Poly temperature transition, inverse

After expression of poly(VPGXG) genes, the biopolymer can easily be purified from a cellular lysate via a simple centrifugation procedure, because of the inverse temperature transition behavior. This causes the ELPs to undergo a reversible phase transition from being soluble to insoluble upon raising the temperature above the and then back to soluble by lowering the temperature below Tt (Fig. 9). The insoluble form can be induced via addition of salt [27]. The inverse transition can... 

The a transition is not included in the considered temperature range. For CMI contents equal to or higher than 10%, two transitions are observed. At low temperatures a shoulder is present, whose extent increases with increasing CMI (y transition). Studies performed on copolymers with maleimide unit N-substituted by isopropyl or phenyl groups [79] do not show this low-temperature transition, which appears to be specific for cyclohexylmaleimide. Such a situation is analogous to the one encountered with poly(cyclohexyl methacrylate) described in Sect. 3. Consequently, this low-temperature transition is assigned to the internal motion of the cyclohexyl ring, i.e. the chair-chair inversion represented in Fig. 7. 

Scheme 9 Chemical structure of the modified, elastin-like poly (pentapeptide) XIV, found to exhibit photomodulated inverse temperature transition. 59 ...

Single-crystal and poly crystalline transition metal carbides have been investigated with respect to creep, microhardness, plasticity, and shp systems. The fee carbides show slip upon mechanical load within the (111)plane in the 110 direction. The ductile-to-brittle transformation temperature of TiC is about 800 °C and is dependent on the grain size. The yield stress of TiC obeys a Hall Petch type relation, that is, the yield stress is inversely proportional to the square root of the grain size. TiC and ZrC show plastic deformation at surprisingly low temperatures around 1000 °C. 

Other successful determinations of glass transition temperatures by inverse gas chromatography indude those of Perrault et al. 22) on poly(butadiene), Nakamura et al 26) on cellulose triacetate and Cahigaru et id. 27) on poly(viiq l acetate). 

To apply the phase inversion principle, the transitional inversion method should be used, as demonstrated by Shinoda and coworkers [11, 12] when using nonionic surfactants of the ethoxylate type. These surfactants are highly dependent on temperature, becoming lipophilic with increasing temperature due to dehydration of the poly(ethylene oxide) (PEO) chain. When an O/W emulsion that has been prepared using a nonionic surfactant of the ethoxylate type is heated, at a critical temperature - the PIT - the emulsion will invert to a W/O emulsion. At the PIT, the droplet size reaches a minimum and the interfacial tension also reaches a minimum, but the small droplets are unstable and coalesce very rapidly. Rapid cooling of an emulsion that has been prepared close to the PIT results in very stable and small emulsion droplets. 

Fig. 27. Experimental (left) and simulated (right) central transition inversion recovery spectra of 47% enriched poly crystalline cristoballite for the temperatures given, recorded as a function of the length t of the relaxation delay.40 All simulations assume a six-site motion between six equally probable sites on a circle orthogonal to the Si-Si axis between adjacent Si04 tetrahedra, with rate constants log( ) = 3.50 at T= 298 K, log(Jfc) = 3.95 at T= 473K and log(fc) = 5.80 at T= 528 K.

Strzegowski LA, Martinez MB, Gowda DC, Urry DW, Tirrell DA. 1994. Photomodulation of the inverse temperature transition of a modified elastin poly(pentapeptide). J Am Chem Soc 116(2) 813 814. 

Table 1. Hydrophobicity scale for protein-based polymers and proteins based on the properties of the inverse temperature transition of elastic protein-based polymers, poly[/v(GVGVP), (GXGVP)]. ...

Table 3b. Effect of pH on inverse temperature transition of poly[0.82(GVGIP), 0.18(GEGIP)], (3)...

Table 3g. Cosolvent effect on inverse temperature transition of poly(GVGVP) in water.

Figure 6 (a) Correlation between the turbidimetric profile as a function of temperature and differential scanning calorimetry (DSC) thermogram for a chemically synthesized polymer of (Val-Pro-Gly-Val-Gly) in water, (b) Photographic illustration of the phase behavior of poly(Val-Pro-Gly-Val-Gly) in aqueous solution at temperatures below (5 °C) and above (40 °C) the inverse temperature transition, 7,. Reprinted from Arias, F. J. Reboto, V. Martin, S. etal. Blotechnol. Lett. 2006,25(10), 687. Copyright 2006, with permission from Springer. 

Despite the absorption of heat for the transition and the overall increase in entropy of -(-4.0 EU for the water plus protein, the protein component actually increases in order on raising the temperature. As unambiguously demonstrated by crystallization of a cyclic analog (see Figure 2.7), in this case the protein component of the water plus protein system becomes more ordered as the temperature is raised. For this and additional reasons, noted below in section 5.1.3, we call this transition exhibited by our model protein, poly (GVGVP), an inverse temperature transition. 

