Phase separation inverse temperature transitions

As demonstrated in Figure 5.3 for several model proteins, essentially unlimited solubility occurs at low temperature, and phase separation (insolubility) occurs as the temperature is raised. Also, for our model protein composi-tions, - the curvature of the coexistence line is inverted, having the shape of a valley instead of a smooth mountain peak. Because of this we call the phase transition, exhibited by elastic-contractile model proteins, an inverse temperature transition. Even more compelling reasons exist for the inverse temperature transition label. 

As mentioned above in reference to Figure 5.5A, as the temperature is raised, contraction of a band composed of elastic-contractile model protein occurs. Contraction occurs as the temperature is raised through a temperature interval. Crossing over the T,-divide, defined in Figure 5.3, is to pass through the temperature interval over which contraction occurs it is the result of the phase separation, specifically of the inverse temperature transition. Furthermore, the temperature interval for contraction occurs at a lower temperature when the model protein is more hydrophobic and at a higher temperature when the model protein is less hydrophobic. 

Figure 5.10. An embodiment of the comprehensive hydrophobic effect in terms of a plot of the temperature for the onset of phase separation for hydrophobic association, Tb, versus AGha. the Gibbs free energy of hydrophobic association for the amino acid residues, calculated by means of Equation (5.10b) using the heats of the phase (inverse temperature) transition (AH,). Values were taken from Table 5.3. Tb and T, were determined from the onset of the phase separation as defined in Figure 5.1C,B, respectively. The estimates of AGha utilized the AH, data listed in Table 5.1 for fx = 0.2 but extrapolated to fx = 1, and the Gly (G) residue was taken as the...

The term inverse transition was first used in connection with the increase in order of the antibiotic stendomycin on raising the temperature (D.W. Urry and A. Ruiter, Conformation of Polypeptide Antibiotics. VI. Circular Dichroism of Stendomycin. Biochem. Biophys. Res. Commun., 38,800-806,1970). The term became specifically inverse temperature transition in relation to coacervation of elastin fragments that exhibited a phase separation with increased order on raising the temperature (B.C. Starcher, G. Saccomani, and D.W. Urry, Coacervation and Ion-Binding Studies on Aortic Elastin. Biochim. Biophys. Acta, 310, 481 86,1973, and D.W. Urry, B. Starcher, and S.M. Partridge, Coacervation of Solubilized Elastin Effects a Notable Conformational Change. Nature, 222,795-796,1%9). 

By T,-type, we mean polymers that exhibit inverse temperature transitions in which the protein-based polymers hydrophobically associate on raising the temperature. T, represents the onset temperature for the transition. For the elastic-contractile model proteins of interest here, the inverse temperature transition is seen as a phase separation resulting from both intermolecular and intramolecular hydrophobic association. On raising the temperature... 

Purification by Phase Separation (Inverse Temperature Transition)... 

Preparation of y-irradiation cross-linked matrices In preparation for y-irradiation cross-linking, the polymer is dissolved in water at low temperature. On raising the temperature above that of the inverse temperature transition for hydrophobic association, phase separation occurs. The phase-separated state is then exposed to 20Mrad of y-irradiation from a cobalt-60 source. 

Disruption of an ordered H-bonded water shell with temperature may provoke conformational changes of biomolecules. Typically, biomolecules undergo denaturation transition upon heating. This process is accompanied by phase separation into dilute (water rich) phase and organic-rich phase, which may appear as viscous liquid or amorphous solid. In real aqueous solutions of large elastin-based polymers, the phase separation into water-rich and organic-rich phases, accompanied by sharp conformational changes of the polymer (the so-called inverse temperature transition), occurs at about 300 K [558]. In solutions of small ELP,... 

Poly(VPGVG) (Fig. 6) has been smdied most thoroughly and it was shown that it exhibits an inverse phase transition. The biopolymer undergoes phase separation from solution upon increasing temperature, resulting in a p-spiral structure and simultaneous release of water molecules associated with the polymer chain (Fig. 7). 

As we will see in Chapter 11, it is usual to describe interactions in polymers using the Flory interaction parameter x, which varies as the inverse of the temperature. Thus if x is relatively small it is possible to form a single phase at temperatures below the degradation point of the polymer. Then, as you cool and X gets larger, the system phase-separates. The temperature or value of x at which this occurs, the order-disorder transition, varies with composition and it is possible to... 

In many foods, both starch and protein can be encountered so that understanding interactions between them would be useful. The selectivity in interaction between proteins and starches is best seen in results of dynamic rheological studies. The results depend upon the molecular structure of protein, the starch state of the granules and the amylose/amylopectin ratio, the composition of protein and starch, as well as the phase transition temperatures are important factors influencing protein-starch interaction. Because proteins and starches are thermodynamically different polymers, their presence together may lead to phase separation, inversion, or mutual interaction with significant consequences on texture (Morris, 1990). 

One limitation of the HLB concept is its failure to account for variations in system conditions from that at which the HLB is measured (e.g., temperature, electrolyte concentration). For example, increasing temperature decreases the water solubility of a nonionic surfactant, ultimately causing phase separation above the cloud point, an effect not captured in a temperature-independent HLB value. When both water and oil are present, the temperature at which a surfactant transitions from being water soluble to oil soluble is known as the phase inversion temperature (PIT). Below the PIT, nonionic surfactants are water soluble, while above the PIT. they are oil soluble. Thus, from Bancroft s rule, a nonionic surfactant will form an 0/W emulsion below its PIT and a W/0 emulsion above its PIT. Likewise, increasing salt concentrations reduces the water solubility of ionic surfactant systems. At elevated salt concentrations, ionic surfactants will eventually partition into the oil phase. This is illustrated in Fig. 13. which shows aqueous micelles at lower salt concentrations and oil-phase inverse micelles at higher salt concentrations. Increasing the system temperature will likewise cause this same transition for nonionic surfactant systems. 

When a latex product is frozen, ice crystals tend to undergo phase separation from the colloidal system therefore, the concentration of polymer particles in the fluid phase continues to increase with the progress of the freezing process. Sooner or later, phase inversion will occur and the probability for the coagulation of polymer particles to take place increases significantly. This is especially true for polymer particles with a glass transition temperature lower than the freezing temperature or with insufficient stabilization by surfactants or protec-... 

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