Poly-N-methylpyrrole

Konno, A., Mogi, I. and Watanabe, K. (2001) Effect of strong magnetic fields on the photocurrent of a poly(N-methylpyrrole) modified electrode. 

Sulfur monochloride was successfully used for the preparation of pentathie-pino-fused poly(N-methylpyrrole) from the corresponding polymer (2005MI345). 

Bartlett P N and Whitaker R G 1987 Electrochemical immobilisation of enzymes. Part 11. Glucose oxidase immobilised in poly-N-methylpyrrole J. Electroanal. Chem 224 37-48... 

Bartlett, P. N., Whitaker, R. G., Electrochemical Immobilization of Enzymes. Part 2. Glucose Oxidase Immobilized in Poly-N-Methylpyrrole , J. Electroanal. Chem. 224 (1987) 37-48. 

As for the case in PAn, the conductivity of PPy and poly(N-methylpyrrole) films is also strongly affected by the applied potential in liquid SO2 [171]. Van Dyke et al [172] reported that the potential domain in which PPy is conductive can be extended in non-aqueous media, e.g., acetonitrile. Normally, the PPy films are conductive above about —0.4 V vs. SCR but this can be extended down to about —1.1 V by simply treating the doped film with sodium hydroxide. This effect was attributed to the shift in the reduction potential of hydoxide-doped PPy because of its large association constant with oxidized pyrrole sites. 

S. Wencheng and O.I. Jude. Electrodeposition mechanism, adhesion and corrosion performance of polypyrrole and poly(N-methylpyrrole) coatings on steel substrates. Synth. Metals, 2000, Vol. 114, pp. 225-234. 

F. Estrany, R. Ohver, E. Armelin, H.I. Iribaren, F. Liesa, and C. Aleman, Electroactive properties and electrochemical stability of poly(3,4-ethylenediox3dhiophene) and poly(n-methylpyrrole) multi-layered films generated by anodic oxidation. Port. Electrochim. Acta, 25, 55-65 (2007). 

On the other hand direct electron transfer between the poly(pyrrole) and GOx has been claimed. Subsequent work on GOx immobilized in poly(N-methylpyr-role) suggests that the process is very inefficient unless the enzyme is partially denatured during immobilization. In this study there was no evidence to support direct oxidation of the enzyme for films grown at 25° C. When films were grown at 50° C, the authors found evidence of direct oxidation of the enzyme, and they observed that selectivity of the enzyme was significantly reduced. They rationalize these observations by suggesting that at 50° C, the enzyme is partially denatured, so it is entrapped within the poly(N-methylpyrrole) film in a more open form, allowing access of polymeric chains to the active site of the enzyme. 

Detailed studies of glucose oxidase immobilized in poly(N-methypyrrole) films using both ferrocene monocarboxylic acid and ferricyanide as the mediator species indicate that in both cases poly(N-methylpyrrole) films are insulating and there is no evidence of direct reoxidation of the mediator on the polymer. This is an unexpected result, since these mediators are electroactive at poly(N-methylpyrrole) films that do not contain GOx. It appears that in addition to catalyzing the oxidation of glucose in the presence of a mediator, GOx can also catalyze the reduction of oxygen to H2O2 in the presence of mediators (M) as electron acceptors... 

The H2O2 produced by this reaction can react with the poly(N-methylpyrrole) and destroy the conductivity of the film. 

In addition to poly(pyrrole) and poly(N-methylpyrrole), other conducting polymers have been used for enzyme immobilization, including poly(thio-phene), poly(indole), and poly(aniline). " Poly(thiophenes) and poly (indole) films have the possible disadvantage that the enzyme/polymer film must be grown from aprotic solvents, conditions that may denature the enzymes. The... 

In devices of the first type, the conducting polymer starts in the oxidized state and is reduced as a result of the enzyme-catalyzed reaction of the substrate. This changes conductivity of the polymer, thus switching on or off the device. To reset the switch, it is necessary to connect the device to a potentiostat and reoxidize the film electrochemically (Fig. 9.14). Two devices have been reported to date, one based on poly(pyrrole)/poly(N-methylpyrrole) and responsive to NADH, the second based on poly(aniline) and responsive to glucose. In the latter case the device is switched from off to on, which appears to be advantageous, since it gives much faster response times. 

