Photophysical characterization of tetrahydroxyphenyl porphyrin Zn(II) and V(IV) complexes: experimental and DFT study

Photodynamic therapy (PDT) is a promising technique for the treatment of various diseases. In this sense, the singlet oxygen quantum yield (& phi;( increment )) is a physical-chemical property that allows to stablish the applicability of a potential photosensitizers (PS) as a drug for PDT. In the herein report, the & phi;( increment ) of three photosensitizers was determined: metal-free tetrahydroxyphenyl porphyrin (THPP), THPP-Zn and the THPP-V metal complexes. Their biological application was also evaluated. Therefore, the in vitro study was carried out to assess their biological activity against Escherichia coli. The metal-porphyrin complexes exhibited highest activities against the bacterial strain Escherichia coli. at the highest concentration (175 & mu;g/mL) and show better activity than the free base ligand (salts and blank solution). Results indicated a relation between & phi;( increment ) and the inhibitory activity against Escherichia coli, thus, whereas higher is the & phi;( increment ), higher is the inhibitory activity. The values of the & phi;( increment ) and the inhibitory activity follows the tendency THPP-Zn > THPP > THPP-V. Furthermore, quantum chemical calculations allowed to gain deep insight into the electronic and optical properties of THPP-Zn macrocycle, which let to verify the most probable energy transfer pathway involved in the singlet oxygen generation.

Automated summary

Photodynamic therapy (PDT) shows promise in treating various diseases. The singlet oxygen quantum yield (φ) is an important factor in determining the effectiveness of potential photosensitizers (PS) for PDT. In this study, the φ values of three photosensitizers, including metal-free tetrahydroxyphenyl porphyrin (THPP), THPP-Zn, and THPP-V metal complexes, were measured, and their biological activity against Escherichia coli was evaluated. The results showed that the metal-porphyrin complexes exhibited the highest activity against Escherichia coli at the highest concentration, and their activity was better than the free base ligand. The study also revealed a positive correlation between the φ values and the inhibitory activity against Escherichia coli, with THPP-Zn > THPP > THPP-V in terms of both φ values and inhibitory activity. Furthermore, quantum chemical calculations provided insights into the electronic and optical properties of THPP-Zn, confirming the most likely energy transfer pathway involved in singlet oxygen generation.