The present invention relates to a complex made up of at least one beta-lactam molecule covalently bonded to at least one hydrocarbon radical including at least 18 carbon atoms and containing at least one unit of 2-methyl-buta-2-ene, to nanoparticles of said complexes, and to a method for preparing same, said complex and/or said nanoparticles optionally being in the form of a lyophilisate. The present invention also relates to a pharmaceutical composition including at least said complex and/or said nanoparticles. The invention finally relates to said complex and/or to said nanoparticles for the treatment and/or prevention of bacterial infections, in particular caused by strains that are sensitive to beta-lactams.