Stabilization of cationic aluminum hydroxide clusters in high pH environments with a CaCl/l-arginine matrix.

We present a way of stabilizing cationic partially hydrolyzed aluminum clusters in a non-acidic environment, through Ca2+ and l-Arginine doping. The Keggin Al13-mer (ε-AlO4Al12(OH)24(H2O)127+) aluminum cluster can be stabilized with CaCl2 and l-arginine in a way to preserve the metal clusters. We use size-exclusion chromatography (SEC) and 27Al nuclear magnetic resonance (NMR) spectroscopy to demonstrate that positively-charged Keggin structures are preserved and that the conversion to Al(OH)3 materials is halted even at alkaline pH. The system serves to stabilize acidic Al clusters in alkaline or neutral conditions, while preserving their inherent cationic behavior.