Ionic Strength Dependence of Protein-Polyelectrolyte Interactions

Abstract

The effect of univalent electrolyte concentration on protein-polyelectrolyte complex formation has been measured by frontal analysis continuous capillary electrophoresis (FACCE) and turbidimetry for the interaction of bovine serum albumin (BSA) with a synthetic hydrophobically modified polyacid, for BSA with (porcine mucosal) heparin (Hp), a highly charged polyanion, and for Hp and insulin. All three highly diverse systems display maxima or plateaus in complex formation in the range of ionic strength 5 < I < 30 mM, confirmed in the case of BSA-Hp by multiple techniques. Similar maxima are reported in the literature, but with little discussion, for BSA-poly(dimethyldiallylammonium chloride), lysozyme-hyaluronic acid, and lysozyme-chondroitin sulfate, always in the I range 5-30 mM. While inversion of salt effect has been discussed specifically for the interaction of gelatin and sodium polystyrenesulfonate with gelatin(28) and with beta-lactoglobulin,(10) the general nature of this phenomenon, regardless of polyelectrolyte origin, molecular weight, and charge sign has not been recognized. The position of the maxima and their occurrence when protein and polyelectrolyte have the same net charge imply that they arise when Debye lengths extend, at low I, beyond half the protein diameter so that addition of salt screens repulsions, as well as attractions. This appears to be a general effect caused by electrostatic repulsions that can coexist simultaneously with hydrophobic interactions. Modeling of protein electrostatics via Delphi is used to visualize this effect for BSA, lysozyme, insulin, and beta-lactoglobulin.

Influence of Chain Stiffness on the Interaction of Polyelectrolytes with Oppositely Charged Micelles and Proteins

“…25 /AAm 75 can be expected to facilitate polymer configurations that will reduce the repulsive effect arising from negatively charged protein domains and favor the alignments around the positively charged protein domains. 44 The stiffness of HA corresponds to a restriction of chain movements, so that the bound configuration may not readily avoid negative domains, and therefore binding cannot take place when the net charge is strongly negative. As seen in the micelle-binding case discussed above, the difference between flexible and semiflexible polyions increases at high salt, while the phase boundaries converge at low salt.…”

Role of Polyelectrolyte Persistence Length in the Binding of Oppositely Charged Micelles, Dendrimers, and Protein to Chitosan and Poly(dimethyldiallyammonium chloride)

“…At these conditions, an additional complexity that arises is that optimal binding occurs when the polycation not only interacts with the negative patch of the protein but also avoids the surrounding positive regions; these regions can be visualized by electrostatic protein modeling. 24 Chain flexibility clearly plays a more interesting and complicated role in these cases.…”

“…Most generally, the strength of the electrostatic interaction was found to depend on polyelectrolyte characteristics such as charge density, chain length, and chain flexibility; colloidal aspects, i.e., colloid surface charge density, size, and shape; and extensive system variables, i.e., temperature, pH, and ionic strength of the medium. [16][17][18][19][20][21][22][23][24][25] The magnitude of the electrostatic interaction between the polyelectrolyte and the oppositely charged colloid is found to increase with colloid surface charge density σ and polyelectrolyte linear charge density and diminish with salt concentration I. One way to express a consensus among the numerous experimental investigations and their theoretical or simulation counterparts would thus be 26 where σ c is the critical colloid surface charge density at the onset of complex formation and κ is the DebyeHuckel parameter, with a and b being either obtained as empirical scaling parameters or derived theoretically.…”

Films based on chitosan polyelectrolyte complexes for skin drug delivery: Development and characterization

“…Turbidimetric measurements were carried out with a UV spectrophotometer (Shimadzu UV visible 1603, Shimadzu Scientific Instruments, Kyoto, Japan) at the wavelength = 420 nm [8,16,37]. Solutions of 0.05% (w/v) of Carbopol and Noveon in distilled water and 0.1% of chitosan (w/v) in 0.1% lactic acid solution (w/v) were prepared.…”