SINGLET OXYGEN GENERATION FROM LIPOSOMES: A COMPARISON OF TIME‐RESOLVED 1270 NM EMISSION WITH SINGLET‐OXYGEN KINETICS CALCULATED FROM A ONE DIMENSIONAL MODEL OF SINGLET‐OXYGEN DIFFUSION and QUENCHING

Abstract

Abstract— Time‐resolved measurements of 1270 nm singlet‐oxygen emission following pulsed‐laser excitation were made from unilamellar dimyristoyl 1‐α‐phosphatidylcholine liposomes labeled with zinc phthalocyanine. The effect of the hydrophobic quenchers, β‐carotene and ethyl β‐apo‐8′trans carotenoate, and the hydrophilic quenchers, histidine and methionine, upon the kinetics of the 1270 nm singlet‐oxygen emission was studied. Hydrophobic quenchers principally lowered the intensity of the 1270 nm emission and caused only modest changes in the lifetime of the 1270 nm emission. The decrease in 1270 nm emission caused by hydrophobic quenchers was related to the size of the liposomes. The larger the radius of the liposome, the greater the decrease in 1270 nm emission caused by a given concentration of hydrophobic quencher. In contrast, hydrophilic quenchers principally decreased the lifetime of the 1270 nm emission. The effect of hydrophilic quenchers was independent of the size of the liposomes. There was good agreement between the experimental results and the kinetics of the singlet‐oxygen emission calculated using a one dimensional model of singlet‐oxygen quenching and diffusion. The kinetics of singlet‐oxygen emission from liposomes without added hydrophobic quenchers closely approximated the theoretical kinetics of singlet oxygen in a homogeneous aqueous solution.

A Hand‐held Fiber‐optic Implement for the Site‐specific Delivery of Photosensitizer and Singlet Oxygen

“…Previous work by Kanofsky et al. showed that photo‐oxidation of cholesterol or other hydrophobic quenchers took place by a 1 O 2 reaction within DMPC liposomes (37,38). As we mentioned in the , our intent was to operate the device for sensitizer photorelease and monitor by absorption and fluorescence spectroscopy, and obtain a qualitative understanding of the influence of the surrounding environment.…”

Experimental evidence suggesting that H2O2 is produced within the thylakoid membrane in a reaction between plastoquinol and singlet oxygen

“…The same reaction would function as a source of intramembranous H 2 O 2 in thylakoids. 1 O 2 produced in the PSII reaction center can diffuse in the membrane to react with PQH 2 ‐9, as the diffusion length of 1 O 2 in lipid membrane is in the range of 20–220 nm [42,43]. The reaction between 1 O 2 and PQH 2 ‐9 is rapid, suggesting that this pathway is an important route for PSII dependent H 2 O 2 formation.…”

Electron Transfer Quenching of the Rose Bengal Triplet State

“…Generation of 02('Ag) in membranes and its subsequent reactions with membrane components have been extensively studied (3)(4)(5). Much less is known about electron transfer reactions of photosensitizers in biological membranes even though many potential electron donors and acceptors are present such as quinones in mitochondria1 membranes, amino acids in proteins (Trp, Tyr and Cys) and membrane-bound antioxidants such as @-tocopherol (a-T)?…”