Electroenzymatic reactions with oxygen on laccase-modified electrodes in anhydrous (pure) organic solvent

The electroenzymatic reactions of Trametes hirsuta laccase in the pure organic solvent dimethyl sulfoxide (DMSO) have been investigated within the framework for potential use as a catalytic reaction scheme for oxygen reduction. The bioelectrochemical characteristics of laccase were investigated in two different ways: (i) by studying the electroreduction of oxygen in anhydrous DMSO via a direct electron transfer mechanism without proton donors and (ii) by doing the same experiments in the presence of laccase substrates, which display in pure organic solvents both the properties of electron donors as well as the properties of weak acids. The results obtained with laccase in anhydrous DMSO were compared with those obtained previously in aqueous buffer. It was shown that in the absence of proton donors under oxygenated conditions, formation of superoxide anion radicals is prevented at bare glassy carbon and graphite electrodes with adsorbed laccase. The influence of the time for drying the laccase solution at the electrode surface on the electroreduction of oxygen was studied. Investigating the electroenzymatic oxidation reaction of catechol and hydroquinone in DMSO reveals the formation of various intermediates of the substrates with different electrochemical activity under oxygenated conditions. The influence of the content of aqueous buffer in the organic solvent on the electrochemical behaviour of hydroquinone/1,4-benzoquinone couple was also studied.     

Cyclic voltammetric studies of Prussian blue and viologens within a paper matrix for electrochromic printing applications

The apparent redox response of Prussian blue (PB, iron(III) hexacyanoferrate(II)) within a paper matrix is similar to that found in conventional liquid electrolyte voltammetry using a PB-modified electrode; however part of the response is from PB which adsorbs onto the glassy carbon (GC) working electrode. Application of a Nafion® coating to the PB-impregnated paper matrix prevents transfer of PB to the GC surface. In contrast to the PB system, the redox response of the 1,1′-dimethyl-4,4′-bipyridilium (MV, methyl viologen) system, where both redox states examined are soluble, is confined wholly to the paper matrix. For the case of 1,1′-diheptyl-4,4′-bipyridilium (HV, heptyl viologen), the electrogenerated insoluble radical cation salt adsorbs onto the GC electrode, the KCl-impregnated paper acting simply as the electrolyte medium. PB can be electrogenerated within a paper matrix, with the possible application in monochrome electrochromic printing systems.     

Voltammetry of a Benzoquinone–Hydroquinone Redox Couple at Electrodes Modified with a Polyvinylpyridine Film Doped with Cobalt Phthalocyanine

The electrochemical properties of a glassy-carbon electrode coated with a polyvinylpyridine film doped with incorporated cobalt phthalocyanine were studied in a reaction involving a benzoquinone–hydroquinone redox couple. It was found that poly-(2-vinylpyridine) film applied to the electrode and cobalt phthalocyanine deposited onto it or incorporated in the polymeric film exhibited electrocatalytic activity on the oxidation of hydroquinone. Conditions were selected for obtaining a polyvinylpyridine film doped with cobalt phthalocyanine on the electrode surface providing a maximum catalytic effect. The current of the hydroquinone oxidation peak and the current of the reverse benzoquinone reduction peak at the chemically modified electrode were linear functions of their concentrations in the range from 1 × 10^–6 to 1 × 10^–3 M.     

Ultrathin Carbon Film Electrodes from Vacuum‐Carbonised Cellulose Nanofibril Composite

