Metallophthalocyanines for antimicrobial photodynamic therapy: an overview of our experience

Metal phthalocyanine complexes with different charges, hydrophobicity and metal ions were synthesized and studied for antimicrobial photodynamic therapy of pathogenic bacterial and fungal model strains. Ten positively charged complexes with the metals Zn ( II ), Al ( III ), Ga ( III ), In ( III ), Si ( IV ) and Ge ( IV ) in the center of the ligand and substituents at the ligand bearing four or eight N-alkylpyridyloxy groups were prepared. In addition, a negatively charged Zn ( II )-phthalocyanine with four sulfophenoxy-groups was synthesized. The absorption spectra showed low intensity of the Soret band in the UV part of the spectrum and the intense Q-band in the red to far red region (λ = 671–697 nm). The fluorescence was determined with quantum yields between 0.1–0.33 and life-times 2.8–4.9 ns in dependence of the kind of metal ion and the substituents. In organic solvents all complexes exist in a monomeric state but in aqueous solution they show aggregation with the exception of Ga ( III ) phthalocyanines. The singlet oxygen quantum yields were evaluated in dependence on the metals, substituents and the media with values between 0.16–0.68. The cationic metal phthalocyanines were taken-up by pathogenic cells in a higher amount as compared to the anionic complex. Three of the studied phthalocyanines namely tetra-N-methylpyridyloxy-phthalocyanine Zn ( II ) and tetra- and octa-N-methylpyridyloxy- Ga ( III ) phthalocyanines showed a high photodynamic efficacy towards most of the studied microorganisms in suspensions.