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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 DOI: 10.3390/polym15122680] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [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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Blanco PM, Madurga S, Garcés JL, Mas F, Dias RS. Influence of macromolecular crowding on the charge regulation of intrinsically disordered proteins. Soft Matter 2021; 17:655-669. [PMID: 33215185 DOI: 10.1039/d0sm01475c] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
In this work we study the coupling between ionization and conformational properties of two IDPs, histatin-5 and β-amyloid 42, in the presence of neutral and charged crowders. The latter is modeled to resemble bovine serum albumin (BSA). With this aim, semi-grand canonical Monte Carlo simulations are performed, so that the IDP charge is a dynamic property, undergoing protonation/deprotonation processes. Both ionization properties (global and specific amino acid charge and binding capacitance) and radius of gyration are analyzed in a large range of pH values and salt concentrations. Without crowder agents, the titration curve of histatin-5, a polycation, is salt-dependent while that of β-amyloid 42, a polyampholyte, is almost unaffected. The salt concentration is found to be particularly relevant at pH values where the protein binding capacitance (directly linked with charge fluctuation) is larger. Upon addition of neutral crowders, charge regulation is observed in histatin-5, while for β-amyloid 42 this effect is very small. The main mechanism for charge regulation is found to be the effective increase in the ionic strength due to the excluded volume. In the presence of charged crowders, a significant increase in the charge of both IDPs is observed in almost all the pH range. In this case, the IDP charge is altered not only by the increase in the effective ionic strength but also by its direct electrostatic interaction with the charged crowders.
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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) of Barcelona University (UB), Barcelona, Catalonia, Spain.
| | - Sergio Madurga
- Physical Chemistry Unit, Materials Science and Physical Chemistry Department & Research Institute of Theoretical and Computational Chemistry (IQTCUB) of Barcelona University (UB), Barcelona, Catalonia, Spain.
| | - Josep L Garcés
- Chemistry Department, Technical School of Agricultural Engineering & AGROTECNIO of Lleida University (UdL), Lleida, Catalonia, Spain
| | - Francesc Mas
- Physical Chemistry Unit, Materials Science and Physical Chemistry Department & Research Institute of Theoretical and Computational Chemistry (IQTCUB) of Barcelona University (UB), Barcelona, Catalonia, Spain.
| | - Rita S Dias
- Department of Physics, Norwegian University of Science and Technology (NTNU), Trondheim, Norway.
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Tang J, Katashima T, Li X, Mitsukami Y, Yokoyama Y, Sakumichi N, Chung UI, Shibayama M, Sakai T. Swelling Behaviors of Hydrogels with Alternating Neutral/Highly Charged Sequences. Macromolecules 2020. [DOI: 10.1021/acs.macromol.0c01221] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Affiliation(s)
- Jian Tang
- Department of Bioengineering, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
| | - Takuya Katashima
- Department of Bioengineering, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
| | - Xiang Li
- The Institute for Solid State Physics, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581, Japan
| | - Yoshiro Mitsukami
- Superabsorbents Research Department, Nippon Shokubai Co., Ltd., 992-1 Aza Nishioki Okihama, Aboshi-ku, Himeji, Hyogo 671-1292, Japan
| | - Yuki Yokoyama
- Superabsorbents Research Department, Nippon Shokubai Co., Ltd., 992-1 Aza Nishioki Okihama, Aboshi-ku, Himeji, Hyogo 671-1292, Japan
| | - Naoyuki Sakumichi
- Department of Bioengineering, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
| | - Ung-il Chung
- Department of Bioengineering, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
| | - Mitsuhiro Shibayama
- Neutron Science and Technology Center, Comprehensive Research Organization for Science and Society, 162-1 Tokai, Ibaraki 319-1106, Japan
| | - Takamasa Sakai
- Department of Bioengineering, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
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Blanco PM, Madurga S, Narambuena CF, Mas F, Garcés JL. Role of Charge Regulation and Fluctuations in the Conformational and Mechanical Properties of Weak Flexible Polyelectrolytes. Polymers (Basel) 2019; 11:polym11121962. [PMID: 31795443 PMCID: PMC6960815 DOI: 10.3390/polym11121962] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2019] [Revised: 11/21/2019] [Accepted: 11/25/2019] [Indexed: 01/29/2023] Open
Abstract
