THE TRIPLET RADICAL-ION PAIR STATE OF THE ZN-PORPHYRIN-VIOLOGEN DYAD AS A MAGNETIC-FIELD SENSITIVE PROBE OF THE LIPID BILAYER DYNAMICS

Magnetic field effect on the recombination kinetics of the triplet rad ical ion pair state (rips) of the Zn-porphyrin-viologen dyad in the sm all unilamellar vesicles of D,L-dipalmitoyl-alpha-phosphatidylcholine has been studied by nanosecond laser flash photolysis technique at 5-6 0-degrees-C. The increase of temperature from 25 to 40-degrees-C enhan ces the rate constant (k(r)) of the RIPS recombination in zero magneti c field from 0.9 . 10(6) s-1 to 1.6 . 10(6) s-1, while k(r) is tempera ture insensitive at 5-25 and 40-60-degrees-C. The typical break of the k(r) temperature dependenceis observed in the temperature range of th e phase transition of the lipid bilayers from the solid to fluid state . The k(r) value in the strong magnetic field (B=0.24 T) is equal to 2 .7 . 10(6) s-1 and it is independent of temperature of 5-60-degrees-C. The shape of the magnetic field dependence of k(r) is unaffected by t he phase transition of the lipid bilayers and is characterized by the existence of an initial plateau of k(r) at B=0-0.5 mT.