The implications of ortho-, meta- and para- directors on the in-vitro photodynamic antimicrobial chemotherapy activity of cationic pyridyl-dihydrothiazole phthalocyanines

Cationic Zn phthalocyanine complexes were derived by alkylation reaction of tetra-(pyridinyloxy) phthalocya-nines (Pcs) at the ortho, meta, and para positions to form Zn (II) tetrakis 3-(4-(2-pyridin-1-ium-1-yl) butyl)-2-mercapto-4,5-dihydrothiazol-3-ium phthalocyanine (2), Zn (II) tetrakis 3-(4-(3-pyridin-1-ium-1-yl) butyl)-2-mercapto-4,5-dihydrothiazol-3-ium phthalocyanine (4) and Zn (II) tetrakis 3-(4-(4-pyridin-1-ium-1-yl) butyl)-2-mercapto-4,5-dihydrothiazol-3-ium phthalocyanine (6). The photophysicochemical behaviors of the Pc com-plexes were assessed. The meta and para-substituted complexes gave high singlet oxygen quantum yields. The cationic Pcs demonstrated good planktonic antibacterial activity against Staphylococcus aureus and Escherichia coli with the high log reduction values of 9.29 and 8.55, respectively. The cationic complexes also showed a significant decrease in the viability of in vitro biofilms after photo-antimicrobial chemotherapy at 100 mu M for both Staphylococcus aureus and Escherichia coli biofilms.

Automated summary

In this study, cationic zinc phthalocyanine complexes were synthesized by alkylation reaction and their photophysicochemical behaviors were evaluated. The meta and para-substituted complexes showed high singlet oxygen quantum yields and demonstrated good antibacterial activity against Staphylococcus aureus and Escherichia coli, as well as significant degradation effect on in vitro biofilms.