Programmable nanomaterials development via kinetically controlled self-assembly of computationally designed peptides
Date
2018
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Publisher
University of Delaware
Abstract
Self-assembly is a spontaneous organization process of components into patterns and structures driven by weak, non-covalent interactions. Well-studied examples are amphiphilic molecules such as surfactants and amphiphilic block co-polymers. Although a significant number of successful examples have been demonstrated for the production of self-assembled materials with various morphologies, the intrinsic polydispersity in chemical structures and chain conformation limits the complexity that can be achieved via the self-assembly of these types of molecules. Therefore, sequence- and shape-specific biomacromolecules, such as polypeptides and polynucleotides, provide a better opportunity to produce complex nanoarchitectures with programmability. ☐ In the collaborative work presented in this Ph.D. dissertation, a computational design method is established by Saven group (University of Pennsylvania) to generate a group of 29-mer peptide sequences that were predicted to form robust, antiparallel, alpha-helical homotetrameric coiled-coil bundles as materials building blocks. The designed peptide coiled-coil bundles share the same interior bundle composition consisting of complementary hydrophobic amino acids for bundle stability in aqueous solution. The bundle exterior composition was varied to implement directional interactions at bundle-bundle interfaces on the basis of various predetermined space groups (P622, P422 and P222) to achieve two-dimensional, self-assembled lattices with programmability. Peptides were synthesized via solid-phase peptide synthesis method and the successful programmable self-assembly behavior are experimentally confirmed. Moreover, the solution condition-dependent self-assembly behavior and the related kinetically controlled assembly pathways for two-dimensional sheet formation were investigated for two groups of designed peptides, including P422 and P222 sequences. The designed hydrophobic bundle core ensures the structure stability to tolerate non-physiological conditions which were applied in the kinetic manipulation processes. Specifically, the solution pH was used to control the charged state of amino acid residues in the exterior part of the coiled-coil bundles thus tuning the inter-bundle interactions. A general pI (isoelectric point)-dependent rule is introduced that peptides exhibit fast assembly kinetics in the pH conditions that are close to the pI values at which peptides carry the least charge. Classic thermal annealing methods can be applied to overcome the possible kinetic traps existing during the assembly process. In the pH conditions that are deviated from the pI values of the sequences, more diverse nanoarchitectures with controllable morphologies, other than the originally designed 2D nano-lattices, were successfully produced, triggered by the differently charged states of peptide bundles in these conditions. Moreover, the self-assembled peptide nanoarchitectures were applied as scaffolds to template the growth of gold nanomaterials. Due to the specific peptide templates, the synthesized gold nanoparticles are organized into 1D or 2D nanostructures exhibiting enhanced surface plasmon resonance properties. Future research should dive into the detailed processing study of the templated synthesis of gold nanoparticles for the development of functional devices as well as co-assembly study with the use of multiple peptide sequences for the production of multi-component, complex nanoarchitectures.