Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session H52: Polyelectrolyte Complexation III: Biology and Applications |
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Sponsoring Units: DPOLY DBIO Chair: Ting Ge, Univ of NC - Chapel Hill Room: LACC 512 |
Tuesday, March 6, 2018 2:30PM - 3:06PM |
H52.00001: Break - Dillon Medal Talk
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Tuesday, March 6, 2018 3:06PM - 3:18PM |
H52.00002: Crystallinity of dsRNA-Antimicrobial Peptide Complexes Modulates TLR3-Mediated Inflammation Ernest Lee, Toshiya Takahashi, Tine Curk, Jure Dobnikar, Richard Gallo, Gerard Wong Double-stranded RNA (dsRNA) induces production of pro-inflammatory cytokine signaling molecules in human keratinocytes by specific binding to endosomal Toll-like receptor-3 (TLR3). In the autoimmune disease psoriasis, it has recently been shown that hyperactivation of TLR3 in keratinocytes by dsRNA can occur in the presence of the human antimicrobial peptide (AMP) LL37. Here, we combine synchrotron X-ray scattering, microscopy, statistical mechanics, computer simulations, and measurements of cytokine production to elucidate a previously unanticipated form of specific molecular pattern recognition. LL37 and similar alpha-helical AMPs can form proinflammatory nanocrystalline complexes with dsRNA that are recognized by TLR3 differently than dsRNA alone. dsRNA complexes that activate IL-6 production in keratinocytes and those that do not are both able to enter cells and colocalize with TLR3. However, the crystallinity of these AMP-dsRNA complexes, specifically the geometric spacing between parallel dsRNA and the repeat number of ordered dsRNA, strongly influence the level of TLR3 activation. Crystalline complexes that present dsRNA at a spacing matching the steric size of TLR3 can recruit and engage multiple TLR3 receptors, driving receptor clustering and immune amplification. |
Tuesday, March 6, 2018 3:18PM - 3:30PM |
H52.00003: Polyelectrolyte - Multivalent Ion Interactions In Jammed Granular Microgels Christopher O'Bryan, Christopher Kabb, Brent Sumerlin, Thomas Angelini Hydrogel particles, commonly called microgels, often rely on charged polyelectrolytes to drive swelling at low polymer concentrations. These highly swollen microgels have found applications across industrial and academic fields as rheological modifiers, drug delivery systems, 3D printing supports, and 3D cell culture media. However, interactions between the polyelectrolytes and multivalent ions in the solvent can limit their applications. Charged polyelectrolytes are strongly sensitive to multivalent ions and can dramatically deswell or collapse driven by osmotic pressure or condensation of counterions. For example, microgels have been swollen in cell growth media to study the behavior of cells in a 3D environment. However, the presence of multivalent ions in cell growth media, including Ca2+ and Mg2+, can have drastic effects on the rheological properties of the microgels as well as the behavior of suspended cells. To mitigate these problems, we create polyacrylamide microgels with anionic, cationic, and zwitterionic comonomers at varying charge densities and investigate the effects of Ca2+ ions on their rheological properties. We extend our findings to 3D cell cultures to explore the effects on cell viability and functionality. |
Tuesday, March 6, 2018 3:30PM - 3:42PM |
H52.00004: Design Rules for Immunomodulation by Host-Defense Peptides Ernest Lee, Changsheng Zhang, Jeremy Di Domizio, Fan Jin, Will Connell, Mandy Hung, Nicolas Malkoff, Veronica Veksler, Michel Gilliet, Pengyu Ren, Gerard Wong Some alpha-helices can form complexes with double-stranded DNA (dsDNA) and potently activate innate immunity via Toll-like receptor 9 (TLR9). In lupus and psoriasis, electrostatic complexes between the antimicrobial peptide (AMP) LL37 and dsDNA can hyperactivate TLR9 in plasmacytoid dendritic cells (pDCs), triggering production of type-I interferons (IFNs) and exacerbating inflammation. However, most alpha-helical motifs do not exhibit this activity. Recent work showed that dsDNA complexes that are proinflammatory via the TLR9 pathway have inter-DNA lattice spacings that match the steric size of TLR9, so that spatially-organized parallel DNA ligands can amplify recruitment and multivalent binding to clustered arrays of TLR9. We examine the self-assembled structures of immunocomplexes formed between dsDNA and alpha-helical AMPs using a combination of high resolution synchrotron small angle X-ray scattering (SAXS) and computer simulations. By correlating these measured structures to their induced immunological activity in pDCs and macrophages, we deduce some fundamental structural rules for alpha-helices that are proinflammatory via the TLR9 pathway. |
