Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session B43: Polyelectrolyte Complexation I: Self-AssemblyFocus
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Sponsoring Units: DPOLY DBIO Chair: Samanvaya Srivastava, University of California, Los Angeles Room: LACC 503 |
Monday, March 5, 2018 11:15AM - 11:27AM |
B43.00001: Liquid-Liquid Phase Separation by Tau-Polyanion Complex Coacervation and Its Relationship to Amyloid Fibrillization. Yanxian Lin, Yuge Hu, Songi Han Complex coacervation of intrinsically disordered proteins and RNA has shown both biological and pathological significance in the human body. We report here recent findings and characterizations of complex coacervates of RNA and tau, the primary constituent of Alzheimer neurofibrillary tangles. We first show that coacervation is sensitive to ionic strength and temperature, with a strong dependence on the Coulombic properties of the polyanion. We further look into the driving force of such coacervation via investigating phase behavior with classical complex coacervation theories. Within the phase diagram boundary, we present a concentrated, fluidic and dynamic liquid phase via characterization using state-of-the-art spectroscopic techniques. Finally, we investigate the connection between such physical specifications with the propensity of tau amyloid fibrilization. |
Monday, March 5, 2018 11:27AM - 11:39AM |
B43.00002: Lyotropic behavior of polyelectrolyte complex micelles Martin In, Melody Mathonat, Anthony Phimphachanh, Philippe Dieudonné, Patrick Lacroix-Desmazes, Nathalie Marcotte, Corine Gérardin Upon pH stimulus, double hydrophilic block copolymers form polyion complexes (PIC) in the micellar form. We used PIC micelles as ecofriendly templates for the synthesis of ordered mesoporous materials. The porosity of the final material is revealed by simple inversion of the pH stimulus. Various mesoporous silica materials have been obtained from cubic to lamellar. |
Monday, March 5, 2018 11:39AM - 11:51AM |
B43.00003: Modeling Multivalent-Induced Structural Inhomogeneities in Polyelectrolyte Brushes Nicholas Jackson, Jing Yu, Xin Xu, Marina Ruths, Blair Brettman, Matthew Tirrell, Juan De Pablo The impact of multivalent salt ions on the morphologies of polyelectrolyte brushes is examined using coarse-grained molecular dynamics simulations, enhanced with free-energy sampling methods. Information derived from simulations is utilized to disentangle the interplay of multivalent and solvophobic effects present in collapsed Na(PSS) polyelectrolyte brushes. Simulations and experiments taken together in both the planar and surface forces apparatus geometries provide evidence for a distinction between the mechanisms of multivalency and solvophobicity in the collapsed brush morphologies, and emphasize the critical role of multivalent ion bridging interactions. The strongly heterogeneous collapsed surface structures observed experimentally are hypothesized to result from the interplay of multivalent and solvophobic effects. |
Monday, March 5, 2018 11:51AM - 12:03PM |
B43.00004: Structure and Properties of Complex Coacervate Core Micelles Taeyoung Heo, Inhye Kim, Eunji Lee, SooHyung Choi Complex coacervation is a liquid-liquid phase separation when two oppositely charged polyelectrolytes are mixed in an aqueous solution. Because of low interfacial tension and hydrophilicity, complex coacervate have been applied to the field of pharmacy and food industry. Complex coacervate core micelles (C3M) are formed by simple mixing of AB and A’B diblock copolyelectrolyte solutions in an aqueous solvent where A and A’ are oppositely charged blocks, and B is neutral and hydrophilic block (e.g., PEO). In this study, we investigate the structure of C3M as a function of molecular weight of charged block, pH, and salt concentration by dynamic light scattering (DLS) and small-angle X-ray scattering (SAXS). Since the charged moieties are introduced by post modification of mother block copolymers, the charge imbalance issue can be neglected. The results reveal that the relatively monodisperse C3Ms are formed by simple mixing, and overall micelle size and core radii reduce as salt concentration increases, and followed by disappearance of C3Ms above a critical salt concentration. In particular, we observed the scaling relationship between core dimension and molecular weight of charged block, which is analogous to traditional block copolymer micelles. |
Monday, March 5, 2018 12:03PM - 12:15PM |
B43.00005: Coacervate core micelles: Controlling size with polymer architecture Debra Audus, Brady Garringer, Hayley Boigenzahn The phenomenon of complex coacervation, where oppositely charged polymers in solution undergo liquid-liquid phase separation forming a polyelectrolyte-rich phase and a solvent-rich phase, can be harnessed to design inhomogeneous structures by controlling polymer architecture. Here we consider diblock copolymers composed of a charged block and a neutral-hydrophilic block. Under relatively dilute conditions, these polymers assemble into coacervate core micelles with a core composed of charged blocks and a highly solvated corona composed of neutral, hydrophilic blocks. As the core can encapsulate charged, hydrophilic drugs, unlike amphiphilic micelles, these micelles have been proposed as drug-delivery vehicles. For such applications, it is essential to understand the dependence of polymer architecture, specifically the charged block length, on the resulting micelle. We probe this dependency focusing on how the critical micelle concentration, core size, core density and corona size vary. We expect that understanding these dependencies will assist in the design of coacervate core micelles. |
