Inverse temperature transitions behavior

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... 

Boutis and coworkers report measurements of the relaxation times of water hydrated N. clavipes and A. aurantia spider silks as a function of temperature by deuterium 2D T1-T2 inverse Laplace transform (ILT) NMR to study the distribution, population and dynamics of hydration water at different temperatures finding correlation times much longer than those for free water and in some cases increasing with increased T. MD simulations reveal that peptides prepared from a number of repeating motifs show inverse temperature transition behavior found for example in protein elastin. 

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. 

Inverted Phase Transitional Behavior of Inverse Temperature Transitions... 

A vital property of these model proteins is that they are more ordered above the transition temperature defined by the binodal or coexistence line in Figure 5.3. The polymer component of this water-polypeptide system becomes more ordered or structured on increased temperature from below to above the transition. This behavior is the inverse of that observed for most systems, as discussed above. In particular, we developed the term inverse temperature transition when the precursor protein and chemical fragmentation products of the mammalian elastic fiber changed from a dissolved state, and therefore when molecules were randomly dispersed in solution, to a state of parallel-aligned twisted filaments as the temperature was raised from below to above the phase transition. - ... 

As reviewed in Chapter 7 with a focus on the issue of insolubility, extensive phenomenological correlations exist between muscle contraction and contraction by model proteins capable of inverse temperature transitions of hydrophobic association. As we proceed to examination of muscle contraction at the molecular level, a brief restatement of those correlations follows with observations of rigor at the gross anatomical level and with related physiological phenomena at the myofibril level. Each of the phenomena, seen in the elastic-contractile model proteins as an integral part of the comprehensive hydrophobic effect, reappear in the properties and behavior of muscle. More complete descriptions with references are given in Chapter 7, sections 7.2.2, and 7.2.3. 

The importance of ELRs resides in the fact that these polymers show a versatile and broad range of interesting properties above and beyond their simple mechanical performance that are not easily found together in other materials, including stimuli-responsive behavior or the ability to self-assemble. These properties arise due to a molecular transition of the polymer chain in the presence of water at temperatures above a certain level. This transition, known as the Inverse Temperature Transition (ITT) [7, 8], has become the key issue in the development of peptide-based polymers for use as molecular machines and materials. 

The responsive behavior of ELRs has been defined as their ability to respond to external stimuli. This property is based on a molecular transition of the polymer chain in the presence of water at a temperature above a certain level, known as the Inverse Temperature Transition (ITT). This transition, whieh shares most of the properties of the lower critical solution temperature (LCST), although it also differs in some respects, particularly as regards the ordered state of the folded state, is clearly relevant for the application of new peptide-based polymers as molecular devices and biomaterials. Below a specific transition temperature (T,), the free polymer chains remain as disordered, random coils [20] that are fully hydrated in aqueous solution, mainly by hydrophobic hydration. This hydration is characterized by ordered, clathrate-like water structures somewhat similar to those described for crystalline gas hydrates [21, 22], although somewhat more heterogeneous and of varying perfection and stability [23], surrounding the apolar... 

Impuritiesand the a P-quartz tranition. The a- 3-quartz transition was the basis for one of the earliest systematic investigations of the variation of transition temperatures in response to impurities. Pure a-quartz undergoes a first-order transition to a microtwinned incommensurate structure at 573°C, and this modulated phase transforms to P-quartz at 574.3°C with second-order behavior (Van Tendeloo et al. 1976, Bachheimer 1980, Dolino 1990). Tuttle (1949) and Keith and Tuttle (1952) investigated 250 quartz crystals and observed that Tc for natural samples varied over a 38°C range. In their examination of synthetic specimens, substitution of Ge for Si raised the critical temperature by as much as 40°C, whereas the coupled exchange of Ar +Li o Si depressed Tc by 120°C. They concluded from their analyses that the departure of the a-P-quartz inversion temperature from 573°C could be used to assess the chemical environ-ment and the growth conditions for natural quartz. 

The conventional, and very convenient, index to describe the random motion associated with thermal processes is the correlation time, r. This index measures the time scale over which noticeable motion occurs. In the limit of fast motion, i.e., short correlation times, such as occur in normal motionally averaged liquids, the well known theory of Bloembergen, Purcell and Pound (BPP) allows calculation of the correlation time when a minimum is observed in a plot of relaxation time (inverse) temperature. However, the motions relevant to the region of a glass-to-rubber transition are definitely not of the fast or motionally averaged variety, so that BPP-type theories are not applicable. Recently, Lee and Tang developed an analytical theory for the slow orientational dynamic behavior of anisotropic ESR hyperfine and fine-structure centers. The theory holds for slow correlation times and is therefore applicable to the onset of polymer chain motions. Lee s theory was generalized to enable calculation of slow motion orientational correlation times from resolved NMR quadrupole spectra, as reported by Lee and Shet and it has now been expressed in terms of resolved NMR chemical shift anisotropy. It is this latter formulation of Lee s theory that shall be used to analyze our experimental results in what follows. The results of the theory are summarized below for the case of axially symmetric chemical shift anisotropy. 

Figure 2. Plot of the self-

Figure 2.6 illustrates the procedure for the identification of the transitions by means of inflection-point analysis. Plotted are the inverse temperature (F") and its energetic derivative y E). There are two regions, where the weak-sensitivity condition applies to E). One is located around the inflection point at E and the other is the backbending regime surrounding the central inflection point at The latter exhibits the already well-described features of a first-order transition y is positive and the intersection points of the inverse transition temperature /S with the E) curve define the coexistence region. The width is interpreted as the latent heat, which is obviously nonzero > 0. The behavior is qual-... 

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