Tuesday, March 6, 2018 3:42PM - 3:54PM |
H52.00005: Unconventional Coacervate Formation between Neutral Polymer and Inorganic Polyanions in Salted Aqueous Solution Benxin Jing, Christopher Wood, Yingxi Elaine Zhu Conventional coacervate complexes are formed between oppositely charged polyelectrolytes via ion pairing with the release of counterions. Yet other intermolecular interactions, such as cation-π interaction and hydrogen bonding, have been employed to produce polymer coacervate complexes. In this work, we report an unconventional coacervate formation between uncharged poly(ethylene glycol) (PEG) and inorganic polyoxometalate (POM) polyanions in LiCl aqueous solution. Composition analysis has confirmed that the dense coacervate consists of PEO and POM with little amount of LiCl in contrast to the higher concentration of LiCl in the supernatant than its bulk concentration, suggesting the entropic contribution to the liquid-liquid separation. More interestingly, the measured electric potential of PEG indicates that PEG is positively charged in the presence of multivalent POM polyanions. Additionally, considerable amounts of heat release are measured upon PEG-POM coacervation by isothermal titration calorimetry, indicating a highly exothermic process. As combined, we speculate a cation-mediated coacervation between neutral PEG and POM polyanions, in which both enthalpy and entropy contribution are significant, distinct from conventional entropy-driven polyelectrolyte coacervation. |
Tuesday, March 6, 2018 3:54PM - 4:06PM |
H52.00006: Effect of Polymer Net Charge on Polyampholyte-Polyanion Coacervate Complexation Manuela Ferreira, Benxin Jing, Yingxi Elaine Zhu Polymer coacervate complexes are commonly formed upon the liquid-liquid separation of the mixture of oppositely charged polyelectrolytes in salted aqueous solution. Recently we have demonstrated that biphasic coacervate complexes and monophasic gel-like complexes can be also formed between net neutral polyzwitterions and inorganic polyoxometalate (POM) polyanions in salted solutions. To further understand the binding between polyzwitterion and polyanion and the resulting structures of dense coacervate complexes, we examine the effect of net charge of polyampholytes on the phase behavior of polyampholyte-POM mixtures in LiCl aqueous solution. By tuning the net charge of polyampholytes from being 10% positively charged to 10% negatively charged, the coacervate complex phase is much narrowed. Moreover, the gel-like complex formation is suppressed in the mixture of net negatively charged polyampholyte and POM polyanions in LiCl solutions. Linear rheological characterization of polyampholyte-POM complexes shows that the measured shear moduli of dense coacervate complexes strongly depend on the net charge of polyampholyte, leading to the presence of an optimal polyampholyte-to-POM charge ratio for the maximal viscoelasticity. |
Tuesday, March 6, 2018 4:06PM - 4:18PM |
H52.00007: PEG-based Polyampholytes as Osmotic Stabilizers during Cryopreservation of Living Cells Aaron Burkey, Neda Ghousifam, Christopher Riley, Taylor Hatridge, Nathaniel Lynd Improved cryopreservatives are necessary to enable complete recovery of living cells and tissue after frozen storage. A key challenge in cryopreservation is osmotic stress on cells as extracellular solutes become concentrated when water freezes. Herein, we synthesized a new class of polyether-based polyampholytes capable of reversibly binding dissolved salt ions. We hypothesize that these polymers act as “osmotic buffers” that stabilize osmotic pressure during freezing and thawing of living cells. Excellent biocompatibility was demonstrated, and cryoprotective ability was evaluated for each material. Salt-binding behavior was studied through conductimetric and calorimetric techniques. Finally, we employed the high compositional tunability of these PEG-based polyampholyte materials to examine the effect of charged group structure on salt-binding and cryoprotection. |
