Molecularly imprinted polypyrrole prepared by electrodeposition for the selective recognition of tryptophan enantiomers

Herein we report the electrosynthesis of polypyrrole with L ‐tryptophan (L ‐Trp) as a template to prepare molecularly imprinted polymers (MIPs). Overoxidized polypyrrole films with cavities complementary to the template were used for the enantioselective detection of L ‐Trp and D ‐tryptophan (D ‐Trp). Important parameters, such as the electropolymerization potential, overoxidization potential and time, thickness of the polypyrrole films, and scanning rate of the stripping voltammetric experiments, were varied to achieve an optimum sensor response. We found that L ‐Trp was inserted about 2 times higher into the imprinted polymer film than D ‐Trp. Also, in this study, an electrochemical quartz crystal microbalance technique was used to investigate the performance of overoxidized polypyrrole films. The enantioselectivity of the MIPs was attributed to the cavities in the imprinted films, which were complementary to the target molecules, both in shape and in positioning of the functional groups. The results also suggest the feasibility of preparing MIPs by electropolymerization for the enantioselective recognition of other amino acid enantiomers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Separation of tryptophan enantiomers with polypyrrole electrode column by potential-induced technique

Polypyrrole (PPy), synthesized by chemical oxidation in the presence of l-tryptophan (l-Trp) as template molecules, was packed into a porous ceramic column as the conductive stationary phase to fabricate an electrode column which can be regarded as a working electrode of a three-electrode system from an electrochemical point of view. The electric potential of this column can be easily controlled by a potentiostat. l-Trp anions were ejected from the PPy backbone after overoxidation of PPy, and thus cavities complementary to l-Trp were left in the stationary phase. When the solution containing l- or d-Trp was pumped through the column packed with imprinted overoxidized polypyrrole (oPPy), a negative potential was applied on the electrode column for re-binding Trp enantiomers. The novel electrode column offers an excellent chiral selectivity for l-Trp over d-Trp as the result of stereochemistry, and it also displays satisfactory selectivity for tyrosine (Tyr) enantiomers which is analogous to Trp in structure. The advantage of this method proposed over previously reported is that the separation of amino acids enantiomers can be performed in a high efficiency by controlling the potential applied on the electrode column.     

Electrosynthesis of pyrrole 3-carboxylic acid copolymer films and nanotubes with tunable degree of functionalization for biomedical applications

Tailoring polypyrrole (PPy), an electroactive polymer, with functional groups to which a variety of bioactive molecules can be tethered is highly attractive for building biological structures on conducting surfaces for a range of biomedical applications. In this respect, we investigate the effects of three independent electrosynthesis parameters, namely the applied potential, the composition of the comonomer solution and the film thickness on the incorporation of carboxylic acid-functionalized pyrrole units (Py-COOH) into polypyrrole/Py-COOH copolymer films. FT-IR, XPS and fluorescence microscopy results show that a larger Py-COOH content is inserted in films electrosynthesized at low potential, that the surface functionality of the copolymer films increases with the molar percentage of Py-COOH in the comonomer solution, and that Py-COOH units are preferentially incorporated in the earlier stage of the electrosynthesis process. The method is further adapted for preparing functionalized PPy copolymer nanotubes with potential application in drug delivery. Specifically, functionalized copolymer nanotubes are electrosynthesized through the template method in polycarbonate membrane. Carboxylic acid groups available at the outer surface of these nanostructures are then derivatized to covalently immobilize poly(ethylene glycol) chains, a protein-repellent polymer, so as to enhance the antifouling properties of these promising delivery vehicles.     

Dopant anion controlled ion transport behavior of polypyrrole

A combination of electrochemical and microgravimetric techniques, utilizing the electrochemical quartz crystal microbalance (EQCM), has been employed to study the ion transport behavior of polypyrrole films, prepared with a variety of electrolytes, during redox switching. Systems investigated include poly(pyrrole chloride), poly(pyrrole dodecylsulfate), poly{pyrrole-co-[3-(pyrrol-1-y1)propanesulfonate]}, and polypyrrole/Nafion composites. It has been demonstrated that controlled ion transport properties of polypyrrole can be achieved by incorporating properly selected dopant anions into the polypyrrole film during electrosynthesis.     

