Poly aniline

As discussed previously, the literature indicates that the best NADH oxidation systems are based on two-electron/one-proton acceptors with redox potentials less that 0.25 V vs. SCE. On this premise, it was proposed 

Analytical models of modified electrodes for NADH oxidation 

Having shown that poly(aniline) films can mediate NADH oxidation, studies of the effect of altering the applied potential and the rotation rate of the electrode were undertaken. Preliminary results from these studies showed that the maximum current response was obtained when the applied potential was 0.2 V vs. SCE and that the currents were two orders of magnitude higher for poly(aniline) modified electrodes when compared to a bare electrode indicating that poly(aniline) is a good catalytic surface for the oxidation of NADH. However, studies of the effect of rotation speed carried out at pH 5 show a decline in current with time (see Fig. 2.12). 

Any decrease in current response with time greatly complicates the kinetic analysis and makes the system unsuitable for use in a biosensor. It is important, therefore, to determine the reason for the poor stability and 

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The optimization of the biorecognition layer by the modification of a transducer used. Nanostmctured poly aniline composite comprising Prussian Blue or poly-ionic polymers has been synthesized and successfully used in the assembly of cholinesterase sensors. In comparison with non-modified sensors, this improved signal selectivity toward electrochemically active species and decreased the detection limits of Chloropyrifos-Methyl and Methyl-Pai athion down to 10 and 3 ppb, respectively. 

The GBR resin works well for nonionic and certain ionic polymers such as various native and derivatized starches, including sodium carboxymethylcel-lulose, methylcellulose, dextrans, carrageenans, hydroxypropyl methylcellu-lose, cellulose sulfate, and pullulans. GBR columns can be used in virtually any solvent or mixture of solvents from hexane to 1 M NaOH as long as they are miscible. Using sulfonated PDVB gels, mixtures of methanol and 0.1 M Na acetate will run many polar ionic-type polymers such as poly-2-acrylamido-2-methyl-l-propanesulfonic acid, polystyrene sulfonic acids, and poly aniline/ polystyrene sulfonic acid. Sulfonated columns can also be used with water glacial acetic acid mixtures, typically 90/10 (v/v). Polyacrylic acids run well on sulfonated gels in 0.2 M NaAc, pH 7.75. 

Polymers like those in the poly aniline family interchange protons and anions with the solution, allowing a local modulation of pH. Composites that interchange cations allow the modulation of any cation concentration. Efforts are being devoted to the synthesis of polymer or polymeric derivatives having great cationic specificity. 

Enzymes are generally classified into six groups. Table 1 shows typical polymers produced with catalysis by respective enzymes. The target macromolecules for the enzymatic polymerization have been polysaccharides, poly(amino acid)s, polyesters, polycarbonates, phenolic polymers, poly(aniline)s, vinyl polymers, etc. In the standpoint of potential industrial applications, this chapter deals with recent topics on enzymatic synthesis of polyesters and phenolic polymers by using enzymes as catalyst. 

The common form of polyaniline is a 1 1 combination of alternating reduced (A) and oxidized (C) units it is termed emeraldine (or emeraldine base). The emeraldine base is essentially non-conductive, but its conductivity increases by 9-10 orders of magnitude by treating with aqueous protonic acids. The conductive form of poly aniline can therefore be roughly depicted as a 1 1 combination of alternating A and D units. 

Tetra(o-aminophenyl)porphyrin, H-Co-Nl TPP, can for the purpose of electrochemical polymerization be simplistically viewed as four aniline molecules with a common porphyrin substituent, and one expects that their oxidation should form a "poly(aniline)" matrix with embedded porphyrin sites. The pattern of cyclic voltammetric oxidative ECP (1) of this functionalized metal complex is shown in Fig. 2A. The growing current-potential envelope represents accumulation of a polymer film that is electroactive and conducts electrons at the potentials needed to continuously oxidize fresh monomer that diffuses in from the bulk solution. If the film were not fully electroactive at this potential, since the film is a dense membrane barrier that prevents monomer from reaching the electrode, film growth would soon cease and the electrode would become passified. This was the case for the phenolically substituted porphyrin in Fig. 1. 

A poly(aniline boronic acid)-based conductimetric sensor for dopamine consisting of an interdigitated microarray electrode coated with poly(aniline boronic acid) has also been developed by the Fabre team. The sensor was found to show a reversible chemoresistive response to dopamine without interference by ascorbic acid from their mixtures.42... 

Because of its sensitivity to electron spin density, EPR is an ideal tool to answer questions concerning the degree of delocalisation in conducting polymers, such as poly(aniline). EPR spectra of radical cations of oligomers, representative of a... 

Figure 29 Some of the molecular structures used to interpret the EPR spectra of poly(aniline) oligomers. The molecules are labelled 1 and 4 in the same fashion as Ref. [149].

C.H. Liu, K.T. Liao, and H.J. Huang, Amperometric immunosensors based on protein A coupled poly-aniline-perfluorosulfonated ionomer composite electrodes. Anal. Chem. 72, 2925-2929 (2000). 

