Photoreduction of a Self-Assembled (Lipidporphyrinato)iron(III) Complex in Saline by LMCT Excitation: Co-Aggregated Hyaluronic Acid Allows an Irreversible Electron Transfer

An amphiphilic (tetraphenylporphyrinato)iron(III) derivative with four alkylphosphocholine groups and a proximal imidazole [(lipidporphyrinato)iron(III); 1a] was self-assembled in phosphate-buffered saline (pH 7.3, [NaCl] = 0.15 M) to form spherical micelles with a diameter of 10 nm. The obtained solution showed a distinct absorption band at 362 nm, which was assigned to the ligand-to-metal [Cl− to iron(III)] charge transfer (LMCT) transition. Light irradiation into this CT band under an Ar atmosphere did not induce any changes in the UV-vis absorption spectrum. On the other hand, the addition of glucose (150 mM) to the solution led to complete photoreduction of the central iron(III) ion, giving a five-N-coordinated high-spin iron(II) complex. It has also been found that a small excess amount of hyaluronic acid ([units] = 100 µM) showed the same effect. The photoreduction was only seen by LMCT irradiation in the presence of the saccharide. It probably occurred via intramolecular electron transfer from Cl−...