Insights Into The Helix-Sense Inversion Of Poly(-Phenethyl-L-Aspartate) By Two-Dimensional Raman Correlation Spectroscopy

In this study, the transition process of the helix-sense inversion of poly(-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 3200-3400cm(-1) showed that the intensity changes of the side-chain ester CO stretching bands occurred prior to those of amide A and amide I bands in the unwinding process of R-helix on heating. The sequential order of the intensity changes for amide A, amide I, and the side-chain ester CO 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 R-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.