Electrostatic interactions complex coacervation

The electrostatic interaction between oppositely charged protein and polysaccharide can be utilized for encapsulation and delivery of hydro-phobic nutraceuticals. As a result of this interaction, we may have either complex coacervation (and precipitation) or soluble complex formation, depending on various factors, such as the type of polysaccharide used (anionic/cationic), the solution pH, the ionic strength, and the ratio of polysaccharide to protein (see sections 2.1, 2.2 and 2.5 in chapter seven for more details) (Schmitt et al, 1998 de Kruif et al., 2004 Livney, 2008 McClements et al, 2008, 2009). The phenomenon of complex... 

Some papers60-61 have been devoted to phase separation of polyionic complexes from partially furated (PVA-S) and aminoacetylated (PVA-AAC)poly(vinyl alcohol) in aqueous salt solutions. The separation liquid-liquid or complex coacervation occurs at a definite value of the charge density on the macromolecule. From the concentration dependence of the reduced viscosity of the initial components PVA-S, PVA-AAc and their equivalent mixture in water it follows that the viscosity of the components noticeably increases with dilution, and the curve of the equivalent mixture is concentration independent. This fact confirms the formation of the neutral polymer salt, due to electrostatic interactions of PVA-S (strong polyadd) and PVA-AAc (weak polybase). 

Formation of electrostatic complexes means mutual neutralisation of the macro-molecular reactant. This mutual neutralization of opposite charges and formation of the concentrated complex coacervate phase, minimizes the electrostatic free energy and reduces both the hydrophilicity and the solubility of the resultant complex. The loss of entropy on complexing may be compensated by the enthalpy contribution from interactions between macro-ions and by liberation of counter-ions and water molecules. 

In complex coacervation (20 pm to 1 nun), for example, aqueous solutions of active component (AC), polyanion (-) and polycation (+) are mixed. The two polymers with opposite charges (electrostatic interactions) will interact to form a deposit of coacervate at the surface of AC (i.e., acacia gum, alginate CMC with gelatine proteins and anionic polysaccharides) (De Kruif et al., 2004). Reticulation may be provoked by dilution, and modification of pH, tanperature (Figure 39.10). Gelatine and acacia gum (opposite charge at low pH) were used to encapsulate flavor lipophilic oil to be used in frozen foods and released upon heating (Yeo et aL, 2005), with liquid or solid core (Leclercq et al., 2009). 

Coacervation in aqneous phase can be classified into simple and complex. In simple coacervation, the polymer is salted ont by the action of electrolytes (sodium sulfate) or desolvated by the addition of an organic miscible water solvent, such as ethanol, or by increasing/decreasing temperature. In these cases, the macromolecule-macromolecule interactions are promoted, instead of the macromolecule-solvent interaction (Martins, 2012). Complex coacervation is defined as a Uqnid-liquid phase separation promoted by electrostatic interactions, hydrogen bonding, hydrophobic interactions, and polarization-induced attractive interactions occurring between two oppositely charged polymers in aqneons solution (Xiao et al., 2014). This technique is based on the ability of cationic and anionic water-solnble polymers to interact in water to form a liquid polymer-rich phase called complex coacervate (Martins, 2012). 

As we are interested in reversible Janus micelles, i.e. non-centrosymmetric nanoparticles with compartmentalised shells (Fig. 1), complex coacervate core micelles are a rather natural choice. As described in the previous section, electrostatic interaction is a rather weak driving force as compared to hydrophobic interaction. C3Ms may thus form under full thermodynamic control. Although ABC triblock copolymers in selective solvents (poor solvent for B good solvent for both A and C) may also yield Janus micelles, they most frequently aggregate into micelles with a quenched rather than a dynamic nature, such that the aggregation number is fixed and no reversible association/dissociation is observed (on experimental time scales). 

When the coordination polymer is mixed with an oppositely charged neutral diblock polymer, the electrostatic interaction will drive complex coacervate formation [40]. But, the growth of the complex coacervate will be constrained by the presence of the neutral blocks, and be stabilized at a finite size. In this way, so-called complex coacervate core micelles (C3Ms), or polyion coacervate (PIC) micelles are formed. This micelle formation is analogous to the formation of C3Ms in covalent polyelectrolyte/ block polymer systems [67, 68]. Obviously, the coordination polymer,... 

Janus-type micelles were reported via electrostatic interaction between two double-hydrophilic block copolymers poly(acrylic acid)-fc-poly(acryl amide) (PAA-fc-PAAm), and poly(2-methylvinylpyridinium iodide)-fe-poly(ethylene oxide) (P2MVP- -PEO). The aggregate forms disc-shaped micelle with PAA/P2MVP complex coacervate core and microphase-separated asymmetric corona, with two distinct domains formed by PEO and PAAm. Eigure 14.20 shows a TEM image of Janus-type micelles... 

Two other complex coacervation theories have been developed by Naka-jima and Sato [11, 12], which is an adaptation of the Voom-Overbeek theory, and by Tainaka [13, 14], which is an adaptation of the Veis-Aranyi theory. Nakajima and Sato agreed with the Voorn-Overbeek theory in that the charges should be treated as distributed uniformly in both phases, but included the Huggins interaction parameter and they altered the electrostatic term. The... 

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