Conducting polymer films as model biological membranes

Poly-3-thienylboronic acid: a chemosensitive derivative of polythiophene

Poly-3-thiopheneboronic acid was synthesized by electrochemical polymerization from 3-thienylboronic acid dissolved in the mixture of boron trifluoride diethyl etherate and acetonitrile. Cyclic voltammetry during electropolymerization shows oxidative and reductive peaks growing in each next cycle. An investigation by scanning electron microscopy displayed the polymer layer like a highly flexible film of 110 nm thick with grains of 60–120 nm in size. Strong negative solvatochromic effect was observed. Optical spectra of poly-3-thienylboronic acid at different potentials and pH were studied. Potential cycling leads to a well reversible electrochromic effect. At pH 7.4, the increase of potential leads to the decrease in the absorption band at 480 nm and to the rise in the absorption band at 810 nm with an isosbestic point at 585 nm. Spectroelectrochemical behavior of poly-3-thienylboronic acid and polythiophene was compared. Binding of sorbitol at fixed electrode potential leads to an increase in the absorbance in the shortwave band and to the decrease in the longwave band; the effect depends on the electrode potential and pH. Perspectives of application of poly-3-thienylboronic acid as new chemosensitive material are discussed.

Effects of high frequency ultrasound irradiation on incorporation of SiO2 particles within polypyrrole films

This paper deals with the effect of ultrasound on polypyrrole/SiO2 composite film elaboration through various steps (particle dispersion, electrosynthesis). Experiments were carried out on stainless steel in phosphoric acid solution. An efficient method for dispersion of SiO2 particles prior to electropolymerization, based on low frequency irradiation (20kHz), was proposed. It was shown that mechanical effects of high frequency ultrasound (i.e. mass transfer improvement) led to enhancement of electropolymerization kinetics. Scanning electron microscopy imaging and glow discharge optical emission spectroscopy revealed localization of SiO2 particles in the outer region of the films as well as better incorporation of particles under high frequency ultrasound irradiation. Finally, anticorrosion behavior of formed films was investigated in sodium chloride solution by Open Circuit Potential and anodic polarization methods. The results showed that polypyrrole/SiO2 films elaborated under ultrasound irradiation exhibit the best protective performances.

Potentiometric determination of pantoprazole using an ion-selective sensor based on polypyrrole doped films

The present work reports for the first time the use of polypyrrole (PPy) doped film for development of a potentiometric disposable sensor for determination of pantoprazole (PTZ), a drug used for ulcer treatment. Selective potentiometric response has been found by using a membrane of PPy doped with PTZ anions prepared under galvanostatic conditions at graphite pencil electrode (GPEM/PPy-PTZ) surface. Potentiometric response has been influenced for conditions adopted in polymerization and measurement step. After optimization of experimental (e.g. pH and time of conditioning) and instrumental parameters (e.g. current density and electrical charge) a linear analytical curve from 1.0 × 10(-5) to 1.1 × 10(-2) mol L(-1) with a slope of calibration of the 57.6 mV dec(-1) and limit of detection (LOD) of 6.9 × 10(-6) mol L(-1) was obtained. The determination of the PTZ content in pharmaceutical samples using the proposed methodology and official method recommended by Brazilian Pharmacopeia are in agreement at the 95% confidence level and within an acceptable range of error.

Controlled electrochemical synthesis of polypyrrole nanoparticle thin film and its redox transition to a highly conductive and stable polypyrrole variant

We demonstrated here a unique method to produce a highly stable and conductive polypyrrole (PPY) nanoparticle film. The procedure entails controlling the redox switching and the electrochemical synthesis of PPY. PPY was synthesized at a very low forming potential or reaction rate in nonaqueous CH2Cl2 solvent to promote the PPY nanoparticle formation. Then its property was further optimized by first electrochemically reducing it at a hydrogen evolution potential in a neutral 0.1 M NaClO4, then in a slightly acidic 0.05 M asparagine electrolyte. The PPY nanoparticle thin film was characterized by AFM, UV-vis and EQCM. The procedures described here have proven to be reproducible. The data provided by the EQCM shows a reversible doping and undoping mechanism of asparagine indicating the presence of a highly conductive PPY variant. Both UV-vis and electrochemical characterization suggest that the PPY film made using our approach has excellent redox activity as well as high stability when characterized in asparagine solution. The reversible doping and undoping of asparagine during redox switching shows great potential of these PPY nanoparticle films as biological membranes for a broad range of biological applications.

An amperometric hydrogen peroxide biosensor based on immobilization of horseradish peroxidase on an electrode modified with magnetic dextran microspheres

A new kind of magnetic dextran microsphere (MDMS) with uniform shape and narrow diameter distribution has been prepared from magnetic iron nanoparticles and dextran. Horseradish peroxidase (HRP) was successfully immobilized on the surface of an MDMS-modified glassy-carbon electrode (GCE), and the immobilized HRP displayed excellent electrocatalytic activity in the reduction of H(2)O(2) in the presence of the mediator hydroquinone (HQ). The effects of experimental variables such as the concentration of HQ, solution pH, and the working potential were investigated for optimum analytical performance. This biosensor had a fast response to H(2)O(2) of less than 10 s and an excellent linear relationship was obtained in the concentration range 0.20 micromol L(-1)-0.68 mmol L(-1), with a detection limit of 0.078 micromol L(-1) (S/N = 3) under the optimum conditions. The response showed Michaelis-Menten behavior at larger H(2)O(2) concentrations, and the apparent Michaelis-Menten constant K(M)(app) was estimated to be 1.38 mmol L(-1). Moreover, the selectivity, stability, and reproducibility of the biosensor were evaluated, with satisfactory results.

A simple approach to the synthesis of highly functionalized 3-alkylidene-2,3-dihydro-1H-pyrrole-2-ol derivatives and related pyrroles

The reaction of various primary amines with acetylenic esters at ambient temperature in THF/H(2)O (50:50) produced related enaminones. Subsequently reaction of these in situ prepared enaminones with dibenzoylacetylene leads to 3-alkylidene-2,3-dihydro-1H-pyrrol-2-ol derivatives in good yields. The reaction of these products with various alcohols in the presence of a catalytic amount of HCl produced highly functionalized pyrroles in nearly quantitative yields.

Conducting polymers in modelling transient potential of biological membranes

The possibility of using conducting polymer (CP) films doped with biological ligands as artificial biological membranes to study potential formation mechanisms is presented. Calcium and magnesium ion-binding anionic sites--asparagine, glutamine, adenosinotriphosphate and heparin are incorporated into the poly(pyrrole) film during electrochemical polymerization. This approach allows the competitive calcium-magnesium ion-exchange to be inspected by open circuit measurements. After a close-to-Nernstian sensitivity of the CP membranes was induced by soaking in alkaline solutions of calcium or magnesium, dynamic experiments were performed by a change in the bulk concentration of magnesium or calcium ions. A characteristic transitory potential response, though distinctively different for the calcium and magnesium ions, was observed and explained using the diffusion layer model (DML).