1
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Wilcox K, Yamagami KR, Roopnarine BK, Linscott A, Morozova S. Effect of Polymer Gel Elasticity on Complex Coacervate Phase Behavior. ACS POLYMERS AU 2024; 4:109-119. [PMID: 38618006 PMCID: PMC11010254 DOI: 10.1021/acspolymersau.3c00027] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/15/2023] [Revised: 12/07/2023] [Accepted: 12/11/2023] [Indexed: 04/16/2024]
Abstract
Gels are key materials in biological systems such as tissues and may control biocondensate formation and structure. To further understand the effects of elastic environments on biomacromolecular assembly, we have investigated the phase behavior and radii of complex coacervate droplets in polyacrylamide (PAM) networks as a function of gel modulus. Poly-l-lysine (PLL) and sodium hyaluronate (HA) complex coacervate phases were prepared in PAM gels with moduli varying from 0.035 to 15.0 kPa. The size of the complex coacervate droplets is reported from bright-field microscopy and confocal fluorescence microscopy. Overall, the complex coacervate droplet volume decreases inversely with the modulus. Fluorescence microscopy is also used to determine the phase behavior and concentration of fluorescently tagged HA in the complex coacervate phases as a function of ionic strength (100-270 mM). We find that the critical ionic strength and complex coacervate stability are nonmonotonic as a function of the network modulus and that the local gel concentration can be used to control phase behavior and complex coacervate droplet size scale. By understanding how elastic environments influence simple electrostatic assembly, we can further understand how biomacromolecules exist in complex, crowded, and elastic cellular environments.
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Affiliation(s)
- Kathryn
G. Wilcox
- Department of Macromolecular
Science and Engineering, Case Western Reserve
University, Cleveland, Ohio 44106, United States
| | - Kai R. Yamagami
- Department of Macromolecular
Science and Engineering, Case Western Reserve
University, Cleveland, Ohio 44106, United States
| | - Brittany K. Roopnarine
- Department of Macromolecular
Science and Engineering, Case Western Reserve
University, Cleveland, Ohio 44106, United States
| | - Adam Linscott
- Department of Macromolecular
Science and Engineering, Case Western Reserve
University, Cleveland, Ohio 44106, United States
| | - Svetlana Morozova
- Department of Macromolecular
Science and Engineering, Case Western Reserve
University, Cleveland, Ohio 44106, United States
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2
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Chou HY, Aksimentiev A. RNA regulates cohesiveness and porosity of a biological condensate. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.01.09.574811. [PMID: 38260307 PMCID: PMC10802450 DOI: 10.1101/2024.01.09.574811] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/24/2024]
Abstract
Biological condensates have emerged as key elements of a biological cell function, concentrating disparate biomolecules to accomplish specific biological tasks. RNA was identified as a key ingredient of such condensates, however, its effect on the physical properties of the condensate was found to depend on the condensate's composition while its effect on the microstructure has remained elusive. Here, we characterize the physical properties and the microstructure of a protein-RNA condensate by means of large-scale coarse-grained (CG) molecular dynamics simulations. By developing a custom CG model of RNA compatible with a popular CG model of proteins, we systematically investigate the structural, thermodynamic, and kinetic properties of condensate droplets containing thousands of individual protein and RNA molecules over a range of temperatures. While we find RNA to increase the condensate's cohesiveness, its effect on the condensate's fluidity is more nuanced with longer molecules compacting the condensate and making it less fluid. We show that a biological condensate has a sponge-like morphology of interconnected channels of size that increases with temperature and decreases in the presence of RNA. Our results suggest that longer RNA form a dynamic scaffold within a condensate, regulating not only its fluidity but also permeability to intruder molecules.
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3
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Yu B, Liang H, Rumyantsev AM, de Pablo JJ. Isotropic-to-Nematic Transition in Salt-Free Polyelectrolyte Coacervates from Coarse-Grained Simulations. Macromolecules 2022. [DOI: 10.1021/acs.macromol.2c01674] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Boyuan Yu
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, Illinois60637, United States
| | - Heyi Liang
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, Illinois60637, United States
| | - Artem M. Rumyantsev
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, Illinois60637, United States
| | - Juan J. de Pablo
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, Illinois60637, United States
- Center for Molecular Engineering, Argonne National Laboratory, Lemont, Illinois60439, United States
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4
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Balzer C, Zhang P, Wang ZG. Wetting behavior of polyelectrolyte complex coacervates on solid surfaces. SOFT MATTER 2022; 18:6326-6339. [PMID: 35976083 DOI: 10.1039/d2sm00859a] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
The wetting behavior of complex coacervates underpins their use in many emerging applications of surface science, particularly wet adhesives and coatings. Many factors dictate if a coacervate phase will condense on a solid surface, including solution conditions, the nature of the polymer-substrate interaction, and the underlying supernatant-coacervate bulk phase behavior. In this work, we use a simple inhomogeneous mean-field theory to study the wetting behavior of complex coacervates on solid surfaces both off-coexistence (wetting transitions) and on-coexistence (contact angles). We focus on the effects of salt concentration, the polycation/polyanion surface affinity, and the applied electrostatic potential on the wettability. We find that the coacervate generally wets the surface via a first order wetting transition with second order transitions possible above a surface critical point. Applying an electrostatic potential to a solid surface always improves the surface wettability when the polycation/polyanion-substrate interaction is symmetric. For asymmetric surface affinity, the wettability has a nonmonotonic dependence with the applied potential. We use simple scaling and thermodynamic arguments to explain our results.
