Beta sheets with a twist: The conformation of helical polyisocyanopeptides determined by using vibrational circular dichroism

Detailed information on the architecture of polyisocyanopeptides based on vibrational circular dichroism (VCD) spectroscopy in combination with DFT calculations is presented. It is demonstrated that the screw sense of the helical polyisocyanides can be determined directly from the Cï£N- stretch vibrational region of the VCD spectrum. Analysis of the VCD signals associated with the amideI and amideII modes provides detailed information on the peptide side-chain arrangement in the polymer and indicates the presence of a helical β-sheet architecture, in which the dihedral angles are slightly different to those of natural β-sheet helices. Good vibrations: The structure elucidation of helical polyisocyanides derived from alanylalanine (PIAA; see figure) by using a combination of DFT calculations and vibrational circular dichroism (VCD) spectroscopy is described. An accurate description of the conformation of the PIAA is attained, which contributes to the current understanding of the conformational architecture of polyisocyanides.