Proteins and Polyampholytes Interacting with Polyelectrolyte Brushes and Microgels: The Charge Reversal Concept Revised

Abstract

Weak polyampholytes and globular proteins among them can be efficiently absorbed from solutions by polyelectrolyte brushes or microgels even if the net charge of the polyampholyte is of the same sign as that of the brush/microgel. We use a mean-field approach for calculating the free energy of insertion of a probe polyampholyte molecule into a polyelectrolyte brush/microgel. We anticipate that the insertion of the polyampholyte into similarly charged brush/microgel may be thermodynamically favorable due to the gain in the cumulative re-ionization free energy of the pH-sensitive acidic and basic residues. Importantly, we demonstrate that the polyampholyte (protein) charge sign inversion upon transfer from the bulk of the solution to the brush/microgel does not provide sufficient conditions to assure negative re-ionization free energy balance. Thus (in the absence of other driving or stopping mechanisms), charge sign inversion does not necessarily provoke spontaneous absorption of the polyampholyte into the brush/microgel.

Both Charge-Regulation and Charge-Patch Distribution Can Drive Adsorption on the Wrong Side of the Isoelectric Point

“…A more systematic paradigm of charge regulation can be found in simulation studies of synthetic PEs, ampholytes, and artificial peptide sequences. − Recently, Laktionov et al used the mean-field theory to show that charge regulation can lead to a charge reversal of ampholytes upon adsorption to polyelectrolyte brushes. Rathee et al have shown that cooperative charge regulation effects account for the association of polyacids with polybases when their p K A values are close to the solution pH, whereas cooperativity vanishes when one or both p K A values are far from the pH .…”

Bovine Serum Albumin Interaction with Polyanionic and Polycationic Brushes: The Case Theoretical Study

“…Following ref. [ 7 ], we present it as where , , , are the respective degrees of ionization of basic and acidic monomer units of type in the globule placed at distance z from the grafting surface or in the bulk of the solution (at ). Because concentration of hydrogen ions in the polyanionic/polycationic brush is larger/smaller than in the bulk of the solution, acidic/basic residues become more strongly/weakly ionized upon insertion of the globule into polyacidic brush and vice versa for the polybasic brush.…”

“…Interactions of globular proteins with polyelectrolyte brushes (layers of charged macromolecules end-attached to a planar substrate or to the surface of colloidal particles and immersed in an aqueous solution) have been extensively studied both experimentally [ 1 , 2 , 3 , 4 ] and theoretically [ 5 , 6 , 7 , 8 , 9 , 10 ] in the past two decades.…”

Current Research on Polyelectrolyte Nanostructures: From Molecular Interactions to Biomedical Applications

“…Block polyelectrolytes with one charged and one hydrophobic block lead to the formation of core-shell micelles where a hydrophobic core is surrounded by a charged polymer corona. This kind of NP allows for the solubilization of hydrophobic molecules, e.g., drugs, in their core while the external shell not only stabilizes them in aqueous media [31,32] but also can bind oppositely charged molecules, e.g., proteins [33][34][35]. On the other hand, random amphiphilic copolymers of polyelectrolyte and hydrophobic monomers, the so called hydrophobically-associating polyelectrolytes, are able to tune viscoelastic properties in aqueous media via a balance between electrostatic repulsions and hydrophobic associative attractions [36,37].…”