Tuesday, March 6, 2018 4:18PM - 4:30PM |
H52.00008: Conformational Structure of Polyelectrolytes in Polyzwitterionic Coacervate Complexes Kehua Lin, Benxin Jing, Yingxi Elaine Zhu Polyelectrolyte coacervarte complexes are formed between oppositely charged polyelectrolytes by releasing screened counterions to aqueous solutions. While much research has strived to understand the phase behaviors, the microstructural details of polyelectrolytes in the coacervate complexes remain unclear. In this work, we examine the conformational structure and local proton concentration of weak polybase, poly(2-vinylpyridine) (P2VP) upon coacervate complexation with zwitterionic poly(sulfobetaine methacrylate) (PSBMA) in KCl aqueous solutions. We have observed that the coacervate phase is much broadened by increasing pH from 2-4 at the same polymer and salt concentrations. The measured hydrodynamic radius of single fluorescence-labeled P2VP chains in the coacervate by fluorescence correlation spectroscopy (FCS) exhibits a swollen conformation with little dependence on solution pH. In contrast, the measured local proton concentration near P2VP shows a non-monotonic change with pH, suggesting possible re-association of released counterions with P2VP. The de-coupling of local proton concentration and conformational structure of weak polyelectrolyte in the coacervate complex is under further investigation with multivalent salt solutions. |
Tuesday, March 6, 2018 4:30PM - 4:42PM |
H52.00009: Effect of Charge Density and Topology on Polyelectrolyte Complex Coacervation Emmanouela Filippidi, Anastasia Patterson, Scott Danielsen, Claus Eisenbach, Glenn Fredrickson, Rachel Segalman, Megan Valentine An aqueous solution of oppositely-charged polyelectrolytes can undergo associative phase separation into polyelectrolyte-dense and polyelectrolyte-dilute phases, a process known as complex coacervation. Recently, there has been a resurgence of interest in predicting the effect of the polyelectrolytes' molecular features on coacervation, driven by new efforts in theory and computation. In particular, chain length, charge density and charge spacing have been examined, alongside the polyelectrolyte and salt concentrations in solution. Experimental coacervation studies have either employed polydisperse statistical copolymers or, more recently, recombinant protein segments with deterministic sequence. Using polypeptoids with a controlled monomer sequence and lack of backbone hydrogen bonding as model polyelectrolytes, we examine the effect of charge density and topology (spacing and grouping of charges) on coacervation. In addition, we compare the experimental results with the theoretical models, and discuss discrepancies and current limitations. |
Tuesday, March 6, 2018 4:42PM - 4:54PM |
H52.00010: Direct assembly of antimicrobials within layer-by-layer films mediated by polyphosphazene polyelectrolytes Victoria Albright, Alexander Marin, Alexander Andrianov, Svetlana Sukhishvili We explore the effects of chain flexibility, charge density, and hydrophobicity on the direct, electrostatic assembly of small molecules with biocompatible polyelectrolytes. Films were assembled by the layer-by-layer (LbL) technique using ionic polyphosphazenes (PPzs) as polyanions and small-molecule antibacterial bioactives as cations. Evolution of dry film thickness was monitored with spectroscopic ellipsometry. PPz/bioactive films grew linearly in a pH dependent manner, which was correlated with ionization degree of PPzs in the films using ATR-FTIR. Deposition and release of bioactives were strongly dependent on charge density and hydrophobicity of polyanions; these effects were compared for the cases of non-fluorinated and fluorinated PPzs. The release rate of bioactives from films was explored as a function of temperature (ambient, physiological, and accelerated (65 °C)) and pH. Non-fluorinated PPz films released antibiotics at low pH following the charge renormalization argument. In contrast, multilayers of fluorinated PPzs enabled antimicrobial retention, due to the enhanced hydrophobic interactions. |
