1
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Akcay Ogur F, Mamasoglu S, Perry SL, Akin FA, Kayitmazer AB. Interactions between Hyaluronic Acid and Chitosan by Isothermal Titration Calorimetry: The Effect of Ionic Strength, pH, and Polymer Molecular Weight. J Phys Chem B 2024; 128:9022-9035. [PMID: 39248492 DOI: 10.1021/acs.jpcb.4c03930] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/10/2024]
Abstract
Hyaluronic acid (HA)/chitosan (CHI) complex coacervates have recently gained interest due to the pH-dependent ionization and semiflexibility of the polymers as well as their applicability in tissue engineering. Here, we apply isothermal titration calorimetry (ITC) to understand the apparent thermodynamics of coacervation for HA/CHI as a function of the pH, ionic strength, and chain length. We couple these ITC experiments with the knowledge of the charge states of HA and CHI from potentiometric titration to understand the mechanistic aspects of complex formation. Our data demonstrate that the driving force for the complex coacervation of HA and CHI is entropic in nature and this driving force decreased with increasing ionic strength. We also observed a decrease in the stoichiometry for ion-pairing with increasing ionic strength, which we suggest is a consequence of the changing degree of ionization for HA at higher ionic strengths. An increase in the strength of interactions with pH was hypothesized to also be a result of changes in the degree of ionization of HA, though stronger interactions were observed at the lowest pH tested, likely due to contributions from hydrogen bonding between HA and CHI.
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Affiliation(s)
- Fatma Akcay Ogur
- Department of Chemistry, Bogazici University, Bebek, Istanbul 34342, Turkiye
| | - Sezin Mamasoglu
- Department of Chemistry, Bogazici University, Bebek, Istanbul 34342, Turkiye
| | - Sarah L Perry
- Department of Chemical Engineering, University of Massachusetts Amherst, Amherst, Massachusetts 01003, United States
| | - Fatma Ahu Akin
- Department of Chemistry, Bogazici University, Bebek, Istanbul 34342, Turkiye
| | - A Basak Kayitmazer
- Department of Chemistry, Bogazici University, Bebek, Istanbul 34342, Turkiye
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2
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Hoover SC, Margossian KO, Muthukumar M. Theory and quantitative assessment of pH-responsive polyzwitterion-polyelectrolyte complexation. SOFT MATTER 2024; 20:7199-7213. [PMID: 39222025 DOI: 10.1039/d4sm00575a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/04/2024]
Abstract
We introduce a theoretical framework to describe the pH-sensitive phase behavior of polyzwitterion-polyelectrolyte complex coacervates that reasonably captures the phenomenon from recent experimental observations. The polyzwitterion is described by a combinatorial sequence of the four states in which each zwitterionic monomer can occupy: dipolar, quasi-cationic, quasi-anionic, and fully neutralized. We explore the effects of various modifiable chemical and physical properties of the polymers-such as, pKa of the pH-active charged group on the zwitterion, equilibrium constant of salt condensation on the permanently charged group on the zwitterion, degrees of polymerization, hydrophobicity (via the Flory-Huggins interaction parameter), and dipole lengths-on the window of complexation across many stoichiometric mixing ratios of polyzwitterion and polyelectrolyte. The properties that determine the net charge of the polyzwitterion have the strongest effect on the pH range in which polyzwitterion-polyelectrolyte complexation occurs. We finish with general guidance for those interested in molecular design of polyzwitterion-polyelectrolyte complex coacervates and opportunities for future investigation.
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Affiliation(s)
- Samuel C Hoover
- Department of Chemical Engineering, University of Massachusetts Amherst, Amherst, MA 01003, USA
| | - Khatcher O Margossian
- Department of Polymer Science and Engineering, University of Massachusetts Amherst, Amherst, MA 01003, USA.
- Rush University Medical Center and John H. Stroger Hospital of Cook County, both in Chicago, IL 60612, USA
| | - Murugappan Muthukumar
- Department of Polymer Science and Engineering, University of Massachusetts Amherst, Amherst, MA 01003, USA.
