Table of Contents
Metal-Based Drugs
Volume 8, Issue 5, Pages 235-248
http://dx.doi.org/10.1155/MBD.2002.235

Solution Equilibria between Aluminum(III) Ion and L-histidine or L-tyrosine

1Faculty of Science, Institute of Chemistry, P.O. Box 60, Kragujevac 34000, Serbia and Montenegro
2Copper and Aluminium Smelting Factory, Sevojno, Uzice 31000, Serbia and Montenegro

Received 8 November 2001; Accepted 21 November 2001

Copyright © 2002 Hindawi Publishing Corporation. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Toxic effects due to high aluminum body loads were observed in a number of conditions following ingestion of Al-containing antacids. Bio-availability of aluminum depends not only on the solubility of the ingested salt but also on the physico-chemical properties of the soluble Al complexes formed in body fluids. Amino acids may, upon interaction with Al-salts, form absorbable Al-complexes. Hence, complex formation equilibria between Al3+ and either, L- histidine or L-tyrosine were studied by glass electrode potentiometric (0.1 mol/L LiCl ionic medium, 298 K), proton NMR and uv spectrophotometric measurements. Non linear least squares treatment of the potentiometric data indicates that in the concentration ranges: 0.5CAl2.0 ; 1.0CHis10.0 ; 2.5PH6.5 , in Al3+ + His solutions, the following complexes (with log overall stability constants given in parenthesis) are formed: Al(HHis)3+(12.21±0.08) ; Al(His)2+ , (7.25±0.08); and Al(HHis)His2+ , (20.3±0.1) . In Al3+ + Tyr solutions in the concentration range 1.0CTyr3.0 mmol/L and ligand to metal concentration ratio from 2:1 to 3:1, in the pH interval from 3.0 to 6.5 the formation of the following complexes was detected: Al(HTyr)2+ , (12.72±0.09); Al(Tyr)2+ , (10.16±0.03) and Al(OH)2Tyr , (2.70±0.05) . Proton NMR data indicate that in Al(His)2+ complex histidine acts as a monodentate ligand but its bidentate coordination is possible with carboxylate oxygen and imidazole 1-nitrogen as donors. In Al(HTyr)3+ complex tyrosine is a monodentate ligand with carboxylate oxygen as donor. The mechanism of the formation of complexes in solution is discussed as well as their possible role in aluminum toxicity.