A novel way to produce ultrathin transparent carbon layers on tin‐doped indium oxide (ITO) substrates is developed. The ITO surface is coated with cellulose nanofibrils (from sisal) via layer‐by‐layer electrostatic binding with poly(diallyldimethylammonium chloride) or PDDAC acting as the binder. The cellulose nanofibril‐PDDAC composite film is then vacuum‐carbonised at 500 °C. The resulting carbon films are characterised by atomic force microscopy (AFM), small angle X‐ray scattering (SAXS), wide‐angle X‐ray scattering (WAXS), and Raman methods. Smooth carbon films with good adhesion to the ITO substrate are formed. The electrochemical characterisation of the carbon films is based on the oxidation of hydroquinone and the reduction of benzoquinone in aqueous phosphate buffer media. A modest effect of the cellulose nanofibril‐PDDAC film on the rate of electron transfer is observed. The effect of the film on the rate of electron transfer after carbonisation is more dramatic. For a 40‐layer cellulose nanofibril‐PDDAC film after carbonisation a two‐order of magnitude change in the rate of electron transfer occurs presumably due to a better interaction of the hydroquinone/benzoquinone system with the electrode surface.     

Studies of the limiting currents associated with several oxidation reactions mediated by tris(2,2′-bipyridyl)iron(III) incorporated in nafion® films on carbon electrodes

The kinetics of the oxidation of ferrocyanide, catechol and tiron at carbon electrodes covered with Nafion films containing tris(2,2′-bipyridyl)iron(III) were studied by rotating-disc methods. Under conditions in which these reactions were confined to the film-solution interface, limiting currents were observed that were independent of both the substrate concentration and the electrode rotation rate. This saturated behaviour was interpreted in terms of the rate of electron transfer within the precursor complex formed between the dissolved substrate and the limited number of active mediator sites accessible on the coating surface.     

Synthesis of α-allenic alcohols from propargylic cyclic carbonates and sulfites

Reaction of cyclic carbonates or sulfites of acyclic alkynyl diols with organocopper reagents proceeded in S_N2′ fashion and afforded α-allenic alcohols of high enantiomeric purity. The stereochemistry of this transformation was shown to be highly anti-diastereoselective.     

Linear sweep voltammetry of 9-β- -ribofuranosyluric acid 5′-monophosphate in aqueous and micellar media

Linear sweep voltammetric behaviour of 9-β- -ribofuranosyluric acid 5′-monophosphate (UA-9R-5′-P) has been studied in phosphate buffers of pH 3.0 and 7.0 at the pyrolytic graphite electrode in aqueous and micellar media. At pH 3.0 in the presence of non-ionic and anionic surfactants, UA-9R-5′-P exhibited a single well-defined 2e, 2H⁺ oxidation peak, whereas in the presence of cationic surfactant (CTAB) the oxidation peak I_a showed a tendency to split into two peaks indicating that the 2e, 2H⁺ oxidation of UA-9R-5′-P in peak I_a reaction occurs in two 1e steps. The effect of cationic surfactant at pH 3.0 is explained on the basis of hydrophobic penetration of cationic species in cationic micelles. The products of electrode reaction in micellar medium were found as alloxan, urea and ribosyl phosphate at pH 3.0 and ribose, allantoin and 5-hydroxyhydantoin 5-carboxamide at pH 7.0 and were similar to those observed in aqueous media.     

Direct electron transfer from modified glassy carbon electrodes carrying covalently immobilised mediators to a dissolved viologen accepting pyridine nucleotide oxidoreductase and dihydrolipoamide dehydrogenase

N,N′-Diaminopropyl-4,4′-bipyridinium dication (DAPV) and cobalt diaminosarcophagine (Co—diamsar) were covalently bound on functionalised glassy carbon electrodes. The electron transfer from the modified electrodes to dissolved dihydrolipoamide dehydrogenase (Lip-DH) or viologen accepting pyridine nucleotide oxidoreductase (VAPOR) was tested by NADH formation in potentiostatically controlled electrochemical cells. The NADH formed was used to reduce pyruvate to -lactate catalysed by -lactate dehydrogenase ( -LDH). The reaction kinetics between the modified electrodes and the dissolved enzymes have been examined.     

