We propose to carry out Inelastic Neutron Scattering experiments to investigate the interaction of mono- and di-cationic phosphonium-based ionic liquids (IL's) with hydrated peptidoglycan samples, representing an accepted model of the protective layer covering bacterial cell walls.The final aim of our project is to identify the microscopic mechanism underlying the anti-bacterial activity of phosphonium IL's, which kill Gramm-positive and Gramm-negative bacteria within minutes, while displaying low toxicity to mammalian cell lines. The detailed characterisation of hydrogen vibrational properties provided by Tosca will allow us to assess the effect of low-concentration IL's solutions on the network of hydrogen bonds that stabilise peptidoglycans. The urgent search for new antibiotics, able to control drug resistant strains of bacteria, could greatly profit from our study.