Characterization of Immobilized Poly-l-aspartate as a Metal Chelator

• Published in: Environmental science & technology 1999-05, Vol.33 (10), p.1664-1670
• Main Authors: Gutierrez, Elizabeth, Miller, Thomasin C, Gonzalez-Redondo, Jose R, Holcombe, James A
• Format: Article
• Language: English
• Subjects: Aminoacid polymers; Applied sciences; Chemical elements; Environmental cleanup; Exact sciences and technology; Ions; Metals; Physicochemistry of polymers; Synthetic biopolymers
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es981166r

Poly-l-aspartic acid (PLAsp), which consists of ca. 50 Asp residues in a linear polypeptide, has been immobilized on controlled pore glass (CPG) and evaluated for its selectivity and binding strength in the complexation of metal ions from aqueous solutions. The carboxylate side chain of Asp (pK a = 5.4 ± 0.2) is thought to be primarily responsible for chelation of the target metals. Of the several metals evaluated, Eu3+, Ce3+, La3+, Cu2+, and Pb2+ exhibited good binding capacities. Quantitative determination of single-element capacities were determined for Cu2+ (12 ± 1 μmol/g PLAsp-CPG) and La3+ (7.1 ± 0.3 μmol/g PLAsp-CPG). Isotherms were constructed from breakthrough curves using a flow injection system. These curves were used to evaluate the effective site capacity and formation constants. A combination of moderate and strong binding sites for Pb2+ was detected, while moderate binding of Cd2+ was observed with a minimal number of strong binding sites. Several cations showed little to no binding by PLAsp-CPG (e.g., Na+, Ca2+, Mg2+, Mn2+, Co2+, and Ni2+). Propensity for metal binding seems to follow the trend seen for binding to carboxylates in such ligands as acetate. The polydentate binding available from the polypeptide chain significantly enhanced the binding strength with equilibrium constants in excess of 108 observed for the strong binding sites. The binding selectivity was complementary, in many cases, with the results previously reported for poly-l-cysteine immobilized on CPG.