Selective Transport of Histamine from a Mixture of Histidine and Histamine by the Use of Organic Liquid Membrane Systems

Abstract

The transport behaviors of histidine (His) and its related compounds through organic liquid membranes were examined. The organic liquid membranes system was composed of two aqueous phases (Phases I and II) which were put on both sides of an organic layer containing a carrier. Chloroform and sodium di-2-ethylhcxyl sulfosuccinate (AOT) were used as the organic layer and the carrier, respectively. No transport reaction occurred without the carrier. The amounts of removal into the organic layer increased with an increase in the concentration of AOT up to 5 mM and maintained at higher concentrations. His and carnocine, which possess the carboxyl group, could be removed into the organic layer from Phase I at pH 4–5 but could not be removed at pH values higher than 5. On the other hand, histamine (Hm) and histidinol, which lack the carboxyl group, could be removed into the organic layer from Phase I at pH 7. Also, the compounds in the organic layer could be removed into Phase II at pH 10. On the basis of these results, the separation of Hm from the Hm-His mixture occurred with pH 7 in Phase I and pH 10 in Phase II through the organic layer containing 5 mM of AOT. Hm was effectively transported from Phase I to Phase II through an organic layer using some molar ratios (1, 50, and 100) of mixtures (molar ratio = concentration of His/concentration of Hm).     

Transport Behavior of Basic Amino Acids through an Organic Liquid Membrane System

Abstract

The transport behavior of basic amino acids (BAA), such as arginine (Arg), histidine (His), and ornithine (Orn), through an organic liquid membrane system (LMS) was investigated. The LMS was composed of two aqueous phases (Phases I and II) separated by an organic phase of chloroform containing sodium di-(2-ethylhexyl) sulfosuccinate (Aerosol OT, AOT). The amount of BAA that moved from Phase I at pH 3 into the organic phase increased with increasing AOT concentration (2–10 mM). The relative amount of extracted BAA was in the following order: Arg > His > Orn. On the other hand, the release of BAA from the organic phase into Phase II at pH 10 did not depend upon their amount in the organic phase. Arg was difficult to release. The relative amount of released BAA was in the following order: Arg = His > Orn. BAA were extracted from Phase I at pH 5 into the organic phase containing 4 mM AOT because they exist as cationic species. Other amino acids possessing nonionic residues were untransportable under these conditions except leucine, tryptophan, and phenylalanin, which have highly hydrophobic residues. However, they were transportable in their cationic forms at pH 1. These transport phenomena are essentially controlled by the interaction of the anionic group of AOT and a cationic form. These results suggested that BAA can be separated from most amino acids under an appropriate pH by using AOT.     

Dendrimer‐encapsulated Pt nanoparticles/polyaniline nanofibers for glucose detection

A novel amperometric glucose biosensor based on self‐assembling glucose oxidase (GOx) and dendrimer‐encapsulated Pt nanoparticles (Pt‐DENs) on nanofibrous polyaniline (PANI) was described. PANI nanofibers were synthesized via an interfacial polymerization method. A sulfonated polyelectrolytes‐poly(sodium 4‐styrenesulfonate) (PSS) was used to form the negative PANI/sulfonated polyelectrolyte complex, which had good disperse in aqueous solution. GOx was immobilized on the PANI/PSS surface by alternatively assembling a cationic Pt‐DENs layer and an anionic GOx layer. The unique sandwich‐like layer structure (Pt‐DENs/GOx/Pt‐DENs/PANI/PSS) formed by self‐assembling provides a favorable microenvironment to keep the bioactivity of GOx and to prevent enzyme molecule leakage. The fabricated Pt‐DENs/GOx/Pt‐DENs/PANI/PSS electrode exhibited excellent response performance to glucose with a detection limit of 0.5 μM, wide linear range from 10 μM to 4.5 mM, short response time within 5 s, improved sensitivity of 39.63 μA/(mM cm²), and good stability (85% remains after 20 days). © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Cu(II)‐incorporated,histidine‐containing,magnetic‐metal‐complexing beads as specific sorbents for the metal chelate affinity of albumin

