Fig. 3. Bands defining the approximate wavelength range for electronic transitions responsible for the CD signals: Yellow: Signals due to aromatic residues (if present) may be detected in 100× pathlength cells; grey: occasionally a signal may be detected here due to the presence of stacked aromatic amino acids,¹ blue: n → π* transition. Green and red: π → π* transition, this transition can give rise to two peaks due to exciton splitting, purple: charge transfer transition (generally only detectable when using synchrotron radiation source) (SRCD spectra). The depicted spectra are from the SP175 dataset²¹ and are available in the PCDDB³⁵ with codes CD0000010000 to CD0000710000. They are shaded according to percentage of helix in the crystal structure of the protein as follows: red: 70% +, orange: 60–70%, yellow: 50–60%, light green: 40–50%, dark green: 30–40%, light blue: 20–30%, dark blue: 10–20%, purple: 0–10%.