Chemical and Electrochemical Syntheses of Soluble Electroconducting Poly(2,5-Thienylene) Derivatives

Soluble electroconducting poly[3 -(ω-phenylalkyl)-2,5 -thienylene)]s are synthesized by electrochemical and chemical polymerizations of 3-(2-phenylethyl)thiophene and 3-(3-phenylpropyl)thiophene, which are synthesized by a Grignard cross-coupling reaction of l-bromo-3-phenylalkane with 3-bromothiophene in the presence of dichloro[1,3-bis(diphenylphosphino)propane]-nickel(II). The chemical, electrochemical, and electrical properties of these polymers are reported, including initial characterization, spectroscopy, and electrochemical cyclic voltammetry.     

Two-Dimensional Perovskite Oxynitride K2LaTa2O6N with an H+/K+ Exchangeability in Aqueous Solution Forming a Stable Photocatalyst for Visible-Light H2 Evolution

Undoped layered oxynitrides have not been considered as promising H₂-evolution photocatalysts because of the low chemical stability of oxynitrides in aqueous solution. Here, we demonstrate the synthesis of a new layered perovskite oxynitride, K₂LaTa₂O₆N, as an exceptional example of a water-tolerant photocatalyst for H₂ evolution under visible light. The material underwent in-situ H⁺/K⁺ exchange in aqueous solution while keeping its visible-light-absorption capability. Protonated K₂LaTa₂O₆N, modified with an Ir cocatalyst, exhibited excellent catalytic activity toward H₂ evolution in the presence of I⁻ as an electron donor and under visible light; the activity was six times higher than Pt/ZrO₂/TaON, one of the best-performing oxynitride photocatalysts for H₂ evolution. Overall water splitting was also achieved using the Ir-loaded, protonated K₂LaTa₂O₆N in combination with Cs-modified Pt/WO₃ as an O₂ evolution photocatalyst in the presence of an I₃⁻/I⁻ shuttle redox couple.     

Synthetic Studies on Sialoglycoconjugates 53: Synthesis of Novel N-Methyl-1-Deoxynojirimycincontaining Sialo-Oligosaccharides Related to Ganglioside GM3 Active as a Biosignal Mediator

Abstract

O-(6-O-Benzoyl-β-d-galactopyranosyl)-(1→4)- and O-(2, 3, 4-tri-O-acetyl-β-d-galactopyranosyl)-(1→4)-2, 3, 6-tri-O-benzyl-N-benzyloxycarbonyl-1, 5-dideoxy-1, 5-imino-d-glucitols (4 and 12) were each coupled with methyl (methyl 5-acetamido-4, 7, 8, 9-tetra-O-acetyl-3, 5-dideoxy-2-thio-d-glycero-d-galacto-2-nonulopyranosid)onate (5) in acetonitrile medium in the presence of dimethyl(methylthio)sulfonium triflate (DMTST) or N-iodosuccinimide/trifluoromethanesulfonic acid to give the corresponding α-sialyl-(2 → 3)- and α-sialyl-(2 → 6)-glycosides (6 and 13α), which were converted to novel ganglioside GM3-related trisaccharides (9 and 15) containing N-methyl-1-deoxynojirimycin.     

