A UV-Visible/Raman spectroelectrochemical study of the stability of poly(3,4-ethylendioxythiophene) films

Poly(3,4-ethylendioxythiophene) films were electropolymerized in aqueous medium without using any surfactant, on glassy carbon electrodes. UV/Vis and Raman spectroelectrochemical techniques were used to analyze the degradation of the polymer film occurring at different pH values. Spectroelectrochemistry has proven to be a very useful analytical tool for this purpose, thanks to its ability to provide information not only about the extent of degradation, but also about mechanistic aspects of the process. From our results we extracted important information about the main factors that play a role in the degradation, in particular about the influence of repetitive doping and de-doping cycles and of photo-induced processes, as a function of the characteristics of the solution, i.e. of pH.     

Influence of Cathodic Pretreatment in the Electrocatalytic Properties PANI Modified Electrodes

Herein, we reported the detection of dopamine (DA) based on use of a cathodically pretreated polyaniline (PANI) modified electrode. The PANI electrode presents a remarkable change in their electrocatalytic properties after a simple cathodic pretreatment, which consisted in applying a potential of ?0.7 V for 3 s. While the as‐prepared PANI shows no electrochemical response for DA, the cathodically pretreated PANI presented reversible electrochemical responses with well‐defined anodic and cathodic peaks. The electrochemical behavior of DA at the PANI electrode was investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Under the optimized experimental conditions, the anodic peak currents increased proportionally to the DA concentration, displaying a linear relationship in the concentration range of 0.11 to 1.75×10^?4 M with a detection limit of 13.7 μM (3 σ/slope). Recovery studies in pharmaceutical formulations presented values between 98 % and 104 %. The cathodically pretreated PANI electrode was successfully applied for DA detection in real samples of pharmaceutical formulation showing good agreement with spectrometric comparative method. The unexpected easily capability of modulate the electrocatalytic properties of the electropolymerized PANI film using a simple pretreatement was successfully demonstrated. The cathodically pretreatment PANI electrode showed electrochemical responses for DA with excellent selectivity, sensitivity, and high stability.     

Major influence of the hydrophobic chain length in the formation of poly(3,4-propylenedioxypyrrole) (PProDOP) nanofibers with special wetting properties

Several species in nature have special wetting properties such as Lotus leaves or rose petals. Both the surface morphology and surface energy play a fundamental role. In particular, nanofibers were found to be exceptional surface structures due to a possible control in both water hydrophobicity and water adhesion as a function of their length, diameter, their orientation to the substrate or the spacing between them. Here, in the aim to prepare nanofibers with high liquid-repellent properties using conducting polymers, we have synthesized 3,4-propylenedioxypyrrole (ProDOP) derivatives with hydrocarbon and fluorocarbon chains in the 3-position, keeping the NH group free (important condition to lead to nanofibers thanks to hydrogen bonds). Different hydrocarbon and fluorocarbon chain lengths are studied. We obtain, for example, nanofibers of different size with octyl, decyl and C₄F₉ chains (intermediate hydrophobicity) with different liquid-repellent properties and liquid adhesion properties. More precisely, PProDOP-H₈ is close to superhydrophobic properties (low water adhesion) while PProDOP-H₁₀ is parahydrophobic (high water adhesion). This works could find many potential applications in the nanotechnology field as water harvesting surfaces, liquid separation membrane, and in anti-bioadhesion. Due to the presence of free NH groups, these materials could also be used as pH-sensitive materials while the nitrogen could also be easily functionalized.     

Synthesis and electropolymerization of 5,12-dihydrothieno[3′,4′:2,3][1,4]dioxocino[6,7-b]quinoxaline and its electrochromic properties

Synthesis of a new thiophene-based monomer; 5,12-dihydrothieno[3′,4′:2,3][1,4]dioxocino[6,7-b]quinoxaline (DDQ), was realized. The chemical structure of the monomer was characterized by ¹H NMR, FTIR and mass spectroscopy techniques. Electrochemical polymerization of DDQ and characterization of the resulting polymer [P(DDQ)] was performed. Moreover, the spectroelectrochemical and electrochromic properties of the polymer film were investigated. P(DDQ) has a low oxidation potential (0.9 V) and low band gap (1.73 eV) compared to polythiophene. In addition, dual-type polymer electrochromic device (ECD) based on P(DDQ) with poly(3,4-ethylenedioxythiophene) (PEDOT) was constructed. Spectroelectrochemistry, electrochromic switching, stability and open-circuit stability of the device were studied. It was observed that polymer have good switching time, reasonable contrast and optical memory.     

