Enantioselective uptake of amino acid with overoxidized polypyrrole colloid templated with L-lactate

An overoxidized polypyrrole colloid, which can recognise enantiomers of amino acids has been prepared by a newly developed molecular imprinting technique. A polypyrrole colloid, which had been polymerised from a mixture of pyrrole (monomer), polyvinylpyrrolidone (steric stabiliser), peroxodisulfate (oxidant) and L-lactate (dopant), was overoxidized to create a dopant-complementary cavity. The enantioselectivity of the overoxidized colloid was evaluated by comparing the uptake of L-alanine and L-cysteine with that of the respective D-enantiomers. The L/D uptake ratios for these amino acids were about 2, while phenylalanine showed suppressed uptake for both the enantiomers. The absence of phenylalanine uptake can be explained in terms of the molecular size, which is too large to be accommodated by the cavity created by L-lactate. In contrast, a colloid templated with L-phenyllactate took up L-phenylalanine with a higher enantioselectivity of about 7. A colloid templated with L-lactate was applied to surface chirality analysis through enantioselective adsorption on cysteine-modified gold surfaces. Quartz microbalance experiments and scanning electron microscope observation of the gold surface revealed that the colloidal particle has higher affinity to a surface modified with L-cysteine than to one modified with D-cysteine.     

Molecularly Imprinted Overoxidized Polypyrrole Colloids: Promising Materials for Molecular Recognition

This article reviews a novel approach to molecular imprinting technology developed by the authors. Preparation, characterization, and performance of the molecularly imprinted overoxidized polypyrrole colloids is discussed to discriminate amino acid enantiomers and structural isomers of naphthalene compounds by using electrochemical and spectroscopic techniques. An overoxidized colloid, which was prepared with L-lactate as a dopant, shows a higher affinity for L-alanine than for D-alanine, and an uptake ratio (L/D) of as high as 11 was observed under optimum conditions. Furthermore, an overoxidized colloid with a cavity created by 1-naphthalenesulfonate (1-NS) showed a higher uptake for 1-NS than 2-NS. Thus, the shape-complementary cavity created at the colloid surface can precisely recognize the difference in the spatial configuration of enantiomers and structural isomers.     

Pulsed amperometric detection of underivatized amino acids using polypyrrole modified copper electrode in acidic solution

The successful pulsed amperometric detection of underivatized amino acids have been carried out in an acidic media on a polypyrrole (PPy) modified Cu electrode. The formation of PPy film doped with glutamate (glu) on a Cu electrode surface changes the mechanism of Cu dissolution. After application of multistep potential waveform, the PPy film was glu free due to the electro-reduction and overoxidation. High anodic potential polarization treatment yielded partially overoxidized PPy film as long as the Cu surface dissolution and amino acid permeation through the film was well controlled. This overoxidized PPy film acted as a charge and size exclusion barrier in order to improve the selectivity and stability of a Cu electrode. Various process parameters such as film modification time, detection and cleaning potential and pH of solution have been optimized to maximize the beneficial electrocatalytic properties of the electrode surface. At an optimized condition, detection limits for positively charged histidine and arginine are 19 and 22 pg respectively, whereas the neutral amino acids detected in amounts of 0.9–2.3 ng. Furthermore, the PPy coated Cu electrode response was long lived, stable and reproducible.     

Interference-free glucose sensor based on glucose-oxidase immobilized in an overoxidized non-conducting polypyrrole film

Summary An amperometric glucose sensor is described; it is based on glucose oxidase immobilized in an overoxidized non-conducting polypyrrole membrane. The overoxidation process of polypyrrole produces a permselective, antifouling membrane capable of rejecting ascorbate, urate, acetaminophen and cysteine, as well as proteins and other surface active components typically present in serum. The amperometric assay of glucose in serum correlates well with an established routine procedure based on an enzymatic-colorimetric method.     

