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QUANTUM YIELD OF PRODUCTION OF SINGLET MOLECULAR OXYGEN ( x δ g ) IN AQUEOUS DISPERSIONS OF SMALL UNILAMELLAR LIPID VESICLES. A TIME‐RESOLVED NEAR‐IR PHOSPHORESCENCE STUDY*,†
Author(s) -
ll Santiago,
Braslavsky Silvia E.,
Schaffner Kurt
Publication year - 1990
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.1751-1097.1990.tb01964.x
Subject(s) - phosphorescence , chemistry , bilayer , quantum yield , vesicle , lipid bilayer , singlet oxygen , liposome , phosphatidylcholine , singlet state , photochemistry , analytical chemistry (journal) , yield (engineering) , fluorescence , excited state , oxygen , membrane , chromatography , organic chemistry , materials science , phospholipid , biochemistry , physics , quantum mechanics , nuclear physics , metallurgy
The quantum yield of formation and kinetic behaviour of O 2 ( 1 δ g ) in D 2 O dispersions of small unilamellar vesicles (SUVs) of dipalmitoyl phosphatidylcholine were studied by time‐resolved detection of near‐IR phosphorescence. At a SUV concentration of 26 n M , O 2 ( 1 δ g ) is not quenched by the vesicles. It diffuses quickly through the lipid bilayer and a partition equilibrium of O 2 ( 1 δ g ) between the lipid bilayer and the buffer is attained before decay occurs. In this equilibrium situation O 2 ( 1 δg/sb>) is mostly located in the buffer phase, which permits the determination of absolute quantum yields for O 2 ( 1 δ g ) production, φ δ , by comparison of the luminescence in the dispersions with that in neat D 2 O. The maximal φ δ values for the sensitizers incorporated in the SUV bilayer were 0.47 ± 0.09 for the dipyridyl complex of zinc(II) phthalocyanine (ZnPc), 0.35 ± 0.08 for porphycene, and 0.36 ± 0.08 for 2,7,12,17‐tetra‐H‐propylporphycene. These values are equal to those in neat organic solvents but lower than those previously obtained in SUVs by using chemical trapping agents. The high degree of organization of the environment around the sensitizers does not influence their efficiency of producing O 2 ( 1 δ g ). While no concentration dependence is observed for ZnPc (at least up to a local concentration of 20 mM in the bilayer), φ δ for both porphycenes significantly decreases above a local concentration of 4 mM in the bilayer. This result is expected in view of previous observations on the concentration dependence of other photophysical parameters of the porphycenes in such microheterog‐eneous media.