Photophysical properties of porphyrin amphiphiles bearing pyridinium alkyl groups

Synthesis, characterization and photochemistry of 5,10,15,20-tetrakis(4-N-pentylpyridyl)porphyrins, [(TPePyP)H2]4+ and [(TPePyP)ZnII]4+

Tetracationic 5,10,15,20-tetrakis(4- N -pentylpyridyl)porphyrins, [( TPePyP ) H 2]4+ and its zinc-porphyrin analogue [( TPePyP ) Zn II]4+ have been synthesized and characterized by 1 H NMR and UV-visible spectroscopic techniques. Photobleaching studies carried out in solutions of varying pH show that, in the presence of oxygen, [( TPePyP ) H 2]4+ undergoes fast photodegradation in aqueous medium when the solution is irradiated with 560 nm light. The steady-state singlet oxygen quantum yields (ΦΔ) for [( TPePyP ) H 2]4+ is 0.80 and that for its Zn analogue is 0.85. These quantities were measured using 1,3-diphenylisobenzofuran (DPBF) as a singlet oxygen scavenger, in N,N-dimethyl-formamide solution. These ΦΔ values are compared with those for other well known sensitizers such as protoporphyrindimethylester PPDME and hematoporphyrindihydrochloride HPDHC.

Effect of zinc insertion and hydrophobicity on the membrane interactions and PDT activity of porphyrin photosensitizers

A series of photosensitizers (PS), which are meso-substituted tetra-cationic porphyrins, was synthesized in order to study the role of amphiphilicity and zinc insertion in photodynamic therapy (PDT) efficacy. Several properties of the PS were evaluated and compared within the series including photophysical properties (absorption spectra, fluorescence quantum yield Phif, and singlet oxygen quantum yield PhiDelta), uptake by vesicles, mitochondria and HeLa cells, dark and phototoxicity in HeLa cells. The photophysical properties of all compounds are quite similar (Phif<or=0.02; PhiDelta approximately 0.8). An increase in lipophilicity and the presence of zinc in the porphyrin ring result in higher vesicle and cell uptake. Binding in mitochondria is dependent on the PS lipophilicity and on the electrochemical membrane potential, i.e., in uncoupled mitochondria PS binding decreases by up to 53%. The porphyrin substituted with octyl groups (TC8PyP) is the compound that is most enriched in mitochondria, and its zinc derivative (ZnTC8PyP) has the highest global uptake. The stronger membrane interaction of the zinc-substituted porphyrins is attributed to a complexing effect with phosphate groups of the phospholipids. Zinc insertion was also shown to decrease the interaction with isolated mitochondria and with the mitochondria of HeLa cells, an effect that has been explained by the particular characteristics of the mitochondrial internal membrane. Phototoxicity was shown to increase proportionally with membrane binding efficiency, which is attributed to favorable membrane interactions which allow more efficient membrane photooxidation. For this series of compounds, photodynamic efficiency is directly proportional to the membrane binding and cell uptake, but it is not totally related to mitochondrial targeting.

Morphological and Spectroscopic Properties of Thin Films of Self-Assembling Amphiphilic Porphyrins on a Hydrophilic Surface as Revealed by Scanning Near-Field Optical Microscopy

We fabricated porphyrin thin films on mica surfaces from acidic aqueous solutions of the preorganized H-aggregates of amphiphilic porphyrins by the simple spin-coating method. The morphological and spectroscopic properties of the film were investigated by scanning near-field optical microscopy. The results obtained in this study demonstrate that the preorganized structure in solution can be transferred as a thin film with a thickness of the monolayer level without losing their substantial structure and photophysical properties.