UV-ozone dry-cleaning process for indium oxide electrodes for protein electrochemistry

The present study reports, for the first time, on electrochemical responses of cytochrome c at a UV-ozone treated indium oxide electrode. Results from surface tension measurements indicate that UV-ozone treatment is an efficient cleaning procedure to remove organic species contamination on surfaces. Well-defined redox responses for cytochrome c were observed at a UV-ozone treated fully hydrophilic indium oxide electrode. Electrochemical parameters, including the diffusion coefficient, the heterogeneous electron transfer rate constant and the redox potential, were in good agreement with those previously reported. However, decrease in peak current for cytochrome c and [Fe(CN)₆]⁴⁻ were observed at a UV-ozone treated electrode. From XPS results, this behavior would be understood to indicate a decrease in homogeneous active electrode surface area by a decrease in conductivity of the indium oxide surface by UV-ozone treatment. Simple and effective UV-ozone treatment methods are useful for surface contamination sensitive electrochemistry.     

Physicochemical properties of hybrid guest-host nanocomposites based on polyaniline

The study concerns the influence of the method of preparation of hybrid guest-host nanocomposites based on polyaniline (a conducting polymer) on their structure, conductivity, electrochemical characteristics, electronic state, and redox activity__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 643–649, March, 2005.     

Synthesis and characterization of novel nano size electroactive poly 4,4′‐diaminodiphenyl sulphone

The modification of electrodeposited polyaniline film by subsequent electrodeposition of 4,4′‐diaminodiphenyl sulfone (DDS) leads to a new material having nanostructure. The coated polymer films were treated with various pH solutions. The film adherent characteristics and surface morphology were studied using SEM. The electrochemically synthesized polyDDS revealed good redox behavior. The DDS was also polymerized by the chemical oxidation method using potassium persulphate. The polymer was characterized by UV‐Vis and FTIR spectral studies. The formation of polymer through the N? H group was understood from the single N? H stretching vibrational frequency at 3459 cm^?1. The X‐ray diffraction studies revealed the formation of nano sized (28 nm) crystalline polymer. The conductivity of the polymer was determined to be 1.07 × 10^?4 S.cm^?1. The solubility of the chemically polymerized powder was ascertained, and polyDDS showed good solubility in DMF and DMSO. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1702–1707, 2005     

Electrochemical behavior of a new electroactive polyimide derived from aniline trimer

The electrochemical behavior of a soluble polyimide (Tani-polyimide) derived from an aniline trimer was investigated. Similar to processes observed in polyaniline, two typical redox processes involving protonation and ion insertion were observed. Due to the presence of an isolated, short quinonediimine or N,N′-diphenyl-p-phenylenediamine segment, Tani-polyimide displayed an electroactivity at higher potentials and did not undergo an electrochemical degradation reaction. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4295–4301, 1999     

Protease Production by Different Thermophilic Fungi

A comparative study was carried out to evaluate protease production in solid-state fermentation (SSF) and submerged fermentation (SmF) by nine different thermophilic fungi – Thermoascus aurantiacus Miehe, Thermomyces lanuginosus, T. lanuginosus TO.03, Aspergillus flavus 1.2, Aspergillus sp. 13.33, Aspergillus sp. 13.34, Aspergillus sp. 13.35, Rhizomucor pusillus 13.36 and Rhizomucor sp. 13.37 – using substrates containing proteins to induce enzyme secretion. Soybean extract (soybean milk), soybean flour, milk powder, rice, and wheat bran were tested. The most satisfactory results were obtained when using wheat bran in SSF. The fungi that stood out in SSF were T. lanuginosus, T. lanuginosus TO.03, Aspergillus sp. 13.34, Aspergillus sp. 13.35, and Rhizomucor sp. 13.37, and those in SmF were T. aurantiacus, T. lanuginosus TO.03, and 13.37. In both fermentation systems, A. flavus 1.2 and R. pusillus 13.36 presented the lowest levels of proteolytic activity.     

Impedance study of thiolated polyaniline

Covalent attachment of thiolated probes to conducting polymers such as polyaniline (PANI) is a promising approach towards the development of electrochemical sensors and biosensors. However, thiolation alters the conjugated polymer backbone and influences the electrochemical behavior of the conducting polymer. PANI studied in this work was electropolymerized on glassy carbon (GC) electrodes from a solution of 0.1 M aniline in 0.5 or 1.0 M H₂SO₄. The GC/PANI electrodes were then functionalized by covalent attachment of 2-mercaptoethanol to the PANI backbone. The progress of thiolation was studied by cyclic voltammetry and electrochemical impedance spectroscopy (EIS). Thiolation of PANI was found to cause an initial decrease in electroactivity at 0–0.25 V and an increase in electroactivity at 0.25–0.6 V. However, prolonged thiolation caused a loss of electroactivity of PANI, which could be seen from EIS measurements as a dramatic decrease in the bulk redox capacitance of PANI.     

