Crosslinking effects on hybrid organic–inorganic proton conducting membranes based on sulfonated polystyrene and polysiloxane

New hybrid semi‐interpenetrating proton‐conducting membranes were obtained using sulfonated polystyrene (SPS) and inorganic–organic polysiloxane phases with the aim of improving the mechanical and thermal characteristics of the pristine polymer and to study the effects of crosslinking in the latter phase in several of their properties, mainly proton conductivity. Siloxane phases were prepared using poly(dimethylsiloxane) (PDMS) and PDMS with tetraethoxysilane (TEOS) or phenyltrimethoxysilane (PTMS) as crosslinking agents. To study the crosslinking effect, membranes were prepared with different TEOS:PDMS and PTMS:PDMS mole ratios. The films obtained were characterized by FTIR, ²⁹Si‐HPDEC MAS‐NMR, ¹³C‐CP‐MAS NMR, elemental and thermal analyses. Certain properties, such as water uptake (WU), ion exchange capacity (IEC) and the state of the water, were determined. The proton conductivity was measured at different temperatures (30°C and 80°C) and relative humidities (50–95%). The water content of the hybrid membranes declined significantly, compared with the SPS membranes, depending on the nature and amount of siloxane phase added. Nonetheless, the conductivity values remained relatively high (>100 mS cm^?1 at 80°C and 95% RH) when compared to Nafion®117 presumably because of the formation of well developed proton channels, which makes them potentially promising as proton exchange membranes for fuel cells. These membranes proved to be thermally stable up to 350°C. Scanning electron microscopy (SEM) and scanning electrochemical microscopy (SECM) were used to characterize the hybrid membranes microstructures; the latter provided contrast for the conductive domains. Copyright © 2015 John Wiley & Sons, Ltd.     

Infinite-dimensional diagonalization and semisimplicity

We characterize the diagonalizable subalgebras of End(V), the full ring of linear operators on a vector space V over a field, in a manner that directly generalizes the classical theory of diagonalizable algebras of operators on a finite-dimensional vector space. Our characterizations are formulated in terms of a natural topology (the “finite topology”) on End(V), which reduces to the discrete topology in the case where V is finite-dimensional. We further investigate when two subalgebras of operators can and cannot be simultaneously diagonalized, as well as the closure of the set of diagonalizable operators within End(V). Motivated by the classical link between diagonalizability and semisimplicity, we also give an infinite-dimensional generalization of the Wedderburn–Artin theorem, providing a number of equivalent characterizations of left pseudocompact, Jacoboson semisimple rings that parallel various characterizations of artinian semisimple rings. This theorem unifies a number of related results in the literature, including the structure of linearly compact, Jacobson semsimple rings and cosemisimple coalgebras over a field.     

Polyethyleneimine‐Coated Gold Nanoparticles: Straightforward Preparation of Efficient DNA Delivery Nanocarriers

A novel one‐pot method for the synthesis of polyethyleneimine (PEI)‐coated gold nanoparticles (AuPEI‐NPs) that combines the reductant–stabilizer properties of PEI with microwave irradiation starting from hydrogen tetrachloroaurate acid (HAuCl₄) and branched PEI 25 kDa (b25kPEI) was explored. The method was straightforward, green, and low costing, for which the Au/PEI ratio (1:1 to 1:128 w/w) was a key parameter to modulate their capabilities as DNA delivery nanocarriers. Transfection assays in CHO‐k1 cells demonstrated that AuPEI‐NPs with 1:16 and 1:32 w/w ratios behaved as effective DNA gene vectors with improved transfection efficiencies (twofold) and significantly lower toxicity than unmodified b25kPEI and Lipofectamine 2000. The transfection mediated by these AuPEI‐NP–DNA polyplexes preferentially used the caveolae‐mediated route for intracellular internalization, as shown by studies performed by using specific internalization inhibitors as well as colocalization with markers of clathrin‐ and caveolae‐dependent pathways. The AuPEI‐NP polyplexes preferentially used the more efficient caveolae internalization pathway to promote transfection, a fact that supports their higher transfection efficiency relative to that of Lipofectamine 2000. In addition, intracellular trafficking of the AuPEI‐NPs was studied by transmission electron microscopy.     

