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

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.