Folding inverse temperature

Fortunately C-terms are readily distinguished from A- and B-terms by their inverse temperature dependence. If present, they usually dominate the MCD spectrum at low temperatures, since they can be enhanced up to 70-fold on going from room temperature to liquid helium temperatures. For biological chromo-phores, which generally possess only low symmetry, ground state degeneracy can... 

Fig. 3.6. Dependences of the chain size (gyration radius) on the inverse temperature calculated through Monte Carlo simulations. (Top) A semiflexible chain with contour length L/a = 512 and Kuhn length l/a 20, and (bottom,) a flexible chain (l/a 2) with the same contour length. The error bars represent the standard deviations. The insets show snapshots of (a) coil states and (b) folded states...

The poly(alkylene oxide)-bound phosphine ligands 1 and 2, as well as a cationic rhodium(I) complex of 1, were demonstrated to possess inverse temperature-dependent solubility. The effects of these solubility properties on catalysis have been demonstrated in the hydrogenation of allyl alcohol in water. An approximately 20-fold decrease in rate is observed when the temperature is raised from 0 °C to 40-50°C [9a], This unusual temperature dependence has been termed smart behavior . 

T[ and Tj, are the on-set temperature for the hydrophobic folding and assembly transition, that is, inverse temperature transition, in pbs (0.15 N NaCl, 0.01 M phosphate) as determined by light scattering and in water as determined by DSC, respectively. Both values are linearly extrapolated tofx = 1 and rounded to a number divisible by 5. AH and AS are the values at/x = 0.2 on the curve for a linear fit of the DSC derived endothermic heats and entropies of the transitions for die polymers in water. 

Quite the inverse occurs for water-dissolved protein of interest here that is, by the consilient mechanism, heating from below to above the folding transition increases the order of the model protein. Because heating increases protein order, the transition is called an inverse temperature transition. 

The inverse temperature transition is a specific mechanism whereby thermal energy (heat) provides an increase in order of the protein part of the system. A decrease in entropy of this sort has been termed negative entropy by Schrodinger. ° While the total entropy (disorder) for the complete system of protein and water increases as the temperature is raised, the structural protein component, critical to the conversion of thermal energy to mechanical work, increases in negative entropy. The protein component increases in order by the folding that shortens length and by the assembly of oillike domains that builds structures. 

The Inverse Temperature Transition A Hydrophobic Folding and Assembly Transition... 

The protein-based polymer is soluble in water at temperatures below its coexistence line where the hydrophobic residues are surrounded by hydrophobic hydration. As the positive (-TAS) term due to hydrophobic hydration becomes larger than the negative AH term, simply due to increasing the value of T, solubility of a protein-based polymer is lost, and it hydrophobicaUy folds and assembles. The inverse temperature transition is a hydrophobic association transition. 

More oil-like R-groups in our model protein studies resulted in lower temperatures for the onset of the inverse temperature transition of hydrophobic folding and assembly (see section 5.3.2). We argued that more oil-like R-groups in... 

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. 

Nonetheless, the merging of loss shear modulus, G", and loss permittivity, e", data for the overlapping frequencies in Figure 5 is truly remarkable. Explanation of the distinctive 40 C curve now becomes obvious. The explanation arises due to the occurrence of the temperature interval of the inverse temperature transition being from 10 to 30 C. During the inverse temperature transition of hydrophobically folding into the structure of Figure 2, the frequency maximum of the loss permittivity peak... 

Figure 1 A. Temperature versus normalized turbidity curves for a series of guest amino acid residues occurring at the frequency of 4 guest residues per 100 residues, i.e., fx = 0.2. The value of Tj, the temperature for the onset of the inverse temperature transition for hydrophobic folding and assembly, is defined as the temperature for 50% of maximal turbidity. Note that more hydrophobic guest residues lower the value of T,. and less hydrophobic, more polar residues raise the value of Ti.

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... 

E. Schreiner, C. Nicolini, B. Ludolph, R. Ravindra, N. Otte, A. Kohlmeyer, R. Rousseau, R. Winter, D. Marx, Folding and unfolding of an elastinlike oligopeptide Inverse temperature transition, reentrance, and hydrogen-bond dynamics, Phys. Rev. Lett. 92 (2004) 148101. 

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