[Petorin]

I was asked to make an estimation/prediction of the redox potential Fe(II)/Fe(III) alginate complexes:

Fe(II)-Alg  Fe(III)-Alg + e^-

As a physicist I struggle with this. I tried comparing to similar ligands, but even the smallest differences in the structure of the ligand seem to influence the potential. How can I be sure I pick the right one?

Thanks in advance!