N‐Methacryloyl‐(L )‐histidine methyl ester (MAH) was synthesized from metharyloyl chloride and histidine. Spherical beads with an average size of 150–250 μm were obtained by the suspension polymerization of ethylene glycol dimethacrylate and MAH in an aqueous dispersion medium. Magnetic poly(ethylene glycol dimethacrylate‐co‐N‐Methacryloyl‐(L )‐histidine methyl ester) [m‐p(EGDMA‐co‐MAH)] microbeads were characterized with swelling tests, electron spin resonance, elemental analysis, and scanning electron microscopy. The specific surface area of the beads was 80.1 m²/g. m‐p(EGDMA‐co‐MAH) microbeads with a swelling ratio of 40.2% and 43.9 μmol of MAH/g were used for the adsorption of bovine serum albumin (BSA) in a batch system. The Cu(II) concentration was 4.1 μmol/g. The adsorption capacity of BSA on the Cu(II)‐incorporated beads was 19.2 mg of BSA/g. The BSA adsorption first increased with the BSA concentration and then reached a plateau, which was about 19.2 mg of BSA/g. The maximum adsorption was observed at pH 5.0, which was the isoelectric point of BSA. The BSA adsorption increased with decreasing temperature, and the maximum adsorption was achieved at 4°C. High desorption ratios (>90% of the adsorbed BSA) were achieved with 1.0M NaSCN (pH 8.0) in 30 min. The nonspecific adsorption of BSA onto the m‐p(EGDMA‐co‐MAH) beads was negligible. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2669–2677, 2004     

Advanced TALSPEAK Separations Using a Malonate Buffer System

The extraction behavior of lanthanides and americium has been evaluated under Advanced TALSPEAK (Trivalent Actinide Lanthanide Separation by Phosphorus-reagent Extraction from Aqueous Komplexes) conditions using malonic acid as the aqueous buffering agent. The extractant 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (HEH[EHP]) was used as an organic phase liquid cation exchanger in n-dodecane diluent, while N-(hydroxyethyl)-ethylenediaminetriacetic acid (HEDTA) served as a selective aqueous holdback reagent. Extractions conducted from malonate media exhibit a pH profile that flattens as the concentration of malonate is increased up to 1.0 M malonate. This relatively flat extraction behavior from pH 2.5–4.0 is reminiscent of previous studies on Advanced TALSPEAK in lactate media. The extraction kinetics with other carboxylic acid buffers as well as the effects of varying HEDTA, HEH[EHP], and malonate concentration are compared.     

Preparation of a novel metal‐chelate affinity beads for albumin isolation from human plasma

In this study, we developed a novel approach to obtain a high protein‐adsorption capacity utilizing 2‐methacryloylamidohistidine (MAH) as a biollgand. MAH was synthesized by reacting methacryloyl chloride and histidine. Spherical beads, with an average size of 150–200 μm, were obtained by the radical suspension polymerization of MAH, ethyleneglycol dimethacrylate (EGDMA), and 2‐hydroxyethyl methacrylate (HEMA) conducted in an aqueous dispersion medium. p(EGDMA–HEMA–MAH) beads had a specific surface area of 17.6 m²/g. The synthesized MAH monomer was characterized by NMR. p(EGDMA–HEMA–MAH) beads were characterized by a swelling test, FTIR, and elemental analysis. Then, Cu(II) ions were incorporated into the beads and Cu(II) loading was found to be 0.96 mmol/g. These beads, with a swelling ratio of 65% and containing 1.6 mmol MAH/g, were used in the adsorption/desorption of human serum albumin (HSA) from both aqueous solutions and human serum. The adsorption of HSA onto p(EGDMA–HEMA–MAH) was low (8.8 mg/g). Cu(II) chelation onto the beads significantly increased the HSA adsorption (56.3 mg/g). The maximum HSA adsorption was observed at pH 8.0 Higher HSA adsorption was observed from human serum (94.6 mg HSA/g). Adsorptions of other serum proteins were obtained as 3.7 mg/g for fibrinogen and 8.5 mg/g for γ‐globulin. The total protein adsorption was determined as 107.1 mg/g. Desorption of HSA was obtained using a 0.1M Tris/HCI buffer containing 0.5M NaSCN. High desorption ratios (to 98% of the adsorbed HSA) were observed. It was possible to reuse Cu(II)‐chelated p(EGDMA–HEMA–MAH) beads without significant decreases in the adsorption capacities. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2840–2847, 2003     

Layer‐by‐layer assembled hydrogel nanocomposite film with a high loading capacity