Polymeric particles with conjugated polymer: Layer on its surface as effective adsorbents of amino acids

In the present paper composite polymeric particles with polypyrrole (PPy) shell have been examined as reservoirs for uptake of amino acids. The particle morphology can be designed in a way that polypyrrole load on the particle surface as well as the PPy shell thickness can be varied easily by control of the pyrrole polymerization conditions, such as monomer concentration and choice of different oxidants. Three different oxidants have been used for the preparation of PPy outer-layers, namely FeCl₃, Na₂S₂O₈, and H₃PMo₁₂O₄₀, which give the possibility to incorporate different anions into PPy structure. l- and d-alanine uptake in the presence of obtained particles has been tested as a function of particle concentration and PPy amount on the particle surface. It has been found that composite particles can adsorb quite high amounts of alanine and even show certain enantioselectivity. The uptake efficiency and selectivity depend strongly on the properties of the PPy layer, such as chemical structure (oxidized or overoxidized state) and the nature of the dopant anion.     

Poly(N-methylpyrrole) electrodeposited on copper: Corrosion protection properties

Electrochemical synthesis of poly(N-methylpyrrole) films on copper electrodes from an aqueous oxalic acid has been achieved. A potential higher than 2 V (SCE) was needed to generate the polymer, for this reason, the polymer was in the overoxidized state. The inhibiting corrosion properties of this coating on copper were investigated for the first time in aqueous 0.1 M sodium chloride solution using potentiodynamic polarization, Tafel analyses, open-circuit potential and electrochemical impedance spectroscopy. Corrosion protection properties comparable to those of polypyrrole (PPy) films were observed for these films. A physical barrier effect is the most likely protection mechanism.     

Pyrrole Electropolymerization on Copper and Brass in a Single-Step Process from Aqueous Solution

The electrosynthesis of polypyrrole (PPy) on copper and brass (Cu–Zn alloy) electrodes was performed by anodic oxidation of pyrrole in a sodium tartrate (C₄H₄Na₂O₆ 0.2 M) aqueous solution. The tartrate counter-ions slow the dissolution of the working electrode by leading to formation of a passivation layer on its surface, and pyrrole electropolymerization takes place. Strongly adherent and homogeneous polypyrrole films were electrodeposited on Cu and Cu–Zn alloy electrodes using different electrochemical techniques, such as potentiodynamic, galvanostatic and potentiostatic modes. The current densities of electropolymerization on brass are generally greater than those observed on copper. The corrosion behaviour of copper-coated electrodes, electrochemically modified by PPy films, was estimated by DC polarization and weight loss at different current densities in 0.1 M HCl solution. The synthesized polypyrrole films were characterised by several microscopic and spectroscopic techniques such as scanning electron microscopy, X-ray photo electron spectroscopy, Fourier transform infrared and Raman analysis. Galvanostatically deposited PPy films are shown to be an alternative to common black-nickel or black-chromium as a decorative top-coating.     

Characterization of polypyrrole/piperazine-1,4-bis(2-ethane sulfonate) film and its application for the immobilization of vitamin B12

Vitamin B12 (B12) - possessing a redox active cobalt centre - is a candidate to be used as a mediator in bioelectrochemical processes. In order to exploit the possible redox activity of B12, Pt has been modified by a bio-conform conducting layer polypyrrole/piperazine-1,4-bis(2-ethane sulfonate) PPy/PIPES. The electrochemical and spectral behaviour of this film proved to be similar to PPy/dodecyl-sulfate (DS), widely considered and accepted as one of the best combinations of conducting polymer films. The capability of the PPy/PIPES film for acting as adsorbant in the accumulation of B12 has been evidenced by the electrochemical quartz crystal microbalance (EQCM) technique. B12 could also be incorporated into the polymer layer during its electrochemical deposition. The results proving the preserved redox activity of B12 within the film open new perspectives towards redox mediated bioelectrochemical applications based on the immobilization of this biomolecule.     

