A comparison of aqueous solvent models used in the calculation of the Raman and ROA spectra of l-alanine Original Research Article

This paper presents a quantum description of L-alanine in aqueous solution predicting the Raman and Raman optical activity (ROA) spectra. We have investigated theoretically the chiral sensitive spectroscopic method of ROA as a probe for secondary structural features. We have utilized the Becke 3LYP/6-31G* description to determine the geometries and Hessians [Theoretical and Computational Genome Research, Plenum Press, New York, 1997, p. 225; J. Phys. Chem. B 102 (1998) 5899; Chem. Phys. 225 (2000) 165], and have calculated the Becke 3LYP/6-31G* level electric dipole–electric dipole polarizability derivatives. The electric dipole–magnetic dipole polarizability derivatives and electric dipole–electric quadrupole polarizability derivatives further required to obtain the ROA spectra have also been calculated. The Raman scattering and ROA spectral simulations for the various structures are compared with the experimentally measured spectra and previously reported spectral simulations. The combination of Raman and ROA spectroscopy is shown to be as sensitive to secondary structural changes as its sister combination of vibrational absorption and vibrational circular dichroism and thus offers a complementary source of information when investigating the secondary structural and chiral features of biomolecules.