Coacervates water content

By far the larger part (at least if the water content of the coacervate is not very small) is to be regarded as occlusion-water, included between the loops of macro-molecular skeins associated together. 

To characterise the maximum coacervation in an isohydric series of mixtures one can choose provisionally all kinds of criteria, for example, maximum turbidity, maximum volume of the coacervate layer, etc. It is however desirable to have at one s disposal a criterion which is calculable from the analytical results and in which the water content of the coacervate layer itself plays no part. 

It is more easy to survey the various points when we set aside for the moment the simultaneously varying water content and thus restrict ourselves to the colloid compositions of the total mixture, the coacervates and the equilibrium liquids. ... 

The dotted line touching the branch of the coacervates at an angle of 45 gives compositions which are equally rich in water. Any line parallel to this which lies closer to the corner gives compositions which again each have the same water content but in which the water content is greater than that of the points on the dotted line. The coacervates at pH 3.8 and 3.0 are thus richer in water than those at pH 3.3 and 3.5. The coacerv-ate at pH 4.0 is still more rich in water. 

With regard to the water content one can in general say that it is large with unfavourable conditions for complex coacervation and decreases in proportion as these become more favourable. 

When thus we draw in such a diagram a tangent at this angle to the coacervate branch the point of contact indicates that coacervate which has the minimum water content. 

Thus the above stated fact is exhibited clearly in this figure the water content is a minimum at the most favourable condition for complex coacervation (here a definite pH at the given mixing proportion). On decrease or increase of the pH the water content increases. 

One would now expect that the water content of the coacervate is a minimum in every isohydric series of mixtures at the equivalent mixing proportion (reversal of charge point). In Fig. 28 the dry weights, that is to say, the A + G contents, of the coacervates for the various isohydric series of mixtures of Fig. 20 (p. 359) are plotted as a function of the mixing proportion. It is seen from these figures that the expectation is not in general borne out. 

It is possible that the explanation of this discrepancy lies in the fact that the accompanying ions of the gelatin, the Cl ions, are only monovalent, those of the arabinate ion, the Ca ions, however are divalent. We have already argued that in principle micro ions counteract the coacervation, that is to say, increase the water content of the coacervate (p. 364, 21). 

The existence of an optimum pH for complex coacervation (p. 360, Fig. 21) appears to speak in favour of a fairly considerable interpenetration of the clews of both kinds. The equivalent coacervate at this pH is poorer in water than equivalent coacervates at other pH values. With strong penetration the pairs of positive and negative charges are to be found more or less uniformly throughout the enclosed volume of a macromolecule and the mutual attraction of these dipoles (which leads to a state of contraction) depends then also on their number. This number would then be the greatest at the optimum pH so that here the water content becomes a minimum. 

The flocculi therefore consisted of a very viscous coacervate. As was to be expected, on the addition of an indifferent salt these flocculi are first transformed into thoroughly liquid coacervate drops and at still higher salt concentrations the coacervation is suppressed. The added salt increases the water content by weakening the complex relations (p. 364), whereby the coacervate becomes less viscous. As a result rapid complete fusion occurs of the innumerable very small coacervate drops, which in the flocculi were only superficially fused together here and there. 

Since however larger charge density (small equivalent weight), as is discussed below ( 2r) results in general in a smaller water content of the complex coacervate, the ultrami-croscopic coacervate drops in the combination with clupein are very viscous or possibly glass-like in nature, which greatly impedes the mutual fusion into larger drops. 

Further one sees that the maximum of the coacervate volume curve lies much lower for G + N than for G + A. This happens because the G + N coacervate is appreciably richer in colloid than the G + A coacervate (the G + N coacervate is also much more viscous). This relatively smaller water content of the G + N coacervate is also to be expected from the much stronger complex relations in this combination ( 2o, p. 370). 

As was to be expected the water content of the coacervates increases from left to right in these series (each time compared at the concentrations of optimum coacervation). The reversal of charge concentrations of the divalent cations (for example Ca) are relatively small compared with other colloids, those of Na and K on the contrary are fairly large. 

A striking peculiarity of these coacervates is that when once they have been produced they are not or difficulty reversible Extra added salts do indeed bring about reversible changes in the water content in the direction which may be expected. For example the water content of a coacervate produced with Ca is increased by NaCl. This coacerv-ate naturally decreases in water content (recognizable for example by vacuolation occurring in the coacervate drops) on the ad tion of a salt with a cation which occupies a place further to the left in the reversal of charge spectrum than Ca. These coacerv-... 

Finally we mention as a last peculiarity that these coacervates can also change their water content tmder the influence of all sorts of organic non-electrolytes In this respect they are similar to coacervates of oleates which are obtained by salting out (KCl) This sensitivity has nothing to do with the dicomplex nature but is closely connected with the presence of long hydrocarbon chains of the esterified fatty acids in the phosphatide molecule (oleate coacervates are further treated in Chapter XIV). 

