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.