In Nature, protein self-assembly into one dimensional (1D), 2D and 3D structures creates materials exhibiting complex functions due to the high information content of the protein sub-units. Developing synthetic systems for which self-assembly can be similarly programmed through interactions between sequence-specific domains, but for which stability and predictability of assembly are enhanced, is critical to realizing bioinspired materials with similarly complex functions. Peptoids are a class of biomimetic sequence-defined polymers that assemble into 1D, 2D and 3D structures depending on the choice of sequence. In this research, we investigate the impact of introducing cyclodextrin headgroups into amphiphilic sequences that otherwise self-assemble into 2D materials by using <i>in situ</i> AFM to observe the pathway and dynamics of assembly in real time. We find that, on mica surfaces at low pH, these peptoids still assemble into 2D membrane-like structures, but rather than growing through the birth and spread of flat 2D islands as observed for small hydrophilic headgroups, the addition of the bulky cyclodextrin headgroup leads to formation of highly convoluted wormlike micelles that grow in length and coalesce to form a continuous 2D material with a uniform thickness of about 4 nm. At high pH and upon addition of Ca ions, assembly of this 2D material is followed by formation of cylindrical micelles many microns in length with uniform diameters that pack into bundles and cover the surface to form a complex 3D spaghetti-like architecture. In addition to altering the final peptoid architecture, increasing the pH leads to a decrease in the kinetics of assembly. When the mica substrate is replaced by SiO<sub>2</sub>, cylindrical micelles form in two steps, starting with deposition of spheroidal precursors that are presumably spherical micelles and transforming into cylindrical micelles on the surface. To understand the evolution of architecture and kinetics with these changes in substrate and solution chemistry, we consider the role of pH and Ca ion concentration in modifying interfacial energy through their impact on both the mica and peptoid surface charge. Because the addition of cyclodextrin provides a large cavity for host-guest chemistry, mastering assembly of the various hierarchical structures reported here offers the potential for a range of applications.

Controllable self-assembly of peptoid material

253rd National Meeting (2017)

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