This work addresses the role of charge regulation (CR) and the associated fluctuations in the conformational and mechanical properties of weak polyelectrolytes. Due to CR, changes in the pH-value modifies the average macromolecular charge and conformational equilibria. A second effect is that, for a given average charge per site, fluctuations can alter the intensity of the interactions by means of correlation between binding sites. We investigate both effects by means of Monte Carlo simulations at constant pH-value, so that the charge is a fluctuating quantity. Once the average charge per site is available, we turn off the fluctuations by assigning the same average charge to every site. A constant charge MC simulation is then performed. We make use of a model which accounts for the main fundamental aspects of a linear flexible polyelectrolyte that is, proton binding, angle internal rotation, bond stretching and bending. Steric excluded volume and differentiated treatment for short-range and long-range interactions are also included. This model can be regarded as a kind of “minimal” in the sense that it contains a minimum number of parameters but still preserving the atomistic detail. It is shown that, if fluctuations are activated, gauche state bond probabilities increase and the persistence length decreases, so that the polymer becomes more folded. Macromolecular stretching is also analyzed in presence of CR (the charge depends on the applied force) and without CR (the charge is fixed to the value at zero force). The analysis of the low force scaling behavior concludes that Pincus exponent becomes pH-dependent. Both, with and without CR, a transition from 1/2 at high pH-values (phantom chain) to 3/5 at low pH-values (Pincus regime) is observed. Finally, the intermediate force stretching regime is investigated. It is found that CR induces a moderate influence in the force-extension curves and persistence length (which in this force regime becomes force-dependent). It is thus concluded that the effect of CR on the stretching curves is mainly due to the changes in the average charge at zero force. It is also found that, for the cases studied, the effect of steric excluded volume is almost irrelevant compared to electrostatic interactions.
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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) of Barcelona University (UB), 08028 Barcelona, Catalonia, Spain;
- Correspondence: (P.M.B.); (F.M.)
| | - Sergio Madurga
- Physical Chemistry Unit, Materials Science and Physical Chemistry Department & Research Institute of Theoretical and Computational Chemistry (IQTCUB) of Barcelona University (UB), 08028 Barcelona, Catalonia, Spain;
| | - Claudio F. Narambuena
- Facultad Regional San Rafael, Universidad Tecnológica Nacional & Instituto de Física Aplicada (INFAP), Universidad Nacional de San Luis-CONICET, 5600 San Rafael, Argentina;
| | - Francesc Mas
- Physical Chemistry Unit, Materials Science and Physical Chemistry Department & Research Institute of Theoretical and Computational Chemistry (IQTCUB) of Barcelona University (UB), 08028 Barcelona, Catalonia, Spain;
- Correspondence: (P.M.B.); (F.M.)
| | - Josep L. Garcés
- Chemistry Department, Technical School of Agricultural Engineering & AGROTECNIO of Lleida University (UdL), 25003 Lleida, Catalonia, Spain;
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Blanco PM, Madurga S, Mas F, Garcés JL. Effect of Charge Regulation and Conformational Equilibria in the Stretching Properties of Weak Polyelectrolytes. Macromolecules 2019. [DOI: 10.1021/acs.macromol.9b01160] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Affiliation(s)
- Pablo M. Blanco
- Physical Chemistry Unit, Materials Science and Physical Chemistry Department & Research Institute of Theoretical and Computational Chemistry (IQTCUB) of Barcelona University (UB), Barcelona 08028, Catalonia, Spain
| | - Sergio Madurga
- Physical Chemistry Unit, Materials Science and Physical Chemistry Department & Research Institute of Theoretical and Computational Chemistry (IQTCUB) of Barcelona University (UB), Barcelona 08028, Catalonia, Spain
| | - Francesc Mas
- Physical Chemistry Unit, Materials Science and Physical Chemistry Department & Research Institute of Theoretical and Computational Chemistry (IQTCUB) of Barcelona University (UB), Barcelona 08028, Catalonia, Spain
| | - Josep L. Garcés
- Chemistry Department, Technical School of Agricultural Engineering & AGROTECNIO of Lleida University (UdL), Lleida 25198, Catalonia, Spain
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Blanco PM, Madurga S, Mas F, Garcés JL. Coupling of Charge Regulation and Conformational Equilibria in Linear Weak Polyelectrolytes: Treatment of Long-Range Interactions via Effective Short-Ranged and pH-Dependent Interaction Parameters. Polymers (Basel) 2018; 10:E811. [PMID: 30960736 PMCID: PMC6403780 DOI: 10.3390/polym10080811] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2018] [Revised: 07/17/2018] [Accepted: 07/23/2018] [Indexed: 01/26/2023] Open
Abstract