Modified Electrodes and Electrochemical Systems Switchable by Temperature Changes

This article is an overview of extensive research efforts in the area of temperature‐controlled electrochemical systems. Electrochemical reactions, including electrocatalytic and bioelectrocatalytic processes, have been reversibly activated and inhibited by temperature changes. This was achieved by modification of electrode surfaces with thermo‐sensitive polymers (e.g., poly(N‐isopropylacrylamide), PNIPAM) which are reversibly switched by temperature changes between two different structures: swollen expanded coil conformation and shrunken collapsed globule state. While the swollen hydrophilic state allows penetration of redox species to the electrode conducting support and activates electrochemical reactions, the collapsed hydrophobic state isolates the electrode surface and inhibits electrochemical processes. Electrodes modified with the thermo‐switchable polymers have been additionally functionalized with photo‐switchable molecules (e.g., spiropyran derivatives) to achieve double‐controlled electrochemical reactions switchable by temperature changes and light signals. Incorporation of metallic nanoparticles or graphene species in the temperature‐sensitive polymer films resulted in sophisticated features and multi‐signal controlled behavior of the nano‐composite systems.     

Poly[N‐(10‐oxo‐2‐vinylanthracen‐9(10H)‐ylidene)cyanamide] as a novel cathode material for li‐organic batteries

Redox‐active polymers draw significant attention as active material in secondary batteries during the last decade. A new anthraquinone‐based redox‐active monomer was designed, which electrochemical behavior was tailored by mono‐modification of one keto group. The monomer exhibits two one‐electron redox reactions and has a low molar mass, resulting in a high theoretical capacity of 207 mAh/g. The polymerization of the monomer was optimized by variation of solvent and initiator. Moreover, the electrochemical behavior was studied using cyclic voltammetry and the polymer was used as active material in a composite electrode in lithium organic batteries. The polymer reveals a cell potential of 2.3 V and a promising capacity of 137 mAh/g. During the first 100 cycles, the capacity drops to 85% of the initial value. The influence of the charging speed on the charging/discharging properties of the batteries was further investigated. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2517–2523     

Visualisation of the local bio-electrocatalytic activity in biofuel cell cathodes by means of redox competition scanning electrochemical microscopy (RC-SECM)

Optimisation of biocatalytic systems for the electroreduction of molecular O₂ in biofuel cell cathodes implies screening of the catalytic activity of enzyme/redoxpolymer assemblies. Os-complex modified electrodeposition polymers are suggested for linking bilirubin oxidase catalysed O₂ reduction via an electron hopping sequence along the redox polymer to the electrode. They can be non-manually precipitated on electrode surfaces by electrochemically induced pH modulation. Cyclic voltammetry provides a good estimation of the electrocatalytic activity of a redox polymer/enzyme modified electrode surface. In addition, scanning electrochemical microscopy operating in redox competition mode (RC-SECM) supplies images of the spatial distribution of the biocatalytic activity.     

Electrochemical nanogravimetric study on the ruthenium(III) trichloride–polyaniline nanocomposite

Ruthenium(III) trichloride microcrystals were soaked in aniline and aniline/acetonitrile mixtures. In all cases, polyaniline (PANI) was formed as a result of the intercalation of aniline into the layered structure of RuCl₃ crystal and the reaction between aniline and the host material. The appearance of polyaniline was proven by infrared spectroscopy. The as-formed (PANI) _x ^z+(RuCl₃) _y ^z− nanocomposites were attached to gold surfaces and studied by cyclic electrochemical nanogravimetry. The sorption of aniline and its effect on the nanocomposites immobilized on gold were also studied in supporting electrolytes. The redox behaviour of the composite shows the electrochemical transformations of both polyaniline and RuCl₃. The redox waves of PANI are similar to those observed for very thin PANI films. It attests that the response is originated from monolayer-like PANI film situated between RuCl₃ layers. The transport of the charge-compensating ions reflects the variation of the oxidation states of both PANI and RuCl₃. The nanocomposites behave as self-doped layers in the potential region when both constituents are charged, i.e. PANI is partially oxidized while RuCl₃ is partially reduced, since the electroneutrality is assured by mutual charge compensation. When PANI is reduced, cations enter the layer to counterbalance the negative charge resulting from the reduction of Ru(III) to Ru(II). It was also found that the intercalation of water molecules is—albeit still substantial—smaller than that of pure RuCl₃ microcrystals, which is related to the presence of PANI between the RuCl₃ layers. Dedicated to Prof. Mikhail A. Vorotyntsev on the occasion of his 60th birthday     