Tuesday, March 6, 2018 4:54PM - 5:06PM |
H52.00011: Effect of a Competitive Solvent on Growth and Chain Intermixing in Hydrogen-Bonded Multilayers Victor Selin, John Ankner, Svetlana Sukhishvili The role of a competitive solvent - dimethyl sulfoxide (DMSO) - on growth and internal structure of hydrogen-bonded layer-by-layer (HB-LbL) films was explored. The films were constructed at acidic pH using poly(methacrylic acid) (PMAA) and polyvinylpyrrolidone (PVPON). Like salt in the case of electrostatically assembled films, DMSO disrupts interpolymer PMAA/PVPON bonds, promoting non-linear film growth and chain intermixing. The internal structure of HB-LbL films was monitored with neutron reflectometry using deuterated PMAA chains, while growth profiles of a multilayers were studied with spectroscopic ellipsometry. Films assembled with short-chain PMAA were less stratified and were more prone to further DMSO-induced film intermixing as compared to films of long-chain PMAA. Moreover, while the presence of DMSO in aqueous assembly solutions had resulted in dramatic weakening of polymer-polymer binding leading to non-linear film growth, addition of the same concentrations of DMSO post-assembly caused only slight changes in the penetration of deuterated material into neighboring layers. The effects of a competitive solvent explored in this work can potentially be extended to other polymer assemblies that employ hydrogen-bonding interactions. |
Tuesday, March 6, 2018 5:06PM - 5:18PM |
H52.00012: Charging Behavior of Associating Weak Polyelectrolytes Vikramjit Rathee, Aristotle Zervoudakis, Hythem Sidky, Ben Sikora, Jonathan Whitmer Weak polyelectrolytes are useful in the creation of “smart” materials for separations and drug delivery. The charges on weak polyelectrolytes are dynamic and sensitive to the surroundings, causing polymer chains to behave differently depending on the acidity and salinity of their environment. In this study, we utilize a hybrid Monte Carlo/Molecular Dynamics formalism to elucidate a novel interplay between weak polyelectrolyte charging and polyion complexation, where associative effects can induce larger than expected charging to weak polyelectrolyte systems. We discuss the implications of these results for materials formed by oppositely charged polymers such as layer-by-layer films and complex coacervates, and how this might affect the performance of these materials. |
Tuesday, March 6, 2018 5:18PM - 5:30PM |
H52.00013: Complex Formation, Emergent States and Electronic Energy Transfer between Oppositely Charged Conjugated Polyelectrolytes William Hollingsworth, Carmen Segura, Arthur Bragg, Alexander Ayzner There is a pressing need to develop inexpensive, light-weight light-harvesting machinery that helps convert the energy of sunlight into chemical potential energy. Nature inspires us to use self-assembly to construct complex light-harvesting super-systems capable of carrying out the “light reactions” of photosynthesis. To this end, we are using oppositely charged conjugated polyelectrolyte (CPE) complexes as the foundation for an ionically assembled electronic energy transfer antenna. For the first time, we have shown that CPE complexation proceeds through a free energy barrier that appears to have a substantial enthalpic contribution. Further, we find that the backbone CPE microstructure is drastically altered in such a way as to qualitatively change the nature of the electronic wavefunction delocalized along the backbone. Using a combination of spectroscopic and structural probes, our recent work shows that the photophysical changes that accompany complexation are highly dependent on the relative polyion charge ratio. As a result, the energy transfer rate depends very strongly on the ionic stoichiometry and thus the physical state of the assembly. Our results point towards a path to using CPEs to construct panchromatic light-harvesting systems using ionic assembly. |
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