The classical Rotational Isomeric State (RIS) model, originally proposed by Flory, has been used to rationalize a wide range of physicochemical properties of neutral polymers. However, many weak polyelectrolytes of interest are able to regulate their charge depending on the conformational state of the bonds. Recently, it has been shown that the RIS model can be coupled with the Site Binding (SB) model, for which the ionizable sites can adopt two states: protonated or deprotonated. The resulting combined scheme, the SBRIS model, allows for analyzing ionization and conformational equilibria on the same foot. In the present work, this approach is extended to include pH-dependent electrostatic Long-Range (LR) interactions, ubiquitous in weak polyelectrolytes at moderate and low ionic strengths. With this aim, the original LR interactions are taken into account by defining effective Short-Range (SR) and pH-dependent parameters, such as effective microscopic protonation constants and rotational bond energies. The new parameters are systematically calculated using variational methods. The machinery of statistical mechanics for SR interactions, including the powerful and fast transfer matrix methods, can then be applied. The resulting technique, which we will refer to as the Local Effective Interaction Parameters (LEIP) method, is illustrated with a minimal model of a flexible linear polyelectrolyte containing only one type of rotating bond. LEIP reproduces very well the pH dependence of the degree of protonation and bond probabilities obtained by semi-grand canonical Monte Carlo simulations, where LR interactions are explicitly taken into account. The reduction in the computational time in several orders of magnitude suggests that the LEIP technique could be useful in a range of areas involving linear weak polyelectrolytes, allowing direct fitting of the relevant physical parameters to the experimental quantities.
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Affiliation(s)
- Pablo M Blanco
- Physical Chemistry Unit, Department of Materials Science and Physical Chemistry & Research Institute of Theoretical and Computational Chemistry (IQTCUB) of Barcelona University (UB), 08028 Barcelona, Catalonia, Spain.
| | - Sergio Madurga
- Physical Chemistry Unit, Department of Materials Science and Physical Chemistry & Research Institute of Theoretical and Computational Chemistry (IQTCUB) of Barcelona University (UB), 08028 Barcelona, Catalonia, Spain.
| | - Francesc Mas
- Physical Chemistry Unit, Department of Materials Science and Physical Chemistry & Research Institute of Theoretical and Computational Chemistry (IQTCUB) of Barcelona University (UB), 08028 Barcelona, Catalonia, Spain.
| | - Josep L Garcés
- Department of Chemistry, Technical School of Agricultural Engineering & Agrotecnio of Lleida University (UdL), 25003 Lleida, Catalonia, Spain.
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Madurga S, Nedyalkova M, Mas F, Garcés JL. Ionization and Conformational Equilibria of Citric Acid: Delocalized Proton Binding in Solution. J Phys Chem A 2017; 121:5894-5906. [PMID: 28703587 DOI: 10.1021/acs.jpca.7b05089] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The microspeciation of citric acid is studied by analyzing NMR titration data. When the site binding (SB) model, which assumes fully localized proton binding to the carboxylic groups, is used to obtain microscopic energy parameters (dissociation constants, pair and triplet interaction energies between charged carboxylate groups), contradictory results are obtained. The resulting macroscopic constants are in very good agreement with the values reported in the literature using potentiometry. However, the found pair interaction energy between the terminal carboxylates and the triplet interaction energy are physically meaningless. To solve this apparent contradiction, we consider the possibility of delocalized proton binding, so that the proton can be exchanged at high velocity in the NMR time scale through short, strong, low-barrier (SSLB) hydrogen bonds. With this aim, ab initio MP2 calculations using the SMD polarizable continuum model for the solvent were performed and the fully roto-microspeciation elucidated. First, fully localized proton binding was assumed, and the resulting microstate probabilities are in reasonable agreement with those reported in previous works that use selective blocking of the carboxylic groups. They are, however, in clear disagreement with the microstate probabilities derived from the NMR titration data, which predict, within a very narrow confidence interval, a unique microspecies for the symmetric di-ionized form. Moreover, counterintuitively, the interaction between terminal charged groups is much larger than that between central and terminal groups. As a consequence, we have explored the possibility of delocalized proton binding by calculating the energy of intermediate proton positions between two carbolxylic groups. The results reveal that the exchange of the proton through the hydrogen bonds is in some cases produced without energetic barrier. This effect is specially relevant in the di-ionized form, with all the most stable conformations forming a SSLB, which together would constitute the only microstate detected by NMR. An alternative reaction scheme for the ionization process, based on proton delocalization, is proposed.
