Photo-ionization and photo-excitation of curcumin investigated by laser flash photolysis.

Curcumin (Cur) has putative antitumor properties. In the current study, we examined photophysical and photochemical properties of Cur using laser flash photolysis. The results demonstrated that Cur could be photo-ionized at 355 nm laser pulse to produce radical cation (Cur(+)) and solvated electron e(sol)(-) in 7:3 ethanol-water mixtures. The quantum yield of Cur photo-ionization and the ratio of photo-ionization to photo-excitation were also determined. Cur(+) could be transferred into neutral radical of Cur (Cur) via deprotonation with the pKa 4.13. The excited singlet of Cur ((1)Cur* could be transferred into excited triplet ((3)Cur*, which could be quenched by oxygen to produce singlet oxygen (1)O2*. Reaction of (3)Cur* with tryptophan was confirmed. The results encourage developing curcumin as a photosensitive antitumor agent.