Spectroscopic studies on antimalarial Artesunate: Raman and surface-enhanced Raman scattering and adsorption geometries of Artesunate on silver nanoparticles

•Antimalarial artesunate has been studied by means of Raman spectroscopy as a neutral species, as an anion in sodium salt, and by means of SERS as anion adsorbed on silver nanoparticles.•The structure of artesunate, as well as that of the anion, has been optimized by means of ab-initio calculations at the DFT/B3LYP/cc-pVDZ calculation level and found in good agreement with the experimental molecular geometry. The conformational minima of the flexible side chain both in the anion and in the anion complexed with Ag+ have been characterized.•The SERS spectrum of chemisorbed species is due to conformers with nearly all-trans side chain, where the artemisinin core lies as far as ≈ 9 Å from the silver ion.•The interaction of artesunate with the silver surface is exclusively through the side chain, leaving untouched the peroxide group responsible of the antimalarial activity.