Singlet oxygen quantum yields of potential porphyrin-based photosensitisers for photodynamic therapy

Abstract

The singlet oxygen formation quantum yield (Phi(Delta)) for solutions of the di-cation, free-base and metallated forms of hematoporphyrin derivative (HpD), hematoporphyrin IX (Hp9) and a boronated protoporphyrin (BOPP) are reported using the method of direct detection of the characteristic phosphorescence following polychromatic excitation. Values of Phi(Delta) for the free-base form of all the porphyrins and the di-cation forms of Hp9 and HpD are in the range of 0.44 to 0.85 in the solvents investigated. Incorporation of zinc ions into the macrocycle reduces Phi(Delta) for all three porphyrins. BOPP facilitates the coordination of certain transition metals (Mn, Co and Cu) compared to Hp9 and HpD and results in a dramatic decrease in Phi(Delta). The experimental data suggest the introduction of low energy charge transfer states associated with the disruption of the planarity of the macrocyclic ring provides alternative non-radiative deactivation pathways. In BOPP, this non-planarity is augmented by the large closo-carborane peripheral substituent groups.

Photophysical and Thermodynamic Parameters of Hematoporphyrin in Solutions and Monolayers

“…These large differences may be due to the experimental conditions, which play a substantial role in estimation of porphyrin cytotoxicity mediated by singlet oxygen, e.g., water/buffered solutions or high concentrated sample, so they can induce dye aggregation. For example, Φ in methanol reported for HP changes from 0.93 to 0.65 [3,5,6,14,16,17] and the latter value is in a good agreement with that obtained by photothermal measurements (Table 1). Analysis of the results confirms high efficiency of triplet-triplet energy transfer between HP and oxygen, independent of the micro-environment, so it can be expected also for HP in lipid moiety.…”

“…Literature values for the quantum yield of singlet oxygen generation by HP vary over wide ranges, from 0.13 to 0.42 in aqueous solutions and from 0.43 to 0.93 in organic solvents [5,16,17]. These large differences may be due to the experimental conditions, which play a substantial role in estimation of porphyrin cytotoxicity mediated by singlet oxygen, e.g., water/buffered solutions or high concentrated sample, so they can induce dye aggregation.…”

Iron(III) Schiff base complexes of arginine and lysine as netropsin mimics showing AT-selective DNA binding and photonuclease activity

“…PDT has emerged as a non-invasive mode of treatment for cancer in which selective photoactivation of the drug at the cancer cells leads to damage only the photo-exposed cells, leaving healthy cells unaffected [13][14][15][16]. Porphyrin and phthalocyanine bases like the PDT drug Photofrin Ò are known to produce singlet oxygen ( 1 O 2 ) as the reactive species from the energy transfer of the excited triplet state of the drug to the triplet oxygen molecule in a Type-II pathway [17].…”

Formation of Au and tetrapyridyl porphyrin complexes in superfluid helium

“…As a result these molecules and their derivatives have long attracted the interest of biologists and biochemists. [1,2] Porphyrins have good thermal stability and versatile chemical properties, making them candidates for a wide variety of applications such as catalysis, [3,4] solar energy conversion, [5,6] and the development of metal-organic frameworks. [7][8][9] Among the porphyrins, 5,10,15,20-Tetra(4-pyridyl)porphyrin (H2TPyP) is one of the meso-substituted prophyrins that have been widely used in various chemical and photochemical studies.…”