Dendritic near-IR absorbing zinc phthalocyanines for antimicrobial photodynamic therapy

Design, synthesis, characterization, and photodynamic activity of dendritic, water-soluble zinc phthalocyanine (ZnPc) isomers 1a and 1b are described. Bearing terminal triethylene glycol (TEG) moieties as water solubilizing groups that were attached to the Pc core using Cu(I) catalyzed alkyne-azide cycloaddition (CuAAC), 1a and 1b are readily soluble in H₂O, polar aprotic, and protic organic solvents. UV/Vis analyses indicate that the Q band of the non-peripheral ZnPc 1b is ca. 80 nm red-shifted relative to the peripheral one with absorption at 805 nm (distilled water). 1a and 1b have log D_7.4 values of 0.22 and 0.05, respectively, suggesting that the non-peripheral substitution improved the overall hydrophilicity. Aggregation studies indicate that non-peripherally substituted 1b is significantly less aggregated in aqueous media than peripherally substituted 1a. Singlet oxygen generation studies are reported. Both ZnPcs showed negligible dark toxicity on bacteria and yeast with 10 μM 1a and 1b. Illumination (400-850 nm) of Pseudomonas aeruginosa with 10 μM of 1a produced a 90% cell inactivation while Acinetobacter baumannii with 10 μM 1b showed detection limit (99.9999+%) cell inactivation, demonstrating the antimicrobial photoactivity of these dyes.