Simulations and analysis of the Raman scattering and differential Raman scattering/Raman optical activity (ROA) spectra of amino acids, peptides and proteins in aqueous solution

The Raman and Raman optical activity (ROA) spectra of amino acids and small peptides in aqueous solution have been simulated by density functional theory and restricted Hartree/Fock methods. The treatment of the aqueous environment in treated in two ways. The water molecules in the first hydration shell which strongly interact with the molecule are treated explicitly while the waters in the bulk are treated by a continuum model. The structures are optimized and the harmonic force elds are calculated. The derivatives needed to simulate the Raman and ROA intensities are calculated from first principles. The simulated Raman and ROA spectra have been compared to recently meassured spectra on amino acids and peptides. The simulations and understanding from them are used to interpret the Raman and ROA spectra of proteins. A comparison to vibrational absorption (VA) and vibrational circular dichroism (VCD) spectra is also given, and the complementarity of the information gained from the Raman and ROA spectra with that gained from VA and VCD spectra is discussed.