Electric field effects on IR absorption of α-helical polypeptide

External electric field effects on the IR absorption spectrum of α-helical poly(γ-benzyl-L-glutamate) have been examined with electric field modulation spectroscopy. The electric-field-induced change in each vibrational band is reproduced by a superposition of the absorption spectrum, and its first and second derivative spectra, suggesting that the electric dipole moment and the molecular polarizability change following vibrational excitation. The N-H stretching band at 3291 cm^-1 shows the largest change in the magnitude of dipole moment following vibrational excitation.