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Affiliation(s)
- Christopher Balzer
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA.
| | - Pengfei Zhang
- State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, Center for Advanced Low-Dimension Materials, College of Material Science and Engineering, Donghua University, Shanghai 201620, China
| | - Zhen-Gang Wang
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA.
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5
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Agrawal A, Douglas JF, Tirrell M, Karim A. Manipulation of coacervate droplets with an electric field. Proc Natl Acad Sci U S A 2022; 119:e2203483119. [PMID: 35925890 PMCID: PMC9372540 DOI: 10.1073/pnas.2203483119] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2022] [Accepted: 06/22/2022] [Indexed: 11/18/2022] Open
Abstract
Many biopolymers are highly charged, and as in the case of many polymer mixtures, they tend to phase separate as a natural consequence of chain connectivity and an associated relatively low entropy of polymer mixing. Recently, it has become appreciated that the phase-separated structures formed by such polyelectrolyte blends, called "complex coacervates," underlie numerous biological structures and processes essential to living systems, and there has been intense interest in understanding the unique physical features of this type of phase-separation process. In the present work, we are particularly concerned with the field responsiveness of stabilized coacervate droplets formed after the phase separation of polyelectrolyte blend solution and then exposed to deionized water, making the droplet interfacial layer acquire a viscoelastic character that strongly stabilizes it against coalescence. We show that we can precisely control the positions of individual droplets and arrays of them with relatively low-voltage electric fields (on the order of 10 V/cm) and that the imposition of an oscillatory field gives rise to chain formation with coarsening of these chains into long fibers. Such a phase-separation-like process is generally observed in electrorheological fluids of solid colloidal particles subjected to much larger field strengths. The key to these coacervates' electrorheological properties is the altered interfacial viscoelastic properties when the droplets are introduced into deionized water and the associated high polarizability of the droplets, similar to the properties of many living cells. Since many different molecular payloads can be incorporated into these stable droplets, we anticipate many applications.
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Affiliation(s)
- Aman Agrawal
- William A. Brookshire Department of Chemical and Biomolecular Engineering, University of Houston, Houston, TX 77204
| | - Jack F. Douglas
- Materials Science and Engineering Division, National Institute of Standards and Technology, Gaithersburg, MD 20899
| | - Matthew Tirrell
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, IL 60637
| | - Alamgir Karim
- William A. Brookshire Department of Chemical and Biomolecular Engineering, University of Houston, Houston, TX 77204
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6
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Liang H, de Pablo JJ. A Coarse-Grained Molecular Dynamics Study of Strongly Charged Polyelectrolyte Coacervates: Interfacial, Structural, and Dynamical Properties. Macromolecules 2022. [DOI: 10.1021/acs.macromol.2c00246] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Heyi Liang
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, Illinois 60637, United States
| | - Juan J. de Pablo
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, Illinois 60637, United States
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7
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Madinya JJ, Sing CE. Hybrid Field Theory and Particle Simulation Model of Polyelectrolyte–Surfactant Coacervation. Macromolecules 2022. [DOI: 10.1021/acs.macromol.2c00187] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Affiliation(s)
- Jason J. Madinya
- Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana−Champaign, 600 S. Matthews Ave., Urbana, Illinois 61820, United States
| | - Charles E. Sing
- Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana−Champaign, 600 S. Matthews Ave., Urbana, Illinois 61820, United States
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8
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Bobbili SV, Milner ST. Closed-Loop Phase Behavior of Nonstoichiometric Coacervates in Coarse-Grained Simulations. Macromolecules 2022. [DOI: 10.1021/acs.macromol.1c02115] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Affiliation(s)
- Sai Vineeth Bobbili
- Department of Chemical Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - Scott T. Milner
- Department of Chemical Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
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9
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Affiliation(s)
- Pengfei Zhang
- State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, Center for Advanced Low-Dimension Materials, College of Material Science and Engineering, Donghua University, Shanghai 201620, China
| | - Zhen-Gang Wang
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States
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10
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Bobbili SV, Milner ST. A simple simulation model for complex coacervates. SOFT MATTER 2021; 17:9181-9188. [PMID: 34585705 DOI: 10.1039/d1sm00881a] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
When oppositely charged polyelectrolytes mix in an aqueous solution, associative phase separation gives rise to coacervates. Experiments reveal the phase diagram for such coacervates, and determine the impact of charge density, chain length and added salt. Simulations often use hybrid MC-MD methods to produce such phase diagrams, in support of experimental observations. We propose an idealized model and a simple simulation technique to investigate coacervate phase behavior. We model coacervate systems by charged bead-spring chains and counterions with short-range repulsions, of size equal to the Bjerrum length. We determine phase behavior by equilibrating a slab of concentrated coacervate with respect to swelling into a dilute phase of counterions. At salt concentrations below the critical point, the counterion concentration in the coacervate and dilute phases are nearly the same. At high salt concentrations, we find a one-phase region. Along the phase boundary, the total concentration of beads in the coacervate phase is nearly constant, corresponding to a "Bjerrum liquid''. This result can be extended to experimental phase diagrams by assigning appropriate volumes to monomers and salts.