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3
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Pineda S, Staňo R, Murmiliuk A, Blanco PM, Montes P, Tošner Z, Groborz O, Pánek J, Hrubý M, Štěpánek M, Košovan P. Charge Regulation Triggers Condensation of Short Oligopeptides to Polyelectrolytes. JACS AU 2024; 4:1775-1785. [PMID: 38818083 PMCID: PMC11134362 DOI: 10.1021/jacsau.3c00668] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/30/2023] [Revised: 02/24/2024] [Accepted: 02/26/2024] [Indexed: 06/01/2024]
Abstract
Electrostatic interactions between charged macromolecules are ubiquitous in biological systems, and they are important also in materials design. Attraction between oppositely charged molecules is often interpreted as if the molecules had a fixed charge, which is not affected by their interaction. Less commonly, charge regulation is invoked to interpret such interactions, i.e., a change of the charge state in response to a change of the local environment. Although some theoretical and simulation studies suggest that charge regulation plays an important role in intermolecular interactions, experimental evidence supporting such a view is very scarce. In the current study, we used a model system, composed of a long polyanion interacting with cationic oligolysines, containing up to 8 lysine residues. We showed using both simulations and experiments that while these lysines are only weakly charged in the absence of the polyanion, they charge up and condense on the polycations if the pH is close to the pKa of the lysine side chains. We show that the lysines coexist in two distinct populations within the same solution: (1) practically nonionized and free in solution; (2) highly ionized and condensed on the polyanion. Using this model system, we demonstrate under what conditions charge regulation plays a significant role in the interactions of oppositely charged macromolecules and generalize our findings beyond the specific system used here.
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Affiliation(s)
- Sebastian
P. Pineda
- Department
of Physical and Macromolecular Chemistry, Faculty of Science, Charles University, Hlavova 8, Prague 2 128 40, Czech Republic
| | - Roman Staňo
- Faculty
of Physics, University of Vienna, Boltzmanngasse 5, Vienna 1090, Austria
- Vienna
Doctoral School in Physics, University of
Vienna, Boltzmanngasse 5, Vienna 1090, Austria
| | - Anastasiia Murmiliuk
- Jülich
Centre for Neutron Science JCNS at Heinz Maier-Leibnitz Zentrum (MLZ), Forschungszentrum Jülich GmbH, Lichtenbergstraße 1, Garching 85748, Germany
| | - Pablo M. Blanco
- Department
of Physical and Macromolecular Chemistry, Faculty of Science, Charles University, Hlavova 8, Prague 2 128 40, Czech Republic
- Department
of Material Science and Physical Chemistry, Research Institute of
Theoretical and Computational Chemistry (IQTCUB), University of Barcelona, C/Martí i Franquès 1, Barcelona 08028, Spain
- Department of Physics, NTNU - Norwegian University of Science and Technology, NO-7491 Trondheim, Norway
| | - Patricia Montes
- Department
of Physical and Macromolecular Chemistry, Faculty of Science, Charles University, Hlavova 8, Prague 2 128 40, Czech Republic
| | - Zdeněk Tošner
- Department
of Physical and Macromolecular Chemistry, Faculty of Science, Charles University, Hlavova 8, Prague 2 128 40, Czech Republic
| | - Ondřej Groborz
- Institute
of Macromolecular Chemistry AS CR, Heyrovský square 2, 162 06 Prague 6, Czech Republic
| | - Jiří Pánek
- Institute
of Macromolecular Chemistry AS CR, Heyrovský square 2, 162 06 Prague 6, Czech Republic
| | - Martin Hrubý
- Institute
of Macromolecular Chemistry AS CR, Heyrovský square 2, 162 06 Prague 6, Czech Republic
| | - Miroslav Štěpánek
- Department
of Physical and Macromolecular Chemistry, Faculty of Science, Charles University, Hlavova 8, Prague 2 128 40, Czech Republic
| | - Peter Košovan
- Department
of Physical and Macromolecular Chemistry, Faculty of Science, Charles University, Hlavova 8, Prague 2 128 40, Czech Republic
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4
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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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5
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Staňo R, van Lente J, Lindhoud S, Košovan P. Sequestration of Small Ions and Weak Acids and Bases by a Polyelectrolyte Complex Studied by Simulation and Experiment. Macromolecules 2024; 57:1383-1398. [PMID: 38370910 PMCID: PMC10867894 DOI: 10.1021/acs.macromol.3c01209] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2023] [Revised: 11/27/2023] [Accepted: 11/29/2023] [Indexed: 02/20/2024]
