Redox Polyelectrolyte Research Articles

Layer-by-layer self-assembled multilayers of redox polyelectrolytes and gold nanoparticles

Construction and characterization of structural and charge transport properties of electrostatically LbL self-assembled multilayers of gold nanoparticles and a viologen-based redox-active polyelectrolyte is reported.

Probe beam deflection study of ion exchange in self-assembled redox polyelectrolyte thin films.

Probe beam deflection during chronoamperometric oxidation-reduction of osmium complex in layer-by-layer self-assembled redox active polyelectrolyte multilayers has shown that the nature of the charge in the topmost layer determines the ion flux that balances the redox charge.

Kinetic analysis of horseradish peroxidase “wiring” in redox polyelectrolyte–peroxidase multilayer assemblies

A hydrogen peroxide sensitive interface based on a self-deposited redox polyelectrolyte–peroxidase assembly was used as model system for investigation of the electron transfer between chemically modified horseradish peroxidase and the redox active centers of poly[(vinylpyridine)Os(bpy) 2Cl] redox polymer. The assembly was built up by sequential adsorption of the redox polymer and the peroxidase on gold electrodes modified with a self-assembled monolayer of 3-mercapto-1-propane sulfonic acid. Making use of a kinetic model, formulated for steady-state conditions, and of the rotating disc electrode technique it was possible to estimate: (i) the second order rate constant of reaction between the modified peroxidase and hydrogen peroxide ( 2.74×10 5 M −1 s −1 ) and (ii) the apparent turnover number of the oxidized enzyme regeneration by the osmium redox center ( 2.14 s −1 ), i.e., two parameters that reflect the efficiency of the electrical communication within the investigated interface.

Donnan permselectivity in layer-by-layer self-assembled redox polyelectrolye thin films.

Redox polyelectrolyte multilayers have been assembled with use of the layer-by-layer (LBL) deposition technique with cationic poly(allylamine) modified with Os(bpy)(2)ClPyCHO (PAH-Os) and anionic poly(styrene)sulfonate (PSS) or poly(vinyl)sulfonate (PVS). Different behavior has been observed in the formal redox potential of the Os(II)/Os(III) couple in the polymer film with cyclic voltammetry depending on the charge of the outermost layer and the electrolyte concentration and pH. The electrochemical quartz crystal microbalance (EQCM) has been used to monitor the exchange of ions and solvent with the external electrolyte during redox switching. At low ionic strength Donnan permselectivity of anions or cations is apparent and the nature of the ion exclusion from the film is determined by the charge of the topmost layer and solution pH. At high electrolyte concentration Donnan breakdown is observed and the osmium redox potential approaches the value for the redox couple in solution. Exchange of anions and water with the external electrolyte under permselective conditions and salt and water under Donnan breakdown have been observed upon oxidation of the film at low pH for the PAH-Os terminating layer. Moreover, at high pH values and with PVS as the terminating layer EQCM mass measurements have shown that cation release was masked by water exchange.

Reagentless biosensors based on self-deposited redox polyelectrolyte-oxidoreductases architectures

Reagentless fructose and alcohol biosensors have been produced with a versatile enzyme immobilisation technique which mimics natural interactions and flexibility of living systems. The electrode architecture is built up on electrostatic interactions by the sequential adsorption of redox polyelectrolytes and redox enzymes giving rise to the efficient transformation of substrate fluxes into electrocatalytic currents. All investigated multilayer structures were self-deposited on 3-mercapto-1-propanesulfonic acid monolayers self-assembled on gold electrodes. Fructose dehydrogenase, horseradish peroxidase (HRP) and the couple HRP-alcohol oxidase were electrochemically connected with a cationic poly[(vinylpyridine)Os(bpy) 2Cl] redox polymer (RP) interface in a layer-by-layer self-deposited architecture. The dependence of the distance on the electrochemical response of this interface was also studied showing a clear decrease in the Faradaic current when the distance to the electrode surface was increased. The sensitivities obtained for each biosensor were 19.3, 58.1 and 10.6 mA M −1 cm −1 for fructose, H 2O 2 and methanol, respectively. The sensitivity values can be easily controlled by a rational deposition and manipulation of the charge in the catalytic layers. The electrostatic assembly of the electrochemical interface and the catalytic layers resulted in integrated biochemical systems in which mass transfer diffusion and heterogeneous catalytic and electron transfer steps are efficiently coupled and can be easily manipulated.

Layer-by-layer electrostatic deposition of biomolecules on surfaces for molecular recognition, redox mediation and signal generation.