Stable immobilisation of macromolecular biomolecules on conducting microsurfaces with complete retention of their biological recognition properties is a crucial problem for the commercial development of miniaturised biosensors. Various conducting polymers have been utilised for immobilisation of enzymes at an electrode surface including PPy [74-76, 103-106], polyindole [79], PANI [77, 107, 108], poly (N-methylpyrrole) [65] and copolymers of N-substituted pyrroles [34]. 

Metal-oxide-semiconductor FETs (MOSFETs) were also prepared by electrochemical polymerization using PPy and N-alkyl substituted PPy films, including poly (N-methylpyrrole) (PNMePy) and poly (N-ethylpyrrole) (PNEtPy) as a p-type semiconductor and p-toluenesulfonic acid monohydrate as a supporting electrolyte [168]. Figure 8.93 represents the cross-sectional view of the fabricated MOSFET. The mobility of PPy and PNEtPy FETs was 1.7 cm s, which is close to the value of silicon inorganic transistors [168]. 

Not only do oxidatively doped polypyrrole films show significant environmental stability, but a number of these films can also be electrochemically prepared and switched in both organic and aqueous solvents [90]. While poly(N-methylpyrrole) was the only polymer of the series that exhibited a comparable electrochromic contrast in both solvents, N-benzyl (19a), N-tolyl (19b), and the parent polypyrrole showed a decrease in electrochromic contrast when comparing results obtained using organic and aqueous electrolytes. Polymers prepared using N-phenyl and N-benzoylpyrrole (20) showed no electrochromic switching in aqueous solutions. 

Massoumi and Entezami [92] reported the controlled release of dexamethasone sodium phosphate (DMP) from a conducting polymer bilayer film consisting of a PPy inner film doped with DMP and poly(N-methylpyrrole)/polystyrene sulfonate (PNMP/PSS) or polyaniline sulfonate (SPANI) outer film. DMP was released from the inner film by an application of less than —0.6 V. In this device, the outer polymer layer functions as an ion and solvent barrier and also effectively reduces the rate of DMP release under an applied reducing electrochemical field, thereby providing an additional route to controlling release rates. 

Bartlett, P.N., Z. Ali, and V. Eastwick-Field. 1992. Electrochemical immobilization of enzymes. Part 4. Co-immobilization of glucose oxidase and ferro/ferricyanide in poly(N-methylpyrrole) films. 

A. Tsumura, H. Koezuka, S. Tsunoda, T. Ando, Chemically prepared poly (N-methylpyrrole) thin-film - its application to the field-effect transistor, Chemistry Letters 1986, 863. 

Poly(N-methylpyrrole) has been used in several studies because of its higher stability than unsubstitut polypyrrole (24,25). A poly(N-methylpyrrole)/Nafion composite was found to be an effective support, and is attractive for use in fuel cells because of its proton conductivity (24). Incorporation of polynuclear rudienium oxide/cyanoruthenates into poly(N-methylpyirole) containing Pt particles produced a synergistic incr se in methanol oxidation activity (25). 

Much of the work done with conductive polymers follows the same trends as that with non-conductive polymers, so will not be described here. There will be important roles for conductive polymers as sophisticated microstructures are designed. One example of early work in this area is the use of poly(pyrrole) as a support for montmorillonite at the surface of electrodes, and in free-standing films (119). Also Kittlesen, White and Wrighton reported in 1984 that electropolymerized poly(pyrrole) and poly(N-methylpyrrole) could be prepared at electrodes with widths of only 1.4 microns (120). These electrodes were part of an ultramicroelectrode array used to demonstrate the possibility of combining surface chemistry with microelectronics technology to prepare microsensors. Since the conductivity of poly(pyrrole) (and many other conductive polymers) depends on redox state, the authors suggest that miniaturized redox sensors may be prepared from systems such as theirs. 

Since suitable conducting polymers with anionic backbones are not available, we have resorted to a more complex approach for cation binding. Following Martin s workio on terpolymer redox films of polyvinylferrocene, we produced a new type of composite polymer, of cationic poly-(N-methylpyrrole) (PMP" ) with anionic poly-styrenesulfonate (PSS ). Upon reduction of a film of this material, cations are taken up. Thus, the entangled polymeric anion is not flushed out by reduction of the pyrrole units. Instead, cations are incorporated to balance the sulfonate charges. This has been shown for a variety of cations including protonated dopamine. The scheme below shows how this polymer works to bind protonated dimethyldopamine (DH ) cathodically and to release it anodically. 

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