In a recent study, Alnahwi and co-workers showed that the 4HMS chelator presented improved chelating properties. Specifically, they found using both in vitro and in vivo studies, that the molar activity of 4HMS complexed with Zr 4+ is at least three times higher than that of DFO. In addition, by performing DFT calculations, they demonstrated that all of the eight oxygen atoms belonging to the four hydroxamate groups are bound to the Zr 4+ , with a distance less than 2.4 Å.