Highly selective electrochemical method for the detection of serotonin at carbon fiber microelectrode modified with gold nanoflowers and overoxidized polypyrrole

A highly selective and sensitive electrochemical method was developed for the detection of serotonin (5-hydroxytryptamine, 5-HT) at gold nanoflowers (Au NFs) and overoxidized polypyrrole (OPPy) modified carbon fiber microelectrode (CFME). Carbon fiber was firstly modified with gold nanoflowers using electroless deposition method, and then modified with overoxidized polypyrrole using electrochemical polymerization and overoxidization to obtain OPPy/Au NFs/CFME. The obtained OPPy/Au NFs/CFME was characterized by field emission scanning electron microscopy and electrochemical techniques. It was found that the OPPy/Au NFs/CFME showed good sensitivity for the detection of 5-HT in the range of 10 nmol/L − 7.0 μmol/L with detection limit of 2.3 nmol/L, and negligible interferences from ascorbic acid, 5-hydroxyindole acetic acid and uric acid. The OPPy/Au NFs/CFME was successfully applied to the detection of 5-HT in human serum samples with good recovery. The work demonstrates that the electrochemical method, incorporating signal amplification of Au NFs with higher cation selection of OPPy, provides a promising tool for the detection of 5-HT in biological systems     

Nonenzymatic sensing of glucose using a carbon ceramic electrode modified with a composite film made from copper oxide,overoxidized polypyrrole and multi-walled carbon nanotubes

Microchimica Acta - A carbon ceramic electrode was modified with a thin film composed of overoxidized polypyrrole, CuO and multi-walled carbon nanotubes. The surface morphology, electrochemical...     

Highly selective electrochemical method for the detection of serotonin at carbon fiber microelectrode modified with gold nanoflowers and overoxidized polypyrrole

A gold nanoflowers and overoxidized polypyrrole modified carbon fiber microelectrode (OPPy/Au NFs/CFME) was fabricated using electroless deposition and electrochemical method for highly selective and sensitive detection of 5-HT.     

An insight into the overoxidation of polypyrrole materials

In aqueous solution, under anodic potentials at which water oxidation occurs, the polypyrrole is irreversibly oxidized leading progressively to an insulating material. In this paper, it is evidenced that this overoxidation process is due to the hydroxyl radicals formed during solvent oxidation. Indeed, it is shown that, at open-circuit potential, polypyrrole films are overoxidized in the presence of hydroxyl radicals produce by Fenton’s reagent (H₂O₂/Fe²⁺). On the contrary, the use of hydroxyl radical scavengers, such as methanol and dimethylthiourea, allows one to increase the stability of polypyrrole films under anodic potentials.     

Template-free one-step electrochemical formation of polypyrrole nanowire array

Oriented polypyrrole nanowire (nanorod) array readily forms using one-step pyrrole electropolymerization without using a template. These nanostructures having diameter in the range of 40–120 nm are obtained by electrogenerating polypyrrole in the presence of jointly non-acidic and weak-acidic anions. The latter are essential, their presence leads to the formation of an overoxidized polypyrrole thin layer that surrounds the polypyrrole nanostructure base. This simple and convenient method allows direct polymer nanowire array fabrication on various conductive substrates, the length of nanostructures being controlled by the polymerization time. Finally, a reaction mechanism involving oxidation of pyrrole and water and polypyrrole overoxidation is discussed.     

Highly selective molecularly imprinted overoxidized polypyrrole colloids: one-step preparation technique.

A convenient "one step" preparation process of molecularly imprinted overoxidized-polypyrrole (oPPy) colloids by chemical polymerization and their high uptake ability and enantioselectivity are described. Since an oxidizing agent gives a different standard redox potential and rate of polymerization, the property of the resulting oPPy colloid can be controlled by the kind and concentration of the oxidizing agent. At higher concentrations of (NH4)2S2O8 (0.3 M), the overoxidation of PPy colloid automatically occurred. The extraction of L-lactate as a dopant has created a shape-complementary cavity on the surface of the oPPy colloid through overoxidation following polymerization. The oPPy colloid exhibited an excellent selectivity not only on the alanine enantiomer but also on the difference in the side-chain size of amino acids. The uptake of oPPy colloid towards L-alanine over D-alanine was 11.3 micromol/g-colloid against 3.6 micromol/g. The molecularly imprinted cavity can also recognize the existences of the OH or CH3 substituents.     

