Potent Antimicrobial Chloroindium(III) Phthalocyanine Sensitizer Targeting Drug-Resistant Microbes: Physicochemical, Photobiological Validation and DFT Insights.

Background/Objectives: An evaluation of the sensitizing properties of chloroindium(III) phthalocyanine complex (InPc) bearing 4-sulfonylphenoxy groups was performed. Methods: The ability to form singlet oxygen under light exposure was assessed, and the quantum yield ΦΔ was calculated to be 0.82 ± 0.04. Under ultrasound exposure of the sensitizer (1 MHz, 3 W, 40% duty cycle), significant 1,3-diphenylisobenzofuran decomposition was observed. Results: Moreover, the macrocycle was assigned to be a moderate-high photo- and sonostable sensitizer. Density functional theory studies supported experimental results, suggesting the InPc to be a good photochemical agent. From the global reactivity parameters analysis, it can be suggested that InPc would interact easily with electron-excess species, such as various free radicals, in the solution phase, and should also be able to interact with electrophilic species. Conclusions: Studied InPc revealed high photodynamic antimicrobial activity and reached >4 log10 reduction in microbial growth against methicillin-resistant Staphylococcus aureus, and 4.08 ± 0.29 log10 against Candida albicans resistant to fluconazole (for dosimetry of 100 μM and 50 J/cm2). Interestingly, the photosensitizer studied was inactive against extended-spectrum β-lactamase-producing Escherichia coli.