M. Hoebeke et al., QUENCHING OF MEROCYANINE-540 TRIPLET-STATE BY NITROXYL RADICALS IN LIPOSOMAL SYSTEMS - A LASER FLASH-PHOTOLYSIS STUDY, Journal of photochemistry and photobiology.B, Biology, 22(3), 1994, pp. 229-233
Laser flash photolysis experiments were undertaken to investigate the
interaction between stearic acid nitroxide spin probes and photoexcite
d merocyanine 540 (MC540) in dimyristoyl-L-alpha-phosphatidylcholine l
iposomes (membrane model). The measurements of the paramagnetic signal
decay kinetics of four different spin-labelled stearic acids (n-DSA)
show that the direct interaction between the dye and the probe is affe
cted by the position of the nitroxyl group along the carbon chain. Las
er flash photolysis results reveal a significant decrease in the MC540
triplet lifetime in the presence of n-DSA, the effect depending on th
e depth at which the nitroxyl moiety is localized in the bilayer. Prev
ious results on the rate of disappearance of the electron spin resonan
ce (ESR) nitroxide signal on continuous photolysis of the same systems
do not show the same dependence on the localization of the nitroxyl m
oiety in the liposome. Although the MC540 triplet state seems to be im
plicated in the reaction process, the results suggest that ESR and las
er flash experiments demonstrate two different kinds of mechanism.