V. V. Yanilkin

Synthesis and photophysical properties of colloids fabricated by the layer-by-layer polyelectrolyte assembly onto Eu(III) complex as a core

The luminescent colloids have been synthesized through the layer-by-layer assembly of poly(sodium 4-styrenesulfonate) (PSS) and polyethyleneimine (PEI) onto the luminescent core. The latter has been obtained by the reprecipitation of complex Eu[(TTA)(3)1] (where TTA(-) and 1 are thenoyltrifluoroacetonate and 2-(5-chlorophenyl-2-hydroxy)-2-phenylethenyl-bis-(2-methoxyphenyl)phosphine oxide, respectively) from organic solvent to aqueous solution. The variation of Eu(III) complexes indicates the role of the complex core in the development of such core-shell colloids. Complex Eu[(TTA)(3)1] is most convenient precursor of Eu-doped luminescent nanocomposites. The fluorometric measurements at each step of the layer-by-layer polyelectrolyte assembly onto Eu[(TTA)(3)1] core, at various pHs and additives reveal the quenching of Eu-centered luminescence as a result of the interfacial interaction of the core and the dye. The AFM images and electrochemical behavior of PSS-(PEI-PSS)(n)-Eu[(TTA)(3)1] colloids deposited on the surface indicate the stability of the polyelectrolyte multilayer in the dried state.

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.

Mediated electrochemical synthesis of Pd0 nanoparticles in solution

Efficient electrosynthesis of palladium(0) nanoparticles is carried out in solution by mediated electrochemical reduction of a complex dianion [PdCl4]2– in the DMSO/0.1 M Bu4NCl medium. The mediator function was performed by methylviologen and tetraviologen calix[4]resorcines MVCA-Cn8+ with methyl (n = 1), n-pentyl (n = 5), and n-decyl (n = 10) substituents in resorcinol rings at the potentials of redox pairs MV2+/MV•+, MVCA-Cn8+/MVCA-Cn4•+. The resulting metal nanoparticles gradually aggregate to yield coarser particles. The smallest size (255 nm) have metal particles obtained in the presence of MVCA-C58+ for the rest mediators, metal particles of the micron size are formed. Sonication results in disintegration of aggregates to nanoparticles.

Electrochemical mediated synthesis of silver nanoparticles in solution

Methyl viologen MV2+ and tetraviologen calix[4]resorcinol MVCA-C58+ with n-pentyl substituents in the resorcinol rings at potentials of MV2+/MV•+ and MVCA-C58+ /MVCA-C54•+ redox couples proved to be effective mediators of the electrochemical reduction of Ag+ ions in DMF/0.1 M Bu4NPF6. The potentiostatic nondiaphragm electrolysis at controlled mediator reduction potentials at room temperature using an Ag anode as an in situ supplier of Ag+ led to the formation of metallic silver nanoparticles in solution. The only resulting effect of electrolysis was the quantitative transfer of the metal anode into the metal nanoparticles in solution. In the case of MV2+, the nanoparticles aggregated into larger particles. MVCA-CC58+ serves not only as a mediator, but also, to some extent, as a stabilizer of silver nanoparticles and can be recorded by a set of experimental methods.

Redox-switchable binding of the Mg2+ ions by 21,31-diphenyl-12,42-dioxo-7,10,13-trioxa-1,4(3,1)-diquinoxaline-2(2,3),3(3,2)-diindolysine-cyclopentadecaphane

The binding of the Li+, Na+, K+, Mg2+, and Co2+ ions by 21,31-diphenyl-12,42-dioxo-7,10,13-trioxa-1,4(3,1)-diquinoxaline-2(2,3),3(3,2)-diindolysine-cyclopentadecaphane containing two indolysine fragments, two quinoxaline fragments, and 3,6,9-trioxyundecane spacer in the acetonitrile/0.1 M Bu4NBF4 environment is studied by the method of cyclic voltammetry. It is demonstrated that the Li+, Na+, K+, and Co2+ ions are not bound by this macrocycle, whereas selective redox-switchable binding is observed for the Mg2+ ions. The macrocycle binds the Mg2+ ions way more efficiently as compared with its radical cation and dication. The indolysinequinoxaline fragments play the determining role in the binding.

3-Indolizin-2-ylquinoxalines and the derived monopodands

The reactions of 3-acetylquinoxalin-2-one with methyl-and benzylpyridines in the presence of iodine produce the corresponding 3-(2-alkylpyridinioacetyl)quinoxalin-2(1H)-one iodides. Treatment of the latter with triethylamine affords the corresponding 3-indolizin-2-ylquinoxalin-2-ones. Due to the presence of the endocyclic carbamoyl group, the reactions of these compounds with bisalkylating reagents give quinoxaline-containing monopodands and monoalkylation products containing spacers with different lengths and of different nature.

