Energy and charge-transfer quenching of flavins in AOTreversed micelles solutions

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

Cordoba

Encuentro; XI Encuentro Latinoamericano de Fotoquímica y Fotobiología ? ELAFOT; 2012

Photochemical Group of the Universidad Nacional de Río Cuarto

Flavins are widely distributed in the biosphere, serve as cofactors inredox proteins and are commonly applied photosensitizers [1]. Riboflavin (RF),present in free form or as flavin mononucleotide (FMN) and flavin adeninedinucleotide (FAD) in cells, is an important and efficient endogenous cellularphotosensitizer [2]. The triplet state of a flavin can be quenched by oxygenand 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 bytryptophan and molecular oxygen in (AOT)-iso-octane-water reversemicelles by laser flash photolysis (LFP) with excitation at 355 nm.The 3RF* quenching efficiency (q) by tryptophan is governed by the localconcentration of the species at the interface of the micelle, and also byfluidity and water content. The presence of neutral radical of tryptophan (TrN•)was confirmed by two structureless bands located around 510 and 330 nm, whichdemostrated an electron transfer quenching mechanism [3].On the other hand, the deactivation of 3RF* by molecularoxygen showed that  hq decreases slightly with the water contentof the micelle, that is in agreement with RF location on the micelar structure[4]. The high increment of quenching efficient at low internal oxygen micellar concentrationis explained by the large constant of quenching (kq ca. 109 M-1s-1)