Type-I and type-II photoprocesses in the system photosense–ascorbic acid

Kuznetsova, Nina A.; Pykhtina, E. V.; Ulanova, L. A.; Kaliya, O. L.

doi:10.1016/j.jphotochem.2004.03.029

Cited by 5 publications

(1 citation statement)

References 28 publications

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“…It is generally believed that the primary biological effect of PDT is caused by singlet oxygen molecules (type II mechanism) formed via energy transfer from photosensitizers to O 2 in tumor and endothelial cells of the tumor tissue. ,, It has recently been suggested that a reactive oxygen species other than singlet oxygen, for example, superoxide anion, is formed by electron transfer from the triplet excited-state of Pd-bacteriopheophorbide to O 2 in aqueous media but not in organic solvents where singlet oxygen almost exclusively forms . It was suggested that photosensitizers with reductants (e.g., ascorbic acid) afforded radical anions of reductants, which are oxidized further by oxygen with superoxide formation, increasing the type I free radical route and hence photodynamic efficiency on the whole. − However, there has been no report on the formation of superoxide anion by photosensitizers alone for PDT in organic solvents.…”

Section: Introductionmentioning

confidence: 99%

Metal Bacteriochlorins Which Act as Dual Singlet Oxygen and Superoxide Generators

et al. 2008

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A series of stable free-base, Zn(II) and Pd(II) bacteriochlorins containing a fused six- or five-member diketo- or imide ring have been synthesized as good candidates for photodynamic therapy sensitizers, and their electrochemical, photophysical, and photochemical properties were examined. Photoexcitation of the palladium bacteriochlorin affords the triplet excited state without fluorescence emission, resulting in formation of singlet oxygen with a high quantum yield due to the heavy atom effect of palladium. Electrochemical studies revealed that the zinc bacteriochlorin has the smallest HOMO-LUMO gap of the investigated compounds, and this value is significantly lower than the triplet excited-state energy of the compound in benzonitrile. Such a small HOMO-LUMO gap of the zinc bacteriochlorin enables intermolecular photoinduced electron transfer from the triplet excited state to the ground state to produce both the radical cation and the radical anion. The radical anion thus produced can transfer an electron to molecular oxygen to produce superoxide anion which was detected by electron spin resonance. The same photosensitizer can also act as an efficient singlet oxygen generator. Thus, the same zinc bacteriochlorin can function as a sensitizer with a dual role in that it produces both singlet oxygen and superoxide anion in an aprotic solvent (benzonitrile).

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