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Photoinduced Electron Transfer in Dry Gelatin Containing Bound Methylene Blue
Author(s) -
Smith Gerald J.,
Harriman Anthony,
Woolhouse Anthony D.,
Haskell Timothy G.,
Barnes Thomas H.
Publication year - 1998
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.1751-1097.1998.tb05171.x
Subject(s) - methylene blue , photochemistry , chemistry , methylene , gelatin , fluorescence , quenching (fluorescence) , excited state , electron transfer , singlet state , organic chemistry , atomic physics , physics , quantum mechanics , photocatalysis , catalysis
Excited states of methylene blue bound to dry gelatin undergo electron‐transfer quenching reactions with neighboring amino acid residues to give reduced, methylene blue‐free radicals. At the low loadings of methylene blue bound to gelatin used in this work, the absorption spectra indicated that the methylene blue existed principally in its monomeric form. The rates of methylene blue fluorescence quenching depended on the temperature at which the gelatin was dried. There was no detectable fluorescence characteristic of the localized excited singlet state of methylene blue when the dye is bound to gelatin dried at 15°C, where a significant proportion of the protein exists in its a ‐helical form. Instead, weak emission with a maximum at 645 nm is observed. It is inferred from this that the rate of quenching of any localized excited singlet states of the dye bound to a ‐helical gelatin is very fast thereby competing efficiently with radiative relaxation. The weak emission at 645 nm is ascribed to a fluorescent exciplex formed between bound methylene blue and a neighboring electron/proton donor residue of the gelatin. While fluorescence characteristic of the localized methylene blue singlet state was observed from dyed gelatin dried at 50°C, i.e. in its random coil form, the triplet state is subject to rapid quenching by electron/proton transfer with protein moieties.