Figure 5.3. Phase diagram for several elastic-contractile model proteins, showing an inverted curvature to the binodal or coexistence line (when compared with petroleum-based polymers) that is equivalent to the T,-divide, with the value of T, determined as noted in Figure 5.IB. Solubility is also inverted with insolubility above and solubility below the binodal line, that is, solubility is lost on raising the temperature whereas solubility is achieved by raising the temperature of most petroleum-based polymers in their solvents. Note that addition of a CHj group lowers the T,-divide and removal of the CH2 group raises the T,-divide. For these and the additional reason of increased ordering on increasing the temperature, the phase transitions of elastic-contractile model proteins are called inverse temperature transitions. (The curve for poly[GVGVP] is adapted with permission from Manno et al. and Sciortino et al. ).

Figure 5.5. Transitions, plotted as independent variable versus dependent variable, showing a response limited to a partieular range of independent variable. (A) Representation of the thermally driven contraction for an elastic-contractile model protein, such as the cross-linked poly(GVGVP), plotted as the percent contraction (dependent variable) versus temperature (independent variable). The plot shows a poorly responsive range below the onset of the transition, the temperature interval of the inverse temperature transition for hydrophobic association, and another poorly responsive region above the tem-...

The usual conditions are for 40mg/ml polymer, 0.15N NaCl and 0.01 M phosphate at pH 7.4. T,=Temperature of inverse temperature transition for poly[/v(VPGVG)/x(VPGXG)]. 

Table 5.3. Hydrophobicity Scale in terms of AGha, the change in Gibbs free energy for hydrophobic association, for amino acid residue (X) of chemically synthesized poly[fv(GVGVP), fx(GXGVP)], 40m ml, mw = 100 kDa in 0.15 N NaCl, 0.01 M phosphate, using the net heat of the inverse temperature transition, AGha = [AH,(GGGVP) - AH.(GXGVP)] for the fx = 0.2 data extrapolated to f = 1.

Early in our studies it was expected that the post-translational modification of proline hydroxylation, so important to proper collagen structure and function, would raise the value of the temperature, T, for the onset of the inverse temperature transition for models of elastin. Accordingly, hydroxyproline (Hyp) was incorporated by chemical synthesis into the basic repeating sequence to give the protein-based polymers poly[fvs,i(Val-Pro-Gly-Val-Gly), fHyp( al-Hyp-Gly-Val-Gly)], where f sl -i- fnyp = 1 and values of fnyp were 0, 0.01, and 0.1. The effect of prolyl hydroxylation is shown in Figure 7.49. Replacement of proline by hydroxyproline markedly raises the temperature for hydrophobic association. Prolyl hydroxylation moves the movable cusp of... 

Now, it has been shown for materials such as poly(propylene diol) (wherein both the absorption maximum for loss shear modulus and loss permittivity overlap near the frequency of IHz) that their normalized curves perfectly superimpose over their frequency band width. - As shown in Figure 9.15, the lower frequency loss shear modulus curves uniquely overlap with the loss permittivity data at higher frequency. As such the former is melded to calibrate the loss permittivity data to obtain a coarse estimate of the elastic modulus values. This provides an independent demonstration of the mechanic il resonance near 3 kHz and also allows reference to the 5 MHz dielectric relaxation as a mechanical resonance. Thus, as the folding and assembly of the elastic protein-based polymers proceed through the phase (inverse temperature) transition, the pentamers wrap up into a structurally repeating helical arrangement like that represented in Figure 9.17. 

When a polymer exhibits a maximum in the imaginary part of the dielectric permittivity (the loss permittivity, e") at frequencies less than 200 Hz, it becomes possible to make comparisons with the frequency dependence of shear moduli and most specifically with the loss shear modulus, G". This has been done for polypropylene diol, also called poly(oxypropy-lene), where there is reported a near perfect superposition of the frequency dependence of the normalized loss shear modulus with that of the normalized loss permittivity as reproduced in Figure 3. The acoustic absorption frequency range of interest here is 100 Hz to 10 kHz, yet present macroscopic loss shear modulus data can be determined at most up to a few hundred Hz. Nonetheless, for X -(GVGIP)32o there is a maximum in loss permittivity, e", near 3 kHz that develops on raising the temperature through the temperature range of the inverse temperature transition. With the width of the loss permittivity curve a distinct set of curves as a function of temperature become... 

Convenient purification of microbially produced transductional protein-based polymers, e.g. poly(GVG T), from the cell lysate is based on a methodologv w hich utilizes the fundamental inverse temperature transitional properties (Urry et al., 1995b McPherson et al, 1996). First the bacterial cells are separated from the growth medium either by centrifugation or filtration and resuspened in Tris-HCl buffer, 50 mM, pH 8.0. Then the cells are lysed by ultrasonic disruption or French press to release the cell contents. The cell lysate is cooled to 4 C and centrifuged at high speed (10,000 x g) to remove the cold insoluble materials. The supernatant... 

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