Investigation by EQCM of the electrosynthesis and the properties of polypyrrole films doped with sulphate ions and/or a Keggin-type heteropolyanion, SiMo12O40

The first part of this paper describes in detail the electrochemical synthesis of polypyrrole (PPy) films monitored by electrochemical quartz crystal microbalance (EQCM). These films are either doped only with a Keggin-type heteropolyanion (HPA), SiMo₁₂O₄₀⁴⁻, or co-doped with such polyanions and sulphate ions. It is evidenced that this HPA catalyses the electropolymerisation of the pyrrole since it is able to oxide pyrrole monomer, and on the other hand, that HPAs are definitively entrapped into the polypyrrole film as shown by their electrochemical response. All the PPy film is electroactive. When the co-doped film is obtained by potentiodynamic method, its anion composition is not homogeneous in depth, there is a concentration gradient of the doping anions. In the second part of this paper, the morphology of the films is shown as well as their electrochemical characterisations that were carried out by EQCM in order to focus on the charge compensation process that occurs during SiMo₁₂ reduction and re-oxidation. In a wide domain of potentials, only the HPA response is observed, the polymer remains in its conducting form. The SiMo₁₂O₄₀⁴⁻ doped PPy films are cationic films. When several types of cations are present in the medium, the influence of the pH on the nature of the cations implied in the charge compensation that occurs during SiMo₁₂ reduction and re-oxidation is important. When the PPy film is co-doped, it is possible to obtain a mixed PPy film. Another important finding is the stability of trapped SiMo₁₂ ions in contact with solutions of pH higher than 4, on the contrary to what occurs when they are in solution.     

铂修饰聚吡咯电极电催化氧化甲醇的CO毒化特性

采用循环伏安法和电化学原位红外光谱技术研究了铂修饰聚吡咯电极(nm-Pt/PPy)对甲醇的电催化氧化反应,结果表明,nm-Pt/PPy对甲醇具有较好的电催化活性,当电位为1000mV时,可清楚地观察到甲醇经电氧化生成了最终产物CO2。但是在电化学氧化过程中仍存在CO的毒化现象,在低电位下,CO分别以桥式和线性方式吸附,随着电位升高,逐渐变为以线性吸附为主。另外,电氧化电位不宜过高,nm-Pt/PPy的电催化活性易因聚吡咯过氧化而降低。     

Chiral recognition of tryptophan enantiomers based on a polypyrrole‐flake graphite composite electrode column

A polypyrrole (PPy)‐flake graphite composite was synthesized by in situ polymerization of pyrrole on flake graphite surface, and the resulting organic–inorganic composite material was developed as the conductive stationary phase in an electrode column for enantioselective recognition of tryptophan (Trp) enantiomers. Compared with the stationary phase made up with conducting PPy, the conductivity of the composite stationary phase was enhanced significantly. As a result, satisfactory enantioselectivity of Trp enantiomers can be achieved easily by modulating the potential applied on the electrode column. Various important parameters influencing the performance of the composite electrode column were investigated to obtain the optimum recognition efficiency. A recognition efficiency of 3.7 could be achieved under the optimum conditions. Enantioselectivity of the composite material for Trp enantiomers is attributed to the reversible doping/de‐doping properties of PPy. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Electrochemical polymerization of polypyrrole-heparin nanotubes: Kinetics and morphological properties

Electrically conductive polypyrrole (PPy) was functionalized with heparin (Hep) to improve its surface biocompatibility. Heparin, which is a bioactive polyelectrolyte, was used as the doping anion. The immobilization of Hep in PPy was facilitated by the use of a nanoporous membrane which acts as templating substrate. In this way we have synthesized nanostructured electrodes based on polypyrrole and heparin as hollow tubules. The aim of this study was to determine the influence of the electrosynthesis parameters (monomer concentration and electrolyte nature) on the morphology and kinetics of the PPy nanomaterials in view of their possible, long-term biomedical applications.     

