IR, Raman, SERS and DFT study of pindolol and verapamil

IR, Raman and surface-enhanced Raman scattering (SERS) spectra of pindolol (PIN) and verapamil (VER) were recorded, and the vibrational bands were assigned on the basis of density functional theory (DFT) calculations. The adsorption geometry to the silver surface of the investigated drugs was derived by considering the molecular electrostatic potential (MEP) and the SERS surface selection rules. Both molecules are adsorbed through the oxygen atoms and π-electrons of the rings to the silver surface. An almost flat structure – parallel to the metallic surface – was concluded for PIN, while a bent geometry, with the two pairs of oxygens situated at the ends of molecule, pointing to the metallic surface is derived for VER. For both molecules, π electrons contribute significantly to their interaction with the silver nanoparticles.