Stimuli-responsive properties of peptide-based copolymers studied via directional growth of self-assembled patterns on solid substrate.

We studied the self-assembly of peptide-based ABA and CBC triblock-copolymers (obtained by bacterial expression) containing random coiled hydrophilic central B blocks flanked with helical A or C blocks. The A and C blocks were of different compositions with respect to the fraction of lysine residues which provided a higher pH sensitivity of the copolymer solutions. The interchain interactions of the copolymers driven by external stimuli (pH and temperature) were explored in the process of macromolecular self-assembling in the thin films of the copolymer solutions deposited on the solid substrate. The interactions involved in the macromolecular association affected the morphology of the developed patterns. The polypeptide of the B block was not involved in the formation of the secondary structures, while the A and C blocks demonstrated helical folding responsible for the intermolecular association. The mechanism of the responsive behavior of the copolymers is based on the reversible assembling of the helices into coiled-coil structures upon the change of pH or temperature. It was found that at low pH values, when electrostatic repulsion was strong and the A/C blocks unfolded, assembling yielded fractal dendrites. Increasing the pH resulted in the recovery of the helical conformation of the A/C blocks and caused a transition from the fractal to compact structures. An elevation of temperature resulted in the disruption of the dendritic structures. The reported here approach to the evaluation of the intermolecular interactions, based on the analysis of the dendritic patterns, provides a rapid and simple method for the characterization of complex processes of self-assembling biomacromolecules.