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Affiliation(s)
- Sai Vineeth Bobbili
- Department of Chemical Engineering, The Pennsylvania State University, University Park, Pennsylvania, USA.
| | - Scott T Milner
- Department of Chemical Engineering, The Pennsylvania State University, University Park, Pennsylvania, USA.
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11
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Tian WD, Ghasemi M, Larson RG. Extracting free energies of counterion binding to polyelectrolytes by molecular dynamics simulations. J Chem Phys 2021; 155:114902. [PMID: 34551524 DOI: 10.1063/5.0056853] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
We use all-atom molecular dynamics simulations to extract ΔGeff, the free energy of binding of potassium ions K+ to the partially charged polyelectrolyte poly(acrylic acid), or PAA, in dilute regimes. Upon increasing the charge fraction of PAA, the chains adopt more extended conformations, and simultaneously, potassium ions bind more strongly (i.e., with more negative ΔGeff) to the highly charged chains to relieve electrostatic repulsions between charged monomers along the chains. We compare the simulation results with the predictions of a model that describes potassium binding to PAA chains as a reversible reaction whose binding free energy (ΔGeff) is adjusted from its intrinsic value (ΔG) by electrostatic correlations, captured by a random phase approximation. The bare or intrinsic binding free energy ΔG, which is an input in the model, depends on the binding species and is obtained from the radial distribution function of K+ around the charged monomer of a singly charged, short PAA chain in dilute solutions. We find that the model yields semi-quantitative predictions for ΔGeff and the degree of potassium binding to PAA chains, α, as a function of PAA charge fraction without using fitting parameters.
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Affiliation(s)
- Wen-de Tian
- Center for Soft Condensed Matter Physics and Interdisciplinary Research, Soochow University, Suzhou 215006, China
| | - Mohsen Ghasemi
- Department of Chemical Engineering, University of Michigan, Ann Arbor, Michigan 48109, USA
| | - Ronald G Larson
- Department of Chemical Engineering, University of Michigan, Ann Arbor, Michigan 48109, USA
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12
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Knoerdel AR, Blocher McTigue WC, Sing CE. Transfer Matrix Model of pH Effects in Polymeric Complex Coacervation. J Phys Chem B 2021; 125:8965-8980. [PMID: 34328340 DOI: 10.1021/acs.jpcb.1c03065] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Oppositely charged polyelectrolytes can undergo an associative phase separation, in a process known as polymeric complex coacervation. This phenomenon is driven by the electrostatic attraction between polyanion and polycation species, leading to the formation of a polymer-dense coacervate phase and a coexisting polymer-dilute supernatant phase. There has been significant recent interest in the physical origin and features of coacervation; yet notably, experiments often use weak polyelectrolytes the charge state of which depends on solution pH, while theoretical or computational efforts typically assume strong polyelectrolytes that remain fully charged. There have been only a few efforts to address this limitation, and thus there has been little exploration of how pH can affect complex coacervation. In this paper, we modify a transfer matrix theory of coacervation to account for acid-base equilibria, taking advantage of its ability to directly account for some local ion correlations that will affect monomer charging. We show that coacervation can stabilize the charged state of a weak polyelectrolyte via the proximity of oppositely charged monomers, and can lead to asymmetric phase diagrams where the positively and negatively charged polyelectrolytes exhibit different behaviors near the pKa of either chain. Specifically, there is a partitioning of one of the salt species to a coacervate to maintain electroneutrality when one of the polyelectrolytes is only partially charged. This results in the depletion of the same salt species in the supernatant, and overall can suppress phase separation. We also demonstrate that, when one of the species is only partially charged, mixtures that are off-stoichiometric in volume fraction but stoichiometric in charge exhibit the greatest propensity to form coacervate phases.