Facile and rapid one-pot microwave-assisted synthesis of Pd-Ni magnetic nanoalloys confined in mesoporous carbons

An easy and rapid one-pot microwave-assisted soft-template synthesis method for the preparation of Pd-Ni nanoalloys confined in mesoporous carbon is reported. This approach allows the formation of mesoporous carbon and the growth of the particles at the same time, under short microwave irradiation (4 h) compared to the several days spent for the classical approach. In addition, the synthesis steps are diminished and no thermopolymerization step or reduction treatment being required. The influence of the Pd-Ni composition on the particle size and on the carbon characteristics was investigated. Pd-Ni solid solutions in the whole composition range could be obtained, and the metallic composition proved to have an important effect on the nanoparticle size but low influence on carbon textural properties. Small and uniformly distributed nanoparticles were confined in mesoporous carbon with uniform pore size distribution, and dependence between the nanoparticle size and the nanoalloy composition was observed, i.e., increase of the particle size with increasing the Ni content (from 5 to 14 nm). The magnetic properties of the materials showed a strong nanoparticle size and/or composition effect. The blocking temperature of Pd-Ni nanoalloys increases with the increase of Ni amount and therefore of particle size. The magnetization values are smaller than the bulk counterpart particularly for the Ni-rich compositions due to the formed graphitic shells surrounding the particles inducing a dead magnetic layer.

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Graphical abstract PdNi nanoalloys confined in mesoporous carbon exhibiting magnetic properties dependent on thealloys composition and size were synthesized by a fast microwave approach

     

Molecular QCA cells. 1. Structure and functionalization of an unsymmetrical dinuclear mixed-valence complex for surface binding

Utilization of binary information encoded in the charge configuration of quantum-dot cells (the quantum-dot cellular automata, QCA, paradigm) requires molecule-sized dots for room temperature operation. Molecular QCA cells are mixed-valence complexes, and the evaluation and functionalization of an unsymmetrical heterobinuclear, two-dot, Fe-Ru molecular QCA cell is described. The solid state structures of trans-RuCl(dppm)(2)(C[triple bond]CFc) (1) (dppm = methylbis(diphenylphosphane), Fc = (eta(5)-C(5)H(5))Fe(eta(5)-C(5)H(4))) and mixed-valence [trans-RuCl(dppm)(2)(C[triple bond]CFc)][BF(4)] (1a) as well as XPS and spectroscopic data suggest class II behavior suitable for the intended application. Utilization of the trans-Cl position of 1 permits functionalization for surface binding. Two "tailed" complexes of 1, trans-Ru(dppm)(2)(C[triple bond]CFc)(C[triple bond]CPhOCH(3)) (2) and trans-[Ru(dppm)(2)(C[triple bond]CFc)(N[triple bond]CCH(2)CH(2)NH(2))][PF(6)] (3), have been prepared and characterized. The solid state structure of 3 and multinuclear NMR experiments define the structures. In addition, the spectroscopic properties of all complexes and their mixed-valence species are used to define the effect of the substituent "tail" on mixed-valence properties. Further, the electrochemistry of these compounds permits assessment of the extent of perturbation of the substituents on the comproportionation constants and overall electrochemical stability. The complexes possess properties necessary for candidate QCA molecules.     

