Synthesis and electrochemistry of biodegradable ligands - iminodiglutaric acid and iminoglutaricsuccinic acid - and their complexes with selected metal ions (Zn²⁺, Cd²⁺, Cu²⁺)

[摘要] ENGLISH ABSTRACT:Two new potentially biodegradable aminopolycarboxylic acid ligands, iminodiglutaricacid tetra sodium salt (IDG-4Na) and iminoglutaricsuccinic acid tetra sodium salt (IGS-4Na), were synthesized in reasonably good yield and purity. The commerciallyunavailable precursor for the two ligands, ethyl p-aminoglutarate, was synthesised in highyield and purity, and together with the two ligands were fully characterized by means ofmelting point measurements and various spectrometric techniques CH-NMR, 13C-NMR,MS and IR).For the first time, an electrochemical study has been conducted on the complexes of theseligands with selected transition metal ions (Zn2+, Cu2+ and Cd2+). An electrochemicaltechnique, cyclic voltammetry (CV), was utilized on the study of the complexing abilityof the ligands to the selected metal ions. An electrochemical cell comprising threeelectrodes was employed: thin film mercury coated carbon microelectrode was used asthe working electrode, a Platinum wire as the auxiliary electrode, and a Ag/AgCI as thereference electrode.CV has been used and proven to offer a convenient route towards the determination ofmetal-ligand complex stability constants in aqueous media. The values of the logarithmsof the metal-ligand formation constants obtained by this technique, when compared withother widely used aminopolycarboxylic acids (APCAs), show better complexing abilityof the ligands with the transition metal ions. When the two ligands are compared, IGSshowed greater affinity towards the selected transition metal ions. This is due to the factthat, in aqueous media, as the side chain ligators decrease, the stabilization energy of thecomplex increases. The formation stability constants were determined by plotting thechange in the reduction potential (ΔE) against solution pH. A process making use of amodification of lingane equation was used.

[发布机构] Stellenbosch University