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Affiliation(s)
- Ashley R Knoerdel
- Program in Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Whitney C Blocher McTigue
- Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Charles E Sing
- Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
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13
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Audus DJ, Ali S, Ma Y, Prabhu VM, Rumyantsev AM, de Pablo JJ. Molecular Mass Dependence of Interfacial Tension in Complex Coacervation. PHYSICAL REVIEW LETTERS 2021; 126:237801. [PMID: 34170179 PMCID: PMC10168025 DOI: 10.1103/physrevlett.126.237801] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/07/2020] [Revised: 02/19/2021] [Accepted: 04/16/2021] [Indexed: 05/11/2023]
Abstract
The interfacial tension of coacervates, the liquidlike phase composed of oppositely charged polymers that coexists at equilibrium with a supernatant, forms the basis for multiple technologies. Here we present a comprehensive set of experiments and molecular dynamics simulations to probe the effect of molecular mass on interfacial tension γ, far from the critical point, and derive γ=γ_{∞}(1-h/N), where N is the degree of polymerization, γ_{∞} is the infinite molecular mass limit, and h is a constant that physically corresponds to the number of monomers of one chain within the coacervate correlation volume.
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Affiliation(s)
| | | | - Yuanchi Ma
- Materials Science and Engineering Division, National Institute of Standards and Technology, Gaithersburg, MD
| | - Vivek M. Prabhu
- Materials Science and Engineering Division, National Institute of Standards and Technology, Gaithersburg, MD
| | - Artem M. Rumyantsev
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, IL
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14
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Tsanai M, Frederix PWJM, Schroer CFE, Souza PCT, Marrink SJ. Coacervate formation studied by explicit solvent coarse-grain molecular dynamics with the Martini model. Chem Sci 2021; 12:8521-8530. [PMID: 34221333 PMCID: PMC8221187 DOI: 10.1039/d1sc00374g] [Citation(s) in RCA: 23] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2021] [Accepted: 05/17/2021] [Indexed: 01/30/2023] Open
Abstract
Complex coacervates are liquid-liquid phase separated systems, typically containing oppositely charged polyelectrolytes. They are widely studied for their functional properties as well as their potential involvement in cellular compartmentalization as biomolecular condensates. Diffusion and partitioning of solutes into a coacervate phase are important to address because their highly dynamic nature is one of their most important functional characteristics in real-world systems, but are difficult to study experimentally or even theoretically without an explicit representation of every molecule in the system. Here, we present an explicit-solvent, molecular dynamics coarse-grain model of complex coacervates, based on the Martini 3.0 force field. We demonstrate the accuracy of the model by reproducing the salt dependent coacervation of poly-lysine and poly-glutamate systems, and show the potential of the model by simulating the partitioning of ions and small nucleotides between the condensate and surrounding solvent phase. Our model paves the way for simulating coacervates and biomolecular condensates in a wide range of conditions, with near-atomic resolution.
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Affiliation(s)
- Maria Tsanai
- Groningen Biomolecular Sciences and Biotechnology Institute and Zernike Institute for Advanced Materials, University of Groningen 9747AG Groningen The Netherlands
| | - Pim W J M Frederix
- Groningen Biomolecular Sciences and Biotechnology Institute and Zernike Institute for Advanced Materials, University of Groningen 9747AG Groningen The Netherlands
| | - Carsten F E Schroer
- Groningen Biomolecular Sciences and Biotechnology Institute and Zernike Institute for Advanced Materials, University of Groningen 9747AG Groningen The Netherlands
| | - Paulo C T Souza
- Groningen Biomolecular Sciences and Biotechnology Institute and Zernike Institute for Advanced Materials, University of Groningen 9747AG Groningen The Netherlands
- Molecular Microbiology and Structural Biochemistry, UMR 5086 CNRS, University of Lyon Lyon France
| | - Siewert J Marrink
- Groningen Biomolecular Sciences and Biotechnology Institute and Zernike Institute for Advanced Materials, University of Groningen 9747AG Groningen The Netherlands
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15
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Abstract
A scaling model for the structure of coacervates is presented for mixtures of oppositely-charged polyelectrolytes of both symmetric and asymmetric charge-densities for different degrees of electrostatic strength and levels of added salt. At low electrostatic strengths, weak coacervates, with the energy of electrostatic interactions between charges less than the thermal energy, k B T, are liquid. At higher electrostatic strengths, strong coacervates are gels with crosslinks formed by ion pairs of opposite charges bound to each other with energy higher than k B T. Charge-symmetric coacervates are formed for mixtures of oppositely-charged polyelectrolytes with equal and opposite charge-densities. While charge-symmetric weak coacervates form a semidilute polymer solution with a correlation length equal to the electrostatic blob size, charge-symmetric strong coacervates form reversible gels with a correlation length on the order of the distance between bound ion pairs. Charge-asymmetric coacervates are formed from mixtures of oppositely-charged polyelectrolytes with different charge-densities. While charge-asymmetric weak coacervates form double solutions with two correlation lengths and qualitatively different chain conformations of polycations and polyanions, charge-asymmetric strong coacervates form bottlebrush and star-like gels. Unlike liquid coacervates, for which an increase in the concentration of added salt screens electrostatic interactions, causing structural rearrangement and eventually leads to their dissolution, the salt does not affect the structure of strong coacervates until ion pairs dissociate and the gel disperses.
