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Ernesto J Calvo

Publications and source records attributed to Ernesto J Calvo.

13 recordsLinked to original sources
PubMed2006

Nanostructured modified electrodes: role of ions and solvent flux in redox active polyelectrolyte multilayer films.

Electrodes modified layer-by-layer by self-assembly of redox active polyelectrolytes comprised of osmium bipyridine-pyridine derivatized poly(allyl-amine) and poly(vinyl) sulfonate have been studied by EQCM, ellipsometry, cyclic voltammetry and electrochemical impedance spectroscopy in aqueous solutions of different anions and cations. Redox driven swelling by solvent exchange during oxidation, in excess to the hydration number, occurs by perturbation of the equilibrium between the osmotic and elastic forces as a result of the electrochemical injection of charge into the film. The exchanged mass and volume change during redox switching strongly depends on the nature of the anion under anion Donnan permselectivity conditions.

Cations↗
PubMed2006

Dynamics of ion exchange between self-assembled redox polyelectrolyte multilayer modified electrode and liquid electrolyte.

A probe beam deflection (PBD) study of ion exchange between an electroactive polymer poly(allylamine)-bipyridyl-pyridine osmium complex film and liquid electrolyte is reported. The PBD measurements were made simultaneously to chronoamperometric oxidation-reduction cycles, to be able to detect kinetic effects in the ion exchange. Layer-by-layer (LbL) self-assembled redox polyelectrolyte films with osmium bipyridyl complex covalently attached to poly(allylamine) (PAH-Os) and poly(styrene sulfonate) (PSS) have been built by alternate electrostatic adsorption from soluble polyelectrolytes. The ionic exchange during initial conditioning of the film ("break-in") undergoing oxidation-reduction cycles and recovery after equilibration in the reduced state have shown an exchange of anions and cations with time lag between them. The effect of the nature of cation on the ionic exchange has been investigated with dilute HCl, LiCl, NaCl, and CsCl electrolytes. The ratio of anion to cation exchanged at the film-electrolyte interface has a strong dependence on the nature of charge in the topmost layer, that is, when negatively charged PSS is the capping layer, a larger proportion of cation exchange is observed. This demonstrates that the electrical potential distribution at the redox polyelectrolyte multilayer (PEM)/electrolyte interface determines the ionic flux in response to charge injection in the film.

Journal Article↗
PubMed2006

Structure and thickness dependence of "molecular wiring" in nanostructured enzyme multilayers.

Supramolecular organized multilayers composed of glucose oxidase (GOx) and osmium-derivatized poly(allylamine) redox polymer have been self-assembled electrostatically from Os-polyelectrolyte solutions of variable pH (5.5-8.8) leading to a decrease of the linear charge density in the PAH-Os with increasing pH. The layer-by-layer enzyme multilayers were studied by ellipsometry, quartz crystal microbalance, AFM, cyclic voltammetry, and electrocatalytic oxidation of beta-D-glucose. At higher adsorption solution pH, an increase in the film thickness, enzyme loading, and redox charge was observed. While the electrocatalytic response increases with the increase of the adsorption solution pH (decrease of the polyelectrolyte linear charge), the FADH2 oxidation bimolecular rate constant has a maximum in the pH range 7.0-7.5 where a change in the film growth mechanism is observed.

Electrochemistry↗
PubMed2005

Biomimetics with a self-assembled monolayer of catalytically active tethered isoalloxazine on Au.

A new biomimetic nanostructured electrocatalyst comprised of a self-assembled monolayer (SAM) of flavin covalently attached to Au by reaction of methylformylisoalloxazine with chemisorbed cysteamine is introduced. Examinations by Fourier transform infrared spectroscopy and scanning tunneling microscopy (STM) show that the flavin molecules are oriented perpendicular to the surface with a 2 nm separation between flavin molecules. As a result of the contrast observed in the STM profiles between areas only covered by unreacted cysteamine and those covered by flavin-cysteamine moieties, it can be seen that the flavin molecules rise 0.7 nm above the chemisorbed cysteamines. The SAM flavin electrocatalyst undergoes fast electron transfer with the underlying Au and shows activity toward the oxidation of enzymatically active beta-NADH at pH 7 and very low potential (-0.2 V vs Ag/AgCl), a requirement for use in an enzymatic biofuel cell, and a 100-fold increase in activity with respect to the collisional reaction in solution.

Biomimetics↗
PubMed2005

Wiring enzymes in nanostructures built with electrostatically self-assembled thin films.

The construction of electrostatically self-assembled intelligent nanostructures on electrodes with redox enzyme layers and redox polymer molecular wires defined in space allowed the analysis of redox charge transport from the redox enzyme to the electrode along nanometric distances. Recent results on the electrical connection of enzymes to electrodes and perspectives of generating electrical signals from molecular recognition in integrated enzyme electrodes are discussed.

Biosensing Techniques↗
PubMed2004

Microgravimetric study of electrochemically controlled nucleophilic addition of sulfite to polyaniline.

