Figure 8.

Photoexcitation of oxidised DHE solubilised in dimethylsulphoxide (DMSO) with visible light in the presence of DMPO as the spin trap results in oxygen-dependent accumulation of DMPO-^●OOH adducts with a quantum yield 2.8-fold smaller than for riboflavin. (A) Representative ESR spectra acquired from samples of lipophilic extracts from liposomes made from oxidised (OxDHE) or freshly opened 16:0-22:6PC (DHE) solubilised in DMSO:benzene (9:1) and exposed to 27 mW/cm² visible light in the presence of 0.1 M DMPO inside the resonant cavity of ESR spectrometer. The spectra were acquired after 28 min of light exposure or incubation in the dark. The samples were saturated with air, except for the sample saturated with argon (Ar). Simulated spectra of DMPO-^●OOH and DMPO-^●CH adducts were created to identify the adducts in the experimental spectra as DMPO adducts with superoxide radical (DMPO-^●OOH) and DMPO adducts with carbon-centred radical (DMPO-^●CR). (B) Representative kinetics of DMPO-^●OOH accumulation during exposure of OxDHE and DHE to visible light. (C) Representative kinetics of DMPO-^●OOH accumulation during irradiation with narrow-band 404 nm light (3 mW/cm²) of 0.35 mM riboflavin (RBFL) or OxDHE having the same absorbances at the excitation wavelength. The initial rates of accumulation obtained from parameters of the fitted lines were used for calculation of the quantum yield.