Synthetic Studies on Sialoglycoconjugates 50: Total Synthesis of Ganglioside GD2

Abstract

As more and more biological functions^1-10 of gangliosides are being revealed, their facile, stereocontrolled synthesis is strongly required. We have developed^11-l4 an α-stereoselective glycosylation of sialic acids, α-sialyl-(2→8)-sialic acid and α-sialyl-(2→8)-α-sialyl-(2→8)-sialic acid, by using their 2-thioglycosides as the glycosyl donor and suitably protected acceptors, and dimethyl(methy1thio)sulfonium triflate (DMTST) or N-iodosuccinimide (NIS)-trifluoromethanesufonic acid (or TMS triflate) as the glycosyl promoter in acetonitrile. In this way, we have synthesized a variety of gangliosides¹⁵ and their analogs.¹⁶ Previously,¹³ we synthesized Ganglioside GD3 containing α-sialyl-(2-8)-sialic acid residue in the molecule, in connection with a novel approach for systematic synthesis of polysialo-glycoconjugates. As a part of our continuing studies on the synthesis and elucidation of the functions of gangliosides, we describe here a facile, stereocontrolled, total synthesis of ganglioside GD2. Ganglioside GD2, which was first isolated from human brain by R. Kuhn et al.,¹⁷ is well known as a human melanoma associated antigen.¹⁸     

Reversible Pore Size Control of Elastic Microporous Material by Mechanical Force

Nanoporous materials, such as zeolites, activated carbons, and metal–organic frameworks (MOFs), are peculiar platforms in which a variety of guest molecules are stored, reacted, and/or separated. The size of the nanopores is essential to realize advanced functions. In this work, we demonstrate a very simple but innovative method for the control of nanopore size, that is, reversible and continuous control by mechanical force loaded to soft nanoporous materials. The elastic properties of several microporous materials, including zeolites, zeolite‐templated carbon (ZTC), activated carbon, and MOFs (e.g., ZIF‐8), are examined and it is found that ZTC is a material that is suitable for the aforementioned idea thanks to its extraordinary soft properties compared to the others. The original pore size of ZTC (1.2 nm) can be contracted to 0.85 nm by using a relatively weak loading force of 135 MPa, whereas the other microporous materials barely contracted. To demonstrate the change in the physical properties induced by such artificial deformation, in situ gas adsorption measurements were performed on ZTC with and without loading mechanical force, by using CO₂, CH₄, and H₂, as adsorbates. Upon the contraction by loading 69 or 135 MPa, CO₂ adsorption amount is increased, due to the deepening of the physisorption potential well inside the micropores, as proved by the increase of the heat of adsorption. Moreover, the adsorption amount is completely restored to the original one after releasing the mechanical force, indicating the fully reversible contraction/recovery of the ZTC framework against mechanical force. The experimental results are theoretically supported by a simulation using Grand Canonical Monte Carlo method. The similar adsorption enhancement is observed also on CH₄, whereas H₂ is found as an exception due to the weak interaction potential.     

Copper‐Catalyzed Extended Pummerer Reactions of Ketene Dithioacetal Monoxides with Alkynyl Sulfides and Ynamides with an Accompanying Oxygen Rearrangement

The first examples of metal‐catalyzed extended Pummerer reactions through the activation of sulfoxides are described. The copper‐catalyzed reactions of ketene dithioacetal monoxides with alkynyl sulfides and ynamides provided a wide variety of γ,γ‐disulfanyl‐β,γ‐unsaturated carbonyl compounds with an accompanying oxygen rearrangement. The products can be easily converted into 1,4‐dicarbonyl compounds and substituted heteroaromatics. DFT calculations and mechanistic experiments revealed a new interesting stepwise addition/oxygen rearrangement mechanism.     

Online wide‐angle X‐ray diffraction/small‐angle X‐ray scattering measurements for the CO2‐laser‐heated drawing of poly(ethylene terephthalate) fiber

Fiber‐structure‐development in the poly(ethylene terephthalate) fiber drawing process was investigated with online measurements of wide‐angle and small‐angle X‐ray scattering with both a high‐luminance X‐ray source and a CO₂‐laser‐heated drawing system. The intensity profile of the transmitted X‐ray confirmed the location of the neck‐drawing point. The diffraction images had a time resolution of several milliseconds, and this still left much room for improvement. Crystal diffraction appeared in the wide‐angle X‐ray images almost instantaneously about 20 ms after necking, whereas a four‐point small‐angle X‐ray scattering pattern appeared immediately after necking. With the elapse of time after necking, the four‐point scattering pattern changed into a meridional two‐point shape. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1090–1099, 2005