In this work, we investigate the stability of two different Zr 4+ -chelator complexes in aqueous solution by means of Molecular Dynamics (MD) simulations which allow for a realistic sampling of both the conformational fluctuations of the chelator and the solvent environment. Specifically, the MD simulations allow for exploring the thermodynamics of the chelating complex where the solvent and temperature effects are included in a realistic manner. The two considered chelators are Deferoxamine-B (DFO) and 4HMS 1 (N1,N5,N10,N14-tetra(Nhydroxy-N-methyl-1,4-dioxo-5-azapentyl)-1,5,10,14-tetraazatetradecane) which has recently been proposed in the literature 1 as a potential chelator of Zr 4+ due to the presence of eight coordination sites. DFO and 4HMS are schematically shown in the left and right panels of Fig. . The metal binding ability of these two chelators is heavily influenced by their hydroxamate groups highlighted in red in Fig. . DFO has three hydroxamate groups allowing in principle, six oxygen atoms for coordination with Zr 4+ . On the other hand, 4HMS has four hydroxamate groups increasing the possible coordination with Zr 4+ to eight.