KINETICS OF THE ELECTRON-TRANSFER REACTION BETWEEN ZN-3TPP-ASTERISK AND METHYL VIOLOGEN IN LECITHIN VESICLES STUDIED BY GLOBAL ANALYSIS

被引:14
作者
COUTINHO, PJG [1 ]
COSTA, SMB [1 ]
机构
[1] Univ Tecn Lisboa, CTR QUIM ESTRUTURAL, COMPLEXO 1, INST SUPER TECN, P-1096 LISBON, PORTUGAL
关键词
D O I
10.1016/1010-6030(94)87010-1
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
Suspensions of lecithin vesicles incorporating zinc tetraphenylporphyrin in high and low local concentrations (lipid-to-porphyrin ratio of 50:1 and 1000:1) and methyl viologen dichloride in the external aqueous phase were studied by laser flash photolysis. Electron transfer from the porphyrin triplet to methyl viologen was shown to occur with low efficiencies ranging from 0.12 to 0.21 depending on the acceptor concentration. The data obtained followed non-homogeneous kinetics which depended on the quencher gradient concentration, on the local porphyrin content in the vesicle interface, and on its asymmetric distribution. Kinetic data were treated with a global analysis method, showing that only 30% of the triplet porphyrin sites were active as regards electron transfer to a quencher solubilized in the aqueous external phase, whereas the remaining 70% of the porphyrin sites were quenched but did not participate in the electron transfer process. In high concentrated vesicles, triplet-triplet annihilation and triplet-ground state interactions compete with electron transfer and were taken into account in the kinetic evaluation. The pre-exponential factor determined for this reaction in the outer membrane of lecithin vesicles is k(ET)(R0) = 5 X 10(9) s-1 and electron transfer occurs at short edge-to-edge distances, ranging from 1.1 angstrom to 3 angstrom.
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页码:149 / 160
页数:12
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