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Rudolf Podgornik - One of the best experts on this subject based on the ideXlab platform.

  • Phase Separation of Polyelectrolytes: The Effect of Charge Regulation
    arXiv: Soft Condensed Matter, 2021
    Co-Authors: Bin Zheng, David Andelman, Yael Avni, Rudolf Podgornik
    Abstract:

    Complex coacervation, known as the liquid-liquid phase separation of solutions with oppositely Charged polyelectrolytes, has attracted substantial interest in recent years. We study the effect of Charge Regulation (CR) mechanism on the complex coacervation, by including short-range interactions between the Charged sites on the polymer chains, as well as an association-dissociation energy parameter in the CR mechanism. We investigate the phase diagrams of two CR models: (i)~the hopping CR model (HCR); and, (ii)~the asymmetric CR model (ACR). It is shown that during the phase separation, the polymers in the condensed phase are more Charged than in the dilute phase, in accord with the Le Chatelier's principle. In addition, "secondary CR" effects also influence the change in the volume fraction of the two phases. The latter can cause the Charge difference between the two phases to change non-monotonically as a function of the CR parameters. These predictions are subject to future experimental verifications.

  • Charge Regulation radically modifies electrostatics in membrane stacks
    Physical Review E, 2019
    Co-Authors: Markus Bier, Arghya Majee, Ralf Blossey, Rudolf Podgornik
    Abstract:

    Motivated by biological membrane-containing organelles in plants and photosynthetic bacteria, we study Charge Regulation in a model membrane stack. Considering (de)protonation as the simplest mechanism of Charge equilibration between the membranes and with the bathing environment, we uncover a symmetry-broken Charge state in the stack with a quasiperiodic effective Charge sequence. In the case of a monovalent bathing salt solution our model predicts complex, inhomogeneous Charge equilibria depending on the strength of the (de)protonation reaction, salt concentration, and membrane size. Our results shed light on the basic reorganization mechanism of thylakoid membrane stacks.

  • Charge Regulation radically modifies electrostatics in membrane stacks
    Physical Review E, 2019
    Co-Authors: Arghya Majee, Markus Bier, Ralf Blossey, Rudolf Podgornik
    Abstract:

    Motivated by biological membrane-containing organelles in plants and photosynthetic bacteria, we study Charge Regulation in a model membrane stack. Considering (de)protonation as the simplest mechanism of Charge equilibration between the membranes and with the bathing environment, we uncover a symmetry-broken Charge state in the stack with a quasiperiodic effective Charge sequence. In the case of a monovalent bathing salt solution our model predicts complex, inhomogeneous Charge equilibria depending on the strength of the (de)protonation reaction, salt concentration, intermembrane separation, and their number in the stack. Our results shed light on the basic reorganization mechanism of thylakoid membrane stacks. * majee@is.mpg.de 1 arXiv:1909.00217v2 [cond-mat.soft]

  • Charge Regulation with fixed and mobile Charged macromolecules
    Current Opinion in Electrochemistry, 2019
    Co-Authors: Yael Avni, David Andelman, Rudolf Podgornik
    Abstract:

    Abstract Uncompensated Charges do not usually occur in Nature and any local Charge should be a result of Charge separation. Dissociable chemical groups at interfaces in contact with ions in solution, whose chemical equilibrium depends both on short-range non-electrostatic and long-range electrostatic interactions, are the physical basis of this Charge separation, known as Charge Regulation phenomena. The Charged groups can be either fixed and immobile, as in the case of solvent-exposed solid substrate and soft bounding surfaces (e.g., atomically smooth mica surfaces and soft phospholipid membranes), or free and mobile, as in the case of Charged macro-ions (e.g., protein or other biomolecules). Here, we review the mean-field formalism used to describe both cases, with a focus on recent advances in the modeling of mobile Charge-regulated macro-ions in an ionic solution. The general form of the screening length is derived, and is shown to combine the concept of intrinsic capacitance (introduced by Lund and Jonsson) with bulk capacitance, resulting from the mobility of small ions and macro-ions. The advantages and disadvantages of different formulations, such as the cell model vs. the collective approach, are discussed, along with several suggestions for future experiments and modeling.