The layer‐by‐layer assembly technique is a method that widely used in the preparation of nanostructured multilayer ultrathin films. We fabricated a hydrogel nanocomposite film by alternating the deposition of a core–shell poly[(dimethylimino)(2‐hydroxy‐1,3‐propanedily) chloride] (PDMIHPC)–laponite solution and poly(acrylic acid). The growth of the deposition procedure was proven by ultraviolet–visible spectroscopy and spectroscopic ellipsometry. The surface morphology of the films was observed by scanning electron microscopy. The films could reversibly load and release methylene blue (MB) dye, which was used as an indicator. It took about 4.5 h to reach loading equilibrium at pH 9.0. The loading capacity of the film for MB was as large as 4.48 μg/cm² per bilayer because of the introduction of the core–shell PDMIHPC–laponite as a film component. Nearly 90% of MB was released at pH 3.0 or in a 300 mM NaCl solution within 2.5 h. The loading and release processes were greatly influenced by the ionic strength and pH value of the MB solution. The hydrogel nanocomposite film showed good pH‐triggered loading‐release reversibility and suggested potential applications in controlled drug‐delivery systems and smart materials. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39352.     

Comparative Equilibrium Studies on the Sorption of Metal Ions with Macroporous Resins Containing a Liquid Ion-Exchanger

Abstract

The distribution of five metal ions (M ^m+) including Fe(III), Co(II), Ni(II), Cu(II), and Zn(II) between dilute sulfate solutions and macroporous resins containing di(2-ethylhexyl) phosphoric acid (D2EHPA, HR) was investigated. Experiments were carried out as a function of aqueous pH, D2EHPA concentration in the resin phase, and temperature. The equilibrium data were numerically analyzed. It was shown that the sorption reaction could be described by assuming the formation of metal complexes with a general composition MR _m (HR) _n in the resin phase. For several systems a change of complex stoichiometry with temperature was observed and discussed. The apparent thermodynamic data for the formation of these complexes were also calculated.     

Enrichment and Separation of Sinomenine and Acutumine from Sinomenium acutum by pH-Zone-Refining Counter-Current Chromatography

Enrichment and separation of alkaloids from a chloroform extract of Sinomenium acutum has been successfully performed for the first time using pH-zone-refining counter-current chromatography. The two-phase solvent system used for enrichment was composed of Methyl tert-butyl ether (MtBE)–acetonitrile (CH₃CN)–water (4:1:5, v/v), where 10 mM triethylamine (TEA) was added to the upper organic stationary phase as a retainer and 10 mM hydrochloric acid (HCl) to the aqueous mobile phase as an eluter, which could enrich the alkaloids from the crude extract well. For the preparative separation, the solvent system consisted of MtBE–CH₃CN–water (4:0.5:5, v/v) with 10 mM TEA in organic stationary phase and 5 mM HCl in the aqueous mobile phase, which could separate and purify the enriched crude alkaloids successfully. 0.82 g of crude alkaloids was enriched from 1.60 g of chloroform extract in the first step separation. From the enriched crude alkaloids, 376 mg of sinomenine and 85 mg of acutumine were obtained in the second step separation with the purity of 98.1% and 98.7%, respectively. The chemical structures of the isolated compounds were identified by UV, ESI-MS and ¹H NMR.     

New metal chelate sorbent for albumin adsorption: Cibacron Blue F3GA-Zn(II) attached microporous poly(HEMA) membranes

Poly(2-hydroxyethyl methacrylate) [poly(HEMA)] membranes were prepared by UV-initiated photopolymerization of HEMA in the presence of an initiator (α-α′-azobis-isobutyronitrile, AIBN). The triazine dye Cibacron Blue F3GA was attached as an affinity ligand to poly(HEMA) membranes, covalently. These affinity membranes with a swelling ratio of 58% and containing 10.7 mmol Cibacron Blue F3GA/m² were used in the albumin adsorption studies. After dye-attachment, Zn(II) ions were chelated within the membranes via attached-dye molecules. Different amounts of Zn(II) ions [650–1440 mg Zn(II)/m²] were loaded on the membranes by changing the initial concentration of Zn(II) ions and pH. Bovine serum albumin (BSA) adsorption on these membranes from aqueous solutions containing different amounts of BSA at different pH was investigated in batch reactors. The nonspecific adsorption of BSA on the poly(HEMA) membranes was negligible. Cibacron Blue F3GA attachment significantly increased the BSA adsorption up to 92.1 mg BSA/m². Adsorption capacity was further increased when Zn(II) ions were attached (up to 144.8 mg BSA m²). More than 90% of the adsorbed BSA was desorbed in 1 h in the desorption medium containing 0.5M NaSCN at pH 8.0 and 0.025M EDTA at pH 4.9. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 657–664, 1998     