A high-yielding supramolecular reaction

The X-ray crystal structure determinations of twelve cocrystals involving iso-nicotinamide and a variety of carboxylic acids have revealed a very consistent pattern of hydrogen-bond preferences. The combination of a monocarboxylic acid, an amide, and a pyridine moiety leads, in every case, to discrete "supermolecules" (consisting of two molecules of iso-nicotinamide and two molecules of the relevant carboxylic acid) with well-defined and robust connectivity. The two dominant (regularly occurring) supramolecular synthons in these crystal structures are (1) the heteromeric carboxylic acid.pyridine hydrogen bond and (2) a self-complementary amide.amide hydrogen-bond interaction, both of which prevail in the presence of widely differing chemical functionalities. In four of these cocrystals, a dicarboxylic acid is employed, which alters the structural outcome from discrete entities to infinite assemblies (or to a hexameric complex in a "U-shaped" dicarboxylic acid), which is fully expected since the two primary supramolecular synthons remain intact. This structural study shows that iso-nicotinamide is a supramolecular reagent that can produce well-defined supermolecules (containing carboxylic acids) in very high yields.     

Pt/SiO2 catalysts obtained by the sol-gel method. Influence of the pH of gelation on the surface and catalytic properties

Pt/SiO₂ catalysts prepared by impregnation and sol-gel method from a platinum acetylacetonate precursor have been studied. The pH was varied in the range of 3–9. Important changes in the surface area and pore distribution were found. High metal dispersity was found in all the catalysts, being lower at pH 9.     

A modular, one-pot, four-component synthesis of polysubstituted 1,3-oxazolidines

A modular, one-pot, two-step, four-component synthesis of polysubstituted 1,3-oxzolidines is described. The method comprises two linked domino processes: an organocatalyzed domino reaction of alkyl propiolate and an aliphatic aldehydes and a microwave-assisted amine addition cyclization domino process. An alternative modular, one-pot, three-step, four-component synthesis has also been developed by linking the organocatalyzed domino process to a sequential amine addition/Yb(OTf)(3)-catalyzed enamine cyclization reaction.     

Improvement of alternariol monomethyl ether detection at gold electrodes modified with a dodecanethiol self-assembled monolayer

The electro-oxidation of alternariol monomethyl ether (AME), one of the main metabolites of the Alternaria genus mycotoxins, is studied at 1-dodecanethiol (DDT)-modified gold electrodes, in acetonitrile (ACN) – aqueous phosphate buffer solutions of different pH values, by using cyclic (CV) and square-wave (SWV) voltammetries. The AME voltammetric response at the bare electrode suffers from two drawbacks: it appears at potentials close to the onset of gold oxide formation, and it is hampered by a fouling of the electrode surface due to the accumulation of oxidized products. These shortcomings are circumvented by the use of DDT-coated electrodes, since the intervening monolayer inhibits gold oxide formation and surface passivation by the electrochemical products, without affecting the oxidation kinetics of AME significantly. Diagnostic criteria based on the voltammetric peak parameters show that the electrochemical behavior of AME at the modified electrode is mainly controlled by reactant diffusion from solution, with a weak adsorption of both the mycotoxin and its oxidation products at monolayer defects. Calibration curves were constructed from the AME square-wave voltammetric response and a detection limit of 9.1 × 10⁻⁸ mol dm⁻³ was determined, which is about three times smaller than a previous estimate at platinum and glassy carbon electrodes, and about fifty times smaller than the limit derived from measurements carried out at a polyphenol oxidase-modified carbon paste electrode.     

Stereoselective synthesis of annular 9-cis-retinoids and binding characterization to the retinoid X receptor

Analogues of 9-cis-retinoic acid incorporating an alicyclic ring between the C19 and C10 positions have been synthesized and evaluated as ligands for the RXRalpha nuclear receptor. The stereocontrolled synthesis of these configurationally constrained retinoids combines a Stille cross-coupling and the Wittig reaction as key bond-forming steps. The palladium-catalyzed cross-coupling reaction of the beta-bromo-alpha,beta-unsaturated aldehydes 5 to dienylstannane 6 is very fast at room temperature, and takes place with preservation of the dienylstannane geometry. A highly stereoselective Wittig reaction afforded the C7-C8 bond connecting the hydrophobic ring to the retinoid side chain. The binding affinities of these compounds for the receptor were determined, and the structural and energetic rationale behind the affinity profile of the cyclic 9-cis-retinoic acid derivatives for the RXRalpha nuclear receptor was characterized by using Molecular Mechanics protocols.