The structure of 5-FU was taken from the PubChem database. While a number of tautomers exist, the diketo form visualised in Figure a is the most stable one, which accounts for >99.9% of the tautomer population at 375 K. The structure of 5-FU was initially optimised using PCFF parameters. Different adsorption configurations of 5-FU in the pores of the FAU models were generated using FF-based Monte Carlo (MC) simulations, making use of the Sorption module integrated in the Materials Studio suite (DS BIOVIA). Details of the MC calculations are provided in the Electronic Supplementary Information (ESI), section S1.1. For each adsorbent model, between 3 and 10 distinct, pre-optimised 5-FU@FAU configurations were used as starting points for DFT optimisations, which are described in the following subsection. For AIMD simulations including co-adsorbed water molecules, which were performed only for a subset of FAU models, a hydration shell of 16 H2O molecules was generated using a FF-based simulated annealing procedure as implemented in the Adsorption Locator module of Materials Studio. Details of these simulations are presented in the ESI, section S1.2. All FF-based simulations used PCFF parameters to describe the guest molecules (5-FU, water), and partial charges and Lennard-Jones parameters reported by Emami et al. to represent framework Si and O atoms. Since that work does not include parameters for framework protons, Al atoms, and O atoms of the AlO4 tetrahedra, partial charges for these atoms were derived from the DFT electrostatic potential of H-FAU_1H. The REPEAT method was used to compute charges, which were then scaled and slightly adjusted. The whole procedure is described in more detail in the ESI, section S1.