Study of the localization of the quinone ring of ubiquinone Q-10 in dipalmitoyl phosphatidylcholine liposomes by the triplet probe method

The method of recording the phosphorescence and annihilation delayed fluorescence has been used to study the kinetics of quenching of the triplet states of the probes of erythrosin (I), 4-(2-anthryl) butanic acid (II) and 12-(2-anthryl) dodecanic acid (III) by the quinone ring of ubiquinone Q-10 (UQ-10) in the liposomes of dipalmitoyl phosphatidylcholine (DPPC). It has been shown that UQ-10 at 45 °C effectively quenches the triplet states of the probes II and III the chromophore part of which is in the hydrophobic region of the lipid bilayer and probe I localized in the polar region of the liposomes. The rate of quenching of probe III is twice that for probe II. The effective quenching constant of probe I is 1·7 x 10⁷ (mm/g lipid)^-1 ·sec^-1. Probe I is also quenched at 30 °C, i.e. at a temperature below the melting point of DPPC (41 °C). It is concluded that the quinone ring of UQ-10 may be both in the hydrophobic and polar parts of the liposomes.