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Affiliation(s)
- Scott P O Danielsen
- Department of Mechanical Engineering and Materials Science, Duke University, Durham, NC 27708, United States
| | - Sergey Panyukov
- P. N. Lebedev Physics Institute, Russian Academy of Sciences, Moscow 117924, Russia
| | - Michael Rubinstein
- Department of Mechanical Engineering and Materials Science, Duke University, Durham, NC 27708, United States
- Departments of Biomedical Engineering, Physics, and Chemistry, Duke University, Durham, NC 27708, United States
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16
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Liu Y, Santa Chalarca CF, Carmean RN, Olson RA, Madinya J, Sumerlin BS, Sing CE, Emrick T, Perry SL. Effect of Polymer Chemistry on the Linear Viscoelasticity of Complex Coacervates. Macromolecules 2020. [DOI: 10.1021/acs.macromol.0c00758] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Affiliation(s)
- Yalin Liu
- Department of Chemical Engineering, University of Massachusetts Amherst, Amherst, Massachusetts 01003, United States
| | - Cristiam F. Santa Chalarca
- Department of Polymer Science & Engineering, University of Massachusetts Amherst, Amherst, Massachusetts 01003, United States
| | - R. Nicholas Carmean
- George & Josephine Butler Polymer Research Laboratory, Center for Macromolecular Science & Engineering, Department of Chemistry, University of Florida, Gainesville, Florida 32611, United States
| | - Rebecca A. Olson
- George & Josephine Butler Polymer Research Laboratory, Center for Macromolecular Science & Engineering, Department of Chemistry, University of Florida, Gainesville, Florida 32611, United States
| | - Jason Madinya
- Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Brent S. Sumerlin
- George & Josephine Butler Polymer Research Laboratory, Center for Macromolecular Science & Engineering, Department of Chemistry, University of Florida, Gainesville, Florida 32611, United States
| | - Charles E. Sing
- Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Todd Emrick
- Department of Polymer Science & Engineering, University of Massachusetts Amherst, Amherst, Massachusetts 01003, United States
| | - Sarah L. Perry
- Department of Chemical Engineering, University of Massachusetts Amherst, Amherst, Massachusetts 01003, United States
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17
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Ghasemi M, Friedowitz S, Larson RG. Analysis of Partitioning of Salt through Doping of Polyelectrolyte Complex Coacervates. Macromolecules 2020. [DOI: 10.1021/acs.macromol.0c00797] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Affiliation(s)
- Mohsen Ghasemi
- Department of Chemical Engineering, University of Michigan, Ann Arbor, Michigan 48109, United States
| | - Sean Friedowitz
- Department of Chemical Engineering, Stanford University, Stanford, California 94305, United States
| | - Ronald G. Larson
- Department of Chemical Engineering, University of Michigan, Ann Arbor, Michigan 48109, United States
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18
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Sing CE, Perry SL. Recent progress in the science of complex coacervation. SOFT MATTER 2020; 16:2885-2914. [PMID: 32134099 DOI: 10.1039/d0sm00001a] [Citation(s) in RCA: 296] [Impact Index Per Article: 74.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Complex coacervation is an associative, liquid-liquid phase separation that can occur in solutions of oppositely-charged macromolecular species, such as proteins, polymers, and colloids. This process results in a coacervate phase, which is a dense mix of the oppositely-charged components, and a supernatant phase, which is primarily devoid of these same species. First observed almost a century ago, coacervates have since found relevance in a wide range of applications; they are used in personal care and food products, cutting edge biotechnology, and as a motif for materials design and self-assembly. There has recently been a renaissance in our understanding of this important class of material phenomena, bringing the science of coacervation to the forefront of polymer and colloid science, biophysics, and industrial materials design. In this review, we describe the emergence of a number of these new research directions, specifically in the context of polymer-polymer complex coacervates, which are inspired by a number of key physical and chemical insights and driven by a diverse range of experimental, theoretical, and computational approaches.
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Affiliation(s)
- Charles E Sing
- Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, 600 S. Mathews, Urbana, IL, USA.
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19
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Perry SL, Sing CE. 100th Anniversary of Macromolecular Science Viewpoint: Opportunities in the Physics of Sequence-Defined Polymers. ACS Macro Lett 2020; 9:216-225. [PMID: 35638672 DOI: 10.1021/acsmacrolett.0c00002] [Citation(s) in RCA: 76] [Impact Index Per Article: 19.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Polymer science has been driven by ever-increasing molecular complexity, as polymer synthesis expands an already-vast palette of chemical and architectural parameter space. Copolymers represent a key example, where simple homopolymers have given rise to random, alternating, gradient, and block copolymers. Polymer physics has provided the insight needed to explore this monomer sequence parameter space. The future of polymer science, however, must contend with further increases in monomer precision, as this class of macromolecules moves ever closer to the sequence-monodisperse polymers that are the workhorses of biology. The advent of sequence-defined polymers gives rise to opportunities for material design, with increasing levels of chemical information being incorporated into long-chain molecules; however, this also raises questions that polymer physics must address. What properties uniquely emerge from sequence-definition? Is this circumstance-dependent? How do we define and think about sequence dispersity? How do we think about a hierarchy of sequence effects? Are more sophisticated characterization methods, as well as theoretical and computational tools, needed to understand this class of macromolecules? The answers to these questions touch on many difficult scientific challenges, setting the stage for a rich future for sequence-defined polymers in polymer physics.