Biomolecules-carbon nanotubes doped conducting polymer nanocomposites and their sensor application

A simple method for preparing bio-functionalized soluble single-walled carbon nanotubes (SWNTs) is described. Different proteins such as bovine serum albumin (BSA), cytochrome c and horseradish peroxidase (HRP) were used to solubilize low functionality SWNTs in water aided by sonication. The unbound proteins were removed by column chromatography and the SWNT-protein conjugate was used as the sole anionic dopant in electropolymerization of polypyrrole from polymerization solution at pH above the isoelectric point of the protein to provide a negative charge. The morphology of the polypyrrole with SWNT-protein dopant was found to be three-dimensional and fibrous with wide open interlocking pores in contrast to smooth and cauliflower-like for chloride doped polypyrrole. Enhanced sensor performance was demonstrated for hydrogen peroxide detection on polypyrrole/SWCNT-HRP nanocomposites modified electrode. Such nanocomposites can be potentially applied for other biosensor and bio-fuel cell applications.     

Voltammmetric Determination of Uric Acid in the Presence of Ascorbates Using Overoxidized Polypyrrol

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A Polypyrrole Based Sensor for the Electrochemical Detection of OH Radicals

Polypyrrole was used as sensitive material in the development of a new device employed for the indirect detection of OH radicals. The polypyrrole film was electrosynthesized on glassy carbon. The modified electrode was exposed to the OH radicals generated by Fenton reaction. As a result of the overoxidation the conductivity of the polymer diminished very much. The overoxidation (%) was directly proportional to the ^.OH amount that reached the electrode surface. ABTS^.+, superoxide and alkylperoxy radicals did not interfere in the determination. The applicability of the device was demonstrated by estimating the ^.OH scavenging ability of ascorbic acid.     

A selective and sensitive film for electrocatalysis of ascorbic acid based on polypyrrole doped with nitroso-R(1-nitroso-2-naphthol-3,6-disulfonic acid disodium)

An electrocatalytic detection of ascorbic acid on a nitroso-R modified polypyrrole electrode has been studied. This functionalized polypyrrole film was electropolymerized by constant potential method on a platinum electrode from solution including pyrrole as monomer and nitroso-R as anionic dopant. Electrocatalytic currents of ascorbic acid were linearly dependent on its concentration in the range of 0.12–18.54 mM, with detection limit and relative standard deviation of 0.02 mM and 1.32%, respectively. This modified electrode can be used for determination of ascorbic acid in various pharmaceutical samples. Also, electrochemical behavior of this system was studied by various methods (RDE voltammetry, chronoamperometry, hydrodynamic amperometry and cyclic voltammetry).     

Interfacial Characterization of Polypyrrole/AuNP Composites towards Electrocatalysis of Ascorbic Acid Oxidation

Polypyrrole (PPy) is an interesting conducting polymer due to its good environmental stability, high conductivity, and biocompatibility. The association between PPy and metallic nanoparticles has been widely studied since it enhances electrochemical properties. In this context, gold ions are reduced to gold nanoparticles (AuNPs) directly on the polymer surface as PPy can be oxidized to an overoxidized state. This work proposes the PPy electrochemical synthesis followed by the direct reduction of gold on its surface in a fast reaction. The modified electrodes were characterized by electronic microscopic and infrared spectroscopy. The effect of reduction time on the electrochemical properties was evaluated by the electrocatalytic properties of the obtained material from the oxidation of ascorbic acid (AA) and electrochemical impedance spectroscopy studies. The presence of AuNPs improved the AA electrocatalysis by reducing oxidation potential and lowering charge transfer resistance. EIS data were fitted using a transmission line model. The results indicated an increase in the electronic transport of the polymeric film in the presence of AuNPs. However, PPy overoxidation occurs when the AuNPs’ deposition is higher than 30 s. In PPy/AuNPs 15 s, smaller and less agglomerated particles were formed with fewer PPy overoxidized, confirming the observed electrocatalytic behavior.     

