Copper(II) Complexation by Hydrophobic Single- and Double-Alkyl Chain Ligands Solubilized in Ammonium Surfactant Vesicles

Copper complexation by hydrophobic ligands solubilized in vesicular systems has been studied as a means to carry out selective metal extraction and decontamination of aqueous effluents. The vesicular systems were constituted of dimethyldi-n-alkylammonium bromides with the alkyl chains being octadecyl (DODAB), hexadecyl (DHAB), or dodecyl (DDAB). The rate of complexation with a single-chain ligand, 6-[(hexadecylamino)methyl]-2-(hydroxymethyl)pyridine (C(16)NHMePyr), and a double-chain one, 6-[(di-n-dodecylamino)methyl]-2-(hydroxymethyl)pyridine (diC(12)NMePyr), was investigated by the stopped-flow technique. The results have shown that rigidifying the amphiphilic layer, compared to those of classical micelles, does not reduce the rate of complexation and that the melting of the alkyl chains (gel to fluid transition) has the result of decreasing the rate, but only as far as double-chain ligands are concerned. The observation of two kinetic processes in some cases is discussed in relation with the problems of lateral diffusion and flip-flop kinetics. The effective removal of copper ions was controlled by ultrafiltration of the vesicles containing the metal/ligand complexes. The yield of copper extracted was found to be lower than that with classical micelles under similar conditions, and only low metal content could be used due to stability problems (osmotic stress).