Simon et al. [92] investigated a biocatalytic anode based on lactate oxidation by lactate dehydrogenase (LDH). The anodic current is generated by the oxidation of NADH (produced by NAD+ and substrate) while LDH catalyzes the electro-oxidation of lactate into pyruvate. As previously mentioned, the oxidation of NADH at bare electrodes requires a large overpotential, so these authors used poly(aniline) films doped with polyanions to catalyze NADH oxidation. Subsequent research by this group focused on targeting mutants of LDH that are amenable to immobilization on the polyaniline surface [93],... 

Thin polymer films have been prepared by surface catalysis in ultrahigh vacuum and electrochemical deposition from solution. These two routes of synthesis result in poly(thiophene), poly(aniline) and poly(3,5-lutidine) films that have similar infrared spectra. These polymer films are highly orientationally ordered the rings are perpendicular to the surface in poly(thiophene) and poly(3,5-lutidine) films, and the phenyl rings are parallel to the surface in poly(aniline). 

Aniline. Aniline black is a well known polymer of aniline formed by electrophilic additionf3.41. Numerous investigators have formed poly(aniline) films by anodic deposition of Pt and other electrode materials. We have examined the interaction of aniline with clean Ni(lll) and Ni(100) surfaces in ultrahigh vacuum and found aniline to form an orientationally ordered, thermally stable polymer film. Electrochemically prepared poly(aniline) films also show the high degree of orientational ordering. 

The AES results indicate that the aniline coverage is more than two times greater than the maximum coverage based on van der Waals radii. The TPR results show this species is too stable to be a condensed multilayer. Hence, we conclude that aniline polymerized forming a very stable polymer layer. In addition, the absence of infrared bands corresponding to C=C stretches or ring vibrations indicated that the poly(aniline) film was formed with the phenyl rings parallel to surface. The infrared results also indicated that the poly(aniline) film had N-H bonds which were oriented perpendicular relative to the surface. 

Poly(aniline) films were prepared electrochemically on a Pt electrode potentiostatically at 0.85 V vs Ag/AgCl for 5 s from a 1 M aniline in 1 M LiClC>4/CH3CN solution. The films were a faint blue-green color. Thicker films were formed at greater potentials. Even the very... 

Infrared spectra of the electrochemically prepared poly(aniline) were taken after emersion from the electrolyte solution at 0.8 V, 0.35 V and 0 V, the spectra are shown in Figure 4. At all three potentials the ir... 

Figure 4. Reflection infrared spectra of aniline films (a) aniline multilayer adsorbed on Ni(111) at 165 K (b) poly(aniline) monolayer on Ni(111) at 400 K (c) electrochemically grown poly(aniline) on Pt oxidized at 0.8 V vs. Ag/AgCI(1M) (d) electrochemically grown poly(aniline) on Pt reduced at 0.35 V vs. Ag/AgCI(1M) (e) electrochemically grown poly(aniline) on Pt reduced at 0.0 V vs. Ag/AgCI(1M)...

Polymers consisting of but not limited to poly thiophene, polypyrrole and poly aniline have been extensively used to make polymer nanofibers. In general, any metal that can be electroplated has most likely appeared in a nanowire. Semiconductors, polymers, and insulators have also been used in the design of nanowires.Furthermore, different metals can be plated in succession to give striped nanowires. 

Nitrite sensor Osmium-bipyridyl-modified quaternized poly(4-vinylpyri-dine) (PVP-Os) PSS or poly[aniline-co-N- (3-sulfopropyl)aniline (PAPSH) [206]... 

Poly[(aniline-2-chloroaniline)-4-toluenesulfonic acid salt] was obtained by oxidative copolymerization of aniline with 2-chloroaniline in solutions containing 4-toluenesulfonic acid. The copolymer salt was subjected to heat treatment under nitrogen atmosphere at elevated (about 150°C) temperatures. The heat-treated samples acquired electric conductivity of 2.7 X 10 f2 cm . According to ESR spectra, the heated poly[(aniline-2-chloroaniline)-4-toluenesulfonic salt] exists as the poly(semiquinone imine ion-radical) in which unpaired electrons are localized on or near the nitrogen atoms (Palaniappan 1997). 

Aniline itself undergoes intramolecular coupling and further oxidation to give aniline black. Poly(aniline) can be deposited as a thin coherent film on the anode by continuously cycling the potential between -0.2 and 0.8 V vs. see [165], Oxidation of aniline using manganese(ll) - roanganese(IIl) as mediator in dilute sulphuric... 

After Little s proposal, many researchers have pursued such an exciting system in vain. Even metallic behavior was rarely seen in doped organic polymers, gels, and actuators. As mentioned in Sect. 3.4.4, MCso with linearly polymerized Ceo" exhibited one-dimensional (M = Rb, Cs) or three-dimensional (M = K) metallic behavior [144]. Recently a doped poly aniline was reported to exhibit a metallic temperature dependence for a crystalline polymer chemical oxidation of monomers grew crystallite polyaniline [329] early doping studies on polypyrrole (PFg) and poly(3,4-ethylene-dioxythiophene)X (X = PFg, BF4, and CF3SO3) prepared by electrooxidation at low temperatures also showed a metallic temperature dependence below 10-20 K (Scheme 16) [330, 331]. 

FIGURE 7.23 The encapsulation of aniline, and formation of poly aniline in MCM-41. 

In an earlier investigation by the authors (2) hehcal poly aniline doped with... 

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