Monday, March 5, 2018 12:15PM - 12:27PM |
B43.00006: Polyelectrolyte Complex Micelles: Formation, Dissociation, and Chain Exchange Kinetics Hao Wu, Jeffrey Ting, Olivia Werba, Samanvaya Srivastava, Matthew Tirrell Polyelectrolyte complex micelles form when oppositely charged block polymers are mixed together in aqueous media. The charged blocks electrostatically associate and phase separate, leading to a dense, polymer-rich core stabilized by a neutral block corona. The resulting polyelectrolyte complex micelles are specifically beneficial for RNA therapeutic delivery because the cationic polymers can condense large nuclei acids into small structures and neutralize the negatively charged moieties on the nucleic acid chains, thereby protecting them from potential enzymatic degradation and promoting successful transfection into various cell types. Yet, little is understood on micelle kinetics, including micelle formation, dissociation, and intermicellar chain exchange. Herein, we comprehensively investigate micelle kinetics with a combination of techniques including time-resolved dynamic light scattering, stopped-flow setup equipped small-angle X-ray scattering, time-resolved small-angle neutron scattering and cryogenic transmission electron microscope. These findings will reveal the mechanisms governing micelle assembly, disassembly, and intermicellar chain exchange, and therefore will shed light on the rational design of polyelectrolyte-based gene delivery systems. |
Monday, March 5, 2018 12:27PM - 1:03PM |
B43.00007: Micelleplexes: Complexation of Polyanions with Cationic AB Diblock and ABC Triblock Micelles Invited Speaker: Timothy Lodge The complexation of polyanions with block copolymer micelles that bear cationic charge has been explored, with the overall goal of using micelle templates as a means to control micelleplex size, shape, colloidal stability, and net charge. Polyanions of interest include flexible polystyrene sulfonate and semiflexible DNA (both linear and plasmid), over wide ranges of molar mass. The micelles feature a hydrophobic core (polystyrene or poly-n-butylmethacrylate) and a cationic poly(dimethylaminoethylmethacrylate) corona block. Micelleplex stability and structure are assessed by a combination of turbidimetric titration, dynamic light scattering, and cryogenic transmission electron microscopy. The role of ionic strength in promoting equilibration of micelleplex structure is also investigated. Furthermore, a third, neutral hydrophilic block, either poly(oligoethylene glycol methacrylate) or poly(ethylene glycol), has been added to the micelle corona, to determine whether increased colloidal stability of charge-neutral micelleplexes can be achieved. |
Monday, March 5, 2018 1:03PM - 1:15PM |
B43.00008: Polyelectrolyte Complex Coacervation by Electrostatic Dipolar Interactions Sabin Adhikari, Michael Leaf, Murugappan Muthukumar To explain complex coacervation, the liquid-liquid phase separation of a solution of oppositely charged polyelectrolyte chains into a polyelectrolyte rich complex coacervate phase and a dilute aqueous phase, we propose a mean field theory based on the interplay of electrostatic dipolar attractions and hydrophobic interactions. We assume that polycations-polyanions complex even in the homogeneous phase and exist as dipolar chain pairs. Phase separation is caused by two driving forces: hydrophobicity and electrostatic dipolar attractions. We predict qualitatively different phase behaviors depending upon the strengths of the two driving forces. For moderately hydrophobic polyelectrolytes at room temperature, neither hydrophobicity nor electrostatics alone is strong enough to cause phase separation, but their combined effect results in phase separation. The constructed phase diagrams capture key experimental observations including the suppression of complex coacervation by salt, temperature and polycation-polyanion chain length asymmetry and its promotion by increasing chain length, and the preferential partitioning of salt into the polyelectrolyte dilute phase. When both driving forces are capable of causing phase instability, two unstable regions, one due to each, are obtained. |
Monday, March 5, 2018 1:15PM - 1:27PM |
B43.00009: Polyelectrolyte Driven Complexation of Sequence Specific Polypeptides Amanda Marciel, Matthew Tirrell Polyelectrolyte complexes form when oppositely charged polymers are mixed together in aqueous media, resulting in a polymer-rich complex phase coexisting with a polymer-depleted supernatant phase. The complex phase exists as an equilibrium liquid coacervate or a glassy precipitate, depending on the strength of electrostatic interactions. In this study, we examined the effects of polyelectrolyte chain length and sequence, as well as solution pH and ionic strength on complexation behavior and polyelectrolyte microstructure using a variety of spectroscopic and scattering techniques. Initially, we used charged homopolymer polypeptides – (poly)-lysine and (poly)-glutamic acid. This model system allows the chain length, side-chain functionality and chirality to be tuned while keeping the backbone chemistry constant, thus enabling a systematic investigation of polyelectrolyte chain conformation. In addition, we modified the polypeptide sequence to study the effects of charge density and hydrophobicity on polyelectrolyte complexation. Overall, understanding the microstructure and the underlying forces that drive polyelectrolyte complexation will enable design of novel materials for applications ranging from drug delivery to coatings. |
