Potentiometric study of complexes formed between (s)-α-amino-3-hydroxy-5-methyl-4-isoxazolepropanoic acid and some transition metal ions

Abstract

Potentiometric study has been carried out on (S)--amino-3-hydroxy-5-methyl-4-isoxazolepropanoic acid [AMPA] in the presence of transition metal ions to measure the thermodynamic stabilities of its complexes; and hence give an insight into its possible role in binding metal ions. The nitrogen donor atom of AMPA is alanine-like with the addition of a hydroxy-isoxazole ring. The first complex [CuHL], which is fully formed by pH 4 is proposed to be with {N,O} bonding which results in the formation of a stable five membered chelate ring. The [CuL] species has some enhanced stability which suggest some form of tridentate co-ordination through {H₂N, COO^-, O^-}. When this changes to [CuL₂], one of these bonds must be broken if Cu(II) is to have a maximum co-ordination number of four. Zn and Cd formed very similar comlexes with AMPA, these were [ZnHL], [ZnL], [ZnL₂] and [CdHL], [CdL], [CdL₂], respectively. [ZnL] and [ZnL₂] are significantly more stable than alanine, suggesting tri-dentate co-ordination. [CdHL] complex is again very important suggesting some bidentate chelation.

KEY WORDS: (S)-a-Amino-3-hydroxy-5-methyl-4-isoxazolepropanoic acid, Transition metal ions, Thermodynamic stability constants, Potentiometry, Speciation

Bull. Chem. Soc. Ethiop. 2003, 17(1), 45-51.