Structural transitions helical

Structural transitions between functionally distinct a-helical and p-sheet... 

Studies of similar structural transitions for hydrogen within the nanotubes have been carried out by Xia et al. [145], Ying et al. [146], and Ma et al. [147] These results exhibit a wide variety of linear, cylindrical, and helical phases, the existence of which is strongly dependent on the tube radius and the molecular density. Obviously, the transitions between these novel phases are of considerable interest, but space considerations prevent us from discussing the results in detail. Scattering experiments would provide ideal probes of these phases but their interpretation wiU be difficult unless the tubes are aligned. 

The requirements for hydrogen bond preservation in the folded structure result in the cooperative formation of hydrogen-bonded secondary structure regions in proteins. The secondary structure specifies regular polypeptide chain folding patterns of helices, sheets, coils and tnms that are combined/folded into tertiary structure. Studies of two-state structural transition suggest that a statistical method can be developed to predict the... 

Fig. 3 Schematic view of the human vimentin protein and force-strain curves of coiled-coil intermediate filament under tensile loadings, (a) Schematic representation of vimentin structure, (b) Force-strain behaviors of a coiled-coil a-helical structures revealing the loading rate dependency of the molecular-level stiffness under tensile loading. (Reprinted from [66], with kind permission from Springer Science and Business Media), (c) a-p secondary structural transition of coiled-coil a-helix under tensile loading. (Reprinted from [67])...

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. 

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