MOF-inspired porphyrinic single sites as promising platforms for stable immobilization of 2-thiouracil: a DFT study

The potential of MOF‑inspired porphyrinic Fe-N₄ and Mg-N₄ single sites as platforms for the stable immobilization of 2‑thiouracil (2TU) was examined using density functional theory (DFT) and time‑dependent DFT (TD‑DFT). Adsorption energies revealed strong chemisorption through both O‑ and S‑anchoring groups, with Fe-N₄ sites exhibiting significantly higher affinity than Mg-N₄ counterparts. Atoms‑in‑Molecules (AIM) and natural bond orbital (NBO) analyses indicated partially covalent Fe-O/S interactions, whereas Mg-O/S contacts remained predominantly electrostatic. Electronic‑structure descriptors and TD‑DFT spectra showed only minor perturbations upon adsorption, suggesting limited sensing capability. The data also show that 2TU adsorption is weaker in an aqueous solution than gas phase. Based on these results, the Mg-N₄NC can release the 2TU drug more easily at its target site than Fe-N₄NC, making it more suitable as a drug delivery vehicle. Conversely, Fe-N₄NC may be used as proper adsorbent for removing unwanted 2TU drugs emitted to water environments.