GENERATION AND CHARACTERIZATION OF PSORALEN RADICAL CATIONS

Radical cations of psoralen, 8-methoxypsoralen (8-MOP) and 5-methoxyps oralen have been generated by photosensitized electron transfer in ace tonitrile and aqueous buffer/acetonitrile (1:1) and have absorption ma xima at 600, 650 and 550 nm, respectively, The radical cations have li fetimes of similar to 5 mu s under these conditions, are unreactive to ward oxygen and show behavior typical of arylalkene radical cations in their reactivity toward nucleophiles and the precursor psoralens. Dir ect 355 nn excitation of 8-MOP in aqueous buffer at physiological pH r esults in monophotonic photoionization to give 8-MOP.+ with a quantum yield of 0.015. The 8-MOP.+ reacts with both guanosine and adenosine m ononucleotides (k = 2.5 x 10(9) and 3.4 x 10(7) M-1 s(-1), respectivel y) 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 o r photoionization may be involved in psoralen/UVA therapy.