High proton mobility with the Aluminum ion on the surface of water cluster
Three neighboring waters of Al3+ (pink) lost their protons shortly (~50 fs) after cation has been artificially moved to the surface of the water cluster.
The lower coordination of aqueous aluminum ion facilitates its hydrolysis.
After equilibration at room temperature, the one proton was found to shuttle between hydrated water and the water in a second solvation shell. While two other protons left first solvation shell and become engaged in exchange of the protons through the hydrogen bonds of the solvent. Although this ''surface'' structure of aqueous aluminum is artificial construction, it clearly demonstrated the crucial role of the coordination of Al3+ in its hydrolysis. Mobile hydrogens are green in this snapshot.
Ab initio molecular dynamics of aluminum solvation
by Mark I. Lubin and John H. Weare, UCSD