Synthesis and antibacterial photosensitizing properties of a novel tricationic subphthalocyanine derivative

A novel chloro[2,9,16(2,9,17)-trikis-4-(N-methylpyridyloxy)]subphthalocyaninnato boron(III) iodide (SubOPc3+) was synthesized by boron trichloride-induced cyclotrimerization of 4-(4-pyridyloxy)phthalonitrile in 1-chloronaphthalene. Exhaustive methylation of SubOPc with methyl iodide yielded the tricationic SubOPc3+. The spectroscopic and photodynamic properties of the SubOPc3+ were compared with those of both the uncharged SubOPc and the subphthalocyanine (SubPc). The cationic SubOPc3+ aggregates in various solvents and is partially dissolved as a monomer in aqueous sodium dodecyl sulfate; photodynamic inactivation was strongly dependent on the medium. The photodynamic inactivation imparted by the subphthalocyanines was investigated in vitro on the Gram-negative bacterium, Escherichia coli. SubOPc3+ rapidly bound to E. coli cells reaching a value of ∼2 nmol/106 cells after 5 min of incubation with 4 μM of sensitizer in the dark. Photosensitized inactivation of E. coli cellular suspensions by SubOPc3+ produced a ∼2.5 log decrease of cell survival (99.7% of cellular inactivation). The growth of E. coli cells was completely arrested when cultures were exposed to 8 μM of cationic subphthalocyanine and irradiated, whereas a negligible effect was found for the non-charged SubOPc. Also, SubOPc3+ was able to inactivate E. coli cells immobilized on agar surfaces.