Biological models metal-containing sites

A model of a flavin-based redox enzyme was prepared.[15] Redox enzymes are often flavoproteins containing flavin cofactors flavin adenine dinucleotide (FAD) or flavin mononucleotide (FMN). They mediate one- or two-electron redox processes at potentials which vary in a range of more than 500 mV. The redox properties of the flavin part must be therefore tuned by the apoenzyme to ensure the specific function of the enzyme. Influence by hydrogen bonding, aromatic stacking, dipole interactions and steric effects have been so far observed in biological systems, but coordination to metal site has never been found before. Nevertheless, the importance of such interactions for functions and structure of other biological molecules make this a conceivable scenario. 

The majority of cyanide-bridged dinuclear complexes described for the combination of metal ions belong to the biologically relevant class of Cu —Fe dimers. These compounds serve as models for the binuclear cyanide-inhibited site of cytochrome c oxidase, an enzyme that contains the heme-copper active site responsible for the O2 reduction chemistry (59). The lethal toxicity of cyanide was traced to its irreversible binding and inhibition of this active site in the enzyme (60). The biologically relevant aspects of these complexes were the subject of many reports (61,62). Our interest is in describing their crystal structure, which will be correlated to the magnetic properties in a later section. 

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