1.2- Dithiolenes biological ligands

The final topic addressed in this chapter is the biosynthesis of the dithiolene cofactor ligand and its coordination to molybdenum and tungsten in the enzymes. Nature has clearly devised a synthetic process to overcome the twin difficulties of building a reactive dithiolene unit bearing a complicated and equally reactive pterin substituent. Molecular biology has been the tool to elucidate the steps in this complex process. Although the dithiolene formation step remains mainly a subject of conjecture, definitive information about the reagent molecule that will eventually be converted to a dithiolene is known. 

The biological studies summarized above have fully defined the oxidized active sites of the enzymes and provided idealized targets for MoHM studies. These targets are represented in structures (l)-(4), in rough order of prevalence in enzymes. In the enzymes, the dithiolene ligand represents MPT (or a dinucleotide derivative thereof) while in models it represents a synthetic simulant of this unique biological ligand. 

Ab initio and semiempirical methods have been applied to the interpretation of many aspects of dithiolene chemistry electronic spectra, ESR, Mossbauer, XPS, charge distributions, redox properties, reaction mechanisms, metal binding in biological systems and ligand-exchange behavior. We shall focus our attention on the theoretical deductions of some representative research groups. For computational details, the reader is referred to the original papers and references therein. 

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