Thiolate-S as anchoring donor in the binary and ternary VO(IV) complexes of mercaptopropionylglycine

The speciation and solution structures of the binary VO(IV) complexes of mertcaptopropionylglycine and its ternary complexes with 2,2′-bipyridyl, tiron, maltol and oxalic acid were studied by pH-potentiometric and spectroscopic (EPR and UV–Vis) methods. The thiolate-S− donor of mercaptopropionylglycine proved to be an efficient anchoring donor which binds VO(IV) strongly enough to be able to promote deprotonation and subsequent coordination of the peptide–amide group. Ternary complex formation and the promotion of amide deprotonation were found to be favoured with the (N,N) donor 2,2′-bipyridyl, but disfavoured with the (O,O) donor ligands tiron, maltol and oxalic acid.