Coacervate systems formation

Oparin and his school in the Biochemical Institute in Moscow worked for many years with coacervate systems. For Oparin, the origin of life was the moment of formation of the first cell. Coacervates are today of only historical importance because of their low thermodynamic stability, they are considered dubious and too unstable. 

Coacervates have been extensively investigated for their possible role as protocells in the origin of life on earth. Early work in this area has been reviewed by Yevreinova (1). Other research on coacervation has centered around microencapsulation of substances to isolate or selectively release them for industrial applications (2-10). The purpose of this paper is to review the formation of coacervate systems and the characteristics and alterations of those characteristics of coacervates, and to discuss the results of our investigations of coacervates as models for plant tissue cells. Much of the background material discussed in this paper is based on the excellent review of coacervates by Yevreinova (1). 

Practical Coacervate Formation. The composition of the various parts of the coacervate system was determined by using l c-labelled kappa-casein as one component of the coacervates, and then performing a mass balance on the system. The C-kappa-casein was prepared by reductive methylation of kappa-casein with l C-formaldehyde (15), This derivatization of kappa-casein was found not to materially affect its physical properties (16). 

Coacervate systems are in dynamic equilibrium and alteration of the conditions may result in either the reformation of a one phase system or the formation of a flocculate or precipitate [1]. For example, the addition of excess nonsolvent to an aqueous gelatin simple coacervate will result in precipitation. The phenomenon of coacervation is closely related to precipitation and flocculation. 

Influence of SDS concentration on relative volume of coacervate phase in the ternary system, and turbidity of the system is shown in Figure 11. Coacervate layer formation appears at the onset of HPMC-SDS interaction. Relative volume of coacervate phase increases with SDS addition, and reaches maximum at the end of HPMC-SDS interaction (i.e. at PSP). The relative volume of coacervate phase increases on addition of SDS due to increased hydrophilic properties of HPMC/SDS complex, as more SDS molecules are bound to HPMC, which results in better solvation of HPMC/SDS complex. At SDS concentrations larger than PSP the coacervate disappears. On increase in SDS concentration turbidity of the ternary mixtures decreases until it reaches constant value, which is the same as is turbidity of binary HPMC/NaCMC mixture (Measured turbidity of the ternary mixtures having lowest SDS concentrations is low due to fast sedimentation of coacervate during the measurement.). The decrease in turbidity is attributed to increase in HPMC/SDS complex solvation as SDS concentration in the ternary system is increased. 

While for the complexation with poly(sodium styrene sulfonate) or sodium cellulosesulfate 1 1 stoichiometry has been reported [150] a non-stoichiometric complex results with sodium carboxymethylcellulose [150]. Optimized conditions make it possible to create membranes with various properties using the PDADMAC/sodium cellulosesulfate system [166-168]. However, the symplex formation with PDADMAC or copolymers mostly results in flocculated precipitates [27,150,169]. Highly ordered mulilayer assemblies were prepared by alternate reaction of PDADMAC and various polyanions [170,171]. Recently, the efficiency and selectictivity of protein separation via PEL coacervation were examined using PDADMAC [172]. 

Extractions Based on the Phase Separation Behavior of Aqueous Micellar Solutions. The extraction and concentration of components in an aqueous mixture can sometimes be effected via use of appropriate surfactant systems that are capable of undergoing a phase separation as a result of altered conditions (i.e. temperature or pressure changes, added salts or other species, etc.). Two general types of such surfactant extraction systems will be described (i) those based on the cloud point phenomenon and (ii) those based on coacervation formation. 

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. 

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