Porphyrins Conjugated with Peripheral Thiolato Gold(I) Complexes for Enhanced Photodynamic Therapy

Porphyrins fused to imidazolium salts across two neighboring β-pyrrolic positions were used as N-heterocyclic carbene (NHC) precursors to anchor Au^I -Cl complexes at their periphery. Synthesis of several thiolato-Au^I complexes was then achieved by substituting chloride for thiolates. Photodynamic properties of these complexes were investigated: the data obtained show that the Au-S bonds could be cleaved upon irradiation. The proposed mechanism to explain the release of thiolate moiety involves the S atom oxidation by singlet oxygen generated in the course of irradiation. In view of photodynamic therapy (PDT) applications, these porphyrins fused to NHC-Au^I complexes were tested as photosensitizers to kill MCF-7 breast cancer cells. Results show the important role played by the ancillary ligands (chloride versus thiolates) on the photodynamic effect.