Photochemical and photophysical properties of lumazine in aqueous solutions

Lumazine (pteridine-2,4(1H,3H)-dione, LU) was investigated for its efficiency of singlet oxygen (O-1(2)) production and quenching in aqueous solution. The quantum yield of O-1(2) production (phi(Delta)) was determined by measurements of the O-1(2) luminescence in the near-infrared upon continuous excitation of the sensitizer. Values of phi(Delta) are sensitive to the pH and were found to be 0.44 +/- 0.01 and 0.080 +/- 0.004 in acidic and alkaline media. respectively. The photochemical stability of LU was investigated under different pH conditions, in the presence and in the absence of O-2. The photochemical consumption of LU in aqueous solution at room temperature under irradiation at 350 nm was followed by UV-vis spectrophotometry and HPLC. Values of the quantum yields of LU disappearance are low, indicating that LU is rather photostable under physiological conditions. (C) 2008 Elsevier B.V. All rights reserved.