Kinetics and mechanism of the complex formation reactions of diaqua(ethylenediamine)- and diaqua(tetraethylenediamine)palladium(II) with the purine nucleosides adenosine and inosine

Complex formation between the diaqua palladium(II) complex of ethylenediamine and adenosine or inosine is a two-step process. The reaction rate depends on the nucleoside concentration and, in the case of adenosine, on the pH level. The adenosine complex is less stable than the inosine complex, probably due to exocyclic amine (6-NH2) group interference. Steric hindrance is more pronounced with the inosine complex, where N(1) is already coordinated to the metal center and only N(7) is available for the other moiety. The mechanism therefore involves more of an associative ligand substitution, as indicated by the activation parameters.