An Example of Head-to-Head Dimerization of β4.4-Helices

¹H-NMR and vapor-pressure osmometry results are presented, which indicate the occurrence of a rapid equilibrium involving the head-to-head dimerization of β⁴⁴-helices in chloroform solutions of HCO-_L-Ile-(_D-AIle-_L-Ile)₄-OMe. This equilibrium typifies the one that, in Urry's view, would be responsible for the formation and breaking down of the ion-conducting channels formed by gramicidin A in lipid bilayers.     

Detection Of 2,4-Dichlorophenoxyacetic Acid in Reverse Micelles AOT/n-Octane by Polarization and Quenching Fluoroimmunoassays

Two fluoroimmunoassays for detection of 2,4-dichlorophenoxyacetic acid (2,4-D) in an apolar organic solvent, reverse micelles of Aerosol OT in n-octane, are proposed. Both assays are homogeneous methods, meaning that no separation of free and bound fraction of analyte and no washing steps are required. To perform the assay just add the fluorescein-labeled 2,4-D (FD) and monoclonal antibody to the sample and measure the analytical signal on the Abbott TDx Analyzer. The binding of antibodies to FD can be detected by the decrease in fluorescence intensity and also by the increase in fluorescence polarization. The sensitivity of the developed methods was strongly dependent on the micellar matrix (micellar hydration degree and surfactant concentration). The detection limits of 2,4-D in optimal reverse micellar medium are 0.10 g/L (polarization method) and 0.12 g/L (quenching method). These sensitivities are significantly better compared to the detection limits in an aqueous medium, 0.6 and 0.4 g/L, respectively, using the same reagents.     

Effect of disperse mineral fillers on the strain-strength properties and crack resistance of cured polyesters

Conclusion The tendency of disperse mineral fillers toward aggregation, with the formation of a continuous framework of particles, when filler content is greater than the SCC is manifest in a sharp increase in the difference between the relative viscosity of polyester binder-pastes in the uncured state and the relative elastic modulus in the cured state. It is also manifest in an increase in the relative modulus and a reduction in crack growth energy in cured composites. In this case, there is an especially large increase in the size of the characteristic defect, which ultimately determines the reduction in the breaking stress. The modification of binder-pastes with surfactants increases filler dispersion and makes it possible to increase the strength of cured composites.Presented at the Sixth All-Union Conference on the Mechanics of Polymer and Composite Materials (Riga, November, 1986).Translated from Mekhanika Kompozitnykh Materialov, No. 5, pp. 819–824, September–October, 1987.     

Switching the Stiffness of Polyelectrolyte Assembly by Light to Control Behavior of Supported Cells

Polyelectrolyte block copolymer micelles assembled thin film is switched in response to local photocatalytic reactions on titanium dioxide, resulting in a layer of variable height, stiffness in response to visible light irradiation. Preosteoblasts migrate toward stiffer side of the substrates.

     

Novel copolymers of styrene. 10. halogen ring-disubstituted butyl 2-cyano-3-phenyl-2-propenoates

Novel trisubstituted ethylenes, halogen ring-disubstituted butyl 2-cyano-3-phenyl-2-propenoates, RPhCH?C(CN)CO₂C₄H₉ (where R is 2,5-diBr, 3,5-diBr, 2,3-diCl, 2,4-diCl, 2,5-diCl, 2,6-diCl, 3,4-diCl, 3,5-diCl) were prepared and copolymerized with styrene. The monomers were synthesized by the piperidine catalyzed Knoevenagel condensation of ring-disubstituted benzaldehydes and butyl cyanoacetate, and characterized by CHN analysis, IR, ¹H and ¹³C-NMR. All the ethylenes were copolymerized with styrene (M₁) in solution with radical initiation (ABCN) at 70°C. The compositions of the copolymers were calculated from nitrogen analysis and the structures were analyzed by IR, ¹H and ¹³C-NMR. Decomposition of the copolymers in nitrogen occurred in two steps, first in the 200–500°C range with residue (2–5% wt.), which then decomposed in the 500–800°C range.     

