Tunable biopolymers for heavy metal removal

Tunable biopolymers were synthesized for the removal of heavy metals from dilute waste streams. Protein-protein interaction was tailored specifically into tunable, metal-binding biopolymers using elastin-like polypeptides composed of either one or two hexahistidine clusters. These tunable biopolymers retained the functionality of the elastin domain, undergoing a reversible phase transition above the transition temperature. Aggregation could be tuned within a wide range of temperatures by controlling the chain length of the biopolymers. The presence of the histidine clusters enabled Cd2+ to bind strongly to the biopolymers. Recovery of biopolymer-Cd2+ complexes was easily achieved by triggering aggregation either by raising temperature or by salt addition. Regenerated biopolymers could be reloaded with Cd2+ and reused for repeated cycles with similar efficiency. This system is very flexible as both domains can be engineered to respond to various phase transition conditions and to provide various levels of metal-binding selectivity. The ability to modulate the properties of the biopolymers simply by tuning process conditions should open up new opportunities for the separation and recovery of other environmental contaminants.