Folding triblock copolymers: consequences of block sequence on the folding structure

Mimicking protein folding by synthetic polymers recently attracted a lot of interests because of its promising potential for biomimetic applications such as artificial enzymatic systems. To explore the possibility of man-made folding polymers, single-chain folding of synthetic polymers using supramolecularly interacting motifs has been developed. Here we synthesized ABA- and BAB-type triblock copolymers possessing pendant self-assembling motifs in each block, where benzene-1,3,5-tricarboxamide (BTA) (Figure 1a) and 2-ureidopyrimidinone (UPy) (Figure 1b) are incorporated in the A and B block, respectively (Figure 1c).

During the folding process, the selected motifs organized into individual helical and dimeric aggregates in an orthogonal fashion, resulting in the final folding structure. Since the ABA- and BAB-type triblock copolymers have chemically identical structure, they are expected to form the same secondary structures (BTA helix and UPy dimer), but may give a different global conformation.

The folding process of the triblock copolymers was monitored by size-exclusion chromatography (SEC) and circular dichroism (CD) spectroscopy. The microstructure of the synthesized single-chain polymeric nanoparticles was imaged by atomic force microscopy (AFM). From the SEC measurements, we found that the block sequences of the folding copolymers do affect the global conformation of the block copolymers in solution (Figure 2). In the presentation, we will discuss differences in folding behavior between ABA- and BAB-type polymers.