Determinação das constantes de estabilidade dos complexos formados entre os aminoácidos cisteína, cistina, ornitina e lisina com alumínio em solução aquosa

Abstract

The complex formation between aluminium and the amino acids ornithine, lysine, cysteine and cystine was evaluated by means of potentiometric titration. The titration was carried out in aqueous solution with constant ionic strength (KCl) and at 25,0 ± 0,1°C. The stability constants were calculated with the computational program BEST, specially designed for the calculation stability constants. The analysis of the results showed that the predominant species in solution were found with a proportion metal:ligand 1:1.The constants found for the Al-amino acid complexes presented the following stability: lysine < cysteine < cystine < ornithine. In order to confirm the interaction between aluminium and the amino acids cystine and cysteine polarographic measurements and experiments with ion-exchange resins were also carried out. The results confirmed the interaction and the stability of the complexes. In these experiments, the interaction increased following the same order: lysine < cysteine < ornithine < cystine.