Coil-a-helix transition

If the intensity of the CD band at 222 nm, which can be considered a function of the a-helix content, is plotted as a function of methanol concentration, it is observed that addition of methanol induces a coil—>a-helix transition in the macromolecular conformation (Figure 7). However, the amount of methanol needed to induce the conformational transition is different for the sample irradiated at 340 (cis azo units) and that irradiated at 417 nm (trans azo units). Therefore, two separate curves are observed for the two samples. At solvent compositions in the range between the two curves, alternating irradiation at 340 and 417 nm gives rise to folding or unfolding of the macromolecular chains. The photoresponse occurs only in a selected and nar-... 

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