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Electron transfer quenching of singlet and triplet excited states of flavins and lumichrome by aromatic and aliphatic electron donors

Article

Authorship
PORCAL, GABRIELA VALERIA
Date
2003
Publishing House and Editing Place
ROYAL SOC CHEMISTRY
Magazine
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, vol. 5 (pp. 4123-4128) ROYAL SOC CHEMISTRY
Summary Information provided by the agent in SIGEVA
The quenching of excited singlet and triplet states of riboflavin, lumillavin and lumichrome was investigated in methanol. The quenchers were aromatic electron donors and aliphatic amines. Bimolecular quenching rate constants were determined from static and dynamic fluorescence measurements. Triplet quenching was studied by laser flash photolysis. Transient absorption spectra showed the presence of semireduced flavins and lumichrome, and the radical cation of quenchers. The results confirm that... The quenching of excited singlet and triplet states of riboflavin, lumillavin and lumichrome was investigated in methanol. The quenchers were aromatic electron donors and aliphatic amines. Bimolecular quenching rate constants were determined from static and dynamic fluorescence measurements. Triplet quenching was studied by laser flash photolysis. Transient absorption spectra showed the presence of semireduced flavins and lumichrome, and the radical cation of quenchers. The results confirm that the quenching rate constants for aliphatic donors are lower than those of aromatic donors of similar oxidation potential. Plots of the quenching rate constants vs. the free energy for the electron transfer reaction, DGº, were fitted by the Rehm-Weller model of electron transfer quenching. The aliphatic quenchers needed a higher intrinsic barrier for the fitting that was ascribed to the internal reorganisation of the amines. For the aromatic donors the singlet quenching rate constants reach the diffusional limit at highly negative DGº. However, for the triplet quenching the limiting value of the rate constants is lower than the plateau of the singlet quenching. This is explained in terms of the non-adiabaticity of the triplet quenching process.
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Key Words
LUMICHROMEFLAVINSELECTRON TRANFER