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Affiliation(s)
- Sarah L. Perry
- Department of Chemical Engineering, University of Massachusetts−Amherst, 686 North Pleasant Street, Amherst, Massachusetts 01003, United States
| | - Charles E. Sing
- Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana−Champaign, 600 South Mathews Avenue Urbana, Illinois 61801, United States
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20
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Sing CE. Micro- to macro-phase separation transition in sequence-defined coacervates. J Chem Phys 2020; 152:024902. [DOI: 10.1063/1.5140756] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Affiliation(s)
- Charles E. Sing
- Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, 600 S. Mathews Ave., Urbana, Illinois 61801, USA
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21
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Choi JM, Dar F, Pappu RV. LASSI: A lattice model for simulating phase transitions of multivalent proteins. PLoS Comput Biol 2019; 15:e1007028. [PMID: 31634364 PMCID: PMC6822780 DOI: 10.1371/journal.pcbi.1007028] [Citation(s) in RCA: 200] [Impact Index Per Article: 40.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2019] [Revised: 10/31/2019] [Accepted: 10/01/2019] [Indexed: 12/21/2022] Open
Abstract
Many biomolecular condensates form via spontaneous phase transitions that are driven by multivalent proteins. These molecules are biological instantiations of associative polymers that conform to a so-called stickers-and-spacers architecture. The stickers are protein-protein or protein-RNA interaction motifs and / or domains that can form reversible, non-covalent crosslinks with one another. Spacers are interspersed between stickers and their preferential interactions with solvent molecules determine the cooperativity of phase transitions. Here, we report the development of an open source computational engine known as LASSI (LAttice simulation engine for Sticker and Spacer Interactions) that enables the calculation of full phase diagrams for multicomponent systems comprising of coarse-grained representations of multivalent proteins. LASSI is designed to enable computationally efficient phenomenological modeling of spontaneous phase transitions of multicomponent mixtures comprising of multivalent proteins and RNA molecules. We demonstrate the application of LASSI using simulations of linear and branched multivalent proteins. We show that dense phases are best described as droplet-spanning networks that are characterized by reversible physical crosslinks among multivalent proteins. We connect recent observations regarding correlations between apparent stoichiometry and dwell times of condensates to being proxies for the internal structural organization, specifically the convolution of internal density and extent of networking, within condensates. Finally, we demonstrate that the concept of saturation concentration thresholds does not apply to multicomponent systems where obligate heterotypic interactions drive phase transitions. This emerges from the ellipsoidal structures of phase diagrams for multicomponent systems and it has direct implications for the regulation of biomolecular condensates in vivo.
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Affiliation(s)
- Jeong-Mo Choi
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO, United States of America
- Center for Science & Engineering of Living Systems (CSELS), Washington University in St. Louis, St. Louis, MO, United States of America
| | - Furqan Dar
- Center for Science & Engineering of Living Systems (CSELS), Washington University in St. Louis, St. Louis, MO, United States of America
- Department of Physics, Washington University in St. Louis, St. Louis, MO, United States of America
| | - Rohit V. Pappu
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO, United States of America
- Center for Science & Engineering of Living Systems (CSELS), Washington University in St. Louis, St. Louis, MO, United States of America
- * E-mail:
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22
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Ali S, Prabhu VM. Characterization of the Ultralow Interfacial Tension in Liquid-Liquid Phase Separated Polyelectrolyte Complex Coacervates by the Deformed Drop Retraction Method. Macromolecules 2019; 52:7495-7502. [PMID: 32636534 PMCID: PMC7340275 DOI: 10.1021/acs.macromol.9b01491] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Dilute droplets form upon changing the temperature of a phase separated polyelectrolyte complex coacervate. This provides an in situ approach to measure the interfacial tension between supernatant (dilute droplet) and dense coacervate by the deformed drop retraction (DDR) method. The aqueous coacervate, formed via a model 1:1 by charge stoichiometric polyelectrolyte blend, exhibits ultralow interfacial tension with the coexisting phase. DDR finds the interfacial tension scales as γ = γ 0(1 - C s/C s,c) μ , with μ = 1.5 ± 0.1, γ 0 = 204 ± 36 μN/m, and C s,c = 1.977 mol/L. The value of μ independently validates the classical exponent of 3/2. The scaling holds between C s/C s,c of 0.75 to 0.94, the closest measurements to date near the critical salt concentration (C s,c). The temperature dependence of the interfacial tension is consistent with observed lower critical solution phase behavior and classical scaling. A detailed account of the DDR method and validation of assumptions are demonstrated.
