title: Even-odd alternation in mass spectrum of thymine and uracil clusters: evidence of intracluster photodimerization.
abstract: Multiphoton ionization of thymine and uracil clusters generated by a supersonic molecular beam gave rise to a remarkable alternation of mass spectral intensities between even- and odd-numbered clusters. Such alternation was observed in clusters of up to 30 molecules. Excitation to the two lowest electronically excited states seemed to be a strong prerequisite. In view of the well known photodimerization reaction of thymine and uracil in the bulk phase, it is proposed that such alternation in the mass spectral intensity resulted from formation of photodimer units within the cluster on intense UV irradiation. Several analogues of thymine with no known propensity for photodimerization in the bulk phase did not exhibit any sign of such alternation in the cluster mass spectrum. The intrinsic UV window for photodimerization, and hence photoinduced mammalian mutagenesis, was estimated to be approximately 210-280 nm, significantly narrower than the previously reported bulk values of 150-300 nm.
authors: School of Chemistry, Seoul National University, Seoul 151-747, Korea.
authors: N J
authors: NJ
authors: Kim
authors: H
authors: H
authors: Kang
authors: G
authors: G
authors: Jeong
authors: Y S
authors: YS
authors: Kim
authors: K T
authors: KT
authors: Lee
authors: S K
authors: SK
authors: Kim
mesh_terms: D004247:DNA / Q000737:chemistry* / Q000378:metabolism / Q000528:radiation effects*; D019281:Dimerization; D013058:Mass Spectrometry; D016296:Mutagenesis / Q000528:radiation effects; D010777:Photochemistry; D017785:Photons; D013941:Thymine / