Vibrational energy-spectra and infrared absorption of α-helical protein molecules

The quantum energy spectra, including high excited states, of vibrational amide-I or of intramolecular excitations in α-helical protein molecules, are calculated by the discrete nonlinear Schrödinger equation together with the parameters appropriate to the systems. The distribution of energy levels obtained is basically consistent with the experimental values obtained by infrared absorption and Raman scattering. Utilizing the energy spectra we explain the laser Raman spectrum from metabolically active escherichia coli and we present some further features of the infrared absorption of the protein molecules.