFS, TEM and FT-IR of adsorbed NO were performed to investigate the nature of the active sites on the developed catalysts. The results showed that the new catalyst has multiple layers of MoS₂ slabs and the edges of MoS₂ are mainly occupied by Co–Mo–S phases. XPS and FT-IR were used to investigate the sulfiding behavior of Co and Mo in the formation process of the active sites during sulfidation. The results showed that addition of carboxylic acid to the impregnation solution postponed the sulfidation of Co at low temperatures, thereby increasing formation of the Co–Mo–S phase.     

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.     

New insights into binding interfaces of coagulation factors V and VIII and their homologues lessons from high resolution crystal structures

The large, multifunctional proteins Factors V and VIII are cofactors in the coagulation cascade and possess a similar domain structure, A1-A2-B-A3-C1-C2. The C domains are related to the discoidin protein family, while the A domains are homologous to the copper-binding protein ceruloplasmin. After proteolytic activation, Factors V and VIII behave as peripheral membrane proteins, binding to negatively charged membranes containing phosphatidylserine, primarily via specific sites on their C2 domains. This type of membrane surface is exposed at sites of tissue damage, where platelets have become activated. The cofactors then accelerate sequential proteolytic activations that occur at critical control points in the blood coagulation cascade via complex formation with specific serine proteinases. Here we compare recent structural and functional studies of the C2 domains of Factors V and VIII, and discuss their respective roles. The membrane-binding motifs consist of several exposed hydrophobic side chains surrounded by a ring of basic residues, and the C2 domains appear poised to insert their hydrophobic "feet" into the membrane interior as basic residues interact favorably with phosphatidylserine head groups. In line with their physiological roles, the membrane-binding surfaces of the C2 domains display a good deal of mobility. We then extend our analysis to other members of the discoidin protein family, which perform diverse physiological functions involving signaling pathways at cell surfaces. Finally, structural similarities between discoidin proteins and the topologically distinct but functionally related membrane-binding "classic C2 domains", including signal-transduction proteins such as Protein Kinase C and phospholipases, are noted.     

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.