Inverse temperature transitions components

Figure 2.7. These crystals of cyclo(GVGVAPGVG-VAP) form when the temperature of aqueous solutions is raised and dissolve when the temperature is lowered. This finding represents an unambiguous demonstration that the model protein component of the aqueous solution becomes more ordered on higher temperature and is one of the reasons that the transition is called an inverse temperature transition. (Adapted with permission from Urry et al. )...

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. 

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. 

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. - ... 

Relative Magnitude of the Endothermic and Exothermic Components of the Inverse Temperature Transition and Relevance to Biology s Protein-based Machines... 

Figuke 8.1. Component heats of hydrophobic association of an inverse temperature transition obtained by means of temperature-modulated differential scanning calorimetry (TMDSC). (Upper curve) An exothermic component of the inverse temperature transition due to the physical (van der Waals) interaction between associating molecules. (Middle curve) The endothermic component (due to disruption of hydrophobic hydration), which is the fundamental feature of an inverse temperature transition of hydrophobic association. (Lower curve) Net endothermic heat of an inverse temperature transi-... 

Jones 6-12 potential or the Buckingham potential functions. It will be interesting, in future work, to determine the relative magnitude of the endothermic and exothermic components for each of the amino acid residues and for other biologically relevant chemical modifications, as they contribute as guest residues to the inverse temperature transition of (GVGVP) and of other informative host model proteins. 

J.C. Rodrfguez-Cabello, J. Reguera, M. Alonso, T.M. Parker, D.T. McPherson, and D.W. Urry, Endothermic and Exothermic Components of an Inverse Temperature Transition for Hydro-phobic Association by TMDSC. Chem. Phys. Lett., 388,127-131,2004. 

Inverse Temperature Transition of Elastin and Component Sequences... 

Recently, the first examples of catalytic enantioselective preparations of chiral a-substituted allylic boronates have appeared. Cyclic dihydropyranylboronate 76 (Fig. 6) is prepared in very high enantiomeric purity by an inverse electron-demand hetero-Diels-Alder reaction between 3-boronoacrolein pinacolate (87) and ethyl vinyl ether catalyzed by chiral Cr(lll) complex 88 (Eq. 64). The resulting boronate 76 adds stereoselectively to aldehydes to give 2-hydroxyalkyl dihydropyran products 90 in a one-pot process.The diastereoselectiv-ity of the addition is explained by invoking transition structure 89. Key to this process is the fact that the possible self-allylboration between 76 and 87 does not take place at room temperature. Several applications of this three-component reaction to the synthesis of complex natural products have been described (see section on Applications to the Synthesis of Natural Products ). 

The issue of isotope effects is further complicated by the recently reported unusual temperature dependences such that either a normal or an inverse isotope effect may be observed for the same reaction depending on the temperature.96 Calculations suggest that significant contributions to the zero-point energy can come from vibrations that do not involve the bonds being made or broken. The transition between the normal and inverse isotope effects occurs because of the inverse enthalpy and normal entropy components that oppose each other and exhibit different temperature dependences. 

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