Turbidity, dynamic light scattering, and electrophoretic mobility were used to study the effects of added salt on coacervation in the system composed of the strong cationic polymer poly(diallyldimethylammonium chloride) (PDADMAC) and oppositely charged mixed micelles of Triton X-100 (TX100) and sodium dodecyl sulfate (SDS). The phase behavior in the range of ionic strengths from 0.05 to 0.60 M includes regimes of soluble complex formation, coacervation, and precipitation. The corresponding phase boundaries are determined from differential turbidity curves. The shift of the phase boundaries to higher ratios of SDS:TX100 with increase in salt concentration is explained on the basis of electrostatic screening. The width of the coacervation region is found to increase with ionic strength. These observations are consistent with previous reports of the “salt suppression” and “salt enhancement” of coacervation. In the coacervation region, the electrophoretic mobility is found to be close to zero. At higher and lower ionic strengths, soluble complexes are positively or negatively charged, respectively. It is suggested that the principal factor governing coacervation in this system is electroneutrality of the polyion−micelle complex which in turn depends on the charge and number of bound micelles.

The effects of micelle charge density, polymer molecular weight, and polymer-to-surfactant ratio on coacervation were studied by turbidity, dynamic light scattering, and electrophoretic mobility in the system composed of the strong cationic polymer poly(diallyldimethylammonium chloride) (PDADMAC) and oppositely charged mixed micelles of Triton X-100 (TX100) and sodium dodecyl sulfate (SDS). Phase boundaries in the range of SDS mole fraction from 0.30 to 0.50 and in the range of polymer molecular weight from 8.2 × 10 3 to 4.28 × 10 5 were obtained, and coacervate volume fraction as a function of polymer molecular weight was subsequently determined. Three-dimensional phase boundaries were used to represent the effects on coacervation of micelle surface charge density, polymer molecular weight, and PDADMAC-to-SDS ratio. The coacervation region is seen to increase with micelle surface charge density and polymer molecular weight (MW). Both higher and lower polyelectrolyte-to-surfactant ratio can suppress coacervation. An increase in MW reduces the micelle charge required for coacervation and also increases coacervate volume fraction. Coacervation is found to occur when the following conditions are satisfied: the electrophoretic mobility is close to zero, and the size of polyelectrolyte-micelle complex is at least about 45 nm.

No abstract

Long-range electrostatic interactions are generally assigned a subordinate role in the high-affinity binding of proteins by glycosaminoglycans, the most highly charged biopolyelectrolytes. The discovery of high and low sulfation domains in heparan sulfates, however, suggests selectivity via complementarity of their linear sulfation patterns with protein charge patterns. We examined how charge sequences in anionic/nonionic copolymers affect their binding to a protein with prominent charge anisotropy. Experiments and united-atom Monte Carlo simulations, together with Delphi electrostatic modeling for the protein, confirm strongest binding when polyanion sequences allow for optimization of repulsive and attractive electrostatics. Simulations also importantly identified retention of considerable polyion conformational freedom, even for strong binding. The selective affinity for heparins of high and low charge density found for this protein is consistent with nonspecific binding to distinctly different protein charge domains. These findings suggest a more nuanced view of specificity than previously proposed for heparinoid-binding proteins.