Abstract
Mixing of oppositely charged polyelectrolytes can result in phase separation into a polymer-poor supernatant and a polymer-rich polyelectrolyte complex (PEC). We present a new coarse-grained model for the Grand-reaction method that enables us to determine the composition of the coexisting phases in a broad range of pH and salt concentrations. We validate the model by comparing it to recent simulations and experimental studies, as well as our own experiments on poly(acrylic acid)/poly(allylamine hydrochloride) complexes. The simulations using our model predict that monovalent ions partition approximately equally between both phases, whereas divalent ones accumulate in the PEC phase. On a semiquantitative level, these results agree with our own experiments, as well as with other experiments and simulations in the literature. In the sequel, we use the model to study the partitioning of a weak diprotic acid at various pH values of the supernatant. Our results show that the ionization of the acid is enhanced in the PEC phase, resulting in its preferential accumulation in this phase, which monotonically increases with the pH. Currently, this effect is still waiting to be confirmed experimentally. We explore how the model parameters (particle size, charge density, permittivity, and solvent quality) affect the measured partition coefficients, showing that fine-tuning of these parameters can make the agreement with the experiments almost quantitative. Nevertheless, our results show that charge regulation in multivalent solutes can potentially be exploited in engineering the partitioning of charged molecules in PEC-based systems at various pH values.
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Affiliation(s)
- Roman Staňo
- Faculty
of Physics, University of Vienna, Boltzmanngasse 5, 1090 Vienna, Austria
- Vienna
Doctoral School in Physics, University of
Vienna, Boltzmanngasse
5, 1090 Vienna, Austria
| | - Jéré
J. van Lente
- Department
of Molecules & Materials, University
of Twente, Drienerlolaan 5, 7522 NB Enschede, The Netherlands
| | - Saskia Lindhoud
- Department
of Molecules & Materials, University
of Twente, Drienerlolaan 5, 7522 NB Enschede, The Netherlands
| | - Peter Košovan
- Department
of Physical and Macromolecular Chemistry, Faculty of Science, Charles University, Hlavova 8, 128 40 Prague 2, Czech Republic
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6
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Joshi P, Decker C, Zeng X, Sathyavageeswaran A, Perry SL, Heldt CL. Design Rules for the Sequestration of Viruses into Polypeptide Complex Coacervates. Biomacromolecules 2024; 25:741-753. [PMID: 38103178 PMCID: PMC10866146 DOI: 10.1021/acs.biomac.3c00938] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2023] [Revised: 11/29/2023] [Accepted: 11/29/2023] [Indexed: 12/17/2023]
Abstract
Encapsulation is a strategy that has been used to facilitate the delivery and increase the stability of proteins and viruses. Here, we investigate the encapsulation of viruses via complex coacervation, which is a liquid-liquid phase separation resulting from the complexation of oppositely charged polymers. In particular, we utilized polypeptide-based coacervates and explored the effects of peptide chemistry, chain length, charge patterning, and hydrophobicity to better understand the effects of the coacervating polypeptides on virus incorporation. Our study utilized two nonenveloped viruses, porcine parvovirus (PPV) and human rhinovirus (HRV). PPV has a higher charge density than HRV, and they both appear to be relatively hydrophobic. These viruses were compared to characterize how the charge, hydrophobicity, and patterning of chemistry on the surface of the virus capsid affects encapsulation. Consistent with the electrostatic nature of complex coacervation, our results suggest that electrostatic effects associated with the net charge of both the virus and polypeptide dominated the potential for incorporating the virus into a coacervate, with clustering of charges also playing a significant role. Additionally, the hydrophobicity of a virus appears to determine the degree to which increasing the hydrophobicity of the coacervating peptides can enhance virus uptake. Nonintuitive trends in uptake were observed with regard to both charge patterning and polypeptide chain length, with these parameters having a significant effect on the range of coacervate compositions over which virus incorporation was observed. These results provide insights into biophysical mechanisms, where sequence effects can control the uptake of proteins or viruses into biological condensates and provide insights for use in formulation strategies.