Ion transport investigations of polypyrroles doped with different anions by EQCM and CER techniques

The ion transfer in redox processes of conducting polypyrrole doped with various anions, such as 1-naphthalenesulfonate, 10-camphorsulfonate, p-toluenesulfonate, dodecylbenzenesulfonate was investigated by electrochemical quartz crystal microbalance (EQCM), contact electric resistance (CER), and cyclic voltamperometry in situ techniques. By using this setup, the doping levels of the synthesized PPy films and mobility of charge carries in these materials in KCl aqueous solution under linear potential scan were determined.     

An EQCM study of the deposition and doping/dedoping behavior of polypyrrole from phosphoric acid solutions

The potentiostatic deposition of polypyrrole (PPy) from 0.1 M aqueous phosphoric acid solution and the doping/dedoping behavior of the resulting films have been investigated by the electrochemical quartz crystal microbalance (EQCM) technique. The change of the complex shear modulus during the film growth and during the doping/dedoping were calculated using the acoustic impedance method. It was found that the films contain only ca. 1 wt% water in the oxidized state which is in accordance with their relatively high storage modulus of 38 MPa and low loss tangent of 0.05. Comparing H₃PO₄ (pH 1) and NaH₂PO₄ (pH 8) it was found that the doping/dedoping in the latter is accompanied by a strong increase of the surface roughness which is a direct result of cation exchange present at pH 8.     

Zinc hexacyanoferrate film as an effective protecting layer in two-step and one-step electropolymerization of pyrrole on zinc substrate

The two-step and one-step electrosynthesis processes of polypyrrole (PPy) films on the zinc substrate are described. The two-step process includes (i) the zinc surface pretreatment with hexacyanoferrate ion in the aqueous medium in order to form a zinc hexacyanoferrate (ZnHCF) film non-blocking passive layer on the surface and with the view to prevent its reactivity and (ii) electropolymerization of pyrrole on the ZnHCF|Zn-modified electrode in aqueous pyrrole solution. In this context, both the non-electrolytic and electrolytic procedures were adapted, and the effect of some experimental conditions such as supporting electrolyte, pH and temperature of the solution at the zinc surface pretreatment step as well as pyrrole concentration and electrochemical techniques at the polymerization step was investigated. By optimizing the experimental conditions in both steps, we have obtained a homogeneous and strongly adherent PPy films on the zinc substrate.The one-step process is based on the use of an aqueous medium containing Fe(CN)₆⁴⁻ and pyrrole. The ferrocyanide ion passivates the substrate by formation of ZnHCF film during the electropolymerization process of pyrrole and therefore makes it possible to obtain strongly adherent PPy films, with controlled thickness, either by cyclic voltammetry or by electrolysis at constant current or constant potential without any previously treatment of the zinc electrode surface. The polypyrrole films deposited on the zinc electrode were characterized by cyclic voltammetry and scanning electron microscopic (SEM) measurement.     

Electrodeposition of polypyrrole on aluminium in aqueous tartaric solution

The electrosynthesis of polypyrrole (PPy) has been achieved on aluminium in aqueous medium of tartaric acid by means of cyclic voltammetry, potentiostatic and galvanostatic techniques. Scanning electron microscopy (SEM) and X-ray microanalysis by energy spectroscopy dispersion (EDS) applying on surfaces show that the PPy coating is developed from the metal surface through the cracks of the initial Al₂O₃ layer.A mechanism involving the participation of the supporting electrolyte and the pyrrole (Py) in distinct active sites was proposed based on the linear sweep voltammetry. It is observed for all applied electrochemical techniques that the pyrrole concentration has to be higher than 0.1 M to allow the polypyrrole electrodeposition in acid medium.Scanning electron microscopy, secondary electrons (SE) and backscattering electrons (BE), shows that the PPy coating obtained in galvanostatic and potentiostatic modes starts with small islands at weak applied potentials or current densities. Moreover, EDS reveals a good homogeneity and compactness of the film achieved in galvanostatic method. The corrosion results in 3% NaCl medium show that the PPy coating decreases the corrosion behaviour of the aluminium. The bilayer Al₂O₃/PPy shows a capacitor with future applications.     

