Inverse temperature transitions characterizations

Furthermore, yet to be computed by any program is the fundamental thermo-mechanical transduction wherein the cross-linked elastic-contractile model proteins contract and perform mechanical work on raising the temperature through their respective inverse temperature transitions. These results first appeared in the literature in 1986 and have repeatedly appeared since that time with different preparations, compositions, and experimental characterizations. Additionally, the set of energies converted by moving the temperature of the inverse temperature transition (as the result of input energies for which the elastic-contractile model protein has been designed to be responsive) have yet to be described by computations routinely used to explain protein structure and function. 

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... 

Once numerical estimates of the weight of a trajectory and its variance (2cr ) are known we are able to use sampled trajectories to compute observables of interest. One such quantity on which this section is focused is the rate of transitions between two states in the system. We examine the transition between a domain A and a domain B, where the A domain is characterized by an inverse temperature - (3. The weight of an individual trajectory which is initiated at the A domain and of a total time length - NAt is therefore... 

Transition temperatures that characterize the stmcture and behavior of polymers have already been dealt with some length. From a practical point of view, limiting temperatures for use is also of interest. One should differentiate between a statistical value derived from use data without material damage and a standard test under prescribed conditions, namely, heat distortion or deflection. In the latter, the temperature is measured wherein the samples undergo a definite deformation under a defined load (usually 264 psi). This temperature is taken to be an upper limit for use of the material without the danger of warping. This value obviously depends on the load (inversely affected). Thermal endurance can also be expressed by time and temperature data that affect mechanical and electrical properties. Data verify that for most polymers, the upper limiting useful temperature is rather low (60 -85 C),... 

The second intent to numerically characterize the formulation concept was the so-called phase-inversion temperature (PIT), originally introduced by Shinoda in 1964 as the temperature at which a nonionic surfactant switched its dominant affinity from the aqueous phase to the oil phase. This inversion occurred in a so-called phase transition process that was both easy to determine experimentally and simple to understand as far as the associated phenomenology was concerned [107,108]. Later, it was related to the temperature at which the emulsion inversion takes place [57,58,109], which is the same in most cases, with scarce exceptions and with no real significance [110]. It was finally fine-tuned again and renamed the HLB temperature [111], as a way of stating that it was the temperature at which the hydrophilic and lipophilic tendencies of the surfactant were balanced (i.e., whenever a Winsor Type III system is occurring). 

Typical H-NMR spectra of polymer II, specifically deuterated at both ends of the aliphatic spacer are shown in Figs 1-3. They refer to three different temperatures and characterize the anisotropic melt (Fig. 1) and the solid polymer above (Fig. 2) and below the glass transition (Fig. 3), respectively. Figure 1 shows H-NMR line shapes in an inversion recovery... 

Figure 2. A schematic of the free energy density of an aperiodic lattice as a function of the effective Einstein oscillator force constant a (a is also an inverse square of the locahzation length used as input in the density functional of the liquid). Specifically, the curves shown characterize the system near the dynamical transition at Ta, when a secondary, metastable minimum in F a) begins to appear as the temperature is lowered. Taken from Ref. [47] with permission.

The conformational entropies of copolymer chains are calculated through utilization of semiempirical potential energy functions and adoption of the RIS model of polymers. It is assumed that the glass transition temperature, Tg, is inversely related to the intramolecular, equilibrium flexibility of a copolymer chain as manifested by its conformational entropy. This approach is applied to the vinyl copolymers of vinyl chloride and vinylidene chloride with methyl acrylate, where the stereoregularity of each copolymer is explicitly considered, and correctly predicts the observed deviations from the Fox relation when they occur. It therefore appears that the sequence distribution - Tg effects observed in many copolymers may have an intramolecular origin in the form of specific molecular interactions between adjacent monomer units, which can be characterized by estimating the resultant conformational entropy. 

A typical loss maximum of this type was observed for poly(methyl methacrylate) containing caprolactam or derivatives of cyclohexane12,13. It is noteworthy70 that in the latter case the relaxation induced by the cyclohexyl group present in the incorporated plasticizer and the secondary relaxation of poly(cyclohexyl methacrylate) or poly(cyclohexyl acrylate) are characterized by an identical temperature position, 190 K (1 Hz), and activation energy, 47.9 kJ/mol (AU = 47.7 kJ/mol is reported for the chair-chair transition of cydohexanol). Hence, it can be seen that the cyclohexyl ring inversion, which represents a specific molecular motion, is remarkably insensitive to the surrounding molecules. 

Like UV absorption and natural CD spectra, the MCD spectrum observed in the UV/VIS region is a superposition of contributions from all electronic transitions in the molecule. Whereas in ordinary isotropic absorption spectra or in natural CD spectra each transition can be characterized by its band shape and a single scalar quantity, the oscillator strength or the rotatory strength, three numbers, A Bj, and C are necessary to describe the contribution of each electronic transition i to the MCD spectrum of an isotropic sample. The three numbers are known as the A term, the B term, and the C term of the i-th transition. The contributions of the B term and of the C term to the MCD curve [0]m(v) have the shape of an absorption peak, which in the simplest case has a Gaussian profile as shown in Figure 3.8. They differ insofar as the contribution of the B term is temperature independent, whereas that of the C term is inversely proportional to the absolute temperature and can therefore dominate the spectra at very low temperatures. If nonzero B and C terms are both present, a measurement of the temperature dependence of the spectrum is needed to separate them. 

Serpinet, using the inverse gas chromatography method, demonstrated the existence of oriented monolayers of long-chain hydrocarbons on silica gel surface [13], on the other hand Untz [31] showed that hydrocarbons also form solid condensed and liquid expanded monolayers on glycerol but not on the water surface. However, the addition of some amount of amphiphilic molecules to the hydrocarbon provokes the mixed monolayer formation on the water surface. The phase transition in such a monolayer occurs at the temperature higher than the melting point of bulk hydrocarbon. It also appeared that the monolayers characterized by 1 1 ratio of hydrocarbon to alcohol molecules were particularly stable [41]. 

The transition between a normal and an inverse EIE reflects the fact that these systems are not characterized by the typical monotonic variation predicted by the van t Hoff relationship. Instead, as discussed in an edifying review by Parkin,194 the EIEs in these systems are zero at OK, increase to a value >1, and then decrease to unity at infinite temperature. This unusual behavior is, nevertheless, rationalized by consideration of the individual factors that contribute to the EIE. As discussed above, the EIE may be expressed in the form EIE = SYM x MMI x EXC x ZPE (where SYM is the symmetry factor, MMI is the mass moment of inertia term, EXC is the excitation term, and... 

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