Specific interactions in complexes formed by polythiophene derivatives bearing polar side groups and plasmid DNA

The interaction between plasmid DNA and polythiophene derivatives bearing substituents with polar groups has been examined using electrophoresis assays, and both UV-Vis and CD spectroscopies. Results clearly indicate that such conducting polymers form stable adducts with DNA, even although the interactions strongly depend on the chemical constitution of the polymers. Furthermore, digestion assays with EcoRI and BamHI evidence that the polymers form specific interactions with the DNA, protecting the target nucleotide sequences of these restriction enzymes. On the other hand, UV-Vis and CD spectra show that the interactions induce a fast and very significant exposition of the nitrogen bases, which is consequence of the structural alterations induced in the circular DNA. These results have been compared with those previously reported for polypyrrole, poly(3,4-ethylenedioxythiophene) and poly(3-methylthiophene). Finally, a model based on the intercalation of the conducting polymer between the two DNA strands has been proposed.     

Conducting polymer sensors for the amperometric detection of proteins in a flow system – the use of sulfonated dye counterions to induce selectivity

In this article, we have demonstrated the feasibility of using dye binding interactions for the amperometric detection of proteins at conducting polymer coated electrodes with flow injection analysis. Incorporation of appropriate dyes into the conducting polymer during synthesis enables sensitive and selective responses to be obtained. The effects of eluent pH and applied potential on the responses obtained for a range of proteins have been investigated. These parameters can be used to modify selectivity and achieve sensitivity.     

Functions of polymers in composite electrodes of lithium ion batteries

The different functions of polymer binders on the processing of the electrode, the electrical (electronic and ionic) and mechanical properties of the electrode, and as a consequence on the electrochemical performance are discussed. The role of the polymer binder on the solid–electrolyte interface (SEI) layer and the cyclability of the graphite- and silicon-based negative electrodes is also addressed. All these properties critically depend on the very thin layer formed by the polymer at the surface of the active and conductive particles. That is where research efforts have to focus on, now, for further optimization of electrodes through tailoring of the binder combination.     

Effect of spacer chemistry on the formation and properties of linear reversible polymers

A series of four pairs of bismaleimide and bisfuran monomers were combined to make thermally reversible linear polymers. The monomers were prepared using diamines having different spacer chemistries, n‐octyl, cyclohexyl, phenyl, and ethylenedioxy, such that a relatively constant spacer dimension among the four monomers was achieved. Heating of the bismaleimide/bisfuran couples resulted in low‐viscosity, easily processable liquids. Subsequent cooling to room temperature resulted in the formation of hard films, with the rate of hardening varying significantly within the series of compounds. The rate and degree of polymerization were determined using ¹H NMR spectroscopy and were both found to be dependent on the chemistry of the spacer group, as was the film rheology, which was measured using nanoindentation. Adhesion of the polymers was quantified by measurement of their tensile adhesive strength, and this was also found to be spacer dependent. Polymerization reversibility was verified using ¹H NMR spectroscopy. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 5056–5066     

In situ Fourier transform infrared attenuated total reflection (FTIR-ATR) spectroscopic investigations on the base—acid transitions of different forms of polyaniline. Base—acid transition in the leucoemeraldine form

Infrared spectroscopic studies on the fully reduced form of polyaniline are discussed in this work. Ex situ FTIR spectra measured in NaReO₄ + HReO₄ electrolytes with different pH values are presented, and the absorption bands are assigned to different vibrational modes. Additionally, a distinct picture of the base—acid transition is evaluated using in situ FTIR-ATR measurements in electrolytes containing the supporting salt NaReO₄ + HReO₄. The results demonstrate that in strong acidic media leucoemeraldine nitrogen atoms can be partly protonated. The protonation process starts in the range between pH = 2.5 and 3 and the intercalation of anions from the electrolyte into the polymer structure is determined semi-quantitatively.     

