Mechanism of electrochemical oxidation of 1-chloro-2,2,6,6-tetramethylpiperidine

In contrast to 2,2,6,6-tetramethylpiperidine and other aliphatic amines, at the electrochemical oxidation of 1-chloro-2,2,6,6-tetramethylpiperidine a sufficiently stable cation-radical is formed. Its formation is confirmed by the data of cyclic voltammetry and electron paramagnetic resonance. Further transformation of the cation-radical leads to the formation of 2,2,6,6-tetramethylpiperidin-1-oxyl.

     

Redox active surface films produced by electrooxidation of substituted indolysines

The electrochemical oxidation of substituted mono-and 3,3′-biindolysines is studied by methods of cyclic voltammetry and electron spin resonance (ESR) combined with in situ electrolysis. In acetonitrile, there occurs easy irreversible electrochemical oxidation and proceed processes of association of generated radical cations via unsubstituted positions of five-membered cycles. Polymeric products of oxidation of 2-arylindolysines, 3-indolysine-2-yl-quinoxalines, and 2,2′-diaryl-3,3′-biindolysines are obtained when cycling potential in the interval ?0.3 V → +0.8 V → ?1.3 V → ?0.3 V (Fc/Fc⁺). The products deposit on the electrode with the formation of redox-active films that are capable of undergoing reversible oxidation with the formation of stable paramagnetic states registered by the ESR method.     

Binding of 1,5-bis(p-sulfonatophenyl)-3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane with tetramethylviologen calix[4]resorcin with a methyl radical in the resorcinol ring

The binding of the amphiphilic 1,5-bis(para-sulfonatophenyl)-3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane dianion (APCO^2?) with the octacation of the amphiphilic tetramethylviologen calix[4]resorcin having a methyl radical in the resorcinol ring (MVCA-C ₁ ⁸⁺ ) in 30% aqueous DMSO in a 0.1M NaCl supporting solution was studied by various methods. The dianion was bound at the upper rim of calixresorcin due to the donor-acceptor interactions between the viologen acceptor units and the nitrogen- and phosphorus-centered electron-donor fragments of APCO^2? and at the lower rim due to hydrophobic interactions. The composition of the complex depended on the MVCA-C ₁ ⁸⁺ : APCO^2? ratio. The complexes aggregated, forming insoluble precipitates. MVCA-C ₁ ⁸⁺ -APCO^2? is a system with reversibly electro-switchable aggregation. The starting MVCA- ₁ ⁸⁺ octacation partially bound APCO^2?, a certain quantity of both substrates remaining in a free state in solution. The MVCA-C ₁ ^4+· tetraradical tetracation formed as a result of the reduction of MVCA-C ₁ ⁸⁺ completely bound APCO^2? due to hydrophobic interactions when the MVCA-C ₁ ⁸⁺ : APCO^2? ratio was 1: 3. The reversible oxidation of MVCA-C ₁ ^4+· to the starting MVCA-C ₁ ⁸⁺ octacation brought the system back to its starting state     

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.     

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.     

Retro-Bingel reaction in the electrochemical reduction of bis(dialkoxyphosphoryl)methanofullerenes

Four steps of reduction were detected for bis(diethoxyphosphoryl)- and bis(diisopropoxyphosphoryl)methano[60]fullerenes (1, 2) and bis(diethoxyphosphoryl)methano[70]fullerene (3) by cyclic voltammetry in the o-dichlorobenzene—DMF (3 : 1, v/v)/Bu₄NBF₄ (0.1 mol L^–1) system on a glass-carbon electrode. At the first step the reversible transfer of one electron affords stable radical anions 1 and 2 (g = 1.9999, H = 1.9 G). When two electrons per molecule are transferred, the methano fragment is rapidly eliminated (retro-Bingel reaction). This process involves the step-by-step cleavage of two C—C bonds of exo-carbon with the fullerene shell in combination with the stepwise transfer of other two electrons and a proton to form finally the carbanion of the methano fragment and fullerene dianion. For all studied compounds, the elimination rate is much higher than that for bis(alkoxycarbonyl)- and dialkoxyphosphoryl(alkoxycarbonyl)methano[60]fullerenes, which makes it possible to propose bisphosphorylmethane groups as protective in synthesis of new fullerene derivatives.     

