Metalloporphyrins supramolecular assembly

Syntheses of porphyrins and metalloporphyrins have been widely investigated over the last three decades to provide models which mimic functions of heme proteins, heme enzymes and supramolecular assembly of chlorophyll in green plants and photosynthesis bacteria. Results on the syntheses and structure of biomimetic porphyrins up to 1985 have been reviewed by Morgan and Dolphin. ... 

Supramolecular assemblies of metalloporphyrins and fullerenes have been also investigated by some of the authors of this book [37]. In an extensive work concerning the NEXAFS and XPS investigation of zinc diethinyl porphyrins vapour deposited on a Cu(l 11) surface and its interaction with increasing amounts of Ceo, a tilting of the macrocycle on the substrate surface, from flat geometry to standing... 

Stemming from their multifarious roles in natural processes, [metallo] porphyrins have found numerous applications in artificial systems aimed at mimicking important biological functions. Many different metalloporphyrins have been designed in order to accomplish specific tasks and, in particular, novel approaches have been used to assemble several porphyrins into a cluster. This ability to concentrate metalloporphyrins into a supramolecular assembly is of special relevance in that it takes us one step closer to constructing practical devices. This chapter will attempt to review the progress made in the assembly of porphyrin derivatives into supramolecular systems and will describe the aptitude of such assemblies to photosensitize particular reactions. The work described here is primarily concerned with trying to reproduce, under controlled conditions, some of the important features of photosynthetic reaction center complexes. 

Figure 5 illustrates the artistic view of how 13 provides a convenient way for building ordered molecular assemblies between CNTs and porphyrins [133]. For the case of metalloporphyrins, Hasobe et al. [125] have reported the SWCNT-driven aggregation of 13 to give supramolecular assemblies. Murakami et al. [134] have prepared Zn(II)-14-carbon nanombes CNTs nanocomposites by dissolving SWCNTs in a Zn(II)-14 DMF solution, attributed to the physical adsorption of porphyrin molecules onto the nanombe sidewall. 

The most important by-product of the analytic and synthetic work accomplished so far is knowledge about the stereochemistry and reactivity of natural compounds. There is an enormous potential for the chemists of the twenty-first century lying in the mastery and application of this knowledge in order to produce organized and finally functional materials. Typical contemporary examples include surface monolayers on metals and colloids made of fatty acid and steroid derivatives, the regio- and stereoselective assembly reactions between steroids and carbohydrates, coupled redox chains of metalloporphyrins and vitamins, noncovalent fibers made of amino acids, nucleotides, and saccharides, and the functionalization of proteins by incorporation of reactive molecules. The field of supramolecular or noncovalent natural compound chemistry has been scientifically fruitful for several decades and is presently exploited for the development of useful molecular devices and machines as well as for medical applications. 

Finally, a DEER study on models for molecular wires made from butadiyne-linked zinc porphyrin oligomers, end-labeled with nitroxide radicals, was performed by Lovett, Anderson, and coworkers [107]. Unlike in [104—106], one can control the conformations of these metalloporphyrin-based strucmres by self-assembly with multidentate amine ligands, which bend the rigid oligomeric structure. The experimentally found end-to-end distances in these complexes match the predictions from molecular dynamics calculations. This study thus presents a proof-of-principle that DEER spectroscopy is also well suited for understanding more complex supramolecular stmctures. 

Diskin-Posner, Y. Patra. G.K. Goldberg. I. Crystal engineering of metalloporphyrin assemblies. New supramolecular architectures mediated by bipyridyl ligands. Chem. Commun. 2002. 1420-1421. 

In this chapter, we will concentrate on the subjects of synthetic strategies for (1) porphyrins and the capability of the products for molecular recognition of small organic substrates via intermolecular and noncovalent interactions (2) effective electron-transfer reaction regulated by intermolecular interaction " and (3) self-assembled porphyrin to construct supramolecular system for the guest. The Structures of porphyrins and their metalloporphyrin derivatives have attracted chemists due to their suitability as a host framework for organic guest molecules. 

Coordinating substituents can be used to assemble supramolecular systems without blocking the metalloporphyrin center. This is the most interesting approach when the catalytic and electrocatalytic properties are considered, since these processes generally involve the coordination of the substrate to the central metal ion. 

If the dye ligands contain their own metal centers, they are able to offer both electron lone pairs and Lewis acidic sites for the self-assembly process. Once the orientation between the ligand and the metal is appropriate, the intermolecular complementary coordination in a head-to-tail manner might lead to macrocyclic architectures. Indeed, quite a few supramolecular macrocycles were produced from metalloporphyrin derivatives through the metal-directed self-cycHzation approach. 

The most used approaches for the construction of multiporphyrin systems are the self-assembly methods. For example, electrostatic assembly is an easy and widely used method based on the interaction of oppositely charged porphyrins for preparation of more complex systems [1-12]. Self-assembly of porphyrins are also possible by coordination of nucleophihc groups to the central metal ion or using compounds having two nucleophihc sites to coordinate two metalloporphyrins [13-22]. These methods have been used not only for the preparation of porphyrin dimers and trimers, but also for the formation of larger supramolecular networks. Despite the apparent simphcity of the preparation methods of multiporphyrin materials by self-assembly, they generally are less stable as compared to covalently bond... 

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