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Affiliation(s)
- Samim Ali
- Material Measurement Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, Maryland 20899, United States
| | - Vivek M. Prabhu
- Material Measurement Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, Maryland 20899, United States
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23
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Danielsen SPO, McCarty J, Shea JE, Delaney KT, Fredrickson GH. Small ion effects on self-coacervation phenomena in block polyampholytes. J Chem Phys 2019; 151:034904. [PMID: 31325933 PMCID: PMC6639116 DOI: 10.1063/1.5109045] [Citation(s) in RCA: 35] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2019] [Accepted: 06/25/2019] [Indexed: 12/15/2022] Open
Abstract
Self-coacervation is a phenomenon in which a solution of polyampholytes spontaneously phase separates into a dense liquid coacervate phase, rich in the polyampholyte, coexisting with a dilute supernatant phase. Such coacervation results in the formation of membraneless organelles in vivo and has further been applied industrially as synthetic encapsulants and coatings. It has been suggested that coacervation is primarily driven by the entropy gain from releasing counter-ions upon complexation. Using fully fluctuating field-theoretic simulations employing complex Langevin sampling and complementary molecular dynamics simulations, we have determined that the small ions contribute only weakly to the self-coacervation behavior of charge-symmetric block polyampholytes in solution. Salt partitioning between the supernatant and coacervate is also found to be negligible in the weak-binding regime at low electrostatic strengths. Asymmetries in charge distribution along the polyampholytes can cause net-charges that lead to "tadpole" configurations in dilute solution and the suppression of phase separation at low salt content. The field and particle-based simulation results are compared with analytical predictions from the random phase approximation (RPA) and postulated scaling relationships. The qualitative trends are mostly captured by the RPA, but the approximation fails at low concentration.
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Affiliation(s)
- Scott P O Danielsen
- Department of Chemical Engineering, University of California, Santa Barbara, California 93106, USA
| | - James McCarty
- Materials Research Laboratory, University of California, Santa Barbara, California 93106, USA
| | - Joan-Emma Shea
- Materials Research Laboratory, University of California, Santa Barbara, California 93106, USA
| | - Kris T Delaney
- Materials Research Laboratory, University of California, Santa Barbara, California 93106, USA
| | - Glenn H Fredrickson
- Department of Chemical Engineering, University of California, Santa Barbara, California 93106, USA
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24
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Ong GMC, Sing CE. Mapping the phase behavior of coacervate-driven self-assembly in diblock copolyelectrolytes. SOFT MATTER 2019; 15:5116-5127. [PMID: 31188388 DOI: 10.1039/c9sm00741e] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Oppositely-charged polymers can undergo an associative phase separation process known as complex coacervation, which is driven by the electrostatic attraction between the two polymer species. This driving force for phase separation can be harnessed to drive self-assembly, via pairs of block copolyelectrolytes with opposite charge and thus favorable coulombic interactions. There are few predictions of coacervate self-assembly phase behavior due to the wide variety of molecular and environmental parameters, along with fundamental theoretical challenges. In this paper, we use recent advances in coacervate theory to predict the solution-phase assembly of diblock polyelectrolyte pairs for a number of molecular design parameters (charged block fraction, polymer length). Phase diagrams show that self-assembly occurs at high polymer, low salt concentrations for a range of charge block fractions. We show that we qualitatively obtain limiting results seen in the experimental literature, including the emergence of a high polymer-fraction reentrant transition that gives rise to a self-compatibilized homopolymer coacervate behavior at the limit of high charge block fraction. In intermediate charge block fractions, we draw an analogy between the role of salt concentration in coacervation-driven assembly and the role of temperature in χ-driven assembly. We also explore salt partitioning between microphase separated domains in block copolyelectrolytes, with parallels to homopolyelectrolyte coacervation.
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Affiliation(s)
- Gary M C Ong
- Department of Chemical and Biomolecular Engineering, 600 S. Mathews Ave., Urbana, IL, USA.
