Hydration Control Through Intramolecular Degrees of Freedom: Molecular Dynamics of [Cu(II)(Imidazole)₄]

Structural characterization of the copper-coordination shell is important in catalysis and biology. Cu-containing domains are prevalent in biological systems and play important roles in oxidation and electron transport process. Here, the solution structure, solvent organization, and dynamics around aqueous [Cu(II)(Imidazole) 4 ] were characterized using atomistic simulations. Asymmetric axial water coordination around the metal atom was found which agrees with results from Minuit X-ray absorption near-edge structure (MXAN) experiments. The simulations reveal that exchange of the axial water occurs on the 25 to 50 ps time scale and is facilitated by and coupled to the flexibility of the copper-out of plane motion relative to the nitrogen atoms. Both concerted and stepwise water exchange of the two axially coordinated water molecules with first-shell water molecules are observed. The results suggest that axial access of a copper center can be fine-tuned by the degree of flexibility of its first coordination sphere.