Active Site of Allantoic Purple Acid Phosphatase and a Model Complex for Strongly Coupled Diiron Sites

Magnetic susceptibility determination is able to make powerful structural predictions for the porcine allantoic purple acid phosphatase which is shown to be a diiron enzyme and for the model complexes of type [Fe(cbpN)]2O, which have the same magnetic properties. The presence of the diiron active site in the purple (oxidized) form of the phosphatase is shown by the very low magnetic susceptibility, which can only be attributed to very strong magnetic coupling between two Fe(III) species, and given the absence of any other plausible bridging group, the site can be assigned as Fe-O-Fe. The model complex [Fe(cbpN)]2O is shown to have this specific site by X-ray crystallography. This complex is also the first example of a central Fe-O-Fe linkage which can be reversed by heating in vacuo or by dissolving in dimethylacetamide. The reduced stability of the Fe-O-Fe linkage is presumably due to the steric strain enforced by the bulky cbpN ligands. © 1983 American Chemical Society