Viologens surface-active

Formation of SA monolayers of phospholipids [217,242] and surface-active viologens [244, 245] on gold substrates, those of long-chain zirconium-phosphonates on silicon substrates [243], and those of alkanethiols on gallium arsenide substrates [246] have also been reported. 

Cooperative effects have been observed when surface active zinc porphyrin derivatives and amphiphilic naphthoxyvioiogens are irradiated in the presence of EDTA.333 Evidence for this comes from the observation that quantum yields of radical cations of the viologens on irradiation into both the absorption band of the zinc porphyrin derivatives and of the viologen are higher than the sum of the quantum yields obtained on irradiation of the individual absorption maxima. Similar results probably occur with surface active [Ru(bipy)3]2+ replacing the zinc porphyrin, but selective excitation is not possible in this case.333... 

Figure 5.52 General molecular structure of the surface active porphyrin-ferrocene-thiol supra-molecular complexes reported by Uosaki and co-workers [82]. (b) Energy diagram illustrating the mechanism behind photocurrent generation in SAMs of such complexes at cathodic electrode potentials of the Fc/Fc+ couple P, porphyrin Fc, ferrocene MV2+, methyl viologen...

More recently we have extrapolated these surface activation experiments to the examination of the reduction of n-heptyl viologen dication to its insoluble cation radical... 

It is not surprising then that the first reported surface mediated reaction made use of vicinal dihalides. In addition to poly-p-nitrostyrene immobilized metallo-porphyrins and viologens were found to be catalytically active. Recently,... 

In 2006, for the first time, the decoration of viral particles with redox-active moieties was reported [83,96]. The decoration of CPMV with a redox-active organo-metallic complex, ferrocene, and also with an organic redox-active compound, viologen, was achieved. Both approaches led to the generation of monodisperse redox-active nanoparticles the redox centers were presented in multiple copies on the solvent-exposed outer surface. 

Cysteamine was used to couple redox-active carboxylalkyl-4,4 -bipyridinium salts to the gold surface . The nonordered monolayer assembly was then transformed into a densely packed monolayer with 1-hexadecanethiol and cyclic voltammetry of the surface bound viologen was performed. The electron transfer rate constants to the bipyridinium sites depended on the alkyl chain length Abridging the redox site to the electrode. Electron transfer rate constants followed the Marcus theory. Cysteic-acid-active ester monolayers chemisorbed on gold were used to electrode-immobilize the protein glutathione reductase, then a bipyridinium carboxylic acid was condensed onto the enzyme in the presence of urea to wire the protein towards electrochemical reduction (Figure 6.26). 

The measurement of the PSII activity can be based on amperometric detection of the reduced form of a specific artificial electron acceptor in an electrochemical cell. The mediator must be present in its oxidized form in the measuring buffer. Under illumination, this artificial electron acceptor is reduced and then reoxidized on the surface of a working electrode. Different mediators were used potassium ferricyanide, parabenzoquinone," duroquinone, 2,6 dimethylbenzoquinone." With whole cells of eukaryotic algae, potassium ferrycianide, methyl-viologen, and DCIP were unable to access the photosynthetic electron transfer chain."... 

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