Poly(l-lysine) as a polychelatogen to remove toxic metals using ultrafiltration and bactericide properties of poly(l-lysine)-Cu2+ complexes

Poly(l-lysine) is a water-soluble, synthetic polypeptide containing functional amine groups that help remove di- and trivalent metal ions from aqueous solutions. This polymer's removal properties were studied under different experimental conditions: (1) competitive and non-competitive conditions; (2) different pHs; and (3) filtration factors. Under the conditions of the Liquid-Phase Polymer-Based Retention (LPR) technique, the cooper (II) ion interaction was found to be selective and efficient when compared to other divalent metal ions studied. However, interestingly, this selectivity disappeared when trivalent metal ions were present. The polymer-metal ion interactions are based on the amino groups of the side-chains as well as the polypeptide backbone chain. The removal of metal ions was strongly dependent on the pH. By structural characterization with FT-IR and EPR spectroscopy, participation of the amide and mainly amine groups was found to take place for the coordination. For the Cu2+, coordination through four amine nitrogen donor atoms in the primary coordination sphere was detected. Antibacterial activity tests were conducted with the poly(l-lysine)-Cu2+ complex and showed a higher activity in comparison with the precursors Cu2+ and poly(l-lysine) at the same concentrations for E. coli (6538P), a Gram-negative bacterium, and S. aureus (ATCC), a Gram-positive bacterium.