Composite materials based on polyaniline and multiwalled carbon nanotubes: Morphology and electrochemical behavior

Composites based on polyaniline are prepared via the chemical oxidative polymerization of aniline in the presence of multiwalled carbon nanotubes modified by the sorption of the co-oxidants IrC ₆ ^2? and 2,2′-azino-bis(3-ethyl-benzthiazolin-6-sulfonate). The approach used here, in combination with corresponding conditions of polymerization, ensures the synthesis of composite materials with a high morphological homogeneity of the polymer phase. The study of the electrochemical properties of composites (the reversibility of redox transitions and the stability of capacity parameters) indicates that that they are strongly influenced by the morphological features of the polymer coating. The composite prepared with the use of nanotubes modified by 2,2′-azino-bis(3-ethyl-benzthiazolin-6-sulfonate) possesses better electrochemical characteristics. This effect is associated with a closer to perfect morphology of the polymer coating, a coaxial polyaniline shell highly uniform in thickness along the entire length of nanotubes.     

Analysis of Redox Activity of Proteins on the Carbon Screen Printed Electrodes

Direct redox activity of different proteins was investigated on the surface of carbon screen printed electrodes (SPE). The signal attributed to the electrochemical oxidation of amino acid residues (cysteine (Cys), tryptophan (Trp) and tyrosine (Tyr)) was registered at E_max from 0.6 to 0.7 V (vs. Ag/AgCl). Based on the difference in the redox behavior of L ‐tyrosine and 3‐nitro‐L ‐tyrosine, the selective electrochemical detection of native and nitrated albumins was demonstrated. It was shown that the electrochemical signal correlated with the surface density of electroactive amino acid residues on the protein molecule. A simple electrochemical method for the total protein analysis was proposed.     

Relation between surface preconditioning and metal deposition in direct galvanic metallization of insulating surfaces

The relation between surface preconditioning and metal deposition in the direct galvanic metallization of different insulating polymer surfaces by the so-called PLATO technique was studied using electrochemical and surface analytical methods. AFM, XPS and contact angle measurements show that the chromic acid etching of original polymer surfaces leads to an increase of the surface energy and hydrophilicity of polymer substrates due to both surface roughening and the formation of -COOH and/or -COH surface groups. However, decisive for the subsequent surface activation with cobalt sulfide is the increase in surface roughness. The influence of the degree of activation and the electrode potential on the kinetics of Ni metallization was studied by current transient measurements on activated line-shaped structures. The results suggest that the electrochemical reduction of cobalt sulfide to cobalt is a necessary step to induce the process of Ni electrodeposition. Successful Ni metallization could be obtained on ABS (acrylonitrile-butadiene-styrene) and PEEK (poly-ether-ether-ketone) surfaces. The lateral propagation rate, V _x , of the depositing Ni layer depends exponentially on the applied potential and was found to be several orders of magnitude higher than the Ni deposition rate, V _z , in the normal z-direction (V _x /V _z =10²–10⁴). It was demonstrated that the approach involving cobalt sulfide pre-activation can also be applied successfully for metallization of oxidized porous silicon surfaces.Presented at the 3rd International Symposium on Electrochemical Processing of Tailored Materials held at the 53rd Annual Meeting of the International Society of Electrochemistry, 15–20 September 2002, Düsseldorf, Germany     

Electrochemical oxidation of catechol at poly(indole-5-carboxylic acid) electrode

In this work we examined the electrochemical properties of poly(indole-5-carboxylic acid), PIn₅COOH. The polymer was produced by electrochemical polymerisation using cyclic voltammetry (CV). It was shown that PIn₅COOH is electroactive in aqueous solutions showing two redox processes in acidic solution and one redox process in solutions with pH > 4. The oxidation of catechol (CT) on Pt/In₅COOH modified electrodes was investigated by cyclic voltammetry (CV) and rotating disc electrode (RDE) voltammetry. It was established that CT was oxidised only after the oxidation of polymer film was initiated and that polymer significantly enhanced the oxidation and reduction peak currents in comparison with bare Pt electrode. The variation of peak currents (i _pa, i _pc) as a function of CT concentration was found to be linear up to 6 mM. Experiments with a rotating disk electrode show that the oxidation reaction of catechol occures not only at the polymer/electrolyte interface but also in the polymer film.     