AFM study of conducting polymer polypyrrole nanoparticles formed by redox enzyme - glucose oxidase - initiated polymerisation

Redox enzyme – glucose oxidase E.C. 1.1.3.4 from Penecillum vitale (GOx) – initiated polypyrrole (Ppy) synthesis was applied for the formation of polypyrrole based nanoparticles. The increase in optical absorbance at λ = 460 nm was exploited for the monitoring of polypyrrole polymerisation process. The shape and size of the formed Ppy nanoparticles was also monitored by means of contact mode AFM. The highest increase in the diameter of the formed Ppy nanoparticles was detected during 15-day period. AFM imaging was performed in contact mode to investigate the shape and flexibility of particles deposited on the SiO₂ and Pt surfaces. Contact mode AFM investigations allowed us to conclude that after drying at 50 °C the formed Ppy particles are more flexibly deposited on the Pt electrode if compared to those deposited on the SiO₂ substrate. The application of well-shaped Ppy nanoparticles in biomedicine, chromatography and bioanalysis may be predicted.     

Sensitivity and Selectivity of Polypyrrole Based AC‐Amperometric Sensors for Electroinactive Ions – Frequency and Applied Potential Influence

Oxidation/reduction of polypyrrole films coupled with ion exchange on the polymer/solution interface can be utilized for amperometric sensing of electroinactive ions. Anion or cation exchanging films (polypyrrole doped by chloride or poly(4‐styrenesulfonate) ions, respectively) can be used to determine common anions (as Cl^?, NO , SO etc) or cations (K⁺, Na⁺, Li⁺, Ca²⁺, Mg²⁺) under conditions of alternating current (AC) amperometry in the range 10^?4–1 M. A sensitivity can be tuned by choosing appropriate electrode potential, corresponding to polypyrrole oxidation (anion‐exchanging films) or reduction (cation‐exchangers). Electrochemical impedance spectroscopy and AC‐voltammetry studies have shown that applied frequency and potential could also affect the observed dependence of the signal (admittance or AC‐current) on ion concentration. For high frequency the sensitivity is higher but selectivity lower, due to influence of solution conductivity on the response. For low frequencies the sensitivity is lower; however, a selectivity increase was observed due to diverse mobility of ions in the polymer film. Selectivity of AC‐amperometric responses was studied both in separate and mixed solutions.     

Electrocatalytic oxidation of some biologically important compounds at conducting polymer electrodes modified by metal complexes

Conducting poly(3-methylthiophene) electrodes were electrochemically prepared. The resulting polymer films were modified with an inorganic complex, ferrocene. The incorporation of the ferrocene/ferrocenium moiety into the polymer film resulted in enhanced charge transfer towards the oxidation of some organic molecules of biological interest. The electrochemical response of the complex-containing polymer electrode was compared to that of the unmodified polymer electrode and that of the substrate. Apparent diffusion coefficients of the redox species were estimated from the cyclic voltammetric data for different biological molecules at the ferrocene-containing polymer electrode. Infra-red spectroscopic measurements for the “as-grown” films revealed the presence of the inorganic complex within the polymer. The modified polymer electrode showed noticeable enhancement for the charge transfer across the film interface and can be used as an electrochemical sensor for biological compounds. Received: 3 June 1997 / Accepted: 7 July 1997     

Pronounced stabilisation of the ferrocenium state of ferrocenecarboxylic acid by salt bridge formation with a benzamidine

Salt bridge formation between ferrocenecarboxylic acid and an excess of a N,N^′-diethylsubstituted benzamidine leads to a −0.27 V shift in the half-wave potential of the ferrocene moiety, corresponding to a 26 kJ mol⁻¹ stabilisation of the ferrocenium state.     

