Tuning the entropic spring: Self-assembly and fracture mechanics of polymer conjugated peptide nanotubes
Sinan Keten (Northwestern University), Luis Ruiz ()
Mechanics and Physics of Biological Cells
Tue 4:20 - 5:40
Barus-Holley 141
Cyclic peptide nanotubes (CPNs) consist of small, synthetic protein building blocks that form rings that self-assemble into rigid macroscopic nanotubes via inter-ring hydrogen bonding (Ghadiri et al., Nature, 1993). Conjugating CP rings with polymer chains has recently enabled formation of long individual nanotubes that can be coassembled in block copolymers into thin films with size-selective transport capability (Xu et al., ACS Nano, 2011). However, fundamental questions regarding the physical behavior of these self-assembling nanotubes are yet to be answered. Here we aim to form a unified theory explaining the assembly and mechanics of polymer conjugated CPNs. All-atom molecular dynamics calculations on the elastic modulus, free-energy landscapes, persistence length, fragmentation probability distributions, and constitutive relations provide important clues toward generating rectilinear, high-toughness CPNs through self-assembly (Ruiz & Keten, JEM, IJAM, 2012). Simulations validated by experiments show that is possible to generate CPNs with functionalized interiors for precisely defining the selectivity of molecules that can diffuse through the pores (Hourani et al., JACS, 2011). Polymer conjugation order and length are identified as two additional parameters that can be used to simultaneously tailor the length and rigidity of formed CPNs via entropic forces. A key observation is the apparent softening and destabilization of assemblies as conjugation order and length is increased, which we explain using theory and multi-scale simulations. We further show that disparate forces that emerge between peptides with different conjugation density can be utilized to control the stacking order of two different subunits purely by non-directional entropic forces. Our work illustrates the potential of theory and simulations for guiding the synthesis of bioinspired artificial ion channels with highly tunable properties.