Cyclic multiporphyrins

Inorganic templating and self-assembly provide coordination compounds whose geometries make possible the synthesis of complex structures, namely of cyclic multiporphyrin arrays [9.13a, 9.179], of inorganic rotaxanes [9.97a, 9.180], of multi-catenates and catenands (see 181) [8.281, 8.282] and even of molecular knots (see 182) [8.282, 9.77, 9.181] (in 181 and 182 a) with, b) without Cu(l) template). 

Figure 52. Cyclic multiporphyrin assemblies based on porphyrins (empty squares) containing two monodentate pendant ligands (arrows) and nonporphyrinic metals as assembling units. The pendant arms are in c/ s [(a) and (c)] or trans [(b) and (d)] relative orientations.

Membrane-s )Anmn have been prepared. Tetraphenylpor-phyrins having jc-carboxy and jc-amino functionalities have been polymerized interfacially to produce chemically asymmetric membrane films.Mercaptoporphyrins have also been polymerized to form ultrathin films of a porphyrin homopolymer based upon 5,10,15,20-tetrakis-(Q -mercapto-j9-tolyl) porphyrin,and thiol-derivatized porphyrins for attachment to electroactive surfaces have been prepared and examined as means of information storage,including those having a ferrocenyl moiety appended in several ways. Various means of linking porphyrins to form arrays have been reviewed. Preparation and investigation of the physical properties of cyclic tetra-, hexa-, hepta-porphyrin and star-shaped multiporphyrin or star-shaped tetra- or octa-porphyrin, or monophthalocyanine arrays have been described and reviewed. As part of this work, methods of forming porphyrins in the presence of acid-labile metalloporphyrins that provide a new route to mixed-metal multiporphyrin arrays have been reported. ... 

As the number of monomeric units of a cyclic assembly increases, its formation in solution becomes unfavorable. Although there is a report regarding the formation of a cyclic hexamer in the solid state [94], to the best of our knowledge, there are no evidences for the complete assembly in solution of simple multiporphyrin rings of order greater than four. 

An overview of the thermodynamic principles governing self-assembly in solution, with particular reference to multiporphyrin architectures, is presented by Gianfranco Ercolani in the fifth chapter. The topic is discussed in order of increasing complexity, from simple acyclic assembhes to multi-cyclic assemblies. The principles are illustrated by selected examples of metal-mediated assemblies of porphyrins, many of which have been described in the previous chapters. 

The cyclic oligomers are another interesting class of synthetic multiporphyrin systems. The.se systems may not only mimic the highly concentrated porphyrin clusters found in biological structures containing closely coupled tetrapyrroles (such as the photo.synthetic reaction center and the cytochrome families of various types),- - but also show an interesting manner of molecular recognition and self-... 

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