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Affiliation(s)
- Pratik
U. Joshi
- Department
of Chemical Engineering, Michigan Technological
University, Houghton, Michigan 49931, United States
- Health
Research Institute, Michigan Technological
University, Houghton, Michigan 49931, United States
| | - Claire Decker
- Department
of Chemical Engineering, Michigan Technological
University, Houghton, Michigan 49931, United States
| | - Xianci Zeng
- Department
of Chemical Engineering, University of Massachusetts
Amherst, Amherst, Massachusetts 01003, United States
| | - Arvind Sathyavageeswaran
- Department
of Chemical 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
- Institute
for Applied Life Sciences, University of
Massachusetts Amherst, Amherst, Massachusetts 01003, United States
| | - Caryn L. Heldt
- Department
of Chemical Engineering, Michigan Technological
University, Houghton, Michigan 49931, United States
- Health
Research Institute, Michigan Technological
University, Houghton, Michigan 49931, United States
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7
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Balzer C, Wang ZG. Electroresponse of weak polyelectrolyte brushes. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2023; 46:82. [PMID: 37707751 PMCID: PMC10501941 DOI: 10.1140/epje/s10189-023-00341-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/18/2023] [Accepted: 08/24/2023] [Indexed: 09/15/2023]
Abstract
End-tethered polyelectrolytes are widely used to modify substrate properties, particularly for lubrication or wetting. External stimuli, such as pH, salt concentration, or an electric field, can induce profound structural responses in weak polyelectrolyte brushes, which can be utilized to further tune substrate properties. We study the structure and electroresponsiveness of weak polyacid brushes using an inhomogeneous theory that incorporates both electrostatic and chain connectivity correlations at the Debye-Hückel level. Our calculation shows that a weak polyacid brush swells under the application of a negative applied potential, in agreement with recent experimental observation. We rationalize this behavior using a scaling argument that accounts for the effect of the surface charge. We also show that the swelling behavior has a direct influence on the differential capacitance, which can be modulated by the solvent quality, pH, and salt concentration.
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Affiliation(s)
- Christopher Balzer
- Division of Chemistry and Chemical Engineering, California Institute of Technology, 1200 E California Blvd, Pasadena, CA, 91125, USA
| | - Zhen-Gang Wang
- Division of Chemistry and Chemical Engineering, California Institute of Technology, 1200 E California Blvd, Pasadena, CA, 91125, USA.
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8
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Abstract
Multivalent proteins and nucleic acids, collectively referred to as multivalent associative biomacromolecules, provide the driving forces for the formation and compositional regulation of biomolecular condensates. Here, we review the key concepts of phase transitions of aqueous solutions of associative biomacromolecules, specifically proteins that include folded domains and intrinsically disordered regions. The phase transitions of these systems come under the rubric of coupled associative and segregative transitions. The concepts underlying these processes are presented, and their relevance to biomolecular condensates is discussed.
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Affiliation(s)
- Rohit V Pappu
- Department of Biomedical Engineering, Center for Biomolecular Condensates (CBC), Washington University in St. Louis, St. Louis, Missouri 63130, United States
| | - Samuel R Cohen
- Department of Biomedical Engineering, Center for Biomolecular Condensates (CBC), Washington University in St. Louis, St. Louis, Missouri 63130, United States
- Center of Regenerative Medicine, Washington University in St. Louis, St. Louis, Missouri 63130, United States
| | - Furqan Dar
- Department of Biomedical Engineering, Center for Biomolecular Condensates (CBC), Washington University in St. Louis, St. Louis, Missouri 63130, United States
| | - Mina Farag
- Department of Biomedical Engineering, Center for Biomolecular Condensates (CBC), Washington University in St. Louis, St. Louis, Missouri 63130, United States
| | - Mrityunjoy Kar
- Max Planck Institute of Cell Biology and Genetics, 01307 Dresden, Germany
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9
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Blanco PM, Narambuena CF, Madurga S, Mas F, Garcés JL. Unusual Aspects of Charge Regulation in Flexible Weak Polyelectrolytes. Polymers (Basel) 2023; 15:2680. [PMID: 37376324 PMCID: PMC10302168 DOI: 10.3390/polym15122680] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2023] [Revised: 06/07/2023] [Accepted: 06/10/2023] [Indexed: 06/29/2023] Open
Abstract
This article reviews the state of the art of the studies on charge regulation (CR) effects in flexible weak polyelectrolytes (FWPE). The characteristic of FWPE is the strong coupling of ionization and conformational degrees of freedom. After introducing the necessary fundamental concepts, some unconventional aspects of the the physical chemistry of FWPE are discussed. These aspects are: (i) the extension of statistical mechanics techniques to include ionization equilibria and, in particular, the use of the recently proposed Site Binding-Rotational Isomeric State (SBRIS) model, which allows the calculation of ionization and conformational properties on the same foot; (ii) the recent progresses in the inclusion of proton equilibria in computer simulations; (iii) the possibility of mechanically induced CR in the stretching of FWPE; (iv) the non-trivial adsorption of FWPE on ionized surfaces with the same charge sign as the PE (the so-called "wrong side" of the isoelectric point); (v) the influence of macromolecular crowding on CR.
