Degree of coacervation

Coacervate drops were quite unstable to pH alterations of the system. The stability of coacervate systems to pH variations was evaluated by measuring the turbidity of systems adjusted to various pH values since turbidity of the mixture serves as an index of the degree of coacervation (17). The coacervate systems formed with gum arabic and protein consisting of 10% kappa-casein and 90% gelatin, at pH 3.8, were most stable at pH 3.8. Some of the coacervates persisted when the pH was varied one pH unit, but were completely dissolved at pH 2.0 and below, and pH 6.0 and above, as shown in Table IV. 

Degree of coacervation, p. p is the fraction of total polymer in the coacervate. 

Degree of coacervation, enrichment, and coacervation intensity (8) were calculated for each experimental point shown in figures 1 and 2. Figure 3 contains the 0 values obtained as well as 8 values for three other coacervation systems. All four systems have the same 9.1/1 (w/w) gelatin (275 bloom)/polyphosphate ratio. They differ only in total solids content which ranges from 7.32 down to 1.22 percent. This variation is responsible for the large... 

The attainment of an extreme value of the degree of coacervation can serve for this purpose. By this term we mean the fraction (expressed in %) of the two colloids (A 4- G) present in the total system which are to be found in the coacervate. 

This quantity can be calculated from the A and G contents of the total system, of the coacervate and of the equilibrium liquid. The curve of the degree of coacerv ... 

From this much smaller displacement of the coacervate composition than that of the equilibrium liquid there is seen an attempt by the processes active in the coacerv-ation to maintain the separation of the equivalent coacervate. In consequence of this the colloid component present in excess goes mainly into the equilibrium liquid. Nevertheless a smaller fraction of this component does penetrate into the coacervate and thereby brings about a change of the composition whereby on the one hand the uncharged equivalent coacervate assumes at its surface the electrophoretic sign of the charge of the colloid component present in excess (see p. 358, Fig. 19b), on the other hand the mutual solubility of coacervate and equilibrium liquid increases (compare the decrease of the degree of coacervation in Fig. 19c, p. 358). 

Besides this displacement of the curves in the direction of the corner W (coacerv-ates) or away from it (equilibrium liquids) still another systematic displacement is present. This manifests itself in a decrease in the slope of the line which connects the corner W to that coacervate (indicated by an arrow) which corresponds in each series of mixtures with the maximum degree of coacervation (p. 358, 2h). Calculation from the analytical figures gave for these optunal mixing proportions blank = 48% A 5 and 7.5 m. equiv. p. 1 = 55 and 56% A. 

Fig. 25. Influence of CaClg on the composition of coacervate and equilibrium liquid produced in isohydric series of mixtures (pH 3.5) of 2% gelatin and arabinic acid sols, a the arrows on the coacervate curves give the position of the coacervate corresponding in each series of mixtures with the maximum degree of coacervation.

Thus in view of the continuous v ency series (p. 353, 2f) previously discussed one can expect a similar but still stronger displacement for an added salt of the type 3—1, on the other hand displacement to the other side for a salt of the type 1—2 and still stronger for a salt of the type 1—3 while a salt 1—1 will have practically no influence on the position of the reversal of charge and of the maximum degree of coacervation in the isohydric series of mixtures. Practically only the first of the influences discussed here will exist in the case of a salt of the type 1—1, that is to say, the suppressive action. 

Similarly on increase of the colloid concentration there occurs a displacement of the mixing proportion at which the maximum degree of coacervation and the reversal of charge point lie, in the same direction as that which we saw for constant colloid concentration and increase of the CaCl2 concentration (see p. 365, Fig. 25). 

In spite of the overwhelming evidence suggesting that recombinant resilin is amorphous, there are some results that suggest that a level of defined stmcmre cannot be completely ruled out. In particular, the fact that the protein solution coacervates when cooled (Figure 9.7) suggests that there is a degree of self-association between protein molecules. 

In coacervation by Polymer 2-Polymer 3 repulsion, the addition of Polymer 3 causes phase separation between the two polymer species dissolved in a common solvent 1. This phase separation produces a viscous, liquid phase of Polymer 2, i.e., the coacervate, and a low-viscous phase of Polymer 3, often called continuous or polymer-poor phase. Under stirring, coacervate droplets are formed and dispersed in the continuous phase. The solubility of Polymer 3 in solvent 1 should be superior to that of Polymer 2 in this common solvent. For particle production, the Polymer 3 should also function as stabilizer for the coacervate droplets to prevent their aggregation. Further, for the entrapment of a biologically active material, the coacervate must have a certain degree of fluidity and a high affinity to the core material, whereas the affinity between core material and continuous phase should be low... 

From the standpoint of Colloid Science we are interested in our study objects in the first place because these contain colloids, that is to say, macromolecules. The nature of a phase containing colloid is then in the first place characterised by the relative arrangement and degree of mobility of the macromolecules present in it. On the grounds of this criterion terms such as Sols and Coacervates have indeed also become current to denote phases variable in composition within wider or narrower limits, in which, after mentally removing the micro-units-still present as well in them, the macromolecules in a certain respect behave similarly to molecules in a gas or in a liquid (see p. 10 Ch. I 4). 

Phase Theory shows however that a system of the type water — salt AB — salt CD, that is to say, in which the two salts possess no common ion, is not a ternary but a quarternary system. Thus at constant temperature and pressure it possesses one more degree of freedom than a ternary system. This is therefore applicable to complex coacervation and it should not surprise us that in the "only ternary diagram of Fig. 27 a displacement of the C and E curves occurs on increase of the colloid concentrations. 

---