A variety of oxidation products of antioxidants based on N,N′-substituted p-phenylenediamines

Electrochemical and spectroscopic (EPR, UV–Vis, IR) studies of the aromatic secondary amines N,N′-diphenyl-1,4-phenylenediamine (DPPD), N-phenyl-N′-isopropyl-p-phenylene diamine (IPPD), N-phenyl-N′-(α-methylbenzyl)-p-phenylenediamine (SPPD) and N-phenyl-N′-(1,3-dimethyl-butyl)-p-phenylenediamine (6PPD), which represent the most important group of antioxidants used in the rubber industry, are presented. During oxidation, all the compounds show reversible redox couples in acetonitrile/0.1 M TBABF₄. The first oxidation potential depends substantially on the R substituent at the –N′H– moiety. Very similar UV–VIS spectra of monocation radicals and dications for all the compounds were observed by applying anodic oxidation as well as oxidation by tert-butyl hydroperoxide both in air and in inert atmosphere. The samples with N′-bonded aliphatic carbon in the molecule (e.g. IPPD) heated in air undergo consecutive chemical reactions leading to the formation of –N′C– group. By the use of RO₂ radicals only very low concentration of nitroxide radicals was obtained. Very high concentration of nitroxide radicals was achieved using 3-chloroperbenzoic acid. In the oxidation of investigated aromatic secondary amines with powder PbO₂ no EPR spectra were observed and UV–Vis and IR studies indicate the rapid formation of the final dehydrogenated oxidation product.     

Catalytic Electron‐Transfer Oxygenation of Substrates with Water as an Oxygen Source Using Manganese Porphyrins

Manganese(V)–oxo–porphyrins are produced by the electron‐transfer oxidation of manganese–porphyrins with tris(2,2′‐bipyridine)ruthenium(III) ([Ru(bpy)₃]³⁺; 2 equiv) in acetonitrile (CH₃CN) containing water. The rate constants of the electron‐transfer oxidation of manganese–porphyrins have been determined and evaluated in light of the Marcus theory of electron transfer. Addition of [Ru(bpy)₃]³⁺ to a solution of olefins (styrene and cyclohexene) in CH₃CN containing water in the presence of a catalytic amount of manganese–porphyrins afforded epoxides, diols, and aldehydes efficiently. Epoxides were converted to the corresponding diols by hydrolysis, and were further oxidized to the corresponding aldehydes. The turnover numbers vary significantly depending on the type of manganese–porphyrin used owing to the difference in their oxidation potentials and the steric bulkiness of the ligand. Ethylbenzene was also oxidized to 1‐phenylethanol using manganese–porphyrins as electron‐transfer catalysts. The oxygen source in the substrate oxygenation was confirmed to be water by using ¹⁸O‐labeled water. The rate constant of the reaction of the manganese(V)–oxo species with cyclohexene was determined directly under single‐turnover conditions by monitoring the increase in absorbance attributable to the manganese(III) species produced in the reaction with cyclohexene. It has been shown that the rate‐determining step in the catalytic electron‐transfer oxygenation of cyclohexene is electron transfer from [Ru(bpy)₃]³⁺ to the manganese–porphyrins.     

Nucleophilic Addition to Acetylenes in Superbasic Catalytic Systems: XIV. Vinilation of Diols in a System CsF-NaOH

A new catalytic system CsF-NaOH was developed for the synthesis of mono- and divinyl ethers of alkanediols exceeding in efficiency KOH. The nucleophilic addition of diols to acetylene in the presence of this system occurs both at enhance pressure (without solvent, 140–160°C) and atmospheric pressure (in DMSO medium, 100°C) of acetylene. Conditions were established of a selective preparation in a high yield of divinyl ethers from diols.__________Translated from Zhurnal Organicheskoi Khimii, Vol. 41, No. 5, 2005, pp. 677–683.Original Russian Text Copyright © 2005 by Oparina, Khil’ko, Chernyshova, Shaikhudinova, Parshina, Preiss, Henkelmann, Trofimov.     

