Macromolecules separation from solution

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). 

Process in which a polymeric material, consisting of macromolecules differing in some characteristic affecting their solubility, is separated from solution into fractions by successively decreasing the solution power of the solvent, resulting in the repeated... 

It will also be convenient in most of the discussion to treat phenomena associated with rigid macromolecules separately from the more complex events encountered in solutions of flexible polymer. 

Thermal precipitation by cooling is the scheme chemists normally use in recrystallizations and is the normal behavior of small molecules. Macromolecules are different in that they can often be phase separated from solution by heating [ 119,120]. Thermal precipitation by heating is a process that produces a solid polymer without addition of anything other than heat. It is the inverse of the process used with the polyethylene oligomers discussed above. This inverse temperature-dependent solubility of macromolecules is a phenomenon that is most simply ascribed to the unfavorable entropy of solvation of a macro-... 

Reverse Osmosis and Ultrafiltration. Reverse osmosis (qv) (or hyperfiltration) and ultrafilttation (qv) ate pressure driven membrane processes that have become well estabUshed ia pollution control (89—94). There is no sharp distinction between the two both processes remove solutes from solution. Whereas ultrafiltration usually implies the separation of macromolecules from relatively low molecular-weight solvent, reverse osmosis normally refers to the separation of the solute and solvent molecules within the same order of magnitude in molecular weight (95) (see also Membrane technology). 

The range of application of the three pressure-driven membrane water separation processes—reverse osmosis, ultrafiltration and microfiltration—is illustrated in Figure 1.2. Ultrafiltration (Chapter 6) and microfiltration (Chapter 7) are basically similar in that the mode of separation is molecular sieving through increasingly fine pores. Microfiltration membranes filter colloidal particles and bacteria from 0.1 to 10 pm in diameter. Ultrafiltration membranes can be used to filter dissolved macromolecules, such as proteins, from solutions. The mechanism of separation by reverse osmosis membranes is quite different. In reverse osmosis membranes (Chapter 5), the membrane pores are so small, from 3 to 5 A in diameter, that they are within the range of thermal motion of the polymer... 

Figure 5.2. Free-energy change of mixing for rods and solvent molecules. Free energy change (AGIRT) of (A) solid phase associated with transfer of a solute molecule (macromolecule) from the liquid to the solid state as a function of solute volume fraction (V2) for low (Z = 10) and high (Z = 200) axial ratios and (B) liquid phase as a function of solute volume fraction in the presence (Xi = 0.1) and absence (Xi = 0) of interactions between solute molecules. The diagrams show that separation of solute and solvent molecules occurs spontaneously for high axial ratios above a critical volume fraction and that the free energy of the solvent is raised by inter-molecular interactions.

Fig. 5 Immobilized nucleic acid assays utilizing redox-active moieties, a Amplified detection of viral DNA by generation of a redox-active replica and the bioelectrocatalyzed oxidation of glucose (Reprinted with permission from [200]. Copyright(2002) American Chemical Society), b Alternative formats for the capture on a gold electrode SAM of solution-extended primers or direct surface extension of primer with electrotides (adapted from [185]). c Ferrocene-labelled hairpin for electrochemical DNA hybridization detection. A Fc-hairpin-SH macromolecule is immobilized on a gold electrode. When a complementary DNA target strand binds to the hairpin, it opens and the ferrocene redox probe is separated from the electrode, producing a decrease in the observed current (Reprinted with permission from [203], Copyright(2004) American Chemical Society)...

Theta conditions are of great theoretical interest because the diameter of the polymer chain random coil in solution is thenequal to the diameter it would have in the amorphous bulk polymer at the same temperature. The solvent neither expands nor contracts the macromolecule, which is said to be in its unperturbed state. The theta solution allows the experimenter to obtain polymer molecules which are unperturbed by solvent but separated from each other far enough not to be entangled. Theta solutions are not normally used for molecular weight measurements, because they are on the verge of precipitation. The excluded volume vanishes under theta conditions, along with the second virial coelTicient. 

When cells in culture are treated with a polymer solution the sur ce of each cell is exposed to the solution. The cell is isolated from its surrounding by a cellular membrane, alternatively named cytoplasmic membrane. When cells in culture are used, all interactions between polymer and cytoplasmic membranes are uniform and can be easily measured. Beyond that point, the situation remains quite cmnplex. The interior cell is again divided by lipid containing membranes into many compartments that p-event a uniform distribution of macromolecules in the cytc lasmk space. Thus, there are cellular spaces, again separated from the qhoplasm by membranes, that can stay completely free of polymer and consequently, free of any inhibition that the polymer may exert. 

As in many other membrane separation applications, the clean water flux is essentially proportional to the transmembrane pressure difference (TMP). When solutes, macromolecules or particulates are to be separated from the solvent (e.g., water), the permeate flux is first a linear function of the TMP and is in the pressure controlled regime. Although similar to the behavior of water flux, the permeate flux is nevertheless lower. Beyond a "threshold pressure," the permeate flux is insensitive to TMP due to concentration and gel polarization near the membrane surface. This behavior is so-called mass transfer controlled. It appears that the larger pore membrane, 50 nm in pore diameter, reaches the threshold pressure sooner than the finer pore membrane, 4 nm in pore diameter. There is a significant advantage of operating the membranes at a higher... 

In the present study, we describe the methods of preparing the silica hybrids of linear and branched fiinctional polysiloxanes which could be used as a support for metal complex catalysts. The way in which the catalyst operates when it is attached to the polysiloxane moiety of the hybrid suspended in a polysiloxane solvent should be similar to the way it operates when in solution. Thus, its high catalytic activity is expected. On the other hand, it is easily separated from the reaction products and may be recycled or used in the continuous process. A high catalytic activity and specificity may be achieved if a polymer with a highly branched structure is used for the immobilization of catalysts [1-3]. Considerable amounts of catalytic groups may be placed in the external part of the branched macromolecule. 

As ionic strength, in Figure 2.3, is increased, the solution again reaches a point where the solute molecules begin to separate from solvent and preferentially form self-interactions among themselves that result in crystals or precipitate. The explanation for this salting-out phenomenon is that the salt ions and macromolecules compete for the attention of solvent molecules, that is, water. Both the salt ions and the protein molecules require hydration layers to maintain their solubility. When competition between ions and proteins becomes sufficiently intense, the protein molecules begin to self-associate in order to satisfy, by intermolecular interactions, their electrostatic requirements. Thus dehydration, or the elimination and perturbation of solvent layers around protein molecules, induces insolubility. 

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