Energy and charge-transfer quenching of flavins in AOT-reversed micelles solutions.

HUGO A. PÉREZ, LORENA VALLE, FAUSTINO E. MORÁN VIEYRA Y CLAUDIO D. BORSARELLI

Cordoba

Congreso; XI ELAFOT; 2012

Flavins are widely distributed in the biosphere, serve as cofactors in redox proteins and are commonly applied photosensitizers [[i]]. Riboflavin (RF), present in free form or as flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) in cells, is an important and efficient endogenous cellular photosensitizer [[ii]]. The triplet state of a flavin can be quenched by oxygen and a variety of electron donors, e.g. ascorbic acid, amines or amino acids, e.g. tyrosine or tryptophan [1]. We have studied RF triplet excited state (3RF*) quenching by tryptophan and molecular oxygen in (AOT)-iso-octane-water reverse micelles by laser flash photolysis (LFP) with excitation at 355 nm. The 3RF* quenching efficiency (hq) by tryptophan is governed by the local concentration of the species at the interface of the micelle, and also by fluidity and water content. The presence of neutral radical of tryptophan (TrN·) was confirmed by two structureless bands located around 510 and 330 nm, which demostrated an electron transfer quenching mechanism [[iii]]. On the other hand, the deactivation of 3RF* by molecular oxygen showed that hq decreases slightly with the water content of the micelle, that is in agreement with RF location on the micelar structure [[iv]]. The high increment of quenching efficient at low internal oxygen micelar concentration is explained by the large constant of quenching (kq ca. 109 M-1 s-1). [i] H. Gorner. Oxygen uptake after electrón transfer from amines, amino acids and ascorbic acid to triplet flavins in air ? saturated aqueous solution. J. Photochem. Photobiol. B. 87, 73 ? 80 (2007). [ii] L. Chang- Yuan, L. Yan- Yun. Electron transfer oxidation of tryptophan and tyrosine by triplet states and oxidized radicals of flavin sensitizers: a laser flash photolysis study. Biochim. Biophys. Acta. 1571, 71 ? 76 (2002). [iii] T.B. Melø, M.A. Ionescu, G.W. Haggquist, K.R. Naqvi. Hydrogen abstraction by triplet flavins. I: time-resolved multi-channel absorption spectra of flash-irradiated riboflavin solutions in water. Spectrochimica. A. 55, 2299 ? 2307 (1999). [iv] L. Valle, F.E. Morán Vieyra, C.D. Borsarelli. Hydrogen-bonding modulation of excitated-state properties of flavins in a model of aqueous confined environment. Photochem. Photobiol. Sci. 11, 1051-1061 (2012).