Synthesis and characterization of short-chain peptides for use in metal remediation and preconcentration
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Designing materials for metal remediation and preconcentration based on naturally occurring metal binding proteins has become of growing interest due to their inherent selective and strong binding, ease of synthesis and available amino acid building blocks, and environmental innocuity. One approach is through the use of immobilized synthetic biohomopolymers which can provide the selectivity based on the amino acid side chain moiety with strong binding, easy on-demand release, and reusability. An attempt to increase metal binding selectivity of these biohomopolymers was done though cross-linking at specific locations as to effectively “lock” in place the preferential binding cavity for a particular metal. The cross-linking of these materials resulted in decreased metal capacities with little to no increases in the targeted metal selectivity. This was likely due to the loss of bound metal during cross-linking and to a lack of rigidity in the overall cross-linked polymer. Short composite peptides synthesized on a commercially available resin, TentaGel were also examined as a means to increase metal selectivity. These peptides showed surprisingly high metal binding capacities, strong binding, and residue per metal binding ratios which were an order of magnitude better than results previously reported for longer chain poly-amino acids (50 – 70 residues) attached to porous glass supports. Metal binding selectivity’s were altered by changing only one amino acid and metal release under acidic conditions was surprisingly rapid for these shorter peptides. As a result of these findings, the metal binding and conformational changes between TentaGel immobilized short and long peptide chains during metal binding and release were monitored using Raman microscopy. These results indicated that metal release occurred via conformational changes in addition to proton displacement. Lastly, a method to screen multi-metal binding capabilities of combinatorial peptide libraries was developed using electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS). With the exception of metals that are bound tightly to the peptide, acid stripping of the metals in a single bead into a small volume appears as a viable quantitative analytical approach when using this method with instrumental precisions of better than ±10% for most metals when larger polymer beads (~250 µm) were employed.