  • anomalous multipole expansion Charge Regulation of patchy inhomogeneously Charged spherical particles
    Journal of Chemical Physics, 2018
    Co-Authors: Anže Losdorfer Božic, Rudolf Podgornik
    Abstract:

    Charge Regulation is an important aspect of electrostatics in biological and colloidal systems, where the Charges are generally not fixed but depend on the environmental variables. Here, we analyze the Charge Regulation mechanism in patchy inhomogeneously Charged spherical particles, such as globular proteins, colloids, or viruses. Together with the multipole expansion of inhomogeneously Charged spherical surfaces, the Charge Regulation mechanism on the level of linear approximation is shown to lead to a mixing between different multipole moments depending on their capacitance-the response function of the Charge distribution with respect to the electrostatic potential. This presents an additional anomalous feature of molecular electrostatics in the presence of ionic screening. We demonstrate the influence of Charge Regulation on several examples of inhomogeneously Charged spherical particles, showing that it leads to significant changes in their multipole moments.

Josep Lluís Garcés - One of the best experts on this subject based on the ideXlab platform.

  • Influence of macromolecular crowding on the Charge Regulation of intrinsically disordered proteins.
    Soft matter, 2020
    Co-Authors: Pablo M. Blanco, Sergio Madurga, Josep Lluís Garcés, Francesc Mas, Rita S. Dias
    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.

  • Role of Charge Regulation and Fluctuations in the Conformational and Mechanical Properties of Weak Flexible Polyelectrolytes.
    Polymers, 2019
    Co-Authors: Pablo M. Blanco, Sergio Madurga, Francesc Mas, Claudio F. Narambuena, Josep Lluís Garcés
    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.

  • Role of Charge Regulation and Fluctuations in the Conformational and Mechanical Properties of Weak Flexible Polyelectrolytes
    2019
    Co-Authors: Pablo M. Blanco, Sergio Madurga, Francesc Mas, Claudio F. Narambuena, Josep Lluís Garcés
    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 i.e. 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 in the model. It can be regarded as a kind of "minimal'' model in the sense that 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 to 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 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.

  • Effect of Charge Regulation and Conformational Equilibria in the Stretching Properties of Weak Polyelectrolytes
    Macromolecules, 2019
    Co-Authors: Pablo M. Blanco, Sergio Madurga, Francesc Mas, Josep Lluís Garcés
    Abstract:

    Weak polyelectrolytes can modulate their Charge in response to external perturbations, such as changes in the pH, ionic strength (I), or electrostatic interactions with other Charged species, a phenomenon known as Charge Regulation (CR). On the other hand, it is well established that CR is highly coupled with the conformational degrees of freedom. In this paper, the influence of CR in the stretching properties of weak polyelectrolytes is analyzed, and the possibility of CR induced by mechanical stretching is explored. With this aim, we make use of a minimal model, which captures the fundamental aspects present in the stretching of a flexible weak linear polyelectrolyte: internal angle rotation, bond stretching, bond bending, and proton binding, which is the paradigmatic mechanism of CR. The angle rotation is described by using the rotational isomeric state approximation, while for protonation, the site binding model is assumed. Mechanical stretching is studied by performing semi-grand canonical Monte Carl...

Arghya Majee - One of the best experts on this subject based on the ideXlab platform.

  • Charge Regulation radically modifies electrostatics in membrane stacks
    Physical Review E, 2019
    Co-Authors: Markus Bier, Arghya Majee, Ralf Blossey, Rudolf Podgornik
    Abstract:

    Motivated by biological membrane-containing organelles in plants and photosynthetic bacteria, we study Charge Regulation in a model membrane stack. Considering (de)protonation as the simplest mechanism of Charge equilibration between the membranes and with the bathing environment, we uncover a symmetry-broken Charge state in the stack with a quasiperiodic effective Charge sequence. In the case of a monovalent bathing salt solution our model predicts complex, inhomogeneous Charge equilibria depending on the strength of the (de)protonation reaction, salt concentration, and membrane size. Our results shed light on the basic reorganization mechanism of thylakoid membrane stacks.

  • Charge Regulation radically modifies electrostatics in membrane stacks
    Physical Review E, 2019
    Co-Authors: Arghya Majee, Markus Bier, Ralf Blossey, Rudolf Podgornik
    Abstract:

    Motivated by biological membrane-containing organelles in plants and photosynthetic bacteria, we study Charge Regulation in a model membrane stack. Considering (de)protonation as the simplest mechanism of Charge equilibration between the membranes and with the bathing environment, we uncover a symmetry-broken Charge state in the stack with a quasiperiodic effective Charge sequence. In the case of a monovalent bathing salt solution our model predicts complex, inhomogeneous Charge equilibria depending on the strength of the (de)protonation reaction, salt concentration, intermembrane separation, and their number in the stack. Our results shed light on the basic reorganization mechanism of thylakoid membrane stacks. * majee@is.mpg.de 1 arXiv:1909.00217v2 [cond-mat.soft]

Pablo M. Blanco - One of the best experts on this subject based on the ideXlab platform.

