Uniting Sequence, Structure, and Function in Amphiphilic Di(phenylalanine)-Based Copolymers for Rare Earth Element Sequestration

Sequence, structure, and function are inherently intertwined. While well-established relationships exist in proteins, they are more challenging to define for synthetic polymer nanoparticles due to their molecular weight, sequence, and conformational dispersities. To explore the impact of sequence on nanoparticle structure and function, we synthesized a set of sixteen compositionally identical, yet sequence distinct, block copolymers comprising dimethyl acrylamide and a bioinspired, structure-driving di(phenylalanine) acrylamide (FF) monomer. Systematic analysis of global (tertiary- and qua-ternary-like) structure in this amphiphilic copolymer series revealed the effect of multiple sequence descriptors. The number of blocks, the hydropathy of terminal blocks, and the patchiness (density) of FF within a block impacted both chain collapse and the distribution of single- and multi-chain assemblies. Further, both the conformational freedom of chain segments and local-scale, β-sheet-like inter-actions were sensitive to the patchiness of FF. To connect sequence, structure, and a target function, we evaluated an additional series of nine sequence-controlled copolymers as sequestrants for rare earth elements (REEs) by incorporating a functional acrylic acid monomer into polymer scaffolds, guided by the original series. We identified key sequence variables that influence the binding affinity, capacity, and selectivity of polymers for REEs. Collectively, these results highlight the potential of sequence control to tune the hierarchical structures and ultimately dictate the functionality polymeric materials, without altering composition.