Macromolecules coacervation

Coa.cerva.tlon, A phenomenon associated with coUoids wherein dispersed particles separate from solution to form a second Hquid phase is termed coacervation. Gelatin solutions form coacervates with the addition of salt such as sodium sulfate [7757-82-6] especially at pH below the isoionic point. In addition, gelatin solutions coacervate with solutions of oppositely charged polymers or macromolecules such as acacia. This property is useful for microencapsulation and photographic apphcations (56—61). 

Phase separation microencapsulation procedures are suitable for entrapping water-soluble agents in lactide/glycolide excipients. Generally, the phase separation process involves coacervation of the polymer from an organic solvent by addition of a nonsolvent such as silicone oil. This process has proven useful for microencapsulation of water-soluble peptides and macromolecules (48). 

Gelatin and albumin nanoparticles have been prepared through desolvation of the dissolved macromolecules by either salts (e.g., sodium sulfate or ammonium sulfate) or ethanol [179-182], This is, in principle, similar to a simple coacervation method. The particles can then be insolubilized through cross-linking with an optimum amount of aldehydes. These phase separation methods avoid the use of oils as the external phase. 

One of the first methods for making capsules involved polymer coacervation. In this method, macromolecules are dissolved in either the dispersed or continuous phase of an emulsion and are induced to precipitate as a shell around the dispersed phase. Coacervation can be brought about in several ways, such as changes in temperature or pH, addition of salts or a second macromolecular substance, or solvent evaporation (Bungenberg de Jong 1949). 

The polymers were fractioned into 8-14 components by coacervate extraction from the benzene - methanol system. For fractions and nonfractioned polymers, characteristic viscosities [t ], were me-asured. Because that was the first example of studying conformations of macromolecules of this ty-pe in diluted solutions, authors of the work [56] paid much attention to selection of an equation, which would adequately describe hydrodynamic behavior of polymeric chains. Figure 10 shows de-pendencies of [q] on molecular mass (MM), represented in double logarithmic coordinates. Parame-ters of the Mark-Kuhn-Hauvink equation for toluene medium at 25°C were determined from the slo-pe and disposition of the straight lines. 

Homogeneous, transparent solutions of proteins, carbohydrates, and other compounds can separate into two layers, one depleted and one enriched with these compounds. The process of separation of macromolecules into discrete entities is termed coacervation. The layer rich in molecules of the dissolved substance, referred to as the coacervate layer, actually consists of liquid "drops" or spherical microcapsules. The equilibrium liquid, which is the medium adjoining the coacervate layer, always contains less substance than the original solutions. The discrete liquid droplets resulting from macromolecular interactions might be made to serve as pseudocells from which pseudo tissues might be derived to constitute a restructured food. 

Because the isoelectric points of alkaline proteins are generally in the range of pH 7 or above, coacervates whose composition includes alkaline proteins can be obtained at a more alkaline pH than when acid proteins are used. The greater the difference between the isoelectric points of the macromolecules, the more readily do they form coacervates. 

As mentioned previously, coacervates are formed at a pH between the isoelectric points of the macromolecules of which they are composed. The desired final pH of the restructured food determines what the range of the isoelectric points should be, and therefore what proteins or macromolecules should be used for the formation of coacervates in the system. 

Gravimetric determinations on coacervate systems have indicated that about 35% of the total macromolecules in the system were incorporated into the coacervate drops. This information, combined with the mass balance data above, indicates that the coacervates were approximately 66% kappa-casein and 34% gum arabic. 

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). 

Watase, M., Nishinari, K., Clark, A. H., and Ross-Murphy, S. B. 1989. ESfferential scanning calorimetry, rheology. X-ray, and NMR of very corrcentrated agarose gels. Macromolecules 22 1196-1201. Weinbreck, F. 2004. Whey protein/Polysaccharide Coacervates Structure and Dynamics. Ph.D thesis, Utrecht University, The Netherlands. 

The large number of variables involved in complex coacervation (pH, ionic strength, macromolecule concentration, macromolecule ratio, and macromolecular weight) affect microcapsule production, resulting in a large number of controllable parameters. These can be manipulated to produce microcapsules with specific properties. Complex coacervate microcapsules have been formulated as suspensions or gels, and have been compounded within suppositories and tablets.[ l... 

In the area of controlled release, the preparation of indomethacin sustained-release microparticles from alginic acid (alginate)-gelatin hydrocolloid coacervate systems has been investigated. In addition, as controlled-release systems for liposome-associated macromolecules, microspheres have been produced encapsulating liposomes coated with alginic... 

Coacervation of macromolecules around the core material, this being induced by temperature change, solvent change or addition of a second macromolecule of appropriate physical properties. 

Coacervation is the term used to describe the separation of macromolecular solutions into colloid-poor and colloid-rich (coacervate) phases when the macromolecules are desol-vated. The liquid or solid to be encapsulated is... 

Desolvation of water-insoluble macromolecules in nonaqueous solvents leads to the deposition of a coacervate layer around aqueous or solid disperse droplets. Table 8.13 lists both water-soluble and water-soluble macromolecules which have been used in coacervation processes. Desolvation, and thus coacervation, can be induced thermally and... 

A survey of the abundant literature shows clearly that pH, ionic strength, type of ions, protein to polysaccharide ratio, size, shape, charge density and flexibility of macromolecules are important parameters controlling the extent of phase separation as determined at equilibrium.3,4,6-10 On the contrary, out of equilibrium conditions have attracted much less attention. Some important questions such as the transition from macromolecular complexes/aggregates to the appearance of coacervates, the structure of coacervates and the phase ordering kinetics... 

Other types of interactions (complexation, adsorption, coacervation) may be of concern for the performance of water-soluble cellulose macromolecules. Only illustrative recent examples will be discussed here. The complexation of various additives (low-molecular solutes, surfactants, other macromolecules) with cellulose derivatives has been investigated using a variety of methods including dialysis [106], osmometry [107], and measurements of electrophoretic mobility... 

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