Deformation-Induced Conformational Changes

PVC films were stretched to various elongation ratios and the dichroic behaviour of 615 and 637 cm bands of the IR spectrum were investigated. The evolution of the dichroic ratios and of the relative absorbance of the bands in the direction perpendicular to that of stretching were compared so the occurrence of local chain orientation related to the conformational change from gttg-tt to gtgttt which occurs when PVC is stretched (51). 

FTIR polarisation spectroscopy was used to study the orientational behaviour of the different constituents of a liquid crystalline block copolymer (copolyester-imide) during uniaxial elongation at different temperatures. Differences in the degree of alignment (as well as in the response to the application of the mechanical load) were observed. With increasing temperature, the level of the applied stress and the induced degree of orientation decreased, while the differences in the orientational behaviour of the mesogen and the flexible spacer were retained (243). 

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The peculiar behaviour of polyftetramethylene terephthalate) 4GT has received considerable attention with studies on multiple melting and crystallization behaviour, - the alpha crystal phase, the hysteresis of the stress-induced crystalline phase transition, and reversible crystal deformation and conformational changes. ... 

Figure 3 Possible mechanisms of MS channel activation by bilayer deformation forces. Hydrophobic mismatch and bilayer curvature are considered as deformation forces of pressure-induced changes in the lipid bilayer causing conformational changes in MS channels as indicated by the example of MscL (13). These changes were studied experimentally by reconstituting purified MscL proteins in liposome bilayers prepared from synthetic phosphatidylcholine lipids of well-defined composition. The changes in functional properties were examined by the patch-clamp technique, whereas the structural changes were determined by EPR and FRET spectroscopy. (Reproduced from Reference 12, with permission).

Studies of deformation-induced changes in polymers by vibrational spectroscopic techniques can lead to a better understanding of structure-property relationships. They may provide insights into the micros true tural mechanisms of orientation, relaxation and conformational rearrangement. 

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