Site-specific structure of Aβ(25-35) peptide: Isotope-assisted vibrational circular dichroism study

► Investigated the structure of Aβ(25-35) peptide in fibrillar aggregated state. ► Used vibrational circular dichroism and absorption spectra of 13C isotope labels. ► Isotope labeled study indicates aperiodic N-terminus. ► Isotope dilution study indicates parallel beta sheet structure. ► The inter-strand coupling enhances the intensity in the amide II′ region.