Molecular understanding of the adhesive interactions between silica surface and epoxy resin: Effects of interfacial water

The molecular mechanism of the adhesion between silica surface and epoxy resin under atmospheric conditions is investigated by periodic density-functional-theory (DFT) calculations. Slab models of the adhesion interface were built by integrating a fragment of epoxy resin and hydroxylated (0 0 1) surface of α-cristobalite in the presence of adsorbed water molecules. Effects of adsorbed water on the adhesion interaction are evaluated on the basis of geometry-optimized structures, adhesion energies, and forces. Calculated results demonstrate that adsorbed water molecules significantly reduce both the adhesion energies and forces of the silica surface–epoxy resin interface. The reduction of adhesion properties can be associated with structural deformation of water molecules confined in the tight space between the adhesive and adherend as well as structural flexibility of the hydrogen-bonding network in the interfacial region during detachment of the epoxy resin from the hydrophilic silica surface. © 2018 Wiley Periodicals, Inc.     

Achillinin B and C,new sesquiterpene dimers isolated from Achillea millefolium

Two novel sesquiterpene dimers, achillinin B and C, were isolated from the flowers of Achillea millefolium. The structures were elucidated by extensive spectroscopic analysis. A plausible biosynthetic pathway of achillinin B and C by Diels–Alder reaction of the corresponding guaiane sesquiterpenoids is also discussed.     

Silicon Oxide Coatings with Very High Rates (>10?nm/s) by Hexamethyldisiloxane-Oxygen Fed Atmospheric-Pressure VHF Plasma: Film-Forming Behavior Using Cylindrical Rotary Electrode

Silicon oxide films are deposited in atmospheric-pressure (AP) He/O₂/HMDSO plasma excited by a 150?MHz VHF power using a cylindrical rotary electrode. The atomic bonding configurations and deposition rate are studied by controlling the O₂ concentration (O₂/HMDSO source ratio) and VHF power density, the other parameters being maintained constant. Under the addition of 0.03?% O₂ to the process gas mixture (O₂/HMDSO????0.09), AP-VHF plasma greatly enhances the fragmentation and oxidation of HMDSO, so that an almost inorganic film is obtained at a very high deposition rate of 33?nm?s^?1. A silicon oxide coating on a polycarbonate pane is demonstrated with no significant thermal deformation of the pane, showing that AP-VHF plasma would be an efficient coating tool for polymer substrates.     

Influence of adding carbon nanotubes on photoelectric conversion properties of dye-doped titania gel

Multiwalled carbon nanotubes (MWCNTs) were incorporated into amorphous dye-doped titania gel by the sol?Cgel method at room temperature. The working electrodes were prepared by coating the ITO glass with the sol?Cgel titania precursor containing the dye and MWCNTs. The photoelectric conversion properties of the electrodes were examined by simple spectroscopic and electric measurements. The photocurrent spectrum originated from the absorption of the dye. The short circuit photocurrent was enhanced by adding a small amount of MWCNTs evenly to the amorphous dye-doped titania gel. The open circuit voltage was due to the semiconducting characteristics property of the titania gel. The experimental results indicated the electron transport from the dye excited states to the MWCNTs through the titania gel. The MWCNTs functioned as bridges between the titania and ITO. Steam treatment of the titania gel electrodes significantly increased the photoelectric performance due to crystallization of the titania and enhancement of the dye?Ctitania interaction forming the chelate complex on the titania particle surface.     

Catalytic direct 1,4-conjugate addition of aldehydes to vinylketones on secondary-amines immobilised in FSM-16 silica

Direct 1,4-conjugate addition of naked aldehydes to vinylketones is catalysed effectively by N-methyl-3-aminopropylated FSM-16 mesoporous silica, which can be regarded as a novel heterogeneous catalysis for a practical C-C bond formation reaction.     

Zinc chelation and photofluorochromic behavior of spironaphthoxazine intercalated into hydrophobically modified montmorillonite

