Porphyrins host-guest chemistry

Chemical transformations at the macroeyclic chromophorc of expanded porphyrins are still not known. The complexation behavior of expanded porphyrins is very different from that of nonexpanded porphinoid macrocycles. The coordination hole of the expanded porphyrins is often too big for the complexation of a single metal ion, so in fact two metal ions can be chelated. With some expanded porphyrins, anion binding is observable, a striking difference to the nonexpanded porphyrins. The complexation behavior and the host-guest chemistry of expanded porphyrins is a rapidly growing field of research. The work in this field has been reviewed. Ie f... 

Attempts to realize enzymatic reactions have been reported over the past four decades in the context of host-guest chemistry, presently a well-established research field. In the field of CPOs, much attention has been paid to identical research objectives. The host-guest chemistry based on CPOs holds a special position, because specific selectivity and reactivity will be achieved using the coordination-bond-forming reactions between the substrate and the incorporated metals in the porphyrins, as well as the redox reaction associated with the porphyrin s rr-electron system. 

A number of examples of the use of host-guest chemistry in the creation of PET active systems have appeared. The reaction of P-cyclodextrin alcoholate with meso-tetrakis(pentafluorophenyl)porphyrin is reported to give a hydrophilic cyclodextrin-porphyrin conjugate in 14% yield. ° In the presence of guests such as 1,4-benzoquinone, anthraquinone-2-sufonate or 8-anilino-l-naphthalene sulfonic acid, PET operates as evidenced by the fluorescence... 

Similar to calix[n]arenes, porphyrins have been known to be one of the support pillars of supramolecular chemistry attributing suitable photoactive and electroactive properties to the molecular structures designed around them for building artificial molecular devices. Thus, various metallated and free base porphyrin-calixarene assemblies could afford attractive scaffolds for application in the areas of multipoint molecular recognition, receptors, host-guest chemistry, catalysis and photoinduced electron transfers. 

Host-Guest Chemistry of Porphyrins in Molecular Recognition.287... 

Interactions between water-soluble porphyrins and nucleic acids have a major topic in porphyrin-based host-guest chemistry. The most intensively studied system is the binding of the cationic porphyrin, 5,10,15,20-tetrakis[A -... 

An illustrative spectrum of porphyrins and expanded porphyrins, as well as examples of practical (or at least interesting ) uses of porphyrins in receptor design and host-guest chemistry, has been presented. The hope is that this survey has helped underscore a large number of opportunities that await those who lake advantage of the porphyrin scaffold or who are keen to develop or exploit expanded porphyrins. It is expected that continued developments, perhaps sparked by readers of this chapter, will have an important impact... 

Porphyrins and phthalocyanines can be used as core, branches, and terminal groups of dendrimers that have been extensively used as bio-inspired models or mimics of natural systems such as hemoproteins and chlorophyll in photosynthesis, but also in host-guest chemistry, biosensors, photodynamic therapy, and catalysis. Aida et al. demonstrated the amplitude of this field in a review of 2009 [98]. In the following paragraphs, some historical backgrounds will be presented before focusing in a topic specifically concerned on the porphyrin-dendrimer electrochemistry and photoinduced electron transfer processes. 

Baldwin, J. E., Perlmutter, P. Bridged, Capped and Fenced Porphyrins, in Topics Current Chem. 121, Host Guest Complex Chemistry III (eds. Vogtle, F., Weber, E.), Berlin - Heidelberg - New York - Tokyo, Springer 1984... 

While supramolecular chemistry of porphyrins has been extensively studied over the last few decades, related study of phthalocyanines is still in its infancy. Despite the great potential of phthalocyanine-based supramolecular arrays in various applications as mentioned earlier, only a handful systems have been reported so far. Self-assembled systems held by hydrogen bonding, donor-acceptor interactions, and host-guest interactions are still very rare. There is certainly much room for further investigation in the chemistry of this important class of compounds, particularly on their structural and functional aspects. We hope this article can provide the grounding for further studies. 

Macrocycles are a highly topical subject. They constitute a large spectrum of compounds involving both artifical substances and natural products such as crowns, cryptands, cyclophanes, porphyrins, or macrolides. The former initiated the exiting area of host-guest supramolecular chemistry, which was highlighted by the award of the Nobel Prize for Chemistry to D. J. Cram, J.-M. Lehn, and C. J. Pedersen in 1987 but is still developing enormously. Porphyrins and macrolides are important active substances. No wonder that macrocycles are of immediate interest and everyone wants to know how they can be synthesized efficiently. 

The demonstrated ability of nonaromatic expanded porphyrins to act as com-plexing agents for both neutral and anionic substrates " led Sessler and coworkers to suggest that systems such as 9.130 and 9.131 might exhibit interesting host-guest-type chemistry. That is to say, the anion and neutral substrate-binding... 

On the other hand, water-soluble porphyrins have usually been obtainable by introduction of polar groups such as amino, carboxylate and sulfate groups to the terminal positions of the meso and //-pyirolic substituents. Aggregation phenomena should be taken into account in host and guest chemistry in aqueous solution. 

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