  • Influence of macromolecular crowding on the Charge Regulation of intrinsically disordered proteins.
    Soft matter, 2020
    Co-Authors: Pablo M. Blanco, Sergio Madurga, Josep Lluís Garcés, Francesc Mas, Rita S. Dias
    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.

  • Role of Charge Regulation and Fluctuations in the Conformational and Mechanical Properties of Weak Flexible Polyelectrolytes.
    Polymers, 2019
    Co-Authors: Pablo M. Blanco, Sergio Madurga, Francesc Mas, Claudio F. Narambuena, Josep Lluís Garcés
    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.

  • Role of Charge Regulation and Fluctuations in the Conformational and Mechanical Properties of Weak Flexible Polyelectrolytes
    2019
    Co-Authors: Pablo M. Blanco, Sergio Madurga, Francesc Mas, Claudio F. Narambuena, Josep Lluís Garcés
    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 i.e. 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 in the model. It can be regarded as a kind of "minimal'' model in the sense that 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 to 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 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.

  • Effect of Charge Regulation and Conformational Equilibria in the Stretching Properties of Weak Polyelectrolytes
    Macromolecules, 2019
    Co-Authors: Pablo M. Blanco, Sergio Madurga, Francesc Mas, Josep Lluís Garcés
    Abstract:

    Weak polyelectrolytes can modulate their Charge in response to external perturbations, such as changes in the pH, ionic strength (I), or electrostatic interactions with other Charged species, a phenomenon known as Charge Regulation (CR). On the other hand, it is well established that CR is highly coupled with the conformational degrees of freedom. In this paper, the influence of CR in the stretching properties of weak polyelectrolytes is analyzed, and the possibility of CR induced by mechanical stretching is explored. With this aim, we make use of a minimal model, which captures the fundamental aspects present in the stretching of a flexible weak linear polyelectrolyte: internal angle rotation, bond stretching, bond bending, and proton binding, which is the paradigmatic mechanism of CR. The angle rotation is described by using the rotational isomeric state approximation, while for protonation, the site binding model is assumed. Mechanical stretching is studied by performing semi-grand canonical Monte Carl...

Markus Bier - One of the best experts on this subject based on the ideXlab platform.

  • Charge Regulation radically modifies electrostatics in membrane stacks
    Physical Review E, 2019
    Co-Authors: Markus Bier, Arghya Majee, Ralf Blossey, Rudolf Podgornik
    Abstract:

    Motivated by biological membrane-containing organelles in plants and photosynthetic bacteria, we study Charge Regulation in a model membrane stack. Considering (de)protonation as the simplest mechanism of Charge equilibration between the membranes and with the bathing environment, we uncover a symmetry-broken Charge state in the stack with a quasiperiodic effective Charge sequence. In the case of a monovalent bathing salt solution our model predicts complex, inhomogeneous Charge equilibria depending on the strength of the (de)protonation reaction, salt concentration, and membrane size. Our results shed light on the basic reorganization mechanism of thylakoid membrane stacks.

  • Charge Regulation radically modifies electrostatics in membrane stacks
    Physical Review E, 2019
    Co-Authors: Arghya Majee, Markus Bier, Ralf Blossey, Rudolf Podgornik
    Abstract:

    Motivated by biological membrane-containing organelles in plants and photosynthetic bacteria, we study Charge Regulation in a model membrane stack. Considering (de)protonation as the simplest mechanism of Charge equilibration between the membranes and with the bathing environment, we uncover a symmetry-broken Charge state in the stack with a quasiperiodic effective Charge sequence. In the case of a monovalent bathing salt solution our model predicts complex, inhomogeneous Charge equilibria depending on the strength of the (de)protonation reaction, salt concentration, intermembrane separation, and their number in the stack. Our results shed light on the basic reorganization mechanism of thylakoid membrane stacks. * majee@is.mpg.de 1 arXiv:1909.00217v2 [cond-mat.soft]