Properties of β-fructosidases (invertases and inulinases) of Fusarium oxysporum grown on an aqueous extract of Cichorium intybus roots

Four different forms of invertase and inulinase named as Invertase, I, II, III, IV and inulinase I, II, III, IV were purified from a culture filtrate of Fusarium oxysporum, grown on a fructan containing medium, by ammonium sulphate fractionation, gel permeation and ion exchange chromatography. Invertases had a higher optimum temperature (55–60°C) as compared to that of inulinases (35–45°C). Of sucrose, raffinose, stachyose and inulin, sucrose was the best substrate for all the four invertases and none of the invertases showed activity with inulin. Inulinases showed maximum activity with inulin. The optimum pH of invertase I and II was 5.5 whereas invertase III and IV showed a maximum activity at pH 4.0. Inulinases I, II, III and IV had an optimum pH of 5.5, 5.5, 6.0 and 6.5, respectively. The thermal stability of invertases was in the order of invertase III > IV > II > I. Inulinase II was more stable than inulinase I whereas inulinase III and IV were the least stable. Inulinases showed a low K_m in the range of 10–95 μmol dm^?3 of inulin, thereby showing their high affinity for inulin. K_m for invertases varied from 2 mmol dm^?3 to 4 mmol dm^?3 of sucrose. HgCl₂ and CuSO₄ were found to be strong inhibitors for both invertases and inulinases.     

Novel building blocks for oligonuclear copper complexes derived from β‐ketoenamines of histidine

Condensation products of L‐histidine with the 3‐oxoenolethers diethyl‐ethoxymethylene‐malonate ( 1 ) and ethyl‐ethoxymethylene‐cyanoacetate ( 2 ) react with copper(II) as di‐anionic ligands to give neutral 1:1 complexes Cu‐ His1 and Cu‐ His2 . Both complexes crystallize as oligonuclear units, even from strongly donating solvents like N‐methylimidazole (Meim) (Cu‐ His1 ) and pyridine (Cu‐ His2 ). X‐ray structure analyses show supramolecular structures, formed of two (Cu‐ His1 ) or four (Cu‐ His2 ) formula units of the complex, which arrange to macrocycles by means of intermolecular coordination of the imidazole‐N. Strong H‐bridges result in a face‐to‐face orientation of the hydrophilic sites of two great rings. ESI‐MS investigations in pyridine solution give evidence for the existence of dimeric, tetrameric and – in case of Cu‐ His2 – trimeric units, besides the monomeric adducts with one pyridine. In contrast to the dimeric or tetrameric (“cubane‐like”) copper(II) complexes of amino alcohols and their β‐ketoenamines, the complexes Cu‐ His1 and Cu‐ His2 show no significant spin coupling from room temperature down to 4 K. The complexes Cu‐ His1 and Cu‐ His2 give no electrochemically reversible Cu^II/I reduction in pyridine. However, the isolation of a stable diamagnetic copper(I) complex of the methylester derivative, Cu^I‐ HisMe1 , supports the assumption, that similar histidine‐derived copper complexes should display reversible redox behaviour and catalytic activity in reactions with O₂.     

Combining CMPO and HEH[EHP] for Separating Trivalent Lanthanides from the Transuranic Elements

Combining octyl(phenyl)-N,N-diisobutyl-carbamoylmethylphosphine oxide (CMPO) and 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (HEH[EHP]) into a single process solvent for separating transuranic elements from liquid high-level waste is explored. The lanthanides and americium can be co-extracted from HNO₃ into 0.2 mol/L CMPO + 1.0 mol/L HEH[EHP] in n-dodecane. The extraction is relatively insensitive to the HNO₃ concentration within 0.1–5 mol/L HNO₃. Americium can be selectively stripped from the CMPO/HEH[EHP] solvent into a citrate-buffered N-(2-hydroxyethyl)ethylenediaminetriacetic acid solution. Separation factors >14 can be achieved in the range pH 2.5–3.7, and the separation factors are relatively insensitive to pH—a major advantage of this solvent formulation.     