Layer-by-layer supramolecular structures composed of alternate layers of negatively charged enzymes and cationic redox polyelectrolyte have been assembled. Glucose oxidase (GOx), lactate oxidase (LOx) and soybean peroxidase (SBP) have been electrically wired to the underlying electrode by means of poly(allylamine) with [Os(bpy)2ClPyCOH]+ covalently attached (PAA-Os) in organized structures with high spatial resolution. Biotinylated glucose oxidase has also been used to assemble step-by-step on antibiotin goat immunoglobulin (IgG) layers and the enzyme was electrically wired by PAA-Os. These spatially organized multilayers with mono- and bienzymatic schemes can work efficiently in molecular recognition, redox mediation and generation of an electrical signal. The concentration of redox mediator integrated into the multilayers, obtained from the voltammetric charge and an estimation of the layer thickness, exceeds by 100-fold the amount of deposited enzyme assessed by quartz crystal microbalance. Differences in GOx electrical wiring efficiency have been detected with the different assembling strategies. The surface concentration of electrically wired enzyme represents a small proportion of all the enzyme molecules present in the multilayers which can be oxidized by the soluble mediator [Os(bpy)2Cl PyCOOH]Cl. This proportion, as well as the rate of FADH2 oxidation by PAA-Os, increases with the number of electrically wired enzyme layers and with the spatial accessibility of the Os moiety to the enzyme active center.

Voltammetric Studies of the Redox Polymer Poly[4,4′-bipyridinium-1,1′-diylcarbonyl-2,5-thiophenediyl Dichloride] in Dimethyl Sulfoxide

Abstract The electrochemical behavior of a redox polyelectrolyte, poly[4,4′-bipyridinium-1,1′-diylcarbonyl-2,5-thiophenediyl dichloride] at mercury electrode has been examined in dimethyl sulfoxide containing different concentrations of tetrabutylammonium iodide. The techniques of sampled DC polarography, pulse polarography (normal and differential), and cyclic voltammetry have been used. All polarograms revealed three one-electron reduction waves which are found either quasi-reversible or irreversible and usually adsorption-controlled by cyclic voltammetric experiments. The results were discussed by taking into account the implications of different concentrations of supporting electrolytes and polycation conformations on the adsorption processes consisting of preceding and following chemical reactions coupled with charge transfer reactions occurring at the electrode.

Electrostatic Control of the Electron-Transfer Enabling Binding of Recombinant Glucose Oxidase and Redox Polyelectrolytes

Electrostatic Control of the Electron-Transfer Enabling Binding of Recombinant Glucose Oxidase and Redox Polyelectrolytes

The Effect of Cadmium Ions on the Polarographic Reduction of Poly[(p-methylbenzyl)viologen] Dibromide in Water

Abstract The d.c. polarographic reduction of a redox polyelectrolyte, poly[(p-methylbenzyl)viologen] dibromide, in the presence of cadmium sulfate salt demonstrated two well-defined, irreversible diffusion-controlled cathodic waves corresponding to the reduction of protonated form as well as the cadmium complex of the polyelectrolyte in aqueous buffers (pH 2.00–6.00). No wave was observed due to the reduction of the unprotonated form of the polymer in the present instance, however, another ill-defined wave of irreversible nature was emerged at relatively higher negative potential presumably because of the catalytic evolution of hydrogen, at the dropping mercury electrode. An attempt has been made to correlate these results in terms of cadmium ion interaction with the polyelectrolyte during the course of electrode processes.

Studies on the Polarographic Reduction of Poly-m-xylylviologen Dibromide in Water

Abstract Polarographic studies on aqueous solutions of the redox polyelectrolyte poly-m-xylylviologen dibromide were carried out in the 1.70–7.90 pH range. The compound revealed two well-defined, diffusion-controlled cathodic waves with half-wave potentials of -0.482 and -0.906 V vs SCE. The electrode processes were found to be irreversible and independent of pH. The system did not conform to the protonation equilibrium (PXVBr2 + H+[dbnd]PXVBr2H+) in contrast to its ortho and para isomeric compounds. A suitable mechanism for the reduction processes is suggested.

Snake‐cage redox polyelectrolytes based on anion‐exchange resins

AbstractRedox polyelectrolytes are described where the polyphenols hydroquinone, pyrogallol, and catechol were absorbed as counterions by a strong base anion‐exchange resin in the hydroxide form, and then polymerized by refluxing in 1:1 mole ratio with formaldehyde in aqueous solution, thus producing a “snake‐cage” configuration. The redox capacities of the resins were determined by oxidation with iodine/iodide solution, and found to approach theoretical at between 5.1 and 5.4 meq/g. The rate of oxidation was found to be controlled by diffusion within the particles. Fe3+ was unsatisfactory as an oxidant, owing to the exclusion effect by the fixed positive charges in the resin matrix. At low pH the resin beads were light to reddish brown in the reduced form, black in the oxidized form. The resins, especially that based on catechol, showed much greater stability in 1N NaOH solution than simple polyphenol–formaldehyde condensation polymers.