Metalloporphyrins redox reactivity

Redox Reactivity of Manganese "Capped Metalloporphyrins L.A. Bottomley, J.F. Luck, F.L. Neely and J.S. Quick... 

First of all, I would like to express my gratitude to the institutions that facilitated this work. Studies related to the formation, properties, and reactivity of metalloporphyrins were supported by grants from the Alexander von Humboldt Stiftung (fellowship 2005-2006), by the Deutsche Forschungsgemeinschaft through SFB 583, Redox-Active Metal Complexes Control of Reactivity via Molecular Architectures and by a grant of computer time on the Hochstleistungsrechner in Bayern II (HLRB II). 

The studies on these Hangman porphyrins and other macrocyclic Hangman platforms [205] clearly demonstrate that exceptional catalysis may be achieved when redox and PT properties of a cofactor are controlled independently. A key requirement is that the PT distance is kept short, which may be accomplished by orthogonalizing ET and PT coordinates. The benefits of incorporating PT functionality into redox catalysis can only be realized when a suitable geometry is established. Moreover, the Hangman platforms show that a multifunctional activity of a single metalloporphyrin-based scaffold is achieved by the addition of proton control to a redox platform. This observation is evocative of natural heme-de-pendent proteins that employ a conserved protoporphyrin IX cofactor to affect a myriad of chemical reactivities. 

Knowledge of the electronic structure of metalloporphyrins is useful, because such compounds can serve as models for biological redox systems. In this context one may wish to know whether, during a redox process, the electron is transferred directly from the metal center or whether porphyrin ligands are also involved in the process. Further, an understanding of the influence of the oxidation state of the metal on the porphyrin ring s charge and reactivity is of interest. 

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. 

Kadish K (1984) Redox tuning of metalloporphyrin reactivity. J Electroanal Chem 168 (l-2) 261-274... 

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