Electrochemically controlled solid-phase microextraction (EC-SPME) based on overoxidized sulfonated polypyrrole

A method for the extraction and selective determination of cations is proposed using electro-synthesized overoxidized sulfonated polypyrrole film. The polymer film is used for the selective extraction of trace levels of nickel and cadmium ions by solid-phase microextraction (SPME). The cation uptake and release properties of the overoxidized sulfonated polypyrrole film electrode were examined under both open circuit and controlled potential conditions for prospective applications in electrochemically controlled solid-phase microextraction. Increased extraction efficiency and selectivity toward cations were achieved in high saline content of water. Simple preparation of film coatings on a platinum wire was possible using a constant potential method. Applied positive and negative potentials facilitated the extraction and desorption of cations, respectively. Nickel and cadmium ions were desorbed into sample aliquot and determined by electrothermal atomic absorption spectrometry (ETAAS). The cation uptake and release mechanism is affected both by the cation exchange at the negative sulfonate and carboxylate moiety on the film and the altered solution pH occurring at the counter electrode caused by the applied potential. The method was validated using a standard reference material and tested for the determination of cadmium ion in commercial table salt samples.     

Permselectivity of neurotransmitters at overoxidized polypyrrole-film-coated glassy carbon electrodes

The permselectivity of neurotransmitters such as dopamine, epinephrine, and norepinephrine at overoxidized polypyrrole (OPPY)-film-coated glassy carbon electrodes has been investigated. The chemically-modified electrodes exhibit attractive permselectivity and antifouling properties of rejecting anionic species, e.g. ascorbate, etc. Compared with the response of neurotransmitters at modified electrodes overoxidized in phosphate buffer solution (pH 7.4), higher sensitivity and reversibility response can be obtained at modified electrodes overoxidized in sodium hydroxide solution. The effect of film thickness on the permselective response was tested. Rotating disk electrode experiments were used to determine the apparent diffusion coefficients of several electroactive solutes in the OPPY films. The influence of the hydrophobicity of the organic ions on the permeability within the polymer films was discussed. Dopamine and epinephrine were determined at the 1 x 10(-6)-1 x 10(-4) M level by means of voltammetry after an exposure period of 2 min in 0.1 M phosphate buffer (pH 7.4) with detection limits of 8 x 10(-7) M and 6 x 10(-7) M respectively.     

电解质溶液对聚吡咯电聚合中过氧化行为的影响

分别以硫酸/水和高氯酸锂/乙腈为电解质溶液, 采用循环伏安法在铂基底电极上电聚合制备了聚吡咯, 研究了电解质溶液对聚吡咯电聚合过程中过氧化行为的影响. 与硫酸/水溶液相比, 在高氯酸锂/乙腈溶液中电聚合制备的聚吡咯发生过氧化的峰电位正移了0.42 V. 采用原位傅里叶变换红外(in situ FTIR)光谱技术检测, 结果表明, 电聚合制备的聚吡咯在2种电解质溶液中均发生了过氧化反应, 其β-C经氧化生成C-OH或CO. 在硫酸/水溶液中, 部分聚吡咯发生电氧化降解生成CO₂, 致使其共轭结构被破坏, 电导率迅速下降. 而在高氯酸锂/乙腈溶液中, 在更高的电位范围内, 聚吡咯并没有氧化降解成CO₂.     

Electrocatalytic Application of an Overoxidized Dopamine Film Prepared on a Gold Electrode Surface to Selective Epinephrine Sensing

A dopamine polymer film was prepared ex situ on a bare gold template from a 10 mM dopamine solution in phosphate buffer, pH 7 followed by an overoxidation in 500 mM NaOH. The modified electrode was used for quantitative determination of epinephrine. A linear relationship between epinephrine concentration and current response was obtained in the range between 2 μM and 800 μM with the detection limit of 0.3 μM. The results have shown that using the overoxidized dopamine film it is possible to perform electrochemical analysis of epinephrine without interference of ascorbic and uric acids.     

A comparative study of structural, thermal and electrical properties of undoped and doped with dodecylbenzenesulphonic acid polypyrrole

Polypyrrole was synthesized and doped with dodecylbenzenesulphonic acid; the latter was confirmed by means of FTIR spectroscopy. The percentage of crystallinity of synthesized polymers was estimated from X-rays diffraction studies. The formation of flaky structure in doped polypyrrole was observed by means of SEM. DC conductivity was found to be influenced by dopant dodecylbenzenesulphonic acid. Temperature dependant DC shows three dimensional variable ranges hopping (3D VRH). Activation energy, density of states and hopping length were calculated and found to be influenced by adding dopant to polypyrrole. The doped polypyrrole was found to be more thermally stable as compared to that of pristine polypyrrole.