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25
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Lytle T, Chang LW, Markiewicz N, Perry SL, Sing CE. Designing Electrostatic Interactions via Polyelectrolyte Monomer Sequence. ACS CENTRAL SCIENCE 2019; 5:709-718. [PMID: 31041391 PMCID: PMC6487445 DOI: 10.1021/acscentsci.9b00087] [Citation(s) in RCA: 72] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/26/2019] [Indexed: 05/12/2023]
Abstract
Charged polymers are ubiquitous in biological systems because electrostatic interactions can drive complicated structure formation and respond to environmental parameters such as ionic strength and pH. In these systems, function emerges from sophisticated molecular design; for example, intrinsically disordered proteins leverage specific sequences of monomeric charges to control the formation and function of intracellular compartments known as membraneless organelles. The role of a charged monomer sequence in dictating the strength of electrostatic interactions remains poorly understood despite extensive evidence that sequence is a powerful tool biology uses to tune soft materials. In this article, we use a combination of theory, experiment, and simulation to establish the physical principles governing sequence-driven control of electrostatic interactions. We predict how arbitrary sequences of charge give rise to drastic changes in electrostatic interactions and correspondingly phase behavior. We generalize a transfer matrix formalism that describes a phase separation phenomenon known as "complex coacervation" and provide a theoretical framework to predict the phase behavior of charge sequences. This work thus provides insights into both how charge sequence is used in biology and how it could be used to engineer properties of synthetic polymer systems.
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Affiliation(s)
- Tyler
K. Lytle
- Department of Chemistry, Department of Chemical and Biomolecular Engineering, and Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Li-Wei Chang
- Department of Chemical Engineering and Institute for Applied Life Sciences, University of Massachuestts Amherst, Amherst, Massachusetts 01003, United States
| | - Natalia Markiewicz
- Department of Chemistry, Department of Chemical and Biomolecular Engineering, and Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Sarah L. Perry
- Department of Chemical Engineering and Institute for Applied Life Sciences, University of Massachuestts Amherst, Amherst, Massachusetts 01003, United States
| | - Charles E. Sing
- Department of Chemistry, Department of Chemical and Biomolecular Engineering, and Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
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26
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Lou J, Friedowitz S, Qin J, Xia Y. Tunable Coacervation of Well-Defined Homologous Polyanions and Polycations by Local Polarity. ACS CENTRAL SCIENCE 2019; 5:549-557. [PMID: 30937382 PMCID: PMC6439447 DOI: 10.1021/acscentsci.8b00964] [Citation(s) in RCA: 49] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/24/2018] [Indexed: 05/23/2023]
Abstract
The ionic complexation of polyelectrolytes is an important mechanism underlying many important biological processes and technical applications. The main driving force for complexation is electrostatic, which is known to be affected by the local polarity near charge centers, but the impact of which on the complexation of polyelectrolytes remains poorly explored. We developed a homologous series of well-defined polyelectrolytes with identical backbone structures, controlled molecular weights, and tunable local polarity to modulate the solvation environment near charged groups. A multitude of systematic, accurate phase diagrams were obtained by spectroscopic measurements of polymer concentrations via fluorescent labeling of polycations. These phase diagrams unambiguously revealed that the liquidlike coacervation is more stable against salt addition at reduced local polarity over a wide range of molecular weights. These trends were quantitatively captured by a theory of complexation that incorporates the effects of dispersion interactions, charge connectivity, and reversible ion-binding, providing the microscopic design rules for tuning molecular parameters and local polarity.
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Affiliation(s)
- Junzhe Lou
- Department
of Materials Science and Engineering, Stanford
University, Stanford, California 94305, United States
| | - Sean Friedowitz
- Department
of Materials Science and Engineering, Stanford
University, Stanford, California 94305, United States
| | - Jian Qin
- Department
of Chemical Engineering, Stanford University, Stanford, California 94305, United States
| | - Yan Xia
- Department
of Chemistry, Stanford University, Stanford, California 94305, United States
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27
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Landsgesell J, Nová L, Rud O, Uhlík F, Sean D, Hebbeker P, Holm C, Košovan P. Simulations of ionization equilibria in weak polyelectrolyte solutions and gels. SOFT MATTER 2019; 15:1155-1185. [PMID: 30706070 DOI: 10.1039/c8sm02085j] [Citation(s) in RCA: 61] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
This article recapitulates the state of the art regarding simulations of ionization equilibria of weak polyelectrolyte solutions and gels. We start out by reviewing the essential thermodynamics of ionization and show how the weak polyelectrolyte ionization differs from the ionization of simple weak acids and bases. Next, we describe simulation methods for ionization reactions, focusing on two methods: the constant-pH ensemble and the reaction ensemble. After discussing the advantages and limitations of both methods, we review the existing simulation literature. We discuss coarse-grained simulations of weak polyelectrolytes with respect to ionization equilibria, conformational properties, and the effects of salt, both in good and poor solvent conditions. This is followed by a discussion of branched star-like weak polyelectrolytes and weak polyelectrolyte gels. At the end we touch upon the interactions of weak polyelectrolytes with other polymers, surfaces, nanoparticles and proteins. Although proteins are an important class of weak polyelectrolytes, we explicitly exclude simulations of protein ionization equilibria, unless they involve protein-polyelectrolyte interactions. Finally, we try to identify gaps and open problems in the existing simulation literature, and propose challenges for future development.
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Affiliation(s)
- Jonas Landsgesell
- Institute for Computational Physics, University of Stuttgart, Allmandring 3, Stuttgart, Germany.
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