Insights into the helix-sense inversion of poly(β-phenethyl-L-aspartate) by two-dimensional Raman correlation spectroscopy.

In this study, the transition process of the helix-sense inversion of poly(β-phenethyl-L-aspartate) was investigated by Raman scattering and 2-dimensional correlation spectroscopy. Temperature-dependent Raman spectra were obtained during the helix-sense inversion. The results of 2-dimensional correlation analysis in the spectral regions of 1600-1800 and 3200-3400 cm showed that the intensity changes of the side-chain ester C═O stretching bands occurred prior to those of amide A and amide I bands in the unwinding process of αR-helix on heating. The sequential order of the intensity changes for amide A, amide I, and the side-chain ester C═O stretching bands during the inversion process was determined. It was found that the conformation change of the side chain occurred prior to that of the main chain for the αR-helix on heating. Thus, we concluded that the transformation of the backbone chain from right-handed to left-handed is triggered by the conformational change of the side chains.