Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session K59: Designing Biomacromolecules for Materials AssemblyInvited
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Sponsoring Units: DPOLY DBIO Chair: Darrin Pochan, Univ of Delaware Room: LACC Petree Hall D |
Wednesday, March 7, 2018 8:00AM - 8:36AM |
K59.00001: Computational design of peptidic materials Invited Speaker: Jeffery Saven Biopolymers open routes to well structured, highly functional materials. The programmability available with sequence-specific biopolymers opens new frontiers in the development of polymer-based materials. Herein we focus on the design of assembling peptides, which require the subtle engineering of noncovalent as well as covalent interactions. Theoretical and computational methods accelerate the identification of amino acid sequences consistent with desired structures and functions. The methods leverage concepts from statistical mechanics and address the structural complexity of proteins and their many possible amino acid sequences. Computationally designed peptide-based systems include self-assembling materials having well-defined lattice structures, linear nanostructures of variable rigidity, and composites comprising peptides and nanoparticles. |
Wednesday, March 7, 2018 8:36AM - 9:12AM |
K59.00002: Designed Protein Cages: Theory and New Applications to Cryo-Electron Microscopy Scaffolding Invited Speaker: Todd Yeates By exploiting principles of symmetry that are shared by nearly all natural self-assembling structures, methods have been developed for engineering novel proteins that assemble to form a variety of complex, symmetric architectures. Recent successful designs include hollow protein cages composed of many identical subunits in cubic arrangements. Symmetric materials that extend by growth in two or three dimensions are also possible. These designed protein structures and materials offer new prospects for applications in fields ranging from synthetic biology to biomedical applications. In a new application area, we are exploiting designed protein cages for cryo-EM imaging. Recent breakthroughs in cryo-EM instrumentation and software have made it possible to image large protein assemblies at near-atomic resolution, but resolving the structures of proteins of ordinary size (typical of cellular proteins) has not been possible. Our new work shows how designed protein cages can overcome this critical barrier by serving as scaffolding to array other target proteins for imaging. Design principles and recent results will be discussed. |
Wednesday, March 7, 2018 9:12AM - 9:48AM |
K59.00003: Thermoresponsive Colloidal Molecules with Tunable Directional Interactions Invited Speaker: Peter Schurtenberger Small clusters assembled from spherical colloids that resemble space-filling moleculular models, so-called colloidal molecules, have emerged as highly interesting model systems in soft matter physics. Here we demonstrate that we can fabricate colloidal molecules with a well-defined number of binding sites and externally tuneable interactions. This is achieved by using microgels based on the temperature-responsive polymers poly-N-isopropylacrylamide (PNIPAM) or poly-N-isopropylmethacrylamide (PNIPMAM) as building blocks, which are then assembled into well-defined small clusters. The use of pNIPAM and pNIPMAM microgels allows for easy manipulation of the interactions between the resulting colloidal molecules via temperature, as the interaction potential between individual microgels changes from soft repulsive below the volume phase transition temperature (VPTT) of the microgels to attractive for T > VPTT. We will present different approaches to fabricate colloidal molecules, and demonstrate that microgel-based colloidal molecules represent an interesting class of colloidal building blocks with the potential to reversibly form complex structures and materials through temperature-tuneable directional interactions. |
Wednesday, March 7, 2018 9:48AM - 10:24AM |
K59.00004: Materials Science & Nanotechnology with Protein Nanofibrils Invited Speaker: Raffaele Mezzenga Protein fibrils are protein aggregates, which can be generated from food-grade proteins by unfolding and hydrolysis. The resulting protein fibrils can be used in a broad context of applications. At length scales above the well-established atomistic fingerprint of amyloid fibrils, these colloidal aggregates exhibit mesoscopic properties comparable to those of natural polyelectrolytes, yet with persistence lengths several orders of magnitude beyond the Debye length. This intrinsic rigidity, together with their chiral, polar and charged nature, provides these systems with some unique physical behavior. In this talk I will discuss our current understanding on the mesoscopic properties of amyloid fibrils at the single molecule level, the implication of their semiflexible nature on their liquid crystalline properties, and I will illustrate how this information prove useful in understanding their collective behavior in bulk and when adsorbed at liquid interfaces. By the careful exploitation of the physical properties of amyloid fibrils, the design of advanced materials with unprecedented physical properties become possible, and I will give a few examples on how these systems can ideally suit the design of biosensors, biomaterials, cellular scaffolds, catalytic and water purification membranes and even shuttles for in-vivo bioavailable nanostructured iron, with a real-cost-effective return, making them promising candidates for building blocks in advanced materials and state of the art nanotechnologies. |
Wednesday, March 7, 2018 10:24AM - 11:00AM |
K59.00005: Conformational switching in chiral self assembly Invited Speaker: Zvonimir Dogic In the presence of a non-adsorbing polymer, monodisperse rod-like particles assemble into colloidal membranes, which are one rod-length thick liquid-like monolayers of aligned rods. We investigated liquid-liquid phase separation in a highly simplified system of colloidal membranes. The bulk phase separation of dissimilar rods is inherently unstable giving way to assembly of finite-sized highly monodisperse colloidal rafts. In membranes composed of rods of opposite chirality the rafts interact by universal long-ranged repulsive interactions. We studied the behaviour of colloidal rafts dissolved in a background membrane composed of achiral rods and find significantly more complex behaviours. In particular, in this limit we observed that rafts can acquire both long-ranged repulsive interactions as well as short-ranged attractions. The change in these effective membrane-mediated interactions is accompanied by the conformational change of the raft structure, wherein they switch their chiral twist. We quantified raft-raft repulsive interactions and correlated them to raft-induced membrane distortions. At high densities colloidal rafts with conformational degrees of freedom can assemble into a number of higher-order structures of increasing complexity. Amongst others these include highly regular trimers, tetramers as well an exotic square crystals comprised of two interdigitated lattices of colloidal rafts of opposite chirality. |
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