Elza D. Sultanova

Methyl viologen and tetraviologen calix[4]resorcinol as mediators of the electrochemical reduction of [PdCl4]2− with formation of finely dispersed Pd0

Methyl viologen and tetraviologen calix[4]resorcinol with decyl substituents in the resorcinol cycles (MVCA-C108+) are mediators of the electrochemical reduction of complex dianion [PdCl4]2− facilitating its reduction on the glassy carbon electrode at 0.5–0.6 V. The reduction product of Pd2+ salt is finely dispersed metallic palladium, and its structure and some properties are determined by the mediator nature. When using methyl viologen, palladium is deposited on the electrode and dispersed as flakes in a solution, whereas in the case of MVCA-C108+ palladium is completely deposited on the electrode as nanoparticles together with calixresorcinol.

Electrochemical control of association and deposition of tetraviologen calix[4]resorcin

The association and deposition of tetraviologen calix[4]resorcin MVCA-C58+ can be controlled using the electrochemical reduction-reoxidation cycle of viologen units. The monomeric MVCA-C58+was converted into the highly molecular (MVCA-C54+·)n associate (π-polymer) by reducing it to the MVCA-C54+· tetra(radical cation) and completely returns to the starting monomeric state by reverse oxidation. The reduction to the neutral state MVCA-C50 allowed calixresorcin to pass from solution to precipitate and the reverse oxidation led to its returning in solution.

Controlling the Size and Morphology of Supramolecular Assemblies of Viologen–Resorcin[4]arene Cavitands

A novel class of self-assembling nanoparticles is formed with viologen-resorcin[4]arene cavitands; the association model is strongly controlled by their hydrophobicity. Interestingly, the cavitand assemblies are designed through click chemistry to form self-assembled noncovalently connected aggregates through counterion displacement. The iodide and benzoate ions are utilized as strongly polarizable counterions to induce cavitand self-assembly. The counterion-mediated decrease in hydrophilicity of the viologen-resorcin[4]arenes is the underlying trigger to induce particle formation. These particles can be used as nanocontainers and find their applications in delivery systems.

Electrochemical synthesis of nanocomposite of palladium nanoparticles with polymer viologen-containing nanocapsule

An efficient mediated electrosynthesis of the spherical (85 nm) nanocomposite material Pd@p(MVCA8+-co-St) was carried out in an aqueous medium. Ultrasmall palladium nanoparticles (3—8 nm) are stabilized in nanocapsules of water-soluble nanoparticles of the copolymer p(MVCA8+-co-St) consisting of tetraviologen calix[4]resorcinol (MVCA8+) with styrene (St). The role of the mediator is played by viologen units of a polymer nanoparticle at potentials of the MV2+/MV∙+ redox couple. The high catalytic activity of the nanocomposite material in the reduction of nitrophenol with sodium borohydride is shown.

Electrochemical switching of monomer—associate in the system tetraviologen calix[4]resorcinol—3,7-di(l-menthyl)-1,5-di(p-sulfonatophenyl)-1,5-diaza-3,7-diphosphacyclooctane

The possibility of controlling the association of tetraviologen calix[4]resorcinol (MVCA-C58+) with 3,7-di(l-menthyl)-1,5-di(p-sulfonatophenyl)-1,5-diaza-3,7-diphosphacyclooctane (APCO-22−) in the electrochemical cycle of reduction-reoxidation of viologen units was shown. Reduction to tetra(radical cation) MVCA-C54+· transforms monomeric MVCA-C58+ and APCO-22- into the associate (π-polymer) (xAPCO-22−·yMVCA-C54+·)n, which is completely returned by reoxidation to the initial state.

