Red- and Blue-Shifting in the Circular Dichroism Spectra of Polypeptides due to Dipole Effects

The peptide transitions which give rise to the characteristic circular dichroism (CD) spectrum of a given polypeptide are influenced by environmental effects, similar to those observed in absorption spectra. The extent of the shift in the CQ spectrum was found to correlate fairly well with solvent dipole. The relative red- or blue-shifting of the transitions due to these effects have important implications concerning the interpretation of the CD spectra of polypeptides and proteins in non-aqueous solvents, such as membrane proteins.