Ethyl viologen

Theoretically, according to the mechanism of biological azo dye reduction, the processes of biological decolorization are oxidation-reduction reactions, in which transfer of electrons match with the proton flow by the help of coenzymes, such as NADPH/NADP+ and NADH/NAD+. The oxidation-reduction potentials of the couples of NADPH/NADP+ and NADH/NAD+ are -324 and -320 mV, respectively [25, 46]. The least AGo value of the conversion NADPH/NADP+ and NADH/NAD+ is 44 kJ [47]. Therefore, —93 mV, which is obtained from (1), could be considered as a rough limited ORP value for ordinary primary electron donors of the third mechanism of biological azo dye reduction. This was demonstrated by the results of many researches (Table 1). Hence, the observed failure of cyanocobala-min [30] and ethyl viologen [48] to act as a mediator is most probably due to their too low Ed values 530 and —480 mV, respectively. 

The photophysics and photochemistry of gaseous PuFe have been ex-amined. Studies involving zinc porphyrins have been reported and include photo-oxidations in aqueous solution, photoreductions of Zn-TPP with hydrazines, and the role of Zn-TPPSa/ethyl viologen in photoredox processes. The mechanism of the photo-oxidation of water to oxygen with silver chloride has been discussed, and the synthesis of bis(chlorosilyl)-mercury compounds described. Colloidal CdSe has been shown to sensitize the photoreduction of O2 and of methyl viologen by cysteine. ... 

Methyl viologen (2+ MV+ ), ethyl viologen (3+ EV+ ), and benzyl viologen (4+ , BV+ ) radical cations were obtained7 similarly to 1+ by photo-... 

Ethyl viologen, I, J-diefhy/-4t4 -bipyridinium, N,N dieth-yby y dipyridylium. Normal potential at 30 —0,449... 

FIGURE 7.17 (a) Three-terminal PQT/viologen memory device, showing EV acceptor in PEO and the PQT structure, (b) Position of incident laser for sampling different regions of the devices, (c) Raman spectra in CHCI3 solution. PEO = polyethylene oxide, EV=ethyl viologen diperchlorate. 

FIGURE 7,23 Schematic of the write process, with N=neutral PQT, P =PQ Ppolaron, EV=ethyl viologen, and A = perchlorate ion. (a) Immediately after initiation of the write pulse, (b) during polaron propagation across the SD gap, and (c) after complete oxidation of PQT. See text for details. 

In the same study, redox polymers (223) were prepared that contained pendant viologens (Scheme 108). An active reducing agent was obtained by chemical reduction with dithionite or zinc, electrochemically, or by exposure to light. Utilization of the reduced poly(viologen) (224) as an electron transfer mediator was demonstrated by addition of a catalytic amount of the polymer to a mixture of zinc powder, ethyl benzoylformate (225) and water-acetonitrile (1 5). A quantitative yield of ethyl mandelate (226) was obtained after two days at room temperature (Scheme 109). Without the polymer, no reaction was observed after a month. 

Photo-induced electron transfer between [Ru(bpy)3]2+-like centres covalently bound to positively-charged polymers (N-ethylated copolymers of vinylpyridine and [Ru(bpy)2(MVbpy)]2+) and viologens or Fe (III) has been studied using laser flash photolysis techniques. It is found that the backbone affects the rates of excited state quenching, the cage escape yield, and the back electron transfer rate because of both electrostatic and hydrophobic interactions. The effect of ionic strength on the reactions has been studied. Data on the electron transfer reactions of [Ru(bpy)3]2+ bound electrostatically or covalently to polystyrenesulphonate are also presented. 

Other evidence was reported by Tsukahara and collaborators from the disproportionation reaction of the radical cation of the optically active bis-viologens, (S)-1 -(1 -naphthyl ethyl)carbamoyln methyl-1 -(4-(4-( 1 -naphthyl ethyl)carbamoyl methyl-pyridinio)pyridinio-4,4 -bi pyridinium tetra chloride, NBVPR2+, 1-phenyl analog, PBVPR2 +, and 1-cyclohexylethyl analog CHBVPR2+ (see Scheme 28) [70]. 

The two species approach in solution to form a sandwichlike 71-complex, and electron transfer takes place with formation of the dimer, whose dissociation leads to radical 2+. Electrochemical results as well as the EPR spectrum observed by reduction of the multicharged viologen Af-ethyl-AAtrimethylaminopentyl-4,4 -bipyridine (C5V3+, 19) indicated that dimerization proceeds through a radical-... 

All routes used toxic substances such as methanol, acetic acid (D), oxalic acid ethyl ester (A-D), cyclohexane (A), toluene, sulfuric acid and hydrochloric acid. Overall, no major differences were observed with the exception of viologen used in A This substance is toxic to fish, meaning that the sewage of A has to be processed in a water treatment plant, which is not necessary in B. 

We prepared three bifunctional redox protein maquettes based on 12 16-, and 20-mer three-helix bundles. In each case, the helix was capped with a Co(III) tris-bipyridyl electron acceptor and also functionalized with a C-terminal viologen (l-ethyl-V-ethyl-4,4 -bipyridinium) donor. Electron transfer (ET) was initiated by pulse radiolysis and flash photolysis and followed spectrometrically to determine average, concentration-independent, first-order rates for the 16-mer and 20-mer maquettes. For the 16-mer bundle, the a-helical content was adjusted by the addition of urea or trifluoroethanol to solutions containing the metal-loprotein. This conformational flexibility under different solvent conditions was exploited to probe the effects of helical secondary structure on ET rates. In addition to describing experimental results from these helical systems, this chapter discusses several additional metalloprotein models from the recent literature. 

Electron transfer catalysts Viologens from ethyl cellulose derivatives... 

Abstract. A -ethyl-A -hexadecyl-4,4 -bipyridinium bromide (Cj6VBr2) and A -ethyl-A -octadecyl-4,4 -bipyridinium bromide (CigVBr2) were used as electroactive probes to assess the interactions between surfactants and cyclodextrins. Cyclic voltammetry, visible spectroscopy, fluorescence spectroscopy and surface tension techniques were used to detect the formation of complexes between the surfactant viologen probes and a- and -cyclodextrins. The voltammetric results suggest the formation of inclusion compounds in which the hydrophobic tail of the surfactant viologens penetrate the cyclodextrin cavity. The dimerization of the viologen cation radicals is essentially suppressed by the presence of a-cyclodex-trin (ACD) while no effects are observed in the presence of )5-cyclodextrin (BCD). The observed results are best explained by the relative solubility in aqueous media of each of the inclusion complexes in the several accessible viologen oxidation states. 

Figure 15 Schematic diagram of an efficient harvesting of photoliberated electrons from ZnTMPyP as a sensitizer by the use of PSV as an electron mediator, TEOA as a sacrificial electron donor, and a bilayer membrane of LEV as an electron pool. ZnTMPyP tetrakis(A -methylpyridinium)porphyrinatozinc TEOA, triethanolamine PSV, sulfonato-propyl)viologen LEV, V-ethyl-V -[5-(VA -dihexadecylcarbamoyl)pentyl]-4,4 -bipyri-dinium dibromide [280],...

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