4.3. Characterization of Helical Structure

The mean residue ellipticities of the peptides were determined by circular dichroism (CD) spectroscopy with an Aviv 401 spectrometer (Aviv Biomedical, Lakewood, NJ, USA) at 25 °C in water and in the presence of α-helix inducing solvent, 2,2,2-trifluoroethanol (TFE) at 50% in water. The concentration of peptides was 100 μg/mL for all the solutions, and they were loaded into a cell of 1 mm thickness. The scan range of wavelengths was from 250 to 190 nm at 1 nm intervals. The CD spectra were measured by averaging three scans. The mean residue molar ellipticity, [θ], is given in deg · cm² · dmol⁻¹and was calculated as [θ] = (θ × 0.1 × MRW)/(L × C), where θ is the experimental ellipticity, MRW is the mean residue weight (in Dalton), L is the light pathlength (in cm) and C is the concentration (in mg/cm³). Percentage helical content of the peptide was calculated as % helix = ([θ]₂₂₂–[θ]2220)/[θ222100] × 100, where [θ]₂₂₂ is the experimentally observed absolute mean residue ellipticity at 222 nm. Values taken for 0% and 100% helix content were [θ]2220 = −2340 and [θ]222100 = −30,300 respectively [43].