Spironaphthoxazine (SNO) and Zn2+ were intercalated into montmorillonite interlayers hydrophobically modified by the alkyltrimethylammonium cation during UV light irradiation. The fluorescence spectra of the montmorillonite composites were observed to vary with an increase in the UV and visible light irradiation times. These composites exhibited two types of fluorescence emissions: F1, which originates from a new species, Xs, which is different from SNO (ring-closed form) and merocyanine (MC; ring-open form), and F2, which originates from the MC-Zn complex. With increasing UV light irradiation time, the F1 intensities decreased, whereas the F2 intensities increased. Xs, which is an intermediate species between SNO and MC, was transformed into MC and then coordinated with Zn2+ (i.e., MC-Zn complex) during the UV light irradiation. The reaction rate of the formation of the MC-Zn complex decreased for the hydrophobically modified montmorillonite due to a longer alkyl chain. The retrieval changes in the F1 and F2 intensities were observed with an increasing visible light irradiation time, implying the dissociation of the MC-Zn complex into Xs and Zn2+. The dissociation especially occurred for the hydrophobically modified montmorillonite with a longer alkyl chain. The formation and disappearance of Xs and the MC-Zn complex obeyed first-order kinetics, and therefore the interconversion between Xs and MC could be regarded as the rate-determining step of the whole reaction during the UV and visible light irradiations. The photoinduced reactions of the SNO species and Zn2+ were profoundly affected by the physicochemical environment provided by the clay interlayers. It is concluded that the present photoreactions can be controlled not only by the amounts of the intercalated SNO species and Zn2+, but also by the hydrophobic environment created by the surfactant molecules.     

Experimental evidence and bond characterization of a cyclopropenylgermylene

The reduction of p-anisyl(1,2,3-tri-tert-butylcycloprop-2-en-1-yl)dichlorogermane (1) with potassium in the presence of an excess of tert-butyldimethylsilane in benzene under reflux gave p-anisyl(tert-butyldimethylsilyl)(1,2,3-tri-tert-butylcycloprop-2-en-1-yl)germane (4) in 15% yield. The formation of 4 indicates that p-anisyl(1,2,3-tri-tert-butylcycloprop-2-en-1-yl)germylene (2), which is the first example of a (cycloprop-2-en-1-yl)germylene derivative, was generated and trapped by the hydrosilane. The DFT calculations revealed that the cis-2-p-anisyl-1,3,4-tri-tert-butyl-2-germabicyclo[1.1.0]butane-2,4-diyl structure cis-5 is 8.0 kJ/mol more stable than cis-2. The NBO analysis revealed that cis-5 has a 2-germabicyclo[1.1.0]butane diradical character.     

Influences of Acid on Molecular Forms of Fluorescein and Photoinduced Electron Transfer in Fluorescein‐Dispersing Sol–Gel Titania Films

Fluorescein‐dispersing titania gel films were prepared by the acid‐catalyzed sol–gel reaction using a titanium alkoxide solution containing fluorescein. The molecular forms of fluorescein in the films, depending on its acid–base equilibria, and the complex formation and photoinduced electron transfer process between the dye and titania surface were investigated by fluorescence and photoelectric measurements. The titanium species were coordinated to the carboxylate and phenolate‐like groups of the fluorescein species. The quantum efficiencies of the fluorescence quenching and photoelectric conversion were higher upon excitation of the dianion species interacting with the titania, i.e. the dye–titania complex. This result indicated that the dianion form was the most favorable for formation of the dye–titania complex exhibiting the highest electron transfer efficiency. Using nitric acid as the catalyst, the titania surface bonded to the fluorescein instead of the adsorbed nitrate ion during the steam treatment. The dye–titania complex formation played an important role in the electron injection from the dye to the titania conduction band.     

Enantiocontrolled total syntheses of breviones A, B, and C

Enantiocontrolled total syntheses of the breviones A, B, and C have been accomplished using a highly diastereoselective oxidative coupling of an α-pyrone with a tricyclic diene prepared from an optically pure Wieland-Miescher ketone derivative through the 7-endo-trig mode of acyl radical cyclization.     

Application of plug–plug technique to ACE experiments for discovery of peptides binding to a larger target protein: A model study of calmodulin‐binding fragments selected from a digested mixture of reduced BSA

To discover peptide ligands that bind to a target protein with a higher molecular mass, a concise screening methodology has been established, by applying a “plug–plug” technique to ACE experiments. Exploratory experiments using three mixed peptides, mastoparan‐X, β‐endorphin, and oxytocin, as candidates for calmodulin‐binding ligands, revealed that the technique not only reduces the consumption of the protein sample, but also increases the flexibility of the experimental conditions, by allowing the use of MS detection in the ACE experiments. With the plug–plug technique, the ACE–MS screening methodology successfully selected calmodulin‐binding peptides from a random library with diverse constituents, such as protease digests of BSA. Three peptides with K_d values between 8–147 μM for calmodulin were obtained from a Glu‐C endoprotease digest of reduced BSA, although the digest showed more than 70 peaks in its ACE–MS electropherogram. The method established here will be quite useful for the screening of peptide ligands, which have only low affinities due to their flexible chain structures but could potentially provide primary information for designing inhibitors against the target protein.