Monday, March 5, 2018 1:27PM - 1:39PM |
B43.00010: Voltage-driven polyelectrolyte complexation inside a nanopore PRABHAT TRIPATHI, Byoung-jin Jeon, Murugappan Muthukumar We have investigated how a pair of oppositely charged macromolecules can be driven by an electric field to form a polyelectrolyte complex inside a nanopore. To observe and isolate an individual complex pair, we employ a model protein nanopore embedded in artificial phospholipid membrane, allowing compartmentalization (cis/trans). A polyanion in the cis and a polycation in the trans compartments are subjected to electrophoretic capture by the pore. We find that the measured ionic current across the pore has the distinguishable signature of complex formation, which is different from the passage of the individual molecules through the pore. Analysis of the complexation events support a four step-mechanism: (i) The polyanion is captured by the pore, (ii) the polyanion starts threading through the pore. (iii) The polycation is captured, a complex pair is formed in the pore, and the polyanion slides along the polycation. (iv) Depending on strength of the applied voltage, the complex pair can be pulled through the pore into the trans compartment or dissociate. |
Monday, March 5, 2018 1:39PM - 1:51PM |
B43.00011: Small Ion Effects on Self-Coacervation Phenomena in Block Polyampholytes Scott Danielsen, Kris Delaney, Glenn Fredrickson Polyelectrolyte complexation is a common phenomenon in natural polymers and has been applied to synthetic materials systems for coatings, adhesives, and encapsulants. Single-component polyelectrolyte complexes are formed when block polyampholytes exhibit self-coacervation, phase separating into a dense liquid coacervate phase rich in the polaympholyte coexisting with a dilute supernatant phase. Using fully fluctuating field theoretic simulations, we explore the phase behavior of block polyampholytes in solution to understand the structure and thermodynamics of the self-coacervate. Results are shown concerning the effects of counterions, added salt, and charge asymmetries. In particular, non-neutral chains are considered, probing the crossover at which electrostatic repulsions dominate the attractions, resulting in suppressed phase separation. Simple analytical and random phase approximation (RPA) expressions are used to discuss scaling relationships. |
Monday, March 5, 2018 1:51PM - 2:03PM |
B43.00012: Polyelectrolyte Assemblies on Demand Claudia Dähling, Felix Plamper, Judith Houston, Aurel Radulescu, Markus Drechsler, Hideharu Mori, Dmitry Pergushov The controlled generation of well-defined micellar assemblies from multi-component polymer systems presently is the focus of polymer science. A straightforward way to obtain polymeric aggregates is the co-assembly of polyions of opposite charges driven by the entropically favored release of counterions and strong electrostatic interactions. In presence of a low molecular weight salt micellar dynamics are facilitated resulting in restructuring toward equilibrium morphologies, in absence of salt restructuring is prevented. We present a sophisticated polyelectrolyte system containing a thermoresponsive polymer compound for the targeted creation of differently shaped assemblies under the same final conditions: In presence of salt spherical and cylindrical micelles are prepared below and above the lower critical solution temperature, respectively. Removing the salt kinetically freezes the assemblies yielding micelles of different morphologies. The transition from equilibrium to non-equilibrium structures is repeatable using the orthogonal switching scheme with temperature and salt concentration as triggers. |
Monday, March 5, 2018 2:03PM - 2:15PM |
B43.00013: Self-Assembly of multiple patchy particles in presence of oppositely charged polyelectrolytes Rituparna Samanta, Venkatraghavan Ganesan We discuss the molecular simulation of self-assembly of nanoparticles with discrete charge distribution called patches in presence of oppositely charged polymers in solution. This is to mimic phase separation due to coacervation of supercharged globular proteins in presence of oppositely charged polyelectrolytes. We have used a hybrid computational method of combined single chain in mean field theory and the solution of general Poisson-Boltzmann equation. We have studied the effect of number of patches, arrangement of charges on them, positive to negative charge ratio, polyelectrolyte charge and mixing ratios of particle to polymer on aggregation of the system. Our results show how by manipulating the number of patches and by changing the charges on them, gives a new parameter to modulate the aggregation of particles and the cluster properties. |
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