Voltammetric study of metal ions binding by biindolizine heterocyclophanes and their acyclic analogues

The binding of ions Li+, Na+, K+, (group I), Mg2+, Al3+, Ga3+ (group II), Ca2+, Pb2+ (group III) ions, Ba2+ and paraquat by heterocyclophanes containing biindolizine and quinoxaline fragments connected by 3,6,9-trioxaundecane and 5,8,11,14,17-pentaoxageneicosane spacers, and also their acyclic analogues, in the acetonitrile-0.1 M Bu4NBF4 is studied by cyclic voltammetry. A conclusion is drawn that the ions of the group I are not bound by these compounds; the paraquat is not bound by heterocyclophane with the 5,8,11,14,17-pentaoxageneicosan spacers. For ions of the group II, reversible redox-switchable binding by the macrocycles with the 3,6,9-trioxaundecane and 5,8,11,14,17-pentaoxageneicosan spacers is observed: the initial compounds show the binding; their radical cations and dications do not. The binding of the ions of the group III and Ba2+ is determined by the macrocycles’ size. In particular, these ions are bound not only by the heterocyclophane with 3,6,9-trioxaundecane spacers but also by its radical cation or dication. The binding results in the corresponding dication stabilization. The heterocyclophane with the 5,8,11,14,17-pentaoxageneicosan spacers demonstrates the redox-switchable binding of Ca2+ and Pb2+ ions; no effect of Ba2+ ions on the cyclic voltammograms of this heterocyclophane was observed. In the ternary system “heterocyclophane with 3,6,9-trioxaundecane spacers + ions of the group II (Al3+, Ga3+) + ions of the group III (Ca2+, Pb2+)” either primary binding of the group III ion Pb2+ or concurrent binding of the ions of the group II and the group III, with the system’s reversible redox-switching from one metal complex to another, was observed.

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.

Binding of 1,5-bis(p-sulfonatophenyl)-3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane with tetra(methyl viologen) calix[4]resorcinol

Binding of an amphiphilic dianion 1,5-bis(p-sulfonatophenyl)-3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane (APCO2−) with an amphiphilic octacation tetra(methyl viologen) calix[4]resorcinol (MVCA8+) in media containing different amounts of water and DMSO using NaClO4 or NaCl as supporting electrolytes was shown for the first time by cyclic voltammetry and spectrophotometry. The stoichiometry of the complex depends on the MVCA8+: APCO2− ratio, medium, and supporting electrolyte. A 1: 1 charge-transfer complex is mainly formed (λmax = 480 nm) in 30% DMSO at a ratio of the compounds of 1: 1. A similar 1: 1 complex of APCO2− with a model compound methyl viologen MV2+ (λmax = 482 nm) is formed under these conditions. A donor-acceptor interaction occurs between the acceptor viologen units and nitrogen-centered electron-donating fragments of the APCO2− dianion. An increase in the content of APCO2− in the solution leads to an additional binding of one (30 vol.% DMSO, water, NaClO4) or two (30 vol.% DMSO, water, NaCl) particles of APCO2− with the hydrophobic fragments of MVCA8+. The complexes aggregate to form insoluble precipitates in aqueous and water-DMSO media. A selective reversible electroswitching from the bound to free state of one of the three bound APCO2− particles was performed when reducing MVCA8+ to MVCA4·+ in a 30 vol.% DMSO/NaCl medium.

Electrochemical reduction and oxidation of fullerenopyrrolidines* and the ESR spectra of paramagnetic intermediates

Electroreduction and electrooxidation of monosubstituted N-methyl[60]fullerenopyrrolidines were studied by cyclic voltammetry and potentiostatic microelectrolysis in the cavity of an ESR spectrometer. Stepwise reversible transfer of three electrons to the fullerenopyrrolidine molecule results in the formation of stable radical anions (according to ESR, g = 2.0000, ΔH = 0.8 G), dianions, and radical trianions (according to ESR, g = 2.0015, ΔH = 1.5 G). The reduction potentials vary over narrow limits depending on the nature of the substituents in the pyrrolidine fragment of the compounds. Electrooxidation is irreversible and occurs in either one or two steps. For compounds containing the aniline, indole, or phenol fragment, the first step is associated with oxidation of these fragments and only after that, is the fullerenopyrrolidine core oxidized. Oxidation of the pyrrolidine fragment is substantially more difficult than that of tertiary amines.