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Affiliation(s)
- Sergio Madurga
- Materials Science and Physical Chemistry Department & Research Institute of Theoretical and Computational Chemistry (IQTCUB), Barcelona University (UB) , C/Martı́ i Franquès, 1, 08028 Barcelona, Catalonia, Spain
| | - Miroslava Nedyalkova
- Inorganic Chemistry Department, Faculty of Chemistry and Pharmacy "St Kliment Ohridski", University of Sofia , 1 James Bourchier Blvd., 1164 Sofia, Bulgaria
| | - Francesc Mas
- Materials Science and Physical Chemistry Department & Research Institute of Theoretical and Computational Chemistry (IQTCUB), Barcelona University (UB) , C/Martı́ i Franquès, 1, 08028 Barcelona, Catalonia, Spain
| | - Josep Lluís Garcés
- Chemistry Department and AGROTECNIO, University of Lleida (UdL) , Rovira Roure, 191, 25198 Lleida Catalonia, Spain
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Abstract
Polyplexes composed of polyethyleneimine (PEI) and DNA or siRNA have attracted great attention for their use in gene therapy. Although many physicochemical characteristics of these polyplexes remain unknown, PEI/DNA complexes have been repeatedly shown to be more stable than their PEI/siRNA counterparts. Here, we examine potential causes for this difference using atomistic molecular dynamics simulations of complexation between linear PEI and DNA or siRNA duplexes containing the same number of bases. The two types of polyplexes are stabilized by similar interactions, as PEI amines primarily interact with nucleic acid phosphate groups but also occasionally interact with groove atoms of both nucleic acids. However, the number of interactions in PEI/DNA complexes is greater than in comparable PEI/siRNA complexes, with interactions between protonated PEI amines and DNA being particularly enhanced. These results indicate that structural differences between DNA and siRNA may play a role in the increased stability of PEI/DNA complexes. In addition, we investigate the binding of PEI chains to polyplexes that have a net positive charge. The binding of PEI to these overcharged complexes involves interactions between PEI and areas on the nucleic acid surface that have maintained a negative electrostatic potential and is facilitated by the release of water from the nucleic acid.
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Affiliation(s)
- Jesse D Ziebarth
- Department of Chemistry, The University of Memphis , Memphis, Tennessee 38152, United States
| | - Dennis R Kennetz
- Department of Chemistry, The University of Memphis , Memphis, Tennessee 38152, United States
| | - Nyles J Walker
- Department of Chemistry, The University of Memphis , Memphis, Tennessee 38152, United States
| | - Yongmei Wang
- Department of Chemistry, The University of Memphis , Memphis, Tennessee 38152, United States
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Garcés JL, Madurga S, Rey-Castro C, Mas F. Dealing with long-range interactions in the determination of polyelectrolyte ionization properties. Extension of the transfer matrix formalism to the full range of ionic strengths. ACTA ACUST UNITED AC 2016. [DOI: 10.1002/polb.24269] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Affiliation(s)
- Josep L. Garcés
- Chemistry Department; Technical School of Agricultural Engineering & AGROTECNIO of Lleida University (UdL); Lleida Catalonia Spain
| | - Sergio Madurga
- Physical Chemistry Unit; Materials Science and Physical Chemistry Department & Research Institute of Theoretical and Computational Chemistry (IQTCUB) of Barcelona University (UB); Barcelona Catalonia Spain
| | - Carlos Rey-Castro
- Chemistry Department; Technical School of Agricultural Engineering & AGROTECNIO of Lleida University (UdL); Lleida Catalonia Spain
| | - Francesc Mas
- Physical Chemistry Unit; Materials Science and Physical Chemistry Department & Research Institute of Theoretical and Computational Chemistry (IQTCUB) of Barcelona University (UB); Barcelona Catalonia Spain
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