Electrochemically stimulated 2‐ethylhexyl phosphate (EHP) release through redox switching of conducting polypyrrole film and polypyrrole/poly (N‐methylpyrrole) or self‐doped polyaniline bilayers

2‐Ethylhexyl phosphate (EHP) released from poly(pyrrole 2‐ethylhexyl phosphate) (PP‐EHP) was investigated at open circuit and compared with electrochemically stimulated release during potential cycling. It was found that the fast EHP release from the PP‐EHP single layer is substantially retarded and that amounts of spontaneously and electrochemically released EHP can be reduced by constructing bilayers, consisting of a PP‐EHP inner layer and a poly(N‐methylpyrrole)‐poly(styrene sulfonate) (PNMP‐PSS) or self‐doped poly(aniline) sulfonate (SPANI) as the outer films. The presence of outer film over the PP‐EHP allowed surface‐property modification, as well as the control of the rate of EHP release, while electrochemically stimulated EHP release from inner films was not substantially hampered by the outer layer. The quantity of the EHP released was investigated using UV‐vis spectrophotometery and an electrochemical quartz‐crystal microbalance (EQCM) during reduction of PP‐EHP from single layer and bilayers through electrochemical stimulation. EHP was reincorporated to the inner film by applying an anodic potential and then the release of EHP was performed again. The results showed that the outer film could act as a barrier to ion‐and solvent‐transport between the inner film and electrolyte, yielding a more balanced counter‐directional movement of anions. © 2002 Society of Chemical Industry     

Covalent immobilization of penicillin G acylase onto amine-functionalized PVC membranes for 6-APA production from penicillin hydrolysis process. II. Enzyme immobilization and characterization

This article describes the covalent immobilization of penicillin G acylase (PGA) onto glutaraldehyde-activated NH₂-PVC membranes. The immobilized enzyme was used for 6-aminopenicillanic acid production from penicillin hydrolysis. Parameters affecting the immobilization process, which affecting the catalytic activity of the immobilized enzyme, such as enzyme concentration, immobilization's time and temperature were investigated. Enzyme concentration and immobilization's time were found of determine effect. Higher activity was obtained through performing enzyme immobilization at room temperature. Both optimum temperature (35°C) and pH (8.0) of immobilized enzyme have not been altered upon immobilization. However, immobilized enzyme acquires stability against changes in the substrate's pH and temperature values especially in the higher temperature region and lower pH region. The residual relative activities after incubation at 60°C were more than 75% compared to 45% for free enzyme and above 50% compared to 20% for free enzyme after incubation at pH 4.5. The apparent kinetic parameters K_M and V_M were determined. K_M of the immobilized PGA (125.8 mM) was higher than that of the free enzyme (5.4 mM), indicating a lower substrate affinity of the immobilized PGA. Operational stability for immobilized PGA was monitored over 21 repeated cycles. The catalytic membranes were retained up to 40% of its initial activity after 10.5 working h. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Reactive red 120 and NI(II) derived poly(2‐hydroxyethyl methacrylate) nanoparticles for urease adsorption

Non‐porous poly(2‐hydroxyethyl methacrylate) [p(HEMA)] nanoparticles were prepared by surfactant free emulsion polymerization. The p(HEMA) nanoparticles was about 200 nm diameter, spherical form, and non‐porous. Reactive Red 120 (RR 120) was covalently attached to the p(HEMA) nanoparticles and Ni(II) ions were incorporated to attach dye molecules. Urease was immobilized onto RR120‐Ni(II) attached p(HEMA) nanoparticles via adsorption. The maximum urease adsorption capacity of RR120‐Ni(II) attached p(HEMA) nanoparticles was 480.01 mg g^?1 nanoparticles at pH 7.0 in phosphate buffer. It was observed that urease could be repeatedly adsorbed and desorbed without significant loss in adsorption amount. K_m values were 21.50 and 34.06 mM for the free and adsorbed enzyme. The V_max values were 4 U for the free enzyme and 3.3 U for the adsorbed enzyme. The optimum pH was 25 mM pH 7 phosphate buffer for free and adsorbed enzyme. The optimum temperature was determined at 35°C and 55°C for the free and adsorbed enzyme, respectively. These findings show considerable promise for this material as an adsorption matrix in biotechnological applications. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39757.     

