IR, Raman, SERS and DFT study of amoxicillin

In this work a joint experimental and theoretical study on amoxicillin is reported. The molecular vibrations of amoxicillin were investigated by FTIR, FT-Raman and SERS spectroscopies. In parallel, quantum chemical calculations based on density functional theory (DFT) were used to determine the geometrical, energetic and vibrational characteristics of the molecule with particular emphasis put on the interaction and adsorption geometry of the molecule to the silver colloidal surface. The SERS spectrum of amoxicillin was recorded using a 532 nm laser line and hydroxylamine reduced silver colloid as SERS substrate. FTIR, FT-Raman and SERS spectra of amoxicillin were assigned based on DFT calculations with the hybrid B3LYP exchange-correlation functional, coupled with the standard 6-31G(d) basis set. The calculated molecular electrostatic potential (MEP) was used in conjunction with SERS data to predict the adsorption geometry of the molecule on the silver surface.