Medium effect on the equilibrium geometries, vibrational frequencies and solvation energies of sulfanilamide

In this paper, the polarizable continuum model (PCM) is used to investigate the effect of solvent on the geometry, vibrational frequencies, IR intensities, Raman scattering activities, solvation free energies and the dipole moment of sulfanilamide. Hartee-Fock (HF), B3LYP and MP2 are employed for all models, both in gas phase and in solution, with basis sets up to 6-311+G(d,p) for HF and B3LYP and 6-31G(d) for MP2. A new SMD model is also used for solvation energy and dipole moment calculations. Some significant changes are observed in the dihedral angles but no noticeable changes appear in vibrational frequencies when sulfanilamide is solvated. Moreover, solvent effects on infrared intensities and Raman scattering activities are quite considerable and they increase as one goes from lower to higher dielectric constant. With PCM, both the solvation free energy and dipole moment of sulfanilamide increase when going from non-polar to polar solvents but no noticeable changes are observed among polar solvents. However, with SMD the solvation free energies are 15.5-33.0 kJ/mol and 9.6-19.7 kJ/mol higher than those of PCM for polar and non-polar solvent, respectively.