The stability of the Keggin polycation epsilon-Al-13 is monitored by Al-27 NMR. and ferron colorirnetric assay upon heating aluminum aqueous, solutions containing different amino acids with overall positive, negative, or no charge at pH 4.2.. A focus on the effect of the amino acids on the isomerization prbceSs from epsilon- to delta-Al-13 is made, compared and discussed as a function of the type of organic additive. Amino acids such as glycine and beta-alanine, with only one functional group interacting relatively strongly with aluminum polycations, accelerate isomerization in a concentration-dependent manner. The effect of this class of amino acids is also found increasing with the plc of their carboxylic acid moiety, from a low impact from proline up to more than a 15-fold increased rate from the stronger binders such as glycine or beta-alanine. Amino acids with relatively low C-terminal pK(a), but bearing additional potential binding Moieties such as free alcohol (hydroxyl group) moiety of serine or the amide of glutamine, speed the isomerization comparatively and even more than glycine or beta-alanine, glutamine leading to the fastest rates observed so far. With aspartic and glutamic acids, changes in aluminum speciation are faster and significant even at room temperature but rather related to the reorganization toward slow reacting complexed oligomers than to the Al-13 isomerization process. The linear relation between the apparent rate constant of isomerization and the additive concentration points to a first-order process with respect to the additives. Most likely, the dominant process is an accelerated epsilon-Al-13 dissociation, increasing the probability of delta isomer formation.