Synthetic approaches towards the models of sulfite oxidase

Molybdenum cofactor, Moco, presents in a number of redox enzymes, such as pyridoxal oxidase, formate dehydrogenase, pyrine hydroxylase, sulphite oxidase (SO), etc. essential for metabolism of all aerobic organisms [1]. After the structure of highly conserved molybdopterin (MPT) ligand was established by Rajagopalan et al. [2], that discovery marked a new wave in the model chemistry of molybdenum- and tungsten-containing enzymes. Continuing our interest in monodithiolene complexes as simplified structural variants of SO, we have considered reactions leading to formation of such compounds in situ. In our group it was found that some pyrazine based bisdithiolene complexes undergo stepwise oxidative ageing either in water solutions (fast) or in the solid state (slow). The progress of such reactions could be monitored by UV–Vis or mass spectroscopy (the later preferably for the solid powders). Other intriguing aspects that deserve, in our opinion, a detailed study, are the structural features that control the geometry and, consequently, the catalytic activity of a model compound. For instance, it was shown that the bite angle of the stabilizing ligand and dihedral angle of a dithiolene had a crucial influence on the oxidation state of the molybdenum active site [3]. Thus, we designed a number of complexes in attempt to approach the redox potentials of SO by tuning the geometry of the models