Tetramethylpyridinium porphyrins

Figure 8. Rate of photocleavage of acetylene (C2H2) and methyl-acetylene (03 ) as a function of illumination time, a) Methane (CHi ) from acetylene and c) ethane (C2H6) from methylacetylene using meso-Zn-tetramethylpyridinium porphyrin as sensitizer, b) Methane (CHi ) from acetylene and d) ethane (C2H6) from methylacetylene with Ru(bpy)f as sensitizer.

Figure 32. Photosensitized regeneration of NAD(P)H cofactor involving enzymes (FDR or LipDH) and the artificial electron-transfer mediator MV +, and using (A) Ru(bpy)j-" or (B) Zn(II) mMo-(A-tetramethylpyridinium)porphyrin, Zn-TMPyP +, as a photosensitizer.

Ru(II)tris(bipyridine) [Ru(bpy)3 +] as a photosensitizer, triammonium ethylene-diaminetetraacetic acid [(NH4)3EDTA] as a sacrificial electron donor and the enzyme ferredoxin NADP+ reductase (FDR) [215, 216]. Oxidative electron-transfer quenching of the excited Ru(bpy)3 + yields the A,A -dimethyl-4,4 -bipyridinium radical cation (reduced methylviologen, MV+), which mediates the reduction of NADP+ in the presence of FDR as a biocatalyst (Figure 32A). The quantum efficiency for NADH production corresponds to = 1.9 x 10 . A related system that includes Zn(II)wc50-(A-tetramethylpyridinium)porphyrin (Zn-TMPyP +) as a photosensitizer, mercaptoethanol as a sacrificial donor and lipoamide dehydrogenase (LipDH) as a biocatalyst has been applied for the photochemical reduction of NAD+ to NADH (Figure 32B). 

In aqueous solution or in water (methanol 1 1), tetracationic porphyrins form molecular assemblies with tetraanionic porphyrins, e.g., meso-tetraphenyl-sulfonato- with meso-tetramethylpyridinium porphyrin. Such assemblies are, however, ill-defined with respect to structure and aggregation number because both surfaces of the chromophores behave identically. They tend to polymerize and precipitate. Only when stereochemically fitting porphyrins are combined by charge interactions and polymerization is prevented by alkyl substituents does one obtain well-defined heterodimers. This has been realized with an isomer mixture of four p-pyridinium—ethyl porphyrins (solubility = 10" M) and meso-tetraphenylsulfonato porphyrin (same solubility) (Scheme 6.6.1). In this case, the porphyrins are forced into close proximity by four charge-charge interactions and into a face-to-face position by the arrangement of charges. The inability of... 

Tetracationic me o-tetramethylpyridinium porphyrin and the anionic lipid L—dimyristoylphosphatidic acid mixed in a ratio of 1 4 form a monolayer on glass. It shows the spectrum of porphyrin monomers, again lying flat on the surface, whereas on water surfaces they appear as stacked dimers. Only those molecules that had been directly attached to the anionic lipid layer on water were transferred to the glass plate (Fig. 6.8.1). The tendency of porphyrin monomers... 

A new effective photocatalyst has been obtained by association of the Zn-tetramethylpyridinium porphyrin photosensitizer with multicopper oxidase laccase. This system merges the oxidation of an electron donor [i.e. an organic molecule) with the four-electron reduction of diojygen to water, thus realising the idea of photo-driven transformations on substrates using enzyme-photosensitizer hybrids. ... 

Ruhlmann L, Zimmermann J, Fudickar W, Siggel U, Fuhrhop J-H (2001) Heterodimers and -trimers of meso-tetra-(isophtalicacid)-porphyrin octaanions with meso- and p-tetramethylpyridinium-porphyrin tetracations and their manganese complexes in water. Electrochemistry, spectroelectrochemistry and fluorescence quenching. J Electroanal Chem 503 1-14... 

Other polymer films have also been proposed, such as amino-substituted polyphenylene oxide , alkylamine-siloxane , polyaniline or zeolite in order to immobilize electroactive metallic tetramethylpyridinium porphyrins . 

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