title: Influence of rhodamine 123 on the photosensitizing properties of porphyrins.
abstract: The photophysical and photochemical properties of porphyrins were profoundly changed upon addition of rhodamine 123. The Soret band of the porphyrins shifted to higher wavelengths, the fluorescence yield of the porphyrins decreased with unaltered decay rates, and their triplet state was quenched. These observations indicate a strong interaction between porphyrins and rhodamine 123 and formation of 1:1 nonfluorescent complexes, of which the binding constants were determined. Illumination of a porphyrin in the presence of rhodamine 123 resulted in the formation of a porphyrin radical cation, which could be detected with ESR spectroscopy. Quenching of the triplet state of the porphyrins by rhodamine 123 resulted in a decreased singlet oxygen yield and a decrease of the photooxidation of histidine, methionine, tyrosine, and tryptophan. However, the oxidation of thiol compounds was increased and the stoichiometry of the reaction between cysteine and oxygen changed from 2 to 3.8 mol cysteine/ mol oxygen. These results show that the presence of rhodamine 123 converted the for porphyrins prevalent energy transfer (type II) reaction to an electron transfer (type I) reaction.
authors.affiliation: Department of Medical Biochemistry, Sylvius Laboratory, Leiden University, The Netherlands.
authors.forename: J W
authors.initials: JW
authors.lastname: Lagerberg
authors.forename: J
authors.initials: J
authors.lastname: Vanderwal
authors.forename: P
authors.initials: P
authors.lastname: Charlesworth
authors.forename: T G
authors.initials: TG
authors.lastname: Truscott
authors.forename: J
authors.initials: J
authors.lastname: Van der Zee
authors.forename: H
authors.initials: H
authors.lastname: Schneckenburger
authors.forename: T M
authors.initials: TM
authors.lastname: Dubbelman
mesh_terms: D002412:Cations; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals; D006639:Histidine / Q000737:chemistry; D008027:Light; D008715:Methionine / Q000737:chemistry; D010100:Oxygen / Q000737:chemistry; D010777:Photochemistry; D017319:Photosensitizing Agents / Q000494:pharmacology*; D011166:Porphyrins / Q000737:chemistry / Q000494:pharmacology*; D020112:Rhodamine 123; D012235:Rhodamines / Q000737:chemistry / Q000494:pharmacology*; D026082:Singlet Oxygen; D013050:Spectrometry, Fluorescence; D013053:Spectrophotometry; D014364:Tryptophan / Q000737:chemistry; D014443:Tyrosine / Q000737:chemistry
chemical_list: D002412:Cations; D005609:Free Radicals; D017319:Photosensitizing Agents; D011166:Porphyrins; D012235:Rhodamines; D026082:Singlet Oxygen; D020112:Rhodamine 123; D014443:Tyrosine; D006639:Histidine; D014364:Tryptophan; D008715:Methionine; D010100:Oxygen