Molecular Oxygen as Mediator in the Metal Nanoparticles’ Electrosynthesis in N,N -Dimethylformamide

Ultra-fine gold (<2 nm), silver (5 ± 2 nm), and palladium (<1–2 nm) nanoparticles stabilized in polyvinylpyrrolidone shell were synthesized in N,N-dimethylformamide, using molecular oxygen dissolved in the electrolyte as mediator, by the reduction of the metals’ ions and complexes at the controlled potential of the oxygen reduction to its radical-anion. Pd-nanoparticles showed high catalytic activity in the reactions of p-nitrophenol reduction and Suzuki cross-coupling. Long-term ageing of spherical Ag-nanoparticles for 60 days in the post- electrolysis solution resulted in their consolidation (up to 17 ± 5 nm; the average size of crystallites 7.5 (3) nm). Upon similar exposure of Au-nanoparticles for 15 days, V-shaped nanoparticles were formed (length 112 ± 53 nm, width 58 ± 22 nm, crystallites 20(2)–31(1) nm); upon the isolation, dispersing into ethanol, and exposure for 48 h, hexagonal nanoparticles (105 ± 29 nm) and polygons (56 ± 25 nm, crystallites 24(2)–51(1) nm; upon dispersing into water and exposure for 8 h, spherical nanoparticles (13 ± 8 nm, crystallites 7(1)–13.4(5) nm). Thus obtained nanoparticles are characterized by methods of cyclic voltammetry, dynamic light scattering, scanning and high resolution transmission electron microscopy, and X-ray powder diffraction.

Highly active Pd–Ni nanocatalysts supported on multicharged polymer matrix

In this article, we report the synthesis of mono- and bimetallic Pd–Ni nanocomposites supported on a multicharged polymeric matrix for catalytic applications. The morphology and catalytic properties of the composites depend on the Pd–Ni ratio. In the Suzuki–Miyaura coupling reaction, the composite with an equal amount of palladium and nickel is the most active and the reaction occurs within six hours in water at room temperature.

Electrochemical synthesis of metal nanoparticles using a polymeric mediator, whose reduced form is adsorbed (deposited) on an electrode

Efficient mediated electrosynthesis of nanocomposite Au@р(MVCA8+-co-St) (~6 nm), in which ultrasmall Au nanoparticles (Au-NP) were bound in nanocapsules of water-soluble nanoparticles of соpolymer р(MVCA8+-co-St) of tetraviologen calix[4]resorcinol (MVCA8+) with styrene (St), was accomplished by the reduction of AuI in aqueous medium. The quanti- tative reduction of AuI was carried out using the theoretically necessary amount of electricity and was not accompanied by the deposition of metal on the electrode. Radical cations of viologen units MV•+ of the molecule р(MVCA4•+-co-St) adsorbed on the electrode and π-dimers MV•+···MV•+ of π-polymers [р(MVCA4•+-co-St)]n deposited on the electrode act- ed as the reducing agents with respect to AuI. During electrolysis, the nanoparticles agglo- merated to 37—50 nm. The nanocomposite particles dispersed in ethanol had sizes of 72±16 nm and also contained Au-NP with sizes of 51±8 and 19±3 nm. The catalytic activity of the nanocomposite in the reduction of p-nitrophenol with sodium borohydride was demon- strated. A similar reduction of AgCl nanoparticles (~250 nm) led to the formation of silver nanoparticles with crystallite sizes in the range of 7—11 nm, the process was inefficient, however, even when using 250% of electricity, an incomplete reduction of AgCl was still observed.

Reduction-controlled substrate release from a polymer nanosphere based on a viologen-cavitand

In this article, we present a new polymeric nanosphere (p(MVCA-co-SS)) for redox-controlled substrate release. The nanosphere consists of a hydrophobic core with disulfide bridges stabilized by the viologen-resorcinarene cavitand shell. The nanosphere is sensitive to thiol-containing reducing agents: glutathione (GSH) and dithiothreitol (DTT). GSH destructs the hydrophobic core of p(MVCA-co-SS) while DTT integrates into the core increasing its size. The nanosphere as shown can be used as nanocarriers for the redox-controlled substrate release for the fluorescent dyes (pyrene, rhodamine b and fluorescein).