Silica Gel–Supported P-, Ge-, and Sb-Porphyrins for Visible Light Inactivation of Bacteria

Abstract

This chapter describes the photocatalysis action of (dihydroxo)tetraphenyl¬porphyrinato complexes of high valent P (V), Ge (IV), and Sb (V) (P(tpp), Ge(tpp), and Sb(tpp)). These chromophores were fixed onto silica gel (SiO2) through Coulombic forces and hydrogen bonding between axial hydroxo ligands and silanol groups to produce M(tpp)/SiO2 (M = P, Ge, and Sb) composites. M(tpp)/SiO2 were applied to the photo-inactivation of Escherichia coli and Legionella pneumophila. Moreover, M(tpp)/SiO2 was subjected to practical experiments for the photoinactivation of L. pneumophila naturally occurring in a cooling tower and a public fountain. It is noteworthy that 80 g of Sb(tpp)/SiO2 catalyst, containing 40 mg of Sb(tpp) maintained a concentration of Legionella species below 100 CFU/100 mL for 120 days in 13 m3 of water in a fountain under sunlight exposure. The photoinactivation proceeded through the liberation of M(tpp) from SiO2, adsorption of M(tpp) inside bacteria, and generation of reactive oxygen species, such as singlet oxygen, under visible light irradiation, thus resulting in bacteria apoptosis. Based on these results, we developed water-soluble porphyrins by modification of P and Sb porphyrin axial ligands to alkyloxo, alkylethylenedioxy, and alkylpyridinium groups. These water-soluble porphyrins were applied to the photodynamic inactivation of E. coli and Saccharomyces cerevisiae.