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PHOTOBLEACHING OF MEROCYANINE 540: INVOLVEMENT OF SINGLET MOLECULAR OXYGEN
Author(s) -
Singh Ravinder Jit,
Feix Jimmy B.,
Kalyanaraman B.
Publication year - 1992
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1992.tb04268.x
Subject(s) - photobleaching , singlet oxygen , merocyanine , chemistry , photochemistry , reaction rate constant , quenching (fluorescence) , azide , singlet state , irradiation , oxygen , kinetics , fluorescence , organic chemistry , excited state , physics , quantum mechanics , photochromism , nuclear physics
— The purpose of this study was to assess the mechanism of merocyanine 540 (MC540) photobleaching in a liposomal system. Broad based visible irradiation of MC540 in unilamellar dilauroylphosphatidylcholine (DLPC) vesicles resulted in dye bleaching that was strictly O 2 dependent. The rate of self‐sensitized photobleaching was enhanced in D 2 O and inhibited by both azide and histidine, consistent with 1 O 2 intermediacy (Type II chemistry). Supportive evidence for this mechanism was obtained by using a Type II sensitizer, aluminum phthalocyanine tetrasulfonate (AIPcS Λ max , = 678 nm). Irradiation of AIPcS and MC540 in DLPC with Λ > 630 nm (absorbed only by AIPcS) light resulted in rapid bleaching of MC540, which was stimulated by D 2 O and inhibited by azide. A rate constant of 10 7 M ‐1 s ‐1 was determined for the chemical quenching of 1 O 2 by MC540. The rate constant for physical quenching of 1 O 2 by MC540 was estimated to be ca 10 9 M ‐1 s ‐1 .