TRIPLET EXCITED STATE OF THE 4'5' PHOTOADDUCT OF PSORALEN AND THYMINE |
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Authors: | R V Bensasson C Salet E J Land F A P Rushton |
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Institution: | Laboratoire de Biophysique, Museum National d'Histoire Naturelle, 61 rue Buffon, 75005 Paris, France;*Paterson Laboratories, Christie Hospital and Holt Radium Institute, Manchester, M20 9BX, England |
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Abstract: | Abstract— The triplet-triplet absorption spectrum of the 4'5' psoralen-thymine mono-adduct has been determined in water and methanol using the technique of laser flash photolysis. The extinction coefficient of the triplet was measured by the energy-transfer method with retinol triplet as standard, and used to determine the singlet → triplet intersystem crossing quantum yield for 353 nm excitation. Reaction rate constants for mono-adduct triplet with thymine and tryptophan were measured in water. Long-lived transient absorptions detected after quenching the mono-adduct triplet with thymine and tryptophan are assigned mainly to the corresponding mono-adduct radical anion, whose spectrum was established in separate pulse radiolysis studies of the mono-adduct in aqueous formate. The significant singlet → triplet quantum yields found for the mono-adduct might be consistent with the involvement of triplet excited mono-adduct in DNA cross-link formation, as also may be the high reactivity obtained for the triplet with thymine. The initial quenching products observed resulted from a charge-transfer reaction. |
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