Electrochemical Polymerization of Aniline in Polyamide and Polyvinyl Alcohol Matrices

The electrochemical polymerization of aniline was studied in polymer matrices (polyamid-12 and polyvinyl alcohol) on an electrode in the potential cycling mode from –0.2 to +0.8 V vs. SCE. The indices of this process such as the potentials and currents of the polyaniline redox peaks, polymerization rate, and properties of the conducting composite formed depend on the nature of the matrix polymer and are a function of the extent of interaction of this matrix polymer with aniline and polyaniline.     

Electrosynthesis of Molecularly Imprinted Poly‐o‐phenylenediamine on MWCNT Modified Electrode for Selective Determination of Meldonium

In this study, a molecularly imprinted polymer (MIP) was synthesized by electrochemical polymerization and used to construct an electrochemical sensor for determination of meldonium (MEL) selectively for the first time. The polymer film was generated by using o‐phenylenediamine (o‐PD) as a monomer on the surface of carboxylic acid functionalized multiwalled carbon nanotube (MWCNT) modified pencil rod electrode in the presence of MEL as a template. MEL imprinted (MEL‐imp) and non‐imprinted (N‐imp) polymer films and coated electrodes were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), profilometry, electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Voltammetric measurements were carried out in a ferrocyanide/ferricyanide redox probe solution for MEL‐imp and N‐imp electrodes in the presence and absence of template molecule. The decrease in peak current of redox probe was linear with the concentration of MEL in the range of 0.1–5 μg/mL and the limit of detection (3 s/b) was found to be 0.066 μg/mL under optimized experimental conditions. The proposed sensor was successfully applied for selective determination of MEL in human urine sample with long term stability and good reproducibility.     

Synthesis of some azacrown derivatives and fabrication of their nanofilms on the glassy carbon surface

The modification of N-phenyl-aza-15-crown-5 (PA15C5) and N-(4-aminophenyl)-aza-15-crown-5 (4APA15C5) on glassy carbon (GC) electrode was performed by the electrochemical oxidation of the corresponding azacrown derivatives in anhydrous acetonitrile media. The electrochemical behavior of the resulting modified GC electrode was investigated in the presence of electroactive redox probes and these results, together with the X-ray photoelectron spectroscopy (XPS) and reflection-absorption infrared spectroscopy were used to confirm the attachment of these molecules onto the GC surface. The ellipsometric thicknesses of PA15C5 and 4APA15C5 films at the GC surface was obtained around 9.28 ± 0.40 and 10.50 ± 1.10 nm, respectively. Azacrown modified nanoscale surfaces serve as alkali metal sensor specific for their cavity in the crown ring.     

Ascorbic Acid Oxidation at Nonmodified and Copper‐Modified Polyaniline and Poly‐ortho‐methoxyaniline Coated Electrodes

The electrochemical oxidation of ascorbate ions is comparatively studied at polyaniline (PANI) and poly‐ortho‐methoxyaniline (POMA) layers in absence and presence of electrodeposited copper species. In comparison to PANI, POMA layers allow decreasing the overpotential necessary for driving the ascorbate oxidation reaction. A nonlinear dependence of the ascorbate oxidation current on the polymer layer redox charge is found. Copper electrodeposited in PANI and POMA layers is electrocatalytically active for the investigated reaction. Two separate oxidation waves are observed in the case of Cu‐PANI whereas a single ascorbate oxidation wave and enhanced currents are found in the Cu‐POMA case.     

Anodic Doping of Electropolymerized Copper 2,9,16,23-Tetraaminophthalocyanine

Anodic polymerization of 2,9,16,23-tetraamino substituted copper phthalocyanine is studied in 0.1 M Bu₄NBF₄and Bu₄NClO₄in dimethylformamide (DMF). The electropolymerization rate in DMF is two to three times that in dimethyl sulfoxide, due to a lesser donor ability of DMF and a weaker blocking of radical cations formed during the oxidation of initial copper phthalocyanine. According to a study of the electrochemical behavior of polymerized copper phthalocyanine in neutral aqueous solutions, the anodic doping of the polymer is accompanied by one redox transition. The two redox transitions, observed in an aqueous solution of acid, are explained by two successive steps of oxidation of an aniline-like structure or by the involvement of two protonated systems in the doping process, specifically, a stacked system (phthalocyanine ligands collected in parallel stacks) and a polyaniline system.