Instantaneous, stoichiometric generation of powerfully reducing states of protein active sites using Eu(II) and polyaminocarboxylate ligands

Addition of an equivalent of a polyaminocarboxylate ligand (L) to a solution of a redox protein and the aqua Eu2+ ion results in the instantaneous in situ generation of a very powerful reductant Eu-II-L that can rapidly drive an electron stoichiometrically onto a redox centre having an extremely negative reduction potential ( lower than -1 V): this is exemplified by straightforward generation of the superreduced state of the Fe-protein of nitrogenase.