“…and the cc-pVTZ [10] basis set. In previous investigations, we have found that this level of theory leads to good agreement with the molecular and vibrational structure for a variety of organic compounds [11][12][13][14][15]. A series of preliminary B3LYP/6-31G* [6] calculations revealed the presence of two stable conformations with respect to rotation around the N-C bond linking the butyryl and the lactone moieties of C4-HSL, corresponding to endo-and exo-conformations, as shown in Fig.…”