Improvement of the anticorrosion properties of polypyrrole by zinc phosphate pigment incorporation

A commercial zinc phosphate pigment was incorporated into polypyrrole (PPy) matrix during its electrochemical synthesis in order to improve the corrosion protection of polypyrrole on AISI 1010 steel. PPy/zinc phosphate composite films were synthesised in sodium salicylate medium with high current efficiency and containing 10% by weight of zinc and 4% by weight of phosphate. The influence of stirring and concentration of the electrolyte on the degree of pigment incorporation were investigated, as well as polymerisation time and applied current density. The morphology of the films was determined by scanning electron microscopy (SEM) and the distribution of pigment in the polymeric matrix was carried out by X-ray photoelectron spectroscopy (XPS). The PPy and PPy/zinc phosphate films were submitted to salt spray corrosion test, weight loss test and to electrochemical measurements like corrosion potential with time. In all tests, the composite films showed an enhancement in its protective action in comparison with PPy films.     

Enantioselective recognition of amino acids based on molecularly imprinted polyaniline electrode column

A novel molecularly imprinted polyaniline (PAn) electrode column is introduced as a new technique for the enantioselective recognition of amino acids. The principle of the molecularly imprinted electrode column is based on the reversible doping/de-doping property of PAn. PAn is an organic semiconductor and thus from an electrochemical point of view the column packed with PAn can be regarded as a packed-bed electrode of a three-electrode arrangement. The electric potential of this column can be easily controlled by a potentiostat. Various important factors influencing the performance of the molecularly imprinted PAn column have been investigated using fluorescence spectrometry in conjugation with the electrochemical quartz crystal microbalance (EQCM) technique. The advantage of this method proposed over previously reported is that the enantio-recognition can be performed in a high efficiency without requiring an expensive chiral column. Especially, the ejection and re-binding of amino acids can be accomplished by adjusting the potential applied on the column packed with molecularly imprinted PAn.     

Ion and solvent transfers accompanying redox switching of polypyrrole films immersed in divalent anion solutions

Electrochemical quartz crystal microbalance (EQCM) data acquired under cyclic voltammetric conditions were used to investigate the interfacial mass transfers accompanying redox switching of polypyrrole (PPy) films immersed in aqueous solutions of divalent anions. In contrast to the dominance of anion transfer in univalent anion (perchlorate) solution, PPy redox switching in 0.1 M Na₂SO₄, 0.1 M Na₂C₂O₄, 0.1 M Na₂HPO₄ and 0.1 M Na₂CO₃ solutions involves mixed anion/cation transfers, with the cation as the dominant species. Cation transfer is accompanied by water transfer, to the extent of 0.5-3 mol of water per mole of cation; in part, solvent transfers as a result of a combined osmotic and a volume constraint. Almost all the injected charge is recovered during PPy redox switching in a given dianion electrolyte, but the EQCM responses evolve with repetitive film redox switching. There is a redox-induced increase in the reduced film's mass. Over the course of a few cycles (the exact number depending on electrolyte and film thickness), the potential dependences of the film charge and mass responses achieve a steady state significantly different from that for an equilibrated undoped film.     

Effect of doping by corrosion inhibitors on the morphological properties and the performance against corrosion of polypyrrole electrodeposited on AA6061-T6

This paper describes the electrosynthesis of polypyrrole (PPy) onto AA6061-T6 aluminum alloy from a sulfuric acid solution doped with molybdate anions (MoO₄²⁻) or 8-hydroxyquinoline (8HQ) species. These dopant compounds were chosen as they have been proven to be effective in mitigating the corrosion in chloride medium. The protectiveness of PPy coatings incorporating these corrosion inhibitors within the polymer matrix is discussed. The coatings were morphologically characterized via scanning electron microscopy (SEM) and evaluated electrochemically via polarization in 0.5 M NaCl. The results show that doping PPy with molybdates or 8HQ changes its morphological properties and its effectiveness in preventing passivity loss for AA6061-T6 in chloride media.