Studies on the chelation of aluminum for neurobiological application

The formation and strength of chelation of A1(III) with salicylic acid (SA), citric acid (CIT), ethylenediaminetetraacetic acid (EDTA), ethylenediamine-di-(o-hydroxyphenylacetic acid) (EDDHA), N,N'-di-(2-hydroxybenzyl)ethylenediamine-N,N'-diacetic acid (HBED), and some mixed ligand systems consisting of the above ligands were examined at an ionic strength of 0.12 M NaCl and 25.0 +/- 0.1 degrees C. All the ligands under consideration form strong chelates with A1(III). The order of the stabilities (log KML) of their A1(III) chelates are SA (13.7) less than EDTA (15.3) less than CIT (18.0) less than EDDHA (24.5) approximately equal to HBED (24.8). An equilibrium analysis of the A1(III)-SA (1:1), A1(III)-CIT (1:1) and A1(III)-SA-CIT (1:1:1) systems indicated the occurrence of hydrolysis and polymerization reactions in each one of them. The A1(III)-EDTA (1:1) chelate was found to undergo hydrolysis even at pH 5. However, EDDHA and HBED each formed a very stable mononuclear chelate with A1(III) and did not show hydrolytic or polymerization tendencies.