Towards tuning PDT relevant photosensitizer properties: comparative study for the free and Zn²⁺ coordinated meso-tetrakis[2,6-difluoro-5-(N-methylsulfamylo)phenyl]porphyrin

Abstract

The spectroscopic, photochemical, and biological studies of 5,10,15,20-tetrakis[2,6-difluoro-5(N-methylsulfamylo)phenyl]porphyrinate Zn(II) (ZnF₂PMet) were carried out including absorption and fluorescence spectra, fluorescence quantum yields, triplet absorption spectra, triplet lifetimes, singlet oxygen quantum yield, and reactive oxygen species (ROS) detection under biological conditions and compared with its free-base analog (F₂PMet). Zinc coordination into the porphyrin ring results in decrease of hydrophobicity and in higher cellular uptake. F₂PMet localized specifically in endoplasmic reticulum and mitochondria while the ZnF₂PMet is more diffused all over the cell, bonded to membrane proteins, as assessed by fluorescence microscopy. Zn-porphyrin exhibits greater singlet oxygen quantum yield than its free-base analog. Studies with fluorescent probes confirm that the ZnF₂PMet produces mostly singlet oxygen, whereas F₂PMet generates more hydroxyl radicals as the ROS. F₂PMet is a more effective photosensitizer in vitro than its zinc complex, thus, the final photodynamic effect depends more on the nature of ROS than on the higher cellular uptake.

Keywords:

• Metalloporphyrins
• Zn(II) complexes
• Photodynamic therapy
• Singlet oxygen
• Hydroxyl radicals

Acknowledgements

We also thank Luzitin SA for supplying some compounds and Luisa Cortes for the assistance in confocal microscopy experiments.

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes

Dedicated to Professor Rudi van Eldik on the occasion of his 70th birthday.

Additional information

Funding

This work was funded by Ministry of Science and Higher Education within the Iuventus Plus programme [grant number 0085/IP3/2015/73]. We also thank National Science Centre for [grant number 2012/05/BST5/00389], [grant number 2013/11/D/ST5/02995]. MMP and LGA thank FCT and FEDER for [grant number PEst-OE/QUI/UI0313/2014], [grant number UID/QUI/00313/2013]. The Faculty of Chemistry of the Jagiellonian University is the beneficiary of the structural funds from the European Union [grant number POIG. 02.01.00-12-023/08].