The sulfonation of polyaniline (PANI) films by nucleophilic addition of sulfite ion has been controlled through the polymer oxidation state under electrochemical control. The process was monitored by in situ electrochemical quartz crystal microbalance (EQCM), and the polymer oxidation was accomplished by electrode potential steps in sulfite aqueous solutions. The nucleophilic addition of sulfite to PANI only takes place on the oxidized polymer. From the ratio of added mass to the injected charge, the degree of sulfonation has been obtained with a yield as high as 50%. It has been observed that the ion-exchange mechanism during the oxidation-reduction process in the resulting sulfonated polymer is analogous to the polymer produced by electrophilic sulfonation of polyaniline or by copolymerization of aniline with aminosulfonic acids, unlike the ionic exchange observed for unmodified PANI.

Journal Article↗
PubMed2002

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.

Electrochemistry↗
PubMed2002

Study of layer-by-layer self-assembled viscoelastic films on thickness-shear mode resonator surfaces.

We describe quartz crystal electroacoustic admittance studies in thickness shear mode resonators loaded with self-assembled multilayers composed of alternate layers of glucose oxidase (GOx) and poly(allylamine) covalently attached to [Os(bpy)2ClPyCOH]- , (PAH-Os), deposited on a 3-mercaptopropanesulfonic acid (MPS)-modified gold on the quartz crystal. The complex acoustic impedance parameters, R(S) and X(LS) of a lumped-element Butterworth-Van Dyke (BVD) resonator have been determined for organized thin films of different thickness obtained by varying the number of enzyme layers, n, in (PAH-Os)n(GOx)n structures. The ellipsometric film thickness and mass for dry enzyme multilayer films and films in contact with water were evaluated, and the average film density was estimated. By combination of the estimated film thickness and density, the expression for the surface mechanical impedance of the lumped-element modified resonator (Granstaff and Martin model), and the liquid density and viscosity, we simulate the layer-by-layer film growth on the basis of the measured electroacoustic impedance. The complex impedance X(LS) and R(S) increase with film thickness and the enzyme films can be regarded as acoustically thin in the reduced state for films thinner than 600 nm. We have also measured electroacoustic parameters for PAH-Os/GOx self-assembled multilayers under electrochemical perturbation in a buffer electrolytic solution. The electrostatically self-assembled multilayers behaved as lossy viscoelastic films at 10 MHz with G'f and G''f on the order of 10(6) Pa. The films became viscoelastic upon oxidation to Os(III), resulting in an increase of R(S) and X(LS) in the oxidized state with the number of (PAH-Os)(GOx) bilayers due to film swelling and an increase in the shear moduli during oxidation.

Allylamine↗
PubMed2002

Molecular "wiring" enzymes in organized nanostructures.

We report on the "molecular wiring" efficiency of glucose oxidase in organized self-assembled nanostructures comprised of enzyme layers alternating with layers of an osmium-derivatized poly(allylamine) cationic polyelectrolyte, acting as redox relays. Varying the relative position of the active enzyme layer in nanostructures alternating active enzyme and inactive apoenzyme we have demonstrated that the specific rate of bimolecular FADH(2) oxidation ("wiring efficiency") is limited by the diffusion-like electron hopping mechanism in the multilayers.

Electrochemistry↗
PubMedDate not supplied

Effect of the polycation nature on the structure of layer-by-layer electrostatically self-assembled multilayers of polyphenol oxidase.

Self-assembled multilayers comprised of alternate layers of polyphenol oxidase (PPO) and poly(allylamine) (PAH) or PPO and poly(diallyldimethylamine) (PDDA), deposited on a 3-mercaptopropanesulfonic acid (MPS)-modified gold surface, were studied "in-situ" (under water) by means of ellipsometry and quartz crystal microbalance (QCM), and "ex-situ" (in open air) by ellipsometry and fourier transform infrared reflection-absorption spectroscopy (FT-IRRAS). Optical ellipsometric properties of (PAH)(n)(PPO)(n) and (PDDA)(n)(PPO)(n) multilayers were obtained at two wavelengths, employing an isotropic single-layer model with the substrate parameters measured after thiol adsorption. Film thickness as well as ellipsometric mass values based on the de Feijter equation were also evaluated. The quartz crystal impedance analysis showed that self-assembled multilayers behaved as acoustically thin films, and therefore, the shifts observed in the film inductive impedance parameter were interpreted in terms of gravimetric mass. The enzyme mass up-take in each adsorption step was determined on PAH or on PDDA topmost layer. A comparative study between the ellipsometric thickness and acoustic mass values allowed us to obtain average values of "apparent" densities of (2.1 +/- 0.1) and (2.4 +/- 0.1) g cm(-3) for (PAH)(n)(PPO)(n) and (PDDA)(n)(PPO)(n) multilayers, respectively. The content of water included in the open polymer-enzyme structure was evaluated by comparison of QCM and ellipsometric mass values. FT-IRRAS spectra of each layer in (PAH)(n)(PPO)(n) and (PDDA)(n)(PPO)(n) films were recorded, and the intensity ratio of the amide bands was evaluated to obtain information about layer-by-layer enzyme conformation. An enzyme/polycation distribution model for (PAH)(n)(PPO)(n)and (PDDA)(n)(PPO)(n) multilayer structures is presented on the basis of combined ellipsometric, QCM, and FT-IRRAS results.

Catechol Oxidase↗