Precipitate–Coacervate Transformation in Polyelectrolyte–Mixed Micelle Systems

Abstract

The polycation/anionic-nonionic mixed micelle, poly(diallyldimethylammonium chloride)-sodium dodecyl sulfate/Triton X-100 (PDADMAC-SDS/TX100), is a model polyelectrolyte-colloid system in that the micellar mole fraction of SDS (Y) controls the micelle surface charge density, thus modulating the polyelectrolyte-colloid interaction. The exquisite temperature dependence of this system provides an important additional variable, controlling both liquid-liquid (L-L) and liquid-solid (L-S) phase separation, both of which are driven by the entropy of small ion release. In order to elucidate these transitions, we applied high-precision turbidimetry (±0.1 %), isothermal titration calorimetry, and epifluorescence microscopy which demonstrates preservation of micelle structure under all conditions. The L-S region at large Y including precipitation displays a remarkable linear, inverse Y-dependence of the L-S transition temperature T. In sharp contrast, the critical temperature for L-L coacervation T, shows nearly symmetrical effects of positive and negative deviations in Y from the point of soluble complex neutrality, which is controlled in solution by the micelle charge and the number of micelles bound per polymer chain n (Z = Z + nZ). In solid-like states, n no longer signifies the number of micelles bound per polymer chain, since the proximity of micelles inverts the host-guest relationship with each micelle binding multiple PE chains. This intimate binding goes hand-in-hand with the entropy of release of micelle-localized charge-compensating ions whose concentration depends on Y. These ions need not be released in L-L coacervation, but during L-S transition their displacement by PE accounts for the inverse dependence of T on micelle charge, Y.

Phase Separation Behavior of Supercharged Proteins and Polyelectrolytes

“…The difference in the salt concentration required to form liquid−liquid phase separations for each mixing regime indicates phase separation behavior of GFP/polyanion pairs is dependent on mixing conditions, a result consistent with previous studies. 19,49 Similar to the behavior seen for each of the GFP/polyanion pairs at different salt concentrations, increasing the net GFP charge resulted in phase separation over a broader pH range (Figure 6). Because there should be no electrostatic driving force for complexation at pH values above each supercharged GFP's isoelectric point (pI), it was predicted that the GFP/ polyanion complexes would form a single miscible phase at the pI of each variant.…”

“…Solid precipitates can be visualized as opaque nonuniform aggregates when observed using optical microscopy, and solid phase separation can result in complex formation that is not reversible. 19 Conversely, liquid−liquid phase separation results in the formation of optically clear, spherical droplets that are dynamic in nature. While most GFP/polyanion pairs phase separated as solids, each pair still exhibited fluorescence in the phase-separated state, indicating the structure of GFP was not greatly affected during phase separation.…”

“…Following complexation, protein–polyelectrolyte mixtures can phase separate, creating a macromolecule rich and a macromolecule dilute phase. The nature of the phase separation, liquid–liquid, liquid–solid, or a combination of both, depends on the concentration of water, polyelectrolyte, and salt. − Liquid–liquid phase separations can coalesce over time and exhibit rapid exchange of their macromolecular components. In some situations, it is possible for liquid protein–polyelectrolyte phase separations to transform into more solid-like precipitates over time. , The protein and polymer molecular properties that govern whether a liquid–liquid or liquid–solid phase separation will form are not yet fully understood.…”

Explicit description of complexation between oppositely charged polyelectrolytes as an advantage of the random phase approximation over the scaling approach

“…Therefore, the electrostatic attraction decreases the solubility of the macroions in the ''symmetric'' system. [10][11][12] In the intermediate cases of the asymmetry or beyond the isoelectric point, the interplay between attractive and repulsive electrostatic interactions is responsible for the clustering of the macroions in soluble aggregates. In many cases, solubility of the aggregates is provided by the effect of overcharging (charge inversion): [13][14][15][16] the total charge of the complex becomes opposite to the bare charge of the macroions.…”

Liquid-liquid phase separated microdomains of an amphiphilic graft copolymer in a surfactant-rich medium

“…The difference between regions 2 and 3, both containing micron-sized LLPs domains, stems from the absence or presence of solid copolymer precipitates, respectively. The simultaneous presence of liquid-liquid and liquid-solid phase separation has also been detected and investigated for complex coacervates [106][107][108].…”