Stabilization of cationic aluminum hydroxide clusters in high pH environments with a CaCl2/l-arginine matrix

Abstract

We present a way of stabilizing cationic partially hydrolyzed aluminum clusters in a non-acidic environment, through Ca²⁺ and L-Arginine doping. The Keggin Al_13-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.