A theoretical approach to the polymerization of N-pyrrolyl ethyl vinyl ether

The oligomerization mechanism of N-pyrrolyl ethyl vinyl ether is studied for two different routes of polymerization by using quantum mechanical calculations. Model compounds for oligomerization between monomers and monomer-pyrrole systems are optimized fully via semiempirical methods. By comparing the enthalpy changes of these two processes, it is found that generally the binding of pyrrole groups on the carbon backbone is favoured; however, the self-polymerization is also thermodynamically competitive. These results support the previous experimental evidence.     

纳米结构分子印迹聚合物及其在药物分析中的应用进展

纳米材料是纳米技术发展的重要基础,它具有许多传统材料所不具备的独特的理化性质,因此有着广泛的应用前景.分子印迹技术是一种通过模拟抗体-抗原相互作用原理,制备具有分子识别功能的聚合物的技术.以纳米材料制备的分子印迹聚合物具有较高的结合容量,较大的选择性和较快的结合动力学特性,近年来备受关注.本文简单概述了零维、一维、二维纳米结构分子印迹聚合物的合成、表征方法及研究现状,并对其在手性药物分析、临床药物分析、传感器及药物残留检测中的应用进行了综述.     

离子液体在导电高分子中的应用

综述了离子液体作为介质，在导电高分子合成及其电化学性能测试，以及导电高分子电化学器件中（电化学电容、发光电化学池、驱动器、太阳能电池）的最新研究进展。在此基础上。展望了离子液体在导电高分子中的应用前景。     

Cellular adhesion and proliferation on poly(3,4-ethylenedioxythiophene): Benefits in the electroactivity of the conducting polymer

Cell adhesion and proliferation in poly(3,4-ethylenedioxythiophene), an electroactive polythiophene derivative generated by anodic polymerization, has been investigated. Results show that epithelial cells Hep-2 present significant activity on the surface of poly(3,4-ethylenedioxythiophene) electrodeposited on stainless steel electrodes, no sign of cytotoxicity being detected for this conducting polymer. Indeed, seeded and cultured cells bound better to poly(3,4-ethylenedioxythiophene) than to uncoated stainless steel, the latter substrate being used as a control. Furthermore, the electrochemical characteristics of poly(3,4-ethylenedioxythiophene) covered with cells was determined in different biological media using cyclic voltammetry experiments. Results reveal a significant increase in the electroactivity of this material when it is covered with a cellular monolayer. The overall of the results evidences not only the biocompatibility of poly(3,4-ethylenedioxythiophene) with Hep-2 cells but also their electrocompatibility.     

Study of electrochemical stability of conducting polymers by bidimensional spectroelectrochemistry: p- and n-doping of poly(4,4′-bis(butylthio)-2,2′-bithiophene) films

UV-vis bidimensional spectroelectrochemistry has been applied to the study of the electrochemical stability of conducting polymer films during p- and n-doping processes. Specifically, poly(4,4′-bis(butylthio)-2,2′-bithiophene) has been chosen as example to prove the usefulness and suitability of this multi-response technique to characterize polymer stability during p- and n-doping. It was found that oxidative doping and corresponding de-doping alone did not result in noticeable polymer film degradation. However, in experiments involving both p- and n-doping of this conducting polymer, soluble species arising from the polymer film were detected in solution for the first time, indicating a lower electrochemical stability of the film under these experimental conditions. Moreover, bidimensional spectroelectrochemistry has enabled us not only to detect the soluble degradation products, but also the potential range in which the degradation takes place.     

The oligomeric approach – the electrochemistry of conducting polymers in the light of recent research

Electrochemical investigations on oligomeric model compounds (β-carotenoids) of polyacetylene varying the chain length in the range between 5 and 23 double bonds provide deeper insights into the redox properties of such systems. Furthermore, cyclic voltammetric studies of α,ω-diphenylpolyenes and phenylenevinylenes give clear evidence that the formation of the radical ions is followed by a rapid reversible dimerization between the oligomeric chains. The thermodynamic and kinetic parameters of the chemical reaction are presented. Applying these results to the properties of conducting polymers opens up new perspectives for interpreting charge storage and conductivity. Received: 27 May 1997 / Accepted: 6 October 1997