Riboflavin-induced photodegradation of tryptophan in sodium sulfosuccinate (AOT)-iso-octane-water

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

Conferencia; 21 IAPS Winter Conference; 2011

Flavins play an important role inphotosensitized reactions that include a wide range of electron donorsubstrates, such as amino acids. In aqueous solutions, triplet state of flavinsreacts with amino acids such as Cys, Trp and Tyr with bimolecular quenching constantsbetween 1-10´109s-1 M-1 [1]. In aerobic conditions, the flavin photosensitized oxidationof aminoacids was attributed to H2O2 produced by dismutation of O2•-, generated by the interaction of O2 with the triplet of the flavins and/or radical species formed by flavintriplet reaction with the aminoacids [2,3]. However, to our knowledge, there are fewstudies about flavin-photosensitized oxidation of amino acid inmicroenvironments which mimic biological system compartmentalization. In thiswork we study the riboflavin (Rf)-mediated reaction of tryptophan innanodroplets made of sodium sulfosuccinate (AOT)-iso-octane-water by continuousblue-LED (460 nm) and laser pulsed (355 nm) photolysis, using both stationaryand dynamic absorption and emission spectroscopies. The absorption and emission spectra of Rfand Trp indicated that both molecules are located in the inner water-surfactantinterface of the reverse micelles. The fluorescence quenching of Rf by Trp is amixing of static (Perrin) and dynamic mechanism. With the increment of thewater content in the reversed micelles (W =[H2O]/[AOT])the fraction of static quenching is reduced while the dynamic component increases.These results are in agreement with the larger micelar size and fluidity as Wincreased. The UV-Vis absorption and fluorescence spectra showed theriboflavin conversion to lumichrome and the photoproducts of the indole-flavintype. The rate of formation of photoproducts, measured with the absorbanceincrement at 320nm was proportional with the increment of the quenching rateconstant of 3Rf* by Trp, e.g. kQT= 2.6´107,6.1´107and 3.3´109M-1 s-1, for W =3, W= 20 and phosphate buffer solution, respectively,indicating that the photodegradation reaction is mainly govern by triplet statephotochemistry. In reverse micelles the product formation is almost six-timeslower that in bulk buffer solution. This indicates that the much rigid micellarenvironmentreduces the Rf-mediated transformation ofTrp.