Macrocyclic Complexes as Models for

Macrocyclic Complexes as Models for Nonporphine Metalloproteins Vickie McKee... 

A molecule that contains one or more binding sites that can accommodate inorganic or organic ions referred to as guests. The binding site could even be a cavity within a crystal structure. Although enzymes clearly qualify as examples of host molecules, the term is usually restricted to structures such as crown ethers, macrocycles, and cyclodextrins. Nevertheless, these hosts do serve as models for molecular recognition. See also Crown Ethers Macrocycles Inclusion Complexes... 

Complexes of metals with tetraaza-macrocycles possessing pendant arms are currently being considered as models for biologically relevant systems. Such species generally possess a metal ion bound to... 

Porphyrins in which the metal is bound to fewer than four pyrrole nitrogen atoms have attracted attention as models for the early steps in the metallation of the macrocycle. The bis[chloromer-cury(II)] complex of N-tosylaminooctaethylporphyrin involves one mercury coordinated to three porphyrin N atoms and one Cl, and the other to Cl and the remaining pyrrole N atom.614... 

Kimura and his associates have been preeminent in exploiting the potential of Zn(II) complexes of pendant-arm polyaza macrocycles to act as models for the hydrolytic Zn(II)-containing enzymes. Collectively, their work in this area involves structurally unmodified macrocycles as well as pendant-arm macrocycles, and the reader is referred to a number of reviews 6-15) that summarize their work in its entirety. The particular object of this section is to examine how different types of pendant arm have been introduced onto a macrocyclic framework and how it has been possible to utilize their presence to elicit information of relevance to a particular group of enzymes. The enzyme groups studied using pendant-arm macrocycles have been the alkaline phosphatases and the class II aldolases. 

The preparation and characterization of novel man-ganese(III) complexes of various porphyrin and porphyrin-likes macrocycles have continued to attract strong attention especially because of their importance in catalytical oxidation processes through the formation of a Mn(V)0 intermediate (see Section 6) and as model for metalloenzymes. In this line, an artificial enzyme formed through a directed assembly of a molecular square that encapsulated a Mn porphyrin has been prepared and investigated as a catalyst. In contrast to symmetrical binuclear bis(phenoxo) bridged macrocyclic Mn(III)Mn(III) complexes, unsymmetrical ones are rare. A new series of these kinds of carboxylate-free complexes has been described and their redox properties investigated. ... 

Dihydropyridine units have been incorporated into the macrocyclic framework of crown ethers (e.g. Figure 17b) and employed as models for the reactions catalyzed by alcohol dehydrogenases. In the presence of Mg ions these molecules reduce carbonyl groups to alcohols presumably via a complex in which the substrate carbonyl oxygen bin ... 

There has been interest in synthetic macrocycles for use as models for biological systems. A macrocycle with the N2S2-donor set was prepared in a good yield by the reaction of the 3,7-dithia-l,9-nonanediamine-Cu(II) perchlorate complex with nitroethane and aqueous formaldehyde in the presence of triethylamine in methanol (method Z-15) (Comba et al., 1988). This syn-... 

Macrocyclic polyamines are assuming a role of increasing importance as models for biological systems. Fifteen- to eighteen-membered macrocycles that bear four to six amine moieties form stable 1 1 complexes with inorganic phosphates, AMP, ADP, and ATP, and the macrocycles play a valuable role in the study of the binding of phosphate in vivo. The com-... 

Scheme 5.3. Suggested mechanism fca- the electrocatalytic behavior of Fe tetraphenyl-porphyrins in the presence of Bronsted acids. Reprinted from Scheme 5.6 J. Costam-agna, G. Ferraudi, B. Matsuhiro, M. Campos-Vallette, J. Canales, M. Villagran, J. Vargas and M.J. Aguirre, Complexes of macrocycles with pendant arms as models for biological molecules, Coordination Chemistry Reviews 196 (2000) 125-164. Copyright 2000, with permission of Elsevier.

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