5′,8-Cyclopurine-2′-deoxynucleosides: Molecular structure and charge distribution – DFT study in gaseous and aqueous phase

Oxidatively generated damage to DNA frequently appears in the human genome as an effect of aerobic metabolism or as the result of exposure to exogenous oxidizing agents. Due to these facts, it has been decided to present the structural propriety and charge distribution of 5′,8-cyclo-2′-deoxyadenosine/guanosine (cdA, cdG) in their 5′R and 5′S diastereomeric forms. For all points of quantum mechanics studies presented, the density functional theory (DFT) with B3LYP parameters on 6-311++G** basis set level was used. The 2-deoxyribose moiety of cyclopurines has adopted the ₀T¹ conformation in their cationic, neutral and anionic forms. The natural population analysis (NPA) of charge distribution between purine/2-deoxyribose moieties exhibited positive/positive value for cations, positive/negative for neutral molecules. NPA data for anionic forms showed negative/negative values in gas (exclude (5′S)cdG) and positive/negative in water. The dipole moments of 5′,8-cyclopurine-2′-deoxynucleosides were found as follows: 7.83(5′R)cdG, 6.86(5′S)cdG, 3.99(5′R)cdA, 1.99(5′S)cdA in the gaseous phase, 11.29(5′R)cdG, 9.99(5′S)cdG, 6.44(5′R)cdA, 4.14(5′S)cdA in the aqueous phase.     

Electrochemistry of Hydroquinone Derivatives at Metal and Iodine-modified Metal Electrodes

IntroductionPlatinumand gold surfaces can adsorb a wide vari-ety of ions, atoms and molecular functional groups,which is often accompanied by oxidation-reduction ordissociation of them. Numerous previous works havemade great progress in studying the surfa…     

Molecular simulation of the interaction between novel type rhodanine derivative probe and bovine serum albumin

The interaction between 3-(4′-methylphenyl)-5-(4′-methyl-2′-sulfophenylazo) rhodanine (M4MRASP) and bovine serum albumin (BSA) was studied by using spectrofluorimetry. It was shown in fluorescence spectrums that the quenching mechanism of BSA by M4MRASP was a static quenching. Meanwhile, the binding constant and binding site numbers were calculated. The action distance (r = 8.03 nm) and energy transfer efficiency (E = 0.12) between donor (BSA) and acceptor (M4MRASP) were obtained according to the theory of Förster non-radiation energy transfer. The effect of M4MRASP on the conformation of BSA was further analyzed by using synchronous fluorescence spectrometry. A new model of the interaction between small organic molecule and biomacromolecule was established. The results offered a reference for the studies on the biological effects and action mechanism of small molecule with protein.     

Study of the cerium(IV)-picrate system in acetonitrile

A potentiometric and spectrophotometric study has been made of the reaction between hexanitratocerate and picrate in dry acetonitrile. Several cerium(IV)-picrate complexes are formed; the formation constant for the first is estimated to be 4 from spectrophotometric measurements. The catalytic effect of picrate on hydroquinone oxidation by nitratocerate is postulated to be due to more rapid electron transfer by cerium picrate complexes.     

Anodic behaviour of mono- and bisdithiafulvenyl-9,9′-spirobifluorene: insertion of vinylogous TTF into the spirobifluorenyle framework

New three-dimensional copolymers containing 9,9′-spirobifluorenyl-ethylene units were prepared by anodic oxidation of 9,9′-spirobifluorenes 2-mono- or 2,7′-disubstituted by a dithiafulvenyl unit. The synthesis, physicochemical properties and electrochemistry of both monomers and derived oligomers and polymers are reported.     

Triplet level-dependent photoluminescence and photoconduction properties of π-conjugated polymer thin films doped by iridium complexes