Complex coacervates sometimes possess a relatively high water content and the diagrams of Fig. 48 (p. 410) invite one to make a comparison with the water content of the demixed salt-rich liquid. Naturally this latter water content depends on the temperature chosen but for a comparison with the water content of the complex coacervate gelatin (positive) 4- gum arabic (negative) it is indicated to choose a temperature sufficiently far below the critical solution point, for example 20°, so that the composition does not change much per degree fall in temperature. This because at temperatures at which the water content of the gelatin — gum arabic coacervate is known, one is far removed from a possible critical solution point and the water content at those temperatures is almost constant (p. 341). 

We now turn to the complex coacervate gelatin — gum arabic. Vacuolation occurs in this coacervate on cooling also but since the water content is independent of the temperature at higher temperatures (33—50°), this vacuolation (which occurs at about 28.5°) is a phenomenon accompanying the gelation itself (and not as in... 

The very fine vacuolation of these, objects, see p.449, Fig. 17, which appears as fine grains under the microscope is in this case not only to be attributed to the rapid cooling but for a considerable part also to the direct contact of the coacervate drops with the distilled water. As a result of this the salt produced in the coacervation from the counter ions (see p. 368) diffuses out of the drops, and this also gives rise to vacuolation (added salts increase the water content, see p. 364, therefore removal of salts from the coacervate will diminish its water content). 

This is surprising at first sight, because with the fixed mixing ratio of the two colloids in the compartment any change in the chosen optimum pH necessarily leads to a coacervate with higher water-content. Compare p. 362, Ch. X, 2k p. 363, Fig. 23 p. 368. This would thus be a divergence from the rule which was given in 2a (p. 443) decrease of the water-content leads to vacuolation, increase however does not. 

These alcohols have a comparable influence on lecithin coacervates which have a much smaller water content. It is only at high alcohol concentrations that complications appear which can be attributed to the fact that lecithin is an amphoteric substance. 

Whereas micellar aggregation numbers are now routinely determined, we know much less about the water and ion content of the micelles. Estimates of the water content of C3Ms range up to 92 %, similar to values obtained for macroscopic coacervates [19, 53-55]. Several groups have used fluorescent probes, such as auramine O, pyrene and l,3-di-(l-pyrenyl)-propane (P3P), to assay the polarity and microviscosity of the micellar core and C3V membrane [47, 56,57]. Estimates of the micro-ion content of microscopic coacervates are lacking. Experimental and theoretical studies on the salt concentration of macroscopic coacervates report at most small differences in ionic strength inside and outside the coacervate phase [7, 8, 58]. Exceptionally, for example, in coacervates of poorly water-soluble polyelectrolytes, there may be larger differences in salt content [7,8]. 

A wide variety of capsules loaded with water-immiscible or water-iasoluble materials have been prepared by complex coacervation. Capsule size typically ranges from 20—1000 p.m, but capsules outside this range can be prepared. Core contents usually are 80—95 wt %. Complex coacervation processes are adversely affected by active agents that have finite water solubiUty, are surface-active, or are unstable at pH values of 4.0—5.0. The shell of dry complex coacervate capsules is sensitive to variations ia atmospheric moisture content and becomes plasticized at elevated humidities. 

The distribution of Hg was in a class by itself. It can be divided by 34° N into north and south parts. In the north, Hg was similar to Cu in the same area, with two sub-high content areas centered around B3-B4 and B7-B8. In the north, there was a large-scale high area in D section whose content decreased from estuary to offshore area. Seeking the cause, this may be the result of a fresh and salt water mixture, which accelerated the absorbed Hg in the solids so as to be deposited in sediments by coacervation. The average of Hg was 0.025 mg/kg, and most of the stations went beyond the backgroimd value of 0.016 mg/kg, but still much less than the first class limit of Marine Sediment Quality (0.20 mg/kg). 

On just exceeding the coacervation limit the coacervate frequently still contains a relatively large amount of water - - micro-units. This content at first decreases further on further addition of the micromolecular substance. 

The water-poorest complex coacervate (pH == 3.5, mixing proportion 50%) only contains about 18% colloids, thus more than 80% water. From the dis rams of Fig. 48 we read off for the procaine salt-rich layer at 20° on the other hand a salt content of about 75—85% and this layer therefore contains only 15— 25% water. 

When through some variable or other the water and micro units content of a coacervate drop increases, one will not in general expect any striking morphological consequences of this . One can on the one hand expect that the coacervate drops... 

The results (see Fig. 30 in which only the ellipse J and the corresponding electrophoretic reversal of charge line j are included in the figure), show that the shaded region is bounded on its left side by those states of the original coacervate in which the above mentioned E.M.F. is just zero (see the dotted curve). To the right of this the isohydric water in the cell is positive with respect to the contents of the vacuole. 

The vacuole contents must be negative with respect to the iso-hydric distilled water . These two conditions speak very much in favour of an electroendosmotic water transport through the negative coacervate lamella to the vacuoles. 

Nevertheless we are still far removed from a really satisfactory explanation, for in fact an electroendosmotic water transport to the primary vacuoles ought to come about in the mirror image situation, viz coacervate lamella positive and vacuole contents positive with respect to the isohydric distilled water . 

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