Dewetting kinetics of thin polymer bilayers: Role of under layer

A combined experimental and computational study is presented to uncover the dewetting kinetics of the PS/PMMA system by changing the film thickness of the PMMA under layer. On the low M_w PMMA (M_w = 15 kg/mol) layer, the dewetting velocity of PS film firstly rapidly decreases (regime I), and then becomes almost invariant (regime II) with the increase of the film thickness of the liquid lower layer. Experiments suggest that the transition from regime I to regime II is correlative with the property of the solid substrates. The linear stability analysis of thin bilayers uncovers a bimodal behaviour of the instability under the experimental conditions and changeover of dominant mode of instability from one interface to the other is the major reason behind the switching of regimes. The nonlinear simulations closely mimic the experimental interfacial morphologies and suggest two different pathways of hole growth for regimes I and II under experimental condition. The simulations also indicate that the rapid reduction in the dewetting velocity is because of the increased excursion or penetration of the upper layer into the lower layer near the three phase contact line as the viscous resistance at the more viscous PMMA layer reduces with its increasing thickness. A qualitative match is thus found between the experimental and theoretical trends of the dewetting velocities. In addition, the experiments show that on a high M_w PMMA (M_w = 365 kg/mol) layer, the kinetics of hole growth of the PS layer is not affected by the PMMA layer thickness.     

An Advanced TALSPEAK Concept for Separating Minor Actinides. Part 1. Process Optimization and Flowsheet Development

A solvent extraction system was developed for separating trivalent actinides from lanthanides. This “Advanced TALSPEAK” system uses 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (HEH[EHP]) to extract the lanthanides into an n-dodecane-based solvent; the actinides are retained in a citrate-buffered aqueous phase by complexation to a polyaminocarboxylate ligand. Several aqueous-phase ligands were investigated, and N-(2-hydroxyethyl)ethylenediamine-N,N’,N’-triacetic acid (HEDTA) was chosen for further study. Batch distribution measurements indicate that the separation of americium (Am) from the light lanthanides increases as the pH increases. However, previous investigations indicated that the extraction rates for the heavier lanthanides decrease with increasing pH. Therefore, a balance between these competing effects is required. An aqueous phase at pH 2.6 was chosen for further process development, because this offered optimal separation. Centrifugal-contactor single-stage efficiencies were measured to characterize the system’s performance under flow conditions, and an Advanced TALSPEAK flowsheet was designed.     

Synthesis of 2‐(9H‐carbazole‐9‐yl)ethyl methacrylate: Electrochemical impedance spectroscopic study of poly(2‐(9H‐carbazole‐9‐yl)ethyl methacrylate) on carbon fiber

In this contribution, 2‐(9H‐carbazol‐9‐yl) ethyl methacrylate (CzEMA) monomer was chemically synthesized. The monomer characterization was performed by FT‐IR, ¹H‐NMR, ¹³C‐NMR, and melting point analysis. The electropolymerization of CzEMA was studied onto carbon fiber microelectrodes (CFMEs) as an active electrode material in 0.1M sodium perchlorate (NaClO₄)/acetonitrile (ACN) solution. The electropolymerization experiments were done from 1 mM to 10 mM. The detailed characterization of the resulting electrocoated Poly (CzEMA)/CFME thin films was studied by various techniques, i.e., cyclic voltammetry (CV), Scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). The effects of initial monomer concentrations (1, 3, 5, and 10 mM) during the preparation of modified electrodes were examined by EIS. Capacitive behaviors of modified CFMEs were defined via Nyquist, Bode‐magnitude, and Bode‐phase plots. Variation of capacitance values by initial monomer concentration and specific capacitance values are presented. The highest specific capacitance value electrocoated polymer thin film by CV method in the initial monomer concentration of 5 mM with a charge of 52.74 mC was obtained about 424.1 μF cm^?2. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Poly(2,5‐dimethoxyaniline) films on mild steel for application to glucose biosensor

Poly(2,5‐dimethoxyaniline) (PDMA) films were electrochemically synthesized on mild steel from an aqueous oxalic acid solution using galvanostatic mode. These films were characterized by potential–time curve, UV‐visible absorption spectroscopy, Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The enzyme glucose oxidase (GOx) was entrapped into the PDMA film by a physical adsorption method. The resulting PDMA–GOx films were characterized by UV‐visible absorption spectroscopy, FTIR, and SEM. The amperometric response of the PDMA–GOx films was measured as a function of glucose concentration in phosphate buffer solution (pH 7.3). The PDMA–GOx films exhibit a fast and linear amperometric response in the range of 2–20 mM glucose. The maximum current density and Michaelis–Menten constant of PDMA/GOx films are found to be ～483 μA/cm² and 1.12 mM, respectively. The shelf stability and thermal stability of these films were also investigated. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008