Mixtures of oppositely charged

Physical interactions result when precipitation or another change in the physical state or solubility of a drug occurs. A common physical drug interaction takes place in the mixture of oppositely charged organic molecules le.g., cationic (benzalkonium chloride) and anionic (soap) detergents]. 

FIGURE 7.36. Schematic model of a vesicle with a corona of segregated polymer chains, as formed in a mixture of oppositely charge block copolymers. Reproduced with permission from the American Chemical Society (2003). 

The early stages of the process are very similar to those occurring in corresponding systems of mixtures of oppositely charged organic polyelectrolyte and surfactant. Organic polyelectrolyte-surfactant systems are much easier to investigate, however, because of the absence of further polymerization reactions, which enables studies to be carried out under equilibrium conditions. It... 

Mixtures of oppositely charged polyelectrolytes dissolved in water can interact to form a variety of precipitates, gels, or phase-separated solutions. What is formed depends on the mixing conditions and the density of ionic charges carried by the polymer chains. Polyelectrolytes with high charge densities usually interact to form precipitates. As the charge density decreases, liquid-liquid phase separation, called complex coacervation, occurs. 

Schrage S, Sigel R, Schlaad H (2003) Formation of amphiphilic polyion complex vesicles from mixtures of oppositely charged block ionomers. Macromolecules 36(5) 1417-1420... 

One of the simplest realistic molecular models of an ionic solution is the restricted primitive model. This consists of an equimolar mixture of oppositely charged but equal-sized hard spheres in a dielectric continuum. 

The addition of P4VPQ into an aqueous solution of the PIB-fe-PMANa micelles was found to induce macroscopic phase separation of the aqueous mixtures of oppositely charged polymeric components only if the ratio between the molar concentrations of their ionic groups Z (Z = [N+]/[COO ], Z < 1) exceeded the certain threshold value of Zm (Fig. 12). At Z < Zm, the aqueous mixtures of the PIB- -... 

One of the very characteristic features of IPECs is their ability to participate in so-called polyion interchange (exchange and substitution) reactions, previously investigated for aqueous mixtures of oppositely charged linear PEs by Kabanov... 

The phase behaviour of PS systems is also affected by specific interactions between the two cosolutes, similar to hydrophobic interactions in the case of HM-polymers. This may enhance phase separation for nonionic systems but decrease it for ionics. For a mixture of oppositely charged polymer and surfactant,... 

The absence of flocculation or coacervation phenomena in a mixture of oppositely charged colloids does not necessarily mean that colloid-colloid interaction is lacking. In mixtures of gum arabic and gelatin at lower pH values (e.g., pH 1.73 — 2.3) no coacervation occurs. Still interaction is present, for in Fig. 43 (p. 324) the curve continues its normal course in this pH range, absolutely different from that in Fig. 50 (p. 332), where the curve ends vertically at 100 % N. Thus in the sol mixture soluble combinations of gelatin and gum arabic are present and they are preferentially absorbed on the carborundum particles, which were used to measure the reversal of charge in these clear sol mixtures. 

W. Lin, M. Kobayashi, M. Skaiba, C. Mu, P. Galletto, M. Borkovec, Heteroaggregation in binary mixtures of oppositely charged colloidal particles. Langmuir 22(3), 1038-1047 (2006). doiilO. 1021/la0522808... 

Thuresson K, Nilsson S, Lindman B. Effect of hydrophobic modification on phase behavior and rheology in mixtures of oppositely charged polyelectrolytes. Langmuir 1996 12 530-537. 

Biesheuvel PM, Lindhoud S, de Vries R et al (2006) Phase behavior of mixtures of oppositely charged nanoparticles heterogeneous Poisson-Boltzmann cell model applied to lysozyme and succinylated lysozyme. Langmuir 22 1291-1300... 

Upon the formation of IPECs, the concentration of a low molecular weight salt (a , b" ") in the system increases. The increasing salt concentration shifts equilibrium (1) to the left, that is, it favors the dissociation of interpolymer salt bonds. This phenomenon is observed at high concentrations of the polymeric components and/or upon addition of low molecular weight salts to mixtures of oppositely charged polyelectrolytes and has been reported in numerous works [8, 24—26]. It is widely used when IPECs are applied. 

If, for simplicity, [h A b ]o = [ F B a ]Q = Co, that is, considering mixtures of oppositely charged polyelectrolytes at the stoichiometric (1 1) ratio between their ionic groups, then dividing the numerator and the denominator in Eq. (2) by the initial concentration (Co) yields ... 

Fig. 3 Behavior of mixtures of oppositely charged linear polyelectrolytes with DPhpe > > DPqpe upon an increasing content of GPE. Z=[GPE]/[HPE]. For descriptions of regions A, B, and C, see text...

Addition of low molecular weight salts into mixtures of oppositely charged polyelectrolytes has a pronounced influence on the behavior of water-soluble nonstoichiometric IPECs. In particular, this manifests itself in a shift of the boundary between the regions A and B, that is, Z, to lower values. The low molecular weight salts induce conformational transformations of particles of nonstoichiometric IPECs, (i.e., a coil-globule transition) followed by phase separation of the solution and macroscopic precipitation of a stoichiometric IPEC [31, 34]. 

The second method is the opposite of the first that is to say, the potassium bromide solution is in the buret and is added to the solution of silver nitrate. The phenomena are quite analogous, but the hydrosols differ in one important particular. In the first case as long as the halide ion is in excess of the silver, the ultramicrons are charged negatively, while in the second case where the silver ion is in excess the ultramicrons are charged positively. The two halide hydro-sols mutually precipitate each other, as is to be expected from a mixture of oppositely charged colloids. 

Figure 6.39 Equilibria possible in mixtures of oppositely charged organic ions when one is a surface-active agent (B ) and the other a solute or drug molecule (A). From Tomlinson [270] with permission.

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