We first performed a 1µsec MD simulation of Zr 4+ -DFO complex in water at room temperature, choosing as the initial configuration, the DFT optimized structure from Ref. 22 with six-fold coordination. This structure was then solvated with over 3000 water molecules and subject to energy minimization. Besides the six-fold coordination involving the hydroxamate groups, two coordinating trans-oriented oxygen atoms from water molecules were found in our optimized structure, consistent with the findings of Holland and co-workers. Starting from this minimized structure, we initiated molecular dynamics simulations at 300K. In order to track the dynamic evolution of the hydroxamate groups coordinating the Zr 4+ we built a variable, CN , mathematically defined in equation 3 in the Methods section, which essentially counts the number of oxygen atoms belonging to the DFO hydroxamate groups that are coordinated to Zr 4+ . Note that CN does not include oxygen atoms arising from coordinating water molecules which will be addressed separately. In this way, the CN can be used to quantify changes in the contribution of the hydroxamate groups to the first coordination sphere of the Zr 4+ cation over the course of the molecular dynamics simulation.