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Vesicles, and Micelles Templated Assembling

Natural systems use proteic environment and protein structures to spatially arrange chromophores. As we will see in this section, interactions of porphyrins with peptide fragments or organized monolayers can help to achieve such topographic control in artificial assemblies. [Pg.674]

It can be seen from UV-visible characterization of the species that the tetraaryl porphyrinic chromophores 125(M) tend to form J-type aggregates (red-shifted absorptions). In these assemblies, the use of equimolar mixtures of 125 (Zn) and 125(H2) led to a very efficient (81%) ET process, via a postulated and reasonable Forster mechanism, with a rate constant of A et = 3.1 X 10 s-l. When iron(III) porphyrins 125(Fe) are used, free base protoporphyrin 124 bearing alkyphosphocholine side arms can be incorporated in the fluid part of the vesicles. In the presence of a sacrificial electron donor on the outside of the vesicle, a vectorial eT process occurs from the excited free base porphyrins to the iron(III) species, leading to photoreduction of the iron(III) to iron(II). Previous work had already shown that this could also be achieved between zinc porphyrins and iron porphyrins in vesicles  [Pg.677]

Finally, an intermediate solution to the noncovalent assembly of porphyrins is the trapping of porphyrin assemblies within membrane models, as depicted in [Pg.677]

The zinc(II) porphyrins 126 are held together and structured by H-bonds and by hydroxyl group coordination to zinc. Table 13.8 summarizes the properties of the aggregates as a function of the concentration of lecithin in the aqueous phase. [Pg.678]

Aggregates secluded in the membrane start forming type II aggregates (tubular rod-like structures) at a concentration of around 10 % in a-lecithin, which corresponds to a surfactant/ZnBChl ratio of 1.6. Incorporation of BChl a (free base BChl) shows that singlet energy transfer to the BChl a is efficient (60%), [Pg.678]


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