Cadmium, copper and zinc complexes of poly-L-cysteine

Abstract

The metal complexes of poly-L-cysteine (PLC) were evaluated for their potential use in trace metal preconcentration and separation. Formation constants (log K) for the Cd²⁺ and Zn²⁺ complexes of PLC estimated by spectrophotometric titration were 8.0 ± 0.8 and 9.5 ± 0.5, respectively. The PLC sulfhydryl groups were most likely oxidized to disulfides by Cu²⁺, and binding of Cu⁺ with the molecule was expected. The moles of metal bound by PLC reflecting its strongest sites relative to a stable competing ligand for Cu²⁺ and Zn²⁺ were 1.4 and 0.40 mmol g^–1 of PLC, respectively. The presence of Na⁺(29 mmol l^–1) or Ca²⁺(0.5 mmol l^–1) had no measurable effect on the amount of Zn-PLC complex formed.