Studies of Cobalt(III) and Chromium(III) Complexes as Mediators in the Silver Nanoparticle Electrosynthesis in Aqueous Media

Metal complexes [Cr(bipy)₃]³⁺, [Co(bipy)₃]³⁺, and [Co(sep)]³⁺ in aqueous media at the potentials of M(III)/M(II) redox couple are shown playing a role of mediators in the electrosynthesis of silver nanoparticles, stabilized in a polyvinylpyrrolidone shell, by means of Ag(I) reduction. [Cr(bipy)₃]³⁺ is consumed under the conditions of long-term preparative electrolysis, the reduction process is accompanied by cathode passivation, therefore, the Ag+ ions complete conversion to the Ag-nanoparticles is unattainable. The two other metal complexes are fully remained unimpaired; the mediated electrosynthesis of the Ag-nanoparticles is carried out well effectively: the Ag-nanoparticles are produced in the solution bulk with a nearly quantitative yield, a theoretical charge being consumed. the [Co(bipy)₃]³⁺-mediated reduction of the Ag⁺ ions, generated by a silver anode in situ dissolution in the course of single compartment cell electrolysis, is accompanied by the anode metal dispersion and results in the formation of polydisperse Ag-nanoparticles. The summary Ag-nanoparticle current efficiency in the solution bulk comes to 128%. Thus formed Ag-nanoparticles are characterized by using dynamic light scattering, scanning and transmission electron microscopy, and X-ray powder diffraction. The Ag-nanoparticles are spherical, with a mean size of 83 ± 53 nm, or have a form of nanowires, with a length of l = 1216 ± 664 nm and diameter of d = 94 ± 17 nm. The [Co(sep)]³⁺-mediated AgCl reduction gives ellipsoidal Ag-nanoparticles sized l = 46 ± 19 nm, d = 27 ± 7 nm; the silver crystallite mean size is 20(1)–34.4(9) nm.     

Electrochemical reduction of 5-halo-5-nitro-1,3-dioxanes and 2-halo-2-nitro-1,3-propanediols

The character of the first stage of reduction of 5-X-5-nitro-1,3-dioxanes 1—10 and 2-X-2-nitro-1,3-propanediols 11 and 12 is independent of the nature of halogen (X = Br, Cl) and substituents in position 2 of the dioxane cycle. The transfer of two electrons to a molecule of compound 1—12 is accompanied by the anionoid elimination of halogen and formation of the anion of nitronic acid. The high mobility of halogen is mainly due to the acceptor nitro group capable of further transformations in the -position to halogen. The direction of further reduction involving the electron transfer to electrochemically active groups in the aromatic fragment of the molecule is determined by the nature of these groups. Chloro-, bromo-, and iodophenyl-substituted derivatives 4, 5, and 8—10 are reduced as typical halobenzenes. In the case of nitrophenyl-substituted compounds 3 and 7, the dioxane cycle opens to form dianions of p- and m-nitrobenzaldehydes along with the reduction of the nitroso group through the stages of formation of the radical anion and radical anion of the nitroso group. The radical anions of the nitro and nitroso derivatives were identified by ESR.     

Electrochemical properties of <Emphasis Type="Italic">n</Emphasis>-sulfonatothiacalyx[4]arene complexes with Fe<Superscript>3+</Superscript> and [Co(dipy)<Subscript>3</Subscript>]<Superscript>3+</Superscript> ions

The electrochemical properties of n-sulfonatothiacalyx[4]arene (H₄XNa₄) complexes with [Co(dipy)₃]³⁺ and Fe³⁺ ions were studied by means of cyclic voltammetry in aqueous solution at pH 2.5. The observed single-electron reduction of [Co(dipy)₃]³⁺ bound extraspherically to the upper rim and Fe³⁺ ion bound intraspherically to the lower rim of n-sulfonatothiacalyx[4]arene in binary [Co(dipy)₃]³⁺ · H₃X^5?, H₃X^5? · Fe³⁺, and ternary [Co(dipy)₃]³⁺ · H₃X^5? · Fe³⁺ heterometal complexes was more difficult than in the free state. The reversible single-electron transfer to the metal ion results in lower binding energy ([Co(dipy)₃]³⁺, ΔΔG ₀ = 3.9 kJ/mol) or in full fast dissociation of the complex (Fe³⁺). The ternary complex in the solution forms the aggregates, in which inner encapsulated Fe(III) and Co(III) ions are not reduced on the electrode. Their quantitative reduction takes place by the relay mechanism of intra- and intermolecular electron transfer through electrochemically generated [Co(dipy)₃]²⁺ outer ions.