ESI‐MS studies of the non‐covalent interactions between biologically important metal ions and N‐sulfonylcytosine derivatives

The aim of this report is to present the electrospray ionization mass spectrometry results of the non‐covalent interaction of two biologically active ligands, N‐1 ‐ (p‐toluenesulfonyl)cytosine, 1‐TsC, 1 and N‐1 ‐ methanesulfonylcytosine, 1‐MsC, 2 and their Cu(II) complexes Cu(1‐TsC‐N3)₂Cl₂, 3 and Cu(1‐MsC‐N3)₂Cl₂ and 4 with biologically important cations: Na⁺, K⁺, Ca²⁺, Mg²⁺ and Zn²⁺. The formation of various complex metal ions was observed. The alkali metals Na⁺ and K⁺ formed clusters because of electrostatic interactions. Ca²⁺ and Mg²⁺ salts produced the tris ligand and mixed ligand complexes. The interaction of Zn²⁺ with 1–4 produced monometal and dimetal Zn²⁺ complexes as a result of the affinity of Zn²⁺ ions toward both O and N atoms. Copyright © 2016 John Wiley & Sons, Ltd.     

Enhancement of proton mobility and mitigation of methanol crossover in sPEEK fuel cells by an organically modified titania nanofiller

An organically functionalized titania, TiO₂-RSO₃H, was evaluated as filler in sulfonated polyetheretherketone (sPEEK)-based composite membranes for application in high temperature direct methanol fuel cells. The presence of propylsulfonic acid groups covalently bound onto the TiO₂ surface and the nanometric nature of the additive were analyzed by Raman spectroscopy and transmission electron microscopy, respectively. The properties of the sPEEK/TiO₂-RSO₃H composite membranes were compared with those of the pure sPEEK membranes and those of the sPEEK/TiO₂ composite membranes containing pristine titania nanoparticles at same filler content. Water and methanol transport properties were investigated by NMR methods, including relaxation times and self-diffusion coefficients as function of temperature (up to 130 °C), and pressure (from 0 up to 2 kbar). The incorporation of the nanoadditivies in the sPEEK polymer demonstrates considerable effects on the morphology and stiffness of the membranes, as well as on the transport properties and barrier effect to the methanol crossover. In particular, the functionalization by propylsulfonic acid groups promotes a higher reticulation between the polymeric chains, increasing the tortuosity of the methanol diffusional paths, so reducing the molecular diffusion, while the proton mobility increases being favored by the Grotthus-type mechanism. Conductivity measurements point out that the filler surface functionalization avoids the reduction of the overall proton conduction of the electrolyte due to the embedding of the low-conducting TiO₂. Finally, remarkable improvements were found when using the sPEEK/TiO₂-RSO₃H composite membrane as electrolyte in a DMFC, in terms of reduced methanol crossover and higher current and power density delivered.     

Regioselective C−H Hydroarylation of Internal Alkynes with Arenecarboxylates: Carboxylates as Deciduous Directing Groups

In the presence of catalytic [Ru(p‐cym)I₂]₂ and the base guanidine carbonate, benzoic acids react with internal alkynes to give the corresponding 2‐vinylbenzoic acids. This alkyne hydroarylation is generally applicable to diversely substituted electron‐rich and electron‐poor benzoic and acrylic acids. Aryl(alkyl)acetylenes react regioselectively with formation of the alkyl‐branched hydroarylation products, and propargylic alcohols are converted into γ‐alkylidene‐δ‐lactones. The hydroarylation can also be conducted decarboxylatively with a different choice of catalyst and reaction conditions. This reaction variant, which does not proceed via intermediate formation of 2‐vinylbenzoic acids, opens up a regioselective, waste‐minimized synthetic entry to vinylarenes.     

Electrocatalytic multicomponent transformation of cyclic 1,3-diketones, isatins, and malononitrile: facile and convenient way to functionalized spirocyclic (5,6,7,8-tetrahydro-4H-chromene)-4,3′-oxindole system

An electrochemically induced catalytic multicomponent transformation of cyclic 1,3-diketones, isatins, and malononitrile in alcohols in an undivided cell in the presence of sodium bromide as an electrolyte results in the formation of spirooxindoles with fused functionalized 5,6,7,8-tetrahydro-4H-chromene system in 83-98% yields. The application of this efficient electrocatalytic method to the formation of medicinally relevant spirocyclic (4H-chromene)-4,3′-oxindoles is beneficial from the viewpoint of diversity-oriented large-scale processes and represents novel, facile, and environmentally benign synthetic concept for multicomponent reaction strategy.