Effect of Counterions on the Interaction among Concentrated Spherical Polyelectrolyte Brushes

Abstract

The effect of counterions on interactions among spherical polyelectrolyte brushes (SPBs) was systematically investigated by rheology, small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS). The SPB particles consist of a solid polystyrene (PS) core with a diameter of ca.100 nm and a chemically grafted poly-(acrylic acid) (PAA) brush layer. Metal ions of different valences (Na+, Mg2+ and Al3+) were used as counterions to study the interactions among concentrated SPBs. The so-called “structure factor peak” in SAXS, the “local ordered structure peak” in WAXS and rheological properties indicated the interactions among concentrated SPBs. Combining SAXS, WAXS and rheology, the formation mechanism of the local ordered structure among PAA chains in the overlapped area of adjacent SPB, which was generated due to the bridge function of counterions, was confirmed. In contrast, excessive counterions shielded the electrostatic interaction among PAA chains and destroyed the local ordered structure. This work enriches our understanding of the polyelectrolyte assembly in concentrated SPBs under the effect of counterions and lays the foundations for SPB applications.

Initiation and modulation of Tau protein phase separation by the drug suramin

“…Since suramin is a negatively charged molecule, we hypothesized that suramin-induced Tau (net charge: + 2.9 at pH 7.4) condensation depends on electrostatic interactions, like complex coacervation of Tau with RNA and heparin. Since electrostatic interactions can be weakened through shielding by counter ions in solution [32][33][34] , we prepared Tau:suramin condensates first at low salt conditions in 10 mM NaCl (R h : ~ 400 nm) and then stepwise increased the NaCl concentration in the buffer to 150 mM NaCl, and then to 300 mM NaCl. Already at 150 mM NaCl, Tau monomers re-appeared along with polydisperse condensates (R h : ~ 100 nm; Fig.…”

“…Our MST data showed moderate binding affinity (Kd ~ 17 μM) of suramin to Tau, supporting the establishment of weak multivalent electrostatic interactions as the driving force for Tau:suramin condensation. Strong molecular interactions [32][33][34] , for example formed between Tau and heparin (Kd ~ 1.2 μM) 57,59 , that immobilize Tau molecules and give beta-structural elements in the repeat domain time to arrange into stacks, could promote aggregation and fibril formation of otherwise highly soluble, unstructured Tau molecules. We postulate that candidate compounds, that allow or promote Tau condensation while inhibiting its aggregation could function and show moderate to weak interactions with Tau and thereby allow for structural flexibility and fluctuations in Tau molecules.…”

Beyond Traditional Stimuli: Exploring Salt-Responsive Bottlebrush Polymers─Trends, Applications, and Perspectives

“…Post-2013, we see an interesting phenomenon being investigated in polymer brushes popularly called “the antipolyelectrolyte effect”. − Intriguingly, certain zwitterionic polymer brushes defy the conventional behavior observed in polyelectrolyte brushes, exhibiting what is known as the “antipolyelectrolyte effect”, a phenomenon in stark contrast to the “polyelectrolyte effect” displayed by typical polyelectrolytes. In the case of polyelectrolyte brushes, as depicted in Figure , these brushes assume a fully stretched chain conformation in pure water but transition to a collapsed chain conformation in a salt solution .…”

“…Conversely, in pure water, without the presence of salts, the zwitterionic brushes exhibit a more collapsed conformation. This salt-responsive behavior of zwitterionic brushes, termed the “antipolyelectrolyte effect”, stands in direct contrast to the behavior of polyelectrolyte brushes. − It is important to note that not all zwitterionic polymers exhibit a strong “antipolyelectrolyte effect”, as the degree of this effect depends on the charge distributions and identities of the specific polymers. For example, conventional zwitterionic polymers like sulfobetaine methacrylate (SBMA) and carboxybetaine methacrylate (CBMA) show no significant change in dimensions with added salt, indicating a weak antipolyelectrolyte effect.…”

Immobilization of Gold Nanoparticles in Spherical Polymer Brushes Observed by Small-Angle X-ray Scattering

“…In the analysis of scattering intensity, I cs ( q ) is a key influencing factor, and the difference between SPB and solvent radial electron cloud density represented by Δρ e ( r ) = ρ e ( r ) – ρ m e is a key parameter. Among different theoretical distribution models, the five-layer model (Figure ) has been proven to be a competent model for simplifying Δρ e ( r ) without victimizing model accuracy. − …”