Triplet energy level-dependent decay pathways of excitons populated on iridium (Ir) complexes within π-conjugated polymeric matrices were studied by means of photoluminescence (PL) and photoconduction action spectroscopy. We chose a set of matrices, poly(9-vinylcarbazole) (PVK), poly[9,9-bis(2-ethylhexyl)fluorene-2,7-diyl] (PF2/6), poly [2-(5′-cyano-5′-methyl-hexyloxy)-1,4-phenylene] (CNPPP), and poly [2-(5′-cyano-5′-methyl-hexyloxy)-1,4-phenylene-co-pridine] (CNPPP-py10 and CNPPP-Py20), having triplet energy levels ranging from 2.2 up to 3.0 eV. As Ir-complex dopants, we selected three phosphorescent emitters, iridium(III)bis(2-(2′-benzothienyl) pyridinato-N-acetylacetonate) (Ir(btp)₂acac), iridium(III)fac-tris(2-phenylpyridine) (Ir(ppy)₃), and iridium(III)bis[(4,6-fluorophenyl)-pyridinato-N,C^2′]picolinate (FIrpic), having triplet energy levels of 2.1, 2.5, and 2.7 eV, respectively. It was found that the triplet emission from the dopants, being populated via energy transfer from the matrices, was strongly dependent on the matching of triplet energy levels between matrix polymers and Ir-complexes. Photocurrent action spectra confirm effective exciton confinement at the dopants sites in the case of PVK matrix systems.     

Dependence of Fluorescence Quenching of CY3 Oligonucleotide Conjugates on the Oxidation Potential of the Stacking Base Pair

To understand the complex fluorescence properties of astraphloxin (CY3)-labelled oligonucleotides, it is necessary to take into account the redox properties of the nucleobases. In oligonucleotide hybrids, we observed a dependence of the fluorescence intensity on the oxidation potential of the neighbouring base pair. For the series I < A < G < 8-oxoG, the extent of fluorescence quenching follows the trend of decreasing oxidation potentials. In a series of 7 nt hybrids, stacking interactions of CY3 with perfect match and mismatch base pairs were found to stabilise the hybrid by 7–8 kJ/mol. The fluorescence measurements can be explained by complex formation resulting in fluorescence quenching that prevails over the steric effect of a reduced excited state trans-cis isomerisation, which was expected to increase the fluorescence efficiency of the dye when stacking to a base pair. This can be explained by the fact that, in a double strand, base pairing and stacking cause a dramatic change in the oxidation potential of the nucleobases. In single-molecule fluorescence measurements, the oxidation of G to 8-oxoG was observed as a result of photoinduced electron transfer and subsequent chemical reactions. Our results demonstrate that covalently linked CY3 is a potent oxidant towards dsDNA. Sulfonated derivatives should be used instead.     

Reaction and relaxation of vibrationally excited molecules: a classical trajectory study of Br + HCl(υ′) and Br + DCl(υ′) collisions

a quasiclassical trajectory study has been carried out to investigate the dynamics of collisions between Br + HCl (1 υ′ 4) and Br + DCl (υ′ = 2,3). For HCl (υ′ 2) and DCl (υ′ = 3), the endoergic reaction producing Cl + HBr occurs readily, and at approximately the same rate as vibrational deactivation in non-reactive collisions. For HCl(υ′ = 2) and DCl(υ′ = 3), where the initial vibrational energies are similar to |ΔE₀ for the reaction, the rates of both reactive and inelastic processes are quite strongly temperature dependent but the ratio of reactive to inelastic encounters is not a strong function of T. Comparison of the calculated results for Br + HCl(υ′ = 1) with experimentally determined rates strongly suggests that, at least at low temperatures, removal of HCl(υ′ = 1) by Br atoms occurs predominantly via electronically non-adiabatic vibrational relaxation.     

DMSO-Enabled Selective Radical O−H Activation of 1,3(4)-Diols

Control of selectivity is one of the central topics in organic chemistry. Although unprecedented alkoxyl-radical-induced transformations have drawn a lot of attention, compared to selective C−H activation, selective radical O−H activation remains less explored. Herein, we report a novel selective radical O−H activation strategy of diols by combining spatial effects with proton-coupled electron transfer (PCET). It was found that DMSO is an essential reagent that enables the regioselective transformation of diols. Mechanistic studies indicated the existence of the alkoxyl radical and the selective interaction between DMSO and hydroxyl groups. Moreover, the distal C−C cleavage was realized by this selective alkoxyl-radical-initiation protocol.