VITAMIN B2-SENSITIZED PHOTOOXIDATION OF STRUCTURALLY RELATED DIHYDROXYFLAVONOIDS

MONTAÑA M.P.; MISKOSKI S.; CRIADO S.; GIANELLO, J. C.; PAPPANO N. B.; DEBATTISTA, N. B.; GARCÍA N. A.

DYES AND PIGMENTS

Elsevier Science Ltd.

Lugar: Reino Unido; Año: 2003 vol. 58 p. 113 - 120

0143-7208

A kinetic study of the processes involved in the vitamin B2 (riboflavin, Rf)-sensitized photooxidation of selected flavonoids (F) was carried out in methanolic solution.   Under aerobic  visible-light-irradiation conditions a complex picture of competitive interactions takes place: the singlet and triplet excited states of Rf  are quenched by three F, namely 5,7-dihydroxy-3’,4’-dimethoxyflavanone (FNN); 5,7-dihydroxy-4’,6,8-trimethoxyflavone (FLV) and 2’,4’-dihydroxychalcone (CHL). Concomitantly,  the species singlet molecular oxygen (O2(1Dg))  and superoxide anion radical (O2·– ) are generated and interact with F and with  Rf. CHN and FNN are photooxidised, probably by means of O2·– , whereas FVN , the poorest quencher of excited triplet Rf, allows the generation of O2(1Dg), which oxidises the very flavonoid. The photodegradation of the vitamin is delayed due to an electron transfer process to ground state oxygen.