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Affiliation(s)
- Pablo M. Blanco
- Physical Chemistry Unit, Materials Science and Physical Chemistry Department & Research Institute of Theoretical and Computational Chemistry (IQTCUB), Barcelona University (UB), 08028 Barcelona, Catalonia, Spain;
| | - Claudio F. Narambuena
- Grupo de Bionanotecnologia y Sistemas Complejos, Infap-CONICET & Facultad Regional San Rafael, Universidad Tecnológica Nacional, San Rafael 5600, Argentina;
| | - Sergio Madurga
- Physical Chemistry Unit, Materials Science and Physical Chemistry Department & Research Institute of Theoretical and Computational Chemistry (IQTCUB), Barcelona University (UB), 08028 Barcelona, Catalonia, Spain;
| | - Francesc Mas
- Physical Chemistry Unit, Materials Science and Physical Chemistry Department & Research Institute of Theoretical and Computational Chemistry (IQTCUB), Barcelona University (UB), 08028 Barcelona, Catalonia, Spain;
| | - Josep L. Garcés
- Chemistry Department, Technical School of Agricultural Engineering & AGROTECNIO, Lleida University (UdL), 25003 Lleida, Catalonia, Spain;
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10
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Schmid F. Virtual Issue on Polymers: Recent Advances from a Physical Chemistry Perspective. J Phys Chem B 2022; 126:8359-8361. [PMID: 36300292 DOI: 10.1021/acs.jpcb.2c06378] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Affiliation(s)
- Friederike Schmid
- Institut für Physik, Johannes Gutenberg-Universität Mainz, Staudingerweg 9, 55128 Mainz, Germany
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11
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Chen S, Wang ZG. Driving force and pathway in polyelectrolyte complex coacervation. Proc Natl Acad Sci U S A 2022; 119:e2209975119. [PMID: 36037377 PMCID: PMC9457374 DOI: 10.1073/pnas.2209975119] [Citation(s) in RCA: 19] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2022] [Accepted: 08/01/2022] [Indexed: 11/18/2022] Open
Abstract
There is notable discrepancy between experiments and coarse-grained model studies regarding the thermodynamic driving force in polyelectrolyte complex coacervation: experiments find the free energy change to be dominated by entropy, while simulations using coarse-grained models with implicit solvent usually report a large, even dominant energetic contribution in systems with weak to intermediate electrostatic strength. Here, using coarse-grained, implicit-solvent molecular dynamics simulation combined with thermodynamic analysis, we study the potential of mean force (PMF) in the two key stages on the coacervation pathway for symmetric polyelectrolyte mixtures: polycation-polyanion complexation and polyion pair-pair condensation. We show that the temperature dependence in the dielectric constant of water gives rise to a substantial entropic contribution in the electrostatic interaction. By accounting for this electrostatic entropy, which is due to solvent reorganization, we find that under common conditions (monovalent ions, room temperature) for aqueous systems, both stages are strongly entropy-driven with negligible or even unfavorable energetic contributions, consistent with experimental results. Furthermore, for weak to intermediate electrostatic strengths, this electrostatic entropy, rather than the counterion-release entropy, is the primary entropy contribution. From the calculated PMF, we find that the supernatant phase consists predominantly of polyion pairs with vanishingly small concentration of bare polyelectrolytes, and we provide an estimate of the spinodal of the supernatant phase. Finally, we show that prior to contact, two neutral polyion pairs weakly attract each other by mutually induced polarization, providing the initial driving force for the fusion of the pairs.
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Affiliation(s)
- Shensheng Chen
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125
| | - Zhen-Gang Wang
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125
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12
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Wessén J, Pal T, Chan HS. Field theory description of ion association in re-entrant phase separation of polyampholytes. J Chem Phys 2022; 156:194903. [DOI: 10.1063/5.0088326] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Phase separation of several different overall neutral polyampholyte species (with zero net charge) is studied in solution with two oppositely charged ion species that can form ion-pairs through an association reaction. A field theory description of the system, that treats polyampholyte charge sequence dependent electrostatic interactions as well as excluded volume effects, is hereby given. Interestingly, analysis of the model using random phase approximation and field theoretic simulation consistently show evidence of a re-entrant polyampholyte phase separation at high ion concentrations when there is an overall decrease of volume upon ion-association. As an illustration of the ramifications of our theoretical framework, several polyampholyte concentration vs ion concentration phase diagrams under constant temperature conditions are presented to elucidate the dependence of phase separation behavior on polyampholyte sequence charge pattern as well as ion-pair dissociation constant, volumetric effects on ion association, solvent quality, and temperature.
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Affiliation(s)
- Jonas Wessén
- Department of Biochemsitry, University of Toronto, Canada
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13
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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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14
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Ghasemi M, Larson RG. Future Directions in Physiochemical Modeling of the Thermodynamics of Polyelectrolyte Coacervates (
PECs
). AIChE J 2022. [DOI: 10.1002/aic.17646] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Affiliation(s)
- Mohsen Ghasemi
- Department of Chemical Engineering University of Michigan Ann Arbor Michigan USA
| | - Ronald G. Larson
- Department of Chemical Engineering University of Michigan Ann Arbor Michigan USA
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15
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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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16
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Fossat MJ, Posey AE, Pappu RV. Quantifying charge state heterogeneity for proteins with multiple ionizable residues. Biophys J 2021; 120:5438-5453. [PMID: 34826385 PMCID: PMC8715249 DOI: 10.1016/j.bpj.2021.11.2886] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2021] [Revised: 11/03/2021] [Accepted: 11/19/2021] [Indexed: 01/07/2023] Open
Abstract
Ionizable residues can release and take up protons and this has an influence on protein structure and function. The extent of protonation is linked to the overall pH of the solution and the local environments of ionizable residues. Binding or unbinding of a single proton generates a distinct charge microstate defined by a specific pattern of charges. Accordingly, the overall partition function is a sum over all charge microstates and Boltzmann weights of all conformations associated with each of the charge microstates. This ensemble-of-ensembles description recast as a q-canonical ensemble allows us to analyze and interpret potentiometric titrations that provide information regarding net charge as a function of pH. In the q-canonical ensemble, charge microstates are grouped into mesostates where each mesostate is a collection of microstates of the same net charge. Here, we show that leveraging the structure of the q-canonical ensemble allows us to decouple contributions of net proton binding and release from proton arrangement and conformational considerations. Through application of the q-canonical formalism to analyze potentiometric measurements of net charge in proteins with repetitive patterns of Lys and Glu residues, we determine the underlying mesostate pKa values and, more importantly, we estimate relative mesostate populations as a function of pH. This is a strength of using the q-canonical approach that cannot be replicated using purely site-specific analyses. Overall, our work shows how measurements of charge equilibria, decoupled from measurements of conformational equilibria, and analyzed using the framework of the q-canonical ensemble, provide protein-specific quantitative descriptions of pH-dependent populations of mesostates. This method is of direct relevance for measuring and understanding how different charge states contribute to conformational, binding, and phase equilibria of proteins.
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Affiliation(s)
- Martin J Fossat
- Department of Biomedical Engineering and Center for Science & Engineering of Living Systems (CSELS), Washington University in St. Louis, St. Louis, Missouri
| | - Ammon E Posey
- Department of Biomedical Engineering and Center for Science & Engineering of Living Systems (CSELS), Washington University in St. Louis, St. Louis, Missouri
| | - Rohit V Pappu
- Department of Biomedical Engineering and Center for Science & Engineering of Living Systems (CSELS), Washington University in St. Louis, St. Louis, Missouri.
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