title: Triplet radical ion pair state of the Zn-porphyrin-viologen dyad as a magnetic field sensitive probe of phase transitions in small unilamellar vesicles.
abstract: The magnetic field effect on the recombination kinetics of the triplet radical ion pair state (RIPS) of the Zn-porphyrin-viologen dyad (P-Ph-Vi2+) in the small unilamellar vesicles (SUV) of D,L-dipalmitoyl-alpha-phosphatidylcholine has been studied by the nanosecond laser flash photolysis technique at 5-60 degrees C. The increase in temperature from 25 to 40 degrees C enhances the rate constant (kr) of the RIPS recombination in zero magnetic field from 0.9 x 10(6) to 1.6 x 10(6) s-1, while kr is temperature insensitive at 5-25 and 40-60 degrees C. The typical break in the kr temperature dependence is observed in the temperature range of the phase transition of the SUV bilayers from the solid to the fluid state. The kr value in a strong magnetic field (B = 0.24 T) is equal to 2.7 x 10(5) s-1 and it is independent of temperature at 5-60 degrees C. The shape of the magnetic field dependence of kr is unaffected by the phase transition of the SUV bilayers and is characterized by the existence of an initial plateau of kr at B = 0 to 0.5 mT.
authors.affiliation: Institute of Chemical Physics, Academy of Sciences of the USSR.
authors.lastname: Shafirovich VYa
authors.forename: E E
authors.initials: EE
authors.lastname: Batova
authors.forename: P P
authors.initials: PP
authors.lastname: Levin
mesh_terms: D004574:Electromagnetic Fields; D005609:Free Radicals; D007700:Kinetics; D008051:Lipid Bilayers; D008665:Metalloporphyrins / Q000737:chemistry / Q000528:radiation effects*; D015335:Molecular Probes; D010782:Photolysis; D014755:Viologens / Q000737:chemistry / Q000528:radiation effects*
chemical_list: D005609:Free Radicals; D008051:Lipid Bilayers; D008665:Metalloporphyrins; D015335:Molecular Probes; D014755:Viologens; C017802:zinc hematoporphyrin