Poly redox reactions

Generation of radicals by redox reactions has also been applied for synthesizing block copolymers. As was mentioned in Section II. D. (see Scheme 23), Ce(IV) is able to form radical sites in hydroxyl-terminated compounds. Thus, Erim et al. [116] produced a hydroxyl-terminated poly(acrylamid) by thermal polymerization using 4,4-azobis(4-cyano pentanol). The polymer formed was in a second step treated with ceric (IV) ammonium nitrate, hence generating oxygen centered radicals capable of starting a second free radical polymeriza-... 

The stoichiometry of the redox reactions of conducting polymers (n and m in reactions 1 and 2) is quite variable. Under the most widely used conditions, polypyrroles and polythiophenes can be reversibly oxidized to a level of one hole per ca. 3 monomer units (i.e., a degree of oxidation, n, of ca. 0.3).7 However, this limit is dictated by the stability of the oxidized film under the conditions employed (Section V). With particularly dry and unreactive solvents, degrees of oxidation of 0.5 can be reversibly attained,37 and for poly-(4,4 -dimethoxybithiophene), a value of n = 1 has been reported.38 Although much fewer data are available for n-doping, it appears to involve similar stoichiometries [i.e., m in Eq. (2) is typically ca. 0.3].34,39"41 Polyanilines can in principle be reversibly p-doped to one... 

On the basis of their results the authors concluded that the crossover from the neutral to oxidised form of poly pyrrole, and vice versa, requires the number of spins to pass through a maximum, i.e. the creation and anihilation of bipolarons involves the passage through the polaron state. They expressed this as a two-step redox reaction ... 

T. Yamamoto and H. Hayashi, ir-Conjugated soluble and fluorescent poly(thiophene-2,5-diyl)s with phenolic, hindered phenolic and /j-C6H4OCH3 substituents. Preparation, optical properties, and redox reaction, J. Polym. Set, Part A Polym. Chem., 35 463-474, 1997. 

Since the oxidative polymerization of phenols is the industrial process used to produce poly(phenyleneoxide)s (Scheme 4), the application of polymer catalysts may well be of interest. Furthermore, enzymic, oxidative polymerization of phenols is an important pathway in biosynthesis. For example, black pigment of animal kingdom "melanin" is the polymeric product of 2,6-dihydroxyindole which is the oxidative product of tyrosine, catalyzed by copper enzyme "tyrosinase". In plants "lignin" is the natural polymer of phenols, such as coniferyl alcohol 2 and sinapyl alcohol 3. Tyrosinase contains four Cu ions in cataly-tically active site which are considered to act cooperatively. These Cu ions are presumed to be surrounded by the non-polar apoprotein, and their reactivities in substitution and redox reactions are controlled by the environmental protein. 

In a system devised to oxidize a dye, glucose oxidase and horseradish peroxidase were coassembled by layer-by-layer alternative adsorption to construct multienzyme films. The peroxidase was adsorbed to poly(styrene sulfonate) while glucose oxidase was adsorbed to poly(ethylene imine), allowing for sequential redox reactions to take place resulting in the subsequent oxidation of the textile dye DA67 [71]. 

Redox initiation is often an efficient method for graft polymerization. Hydroxyl-containing polymers such as cellulose and poly(vinyl alcohol) undergo redox reaction with ceric ion or other oxidizing agents to form polymer radicals capable of initiating polymerization... 

Control of the electron-transfer step was also attempted by combining two metal species on a polymer ligand167. We prepared polymer-metal complexes involving both the Cu(II) and Mn(III) ions. The oxidative polymerization of XOH catalyzed by the PVP-Cu, Mn mixed complex or the diethylaminomethylated poly(styrene)(PDA)-Cu Mn mixed complex proceeded 10 times faster than the polymerization catalyzed by either PVP- or PDA-metal complex. The maxima of the activity observed at [Cu]/[Mn] = 1 and [polymer]/[Cu,Mn] moderately small where Cu and Mn ions were crowded within the contracted polymer chain. Cooperative interaction between Cu and Mn was inferred. The rate constant of the electron-transfer step (ke in Scheme 14) for Cu(II) -> Cu(I) was much larger than that for Mn(III) -> Mn(II). The rate constants of the reoxidation step (k0) were polymer-Mn ex polymer-Cu.Mn > polymer-Cu, so the rapid redox reaction... 

Poly(pyridyl)ruthenium complexes, typically, [Ru(bpy)3]2+ have frequently been used as photocatalysts in the redox reactions between electron donors (Dred) and acceptors (Aox) to yield the oxidized (Dox) and reduced (Ared) forms (Eq. 20) [34-37] ... 

Cyclic Voltammetric Behavior of the PPy-GOD Film. Figure 1 shows the cyclic voltammetric curves of a PPy-GOD film (4000 A) in phosphate buffer solution with pH 7.4 at different scan rates. Both anodic and cathodic peaks should correspond to the redox reactions of PPy chains. The peak potentials, which were recorded at the scan rate of 200 mV/s, were -380 mV and -200 mV for cathodic and anodic peaks, respectively. This is similar to the potential shifts of the PPy film doped with large anions (27) such as poly(p-styrenesulfonate). Enzyme protein molecules are composed of amino acid and have large molecular size, which can not move out freely from the PPy-GOD film by the application of the reduction potential. In order to balance the charge of the Pfy-GOD film, cations must move into the film, and redox potentials move toward a more negative potential. This behavior is different from the one observed for the PPy-GOD film, which was prepared in the solution of GOD... 

According to the standard electrochemical potentials (Table 1), with Cu/Cu2+ and Ru/Ru3+ couples, the amount of ruthenium deposited on metallic copper will be small, whereas the redox reaction carried out in presence of platinum or gold salts will occur to a large extent. On the other hand, for electrodes of first type (metal immersed in a solution of a salt of that metal), the standard electrochemical potentials as defined by thermodynamics are calculated with regard to a poly-crystalline metallic phase of infinite size. However, in the case of small metallic particles, characterized by metallic atoms of different coordination numbers, the notion of a local potential can be introduced. That no-... 

The nicotinamide nucleotide coenzymes function as electron carriers in a wide variety of redox reactions. In addition, NAD is the precursor of adenine dinucleotide phosphate (ADP)-ribose for ADP-ribosylation and poly(ADP-ribosylation) of proteins and cADP-ribose and nicotinic acid adenine dinucleotide phosphate (NAADP). They act as second messengers and stimulate increases in intracellular calcium concentrations. 

In the near future, it is believed that a major part of macromolecular chemistry will receive a strong impact from homogeneous organometallic catalysis. Thus, poly-coupling reactions with redox-sensitive precursor compounds to give polymers like 38 were discovered [72]. 

Oxidoreductases these enzymes catalyze redox reactions. Examples are oxidases that catalyze oxidation of a substrate by reducing molecular oxygen (02), and peroxidases that reduce H202. Laccases (EC 1.10.3.2) are oxidases that catalyze the oxidation of (poly)phenolic substrates. Reductases and dehydrogenases (EC 1.1.1) catalyze the reduction of carbonyls, using NADH/NADPH cofactors. Catalases (EC 1.11.1.6) catalyze the decomposition of H202 to 02 and H20. 

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