Photophysics and photochemistry of aflatoxins B1 and B2

Abstract

Aflatoxins are mycotoxins produced by fungi of the genus Aspergillus, which is widely spread in the tropics and subtropics. To date, aflatoxin phototoxicity has been recognized, but the mechanism responsible for this phototoxicity has not been fully characterized. In the present paper, nanosecond laser flash photolysis studies allowed us to elucidate the photochemical processes undergone by two mycotoxins, namely aflatoxin B₁ and B₂, upon UV irradiation. In brief, photolysis (308 nm) of the aflatoxins leads to intersystem crossing, giving rise to their triplet excited state. The triplet state can readily be quenched by indole and hydroquinone, and also by molecular oxygen yielding singlet oxygen (singlet oxygen quantum yields of 0.51 and 0.59 were found for aflatoxin B₁ and B₂, respectively). In addition, our data indicate the ability of the two aflatoxins to photoionize upon 248 nm excitation. The photoionization quantum yield for aflatoxin B₁ and B₂ have been estimated to be 0.11 and 0.29, respectively.