Porphyrins cyclodextrin-appended

Cyclodextrin-appended porphyrins are one of the suitable types of compound for ET models, since cyclodextrin (CD) has a hydrophobic cavity able to capture a small nonpolar molecule such as a quinone in aqueous solution. The fir.st example of a porphyrin- -CD photochemical system 137 was reported by Bolton, Weedon and coworkers in 1984. They monitored the photoinduced ET reaction in a frozen mixture of porphyrin 137 and p-benzoquinone by ESR spectroscopy. Irradiation of the solution showed the characteristic single ESR signal due to the generation of porphyrin cation radical and quinone anion radical species. The signal intensities in the ESR spectra, using a variety of quinones, indicated that the efficiency of the ET depended upon the reduction potential of the quinone acceptors. 

Scheme 6-16 Porphyrins 34-36 with appended P cyclodextrins catalyze the epoxidation of double bonds in substrates with hydro-phobic termini which are bound in the cyclodextrin cavities.

Highly conjugated systems, such as a hydrophilic porphyrin, can be appended to a 8-cyclodextrin conjugate system utilizing excess NaBH3CN as the reducing agent (eq 36). ... 

Compared to systems based on a single interaction, cooperative sensors based on multiple, concerted, inter-molecular interactions between the components exhibit higher discrimination capabilities and enhanced functions. As examples for this class of sensors, two systems, both based on the absorption/luminescence properties of the porphyrin nucleus are illustrated in Fig. 5. Structure (a) represents a ditopic receptor where cooperative binding of a cation by the amide-appended calixarene and of an anion by the Zn-porphyrin allows recognition of complete binary metal salts. Structure (b) incorporates two cyclodextrin cavities and relies on the modification of the Fe(III) complex spectroscopic properties by inclusion of guests in these hydrophobic sites.This species is able to sense the presence of benzylmercaptane and 1-adamantanecarboxylate in four... 

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