Grzegorz Milczarek

Polyeugenol-Modified Platinum Electrode for Selective Detection of Dopamine in the Presence of Ascorbic Acid

A platinum electrode was modified with electropolymerized films of 4-allyl-2-methoxyphenol (eugenol) by its oxidative polymerization from an alkaline solution by cyclic voltammetry. The modified electrode was than used to determine dopamine (DA) in an excess of ascorbic acid (AA) by differential pulse voltammetry. The peak positions as well as relative sensitivity DA/AA were affected by the potential window applied for the polymerization. For polymerization between 0 and 2.2 V, the peak potentials recorded in a phosphate buffer solution (pH 7.4) were -61 and +152 mV vs Ag/AgCl for AA and DA, respectively. After a 5-min equilibration, relative sensitivity DA/AA was 164 and the current sensitivity for DA was 7.9 nA μM(-)(1). The detection limit for S/N = 3 is 0.1 μM. The high selectivity and sensitivity for DA was found to be due to charge discrimination/analyte accumulation and an effect of catalytic mediation of redox sites. Chronocoulometric data reveal that DA is accumulated on the electrode as a monolayer. The electrode is stable, reversible, and free of fouling problems.

Renewable cathode materials from biopolymer/conjugated polymer interpenetrating networks

Lignin to the Rescue? The increasing demand for rechargeable batteries is putting a strain on the availability of certain key raw materials. Lignin is the second most common biopolymer and typically makes up 25% of wood. Lignin derivatives are also readily available as by-products from the pulp and paper industry. Milczarek and Inganäs (p. 1468) combined lignin derivatives, which are electronic insulators, with polypyrole, a conductive polymer, into an interpenetrating composite suitable for use as a cathode. Lignin derivatives that can be sourced from paper-industry waste are examined as a battery cathode component. Renewable and cheap materials in electrodes could meet the need for low-cost, intermittent electrical energy storage in a renewable energy system if sufficient charge density is obtained. Brown liquor, the waste product from paper processing, contains lignin derivatives. Polymer cathodes can be prepared by electrochemical oxidation of pyrrole to polypyrrole in solutions of lignin derivatives. The quinone group in lignin is used for electron and proton storage and exchange during redox cycling, thus combining charge storage in lignin and polypyrrole in an interpenetrating polypyrrole/lignin composite.

Electrocatalytic oxidation of alcohols on glassy carbon electrodes electrochemically modified by conductive polymeric nickel(II) tetrakis(3-methoxy-4-hydroxyphenyl) porphyrin film

The electrocatalytic oxidation of methanol and other simple alcohols in alkaline solution at a nickel-based chemically modified glassy carbon electrode was investigated. As a modifier a conductive polymeric nickel(II) tetrakis(3-methoxy-4-hydroxyphenyl)porphyrin film was used. The modified electrode was characterized by cyclic voltammetry, and its analytical utility was checked by using batch injection analysis.

Electrochemical detection of nitric oxide using polymer modified electrodes

Electrochemical sensors based on chemical surface modification are very attractive because they combine high sensitivity of amperometry with new dimensions of selectivity and stability provided by the surface modifier. This review shows a few strategies employed to facilitate the detection, determination and monitoring of nitric oxide using polymer modified electrodes. Conducting and nonconducting polymer films and composite films are considered. The most significant achievements reached in this field, during the last decade, are critically reviewed. The collected data are also presented in three tables.

Glassy carbon electrode modified by conductive, polymeric nickel(II) porphyrin complex as a 3D homogeneous catalytic system for methanol oxidation in basic media

Abstract The voltammetric behaviour in alkaline solution of a nickel-based chemically modified electrode (poly-NiTMHPP) prepared by oxidative electropolymerization of a nickel tetrakis(3-methoxy-4-hydroxyphenyl)porphyrin for electro-oxidation of methanol was investigated by cyclic voltammetry and the rotating disk technique. The oxidation of methanol occurs at 0.61 V vs. SCE, where oxidation is not observed at the bare electrode. The dependence of the oxidation current on the methanol concentration and on the number of redox centres Ni(II)/Ni(III) is discussed. From the fact that the oxidation current increases with increasing film thickness it is evident that the electrocatalytic reaction occurs inside the polymer film. The system examined is a typical example of a redox polymer with 3D properties. It is also concluded that the reaction mechanism of methanol electro-oxidation is of the so-called “R” case, according to the concept of Saveant and Andrieux, i.e. a cross-exchange reaction is the limiting step.

Physicochemical and electrokinetic properties of silica/lignin biocomposites

A new method of synthesis of novel composites obtained from silica and Kraft lignin has been proposed. Silica used in the study was obtained by three methods (hydrolysis and condensation of tetraethoxysilane, precipitation in a nonpolar and polar medium with the use of sodium silicate). To extend the possible range of applications, the silica was preliminary modified with N-2-(aminoethyl)-3-aminopropyltrimethoxsysilane, and finally it was modified with Kraft lignin earlier oxidised with sodium periodate (lignin bonded to SiO2 by covalent interactions). The products physicochemical and electrokinetic properties were thoroughly analysed. The dispersive properties and surface morphology were evaluated on the basis of particle size distributions and SEM images. The stability of dispersion in inorganic-organic systems were characterised on the basis of the zeta potential, whose value also permitted concluding on the interactions between colloidal molecules dispersed in water solutions. The products were subjected to elemental analysis to get percentage contents of N, C, H, S elements and were also characterised by XPS and FT-IR spectroscopy. Results of the study are of practical importance in prospective applications of SiO2/lignin biocomposites.

Kinetics of electrocatalytic oxidation of formaldehyde on a nickel porphyrin-based glassy carbon electrode

Abstract Electrocatalytic oxidation of formaldehyde on a glassy carbon modified with electropolymerised films derived from tetrakis(4-hydroxy-3-methoxyphenyl)porphinato nickel(II) (THMPPNi(II)) was studied in 0.1 M NaOH on stationary and rotating electrodes by cyclic voltammetry and rotating disc amperometry, respectively. The data from rotating disc experiments were analysed according to Albery–Hillman theory. The findings showed that the poly-THMPPNi(II) behaves as an efficient electrocacalyst for the oxidation of formaldehyde with the cross-exchange reaction occurring throughout the layer at a low concentration of formaldehyde and for a thin modifier, i.e. the mediating process corresponds to the Lk kinetic case, with a change over to the LEk regime at higher substrate concentration or for thicker films.

A New Nafion‐Free Bipolymeric Sensor for Selective and Sensitive Detection of Nitric Oxide

An amperometric/voltammetric sensor for the determination of nitric oxide based on its oxidation on a glassy carbon (GC) electrode modified by polymerized nickel(II) tetrakis(4-hydroxy-3-methoxyphenyl)porphyrin (NiTHMPP) and additionally covered by polymerized eugenol (4-allyl-2-methoxyphenol) (PE) is described. Cyclic voltammetry was used to compare the performance of Nafion and PE as selective membranes for NO sensors. Our findings showed that the electrodes with PE can be successfully applied to NO detection either by DPV (oxidation peak appeared at +0.75 V vs. Ag/AgCl) or by amperommetry at +0.8 V. The electrodes were very sensitive to NO, with detection limit of 85 nM (S/N = 3), and at the same time were also very selective against ureate (> 104:1), ascorbate (> 5 × 103:1) and nitrite (>103:1). Moreover, PE coated electrodes, comparing with those with Nafion, displayed significantly better selectivity against positively charged species: dopamine (ca. 80:1) and epinephrine (ca. 150:1).

Preparation and General Properties of Chemically Modified Electrodes Based on Electrosynthesized Thin Polymeric Films Derived from Eugenol

Eugenol (4-allyl-2-methoxyphenol) was polymerized oxidatively by cyclic voltammetry at platinum and glassy carbon electrodes. It was found that at platinum the polymerization gives rise to a uniform, compact film which could serve as a permselective membrane for analytes of small molecular size. Applications of such films in selective detection of hydrogen peroxide and nitric monoxide were proposed. Monomer oxidation at glassy carbon resulted in less compact films. Interestingly, at higher potentials a porous structure containing large amount of unoxidized o-methoxyphenyl groups was created. This structure underwent electrochemical demethoxylation leading to the generation of redox active o-quinone functionalities when the modified electrode was cycled in acidic solution. A small amount of p- quinone functionalities was also generated. As could be anticipated the redox couples were capable of mediating electrochemical oxidation of ascorbic acid and NADH. Additionally polymeric eugenol-coated GC exhibited preconcentration capabilities towards dissolved metal cations. This effect was demonstrated on the electrochemical oxidation of preconcentrated Ce(III) and reduction of Cu(II).

Nitric oxide, induced by wounding, mediates redox regulation in pelargonium leaves.

The subject of this study was the participation of nitric oxide (NO) in plant responses to wounding, promoted by nicking of pelargonium (Pelargonium peltatum L.) leaves. Bio-imaging with the fluorochrome 4,5-diaminofluorescein diacetate (DAF-2DA) and electrochemical in situ measurement of NO showed early (within minutes) and transient (2 h) NO generation after wounding restricted to the site of injury. In order to clarify the functional role of NO in relation to modulation of the redox balance during wounding, a pharmacological approach was used. A positive correlation was found between NO generation and regulation of the redox state. NO caused a slight restriction of post-wounded O(2) (-) production, in contrast to the periodic and marked increase in H(2)O(2) level. The observed changes were accompanied by time-dependent inhibition of catalase (CAT) and ascorbate peroxidase (APX) activity. The effect was specific to NO, since the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5 tetramethylimidazoline-1-oxyl-3-oxide (cPTIO) reversed the inhibition of CAT and APX, as well as temporarily enhancing H(2)O(2) synthesis. Finally, cooperation of NO/H(2)O(2) restricted the depletion of the low-molecular weight antioxidant pool (i.e. ascorbic acid and thiols) was positively correlated with sealing and reconstruction changes in injured pelargonium leaves (i.e. lignin formation and callose deposition). The above results clearly suggest that NO may promote restoration of wounded tissue through stabilisation of the cell redox state and stimulation of the wound scarring processes.