Generation and Characterization of Psoralen Radical Cations

Article abstract of DOI:10.1111/j.1751-1097.1997.tb03201.x

Radical cations of psoralen, 8-methoxypsoralen (8-MOP) and 5-methoxypsoralen have been generated by photosensitized electron transfer in acetonitrile and aqueous buffer/acetonitrile (1:1) and have absorption maxima at 600, 650 and 550 nm, respectively. The radical cations have lifetimes of ～5 us under these conditions, are unreactive toward oxygen and show behavior typical of arylalkene radical cations in their reactivity toward nucleophiles and the precursor psoralens. Direct 355 nm excitation of 8-MOP in aqueous buffer at physiological pH results in monophotonic photoionization to give 8-MOP^.+ with a quantum yield of 0.015. The 8-MOP^.+ reacts with both guanosine and adenosine mononucleotides (k = 2.5 × 10⁹ and 3.4 × 10⁷ M^-1 s^-1, respectively) via electron transfer to give the purine radical cations, but does not react with pyrimidine mononucleotides. These results suggest that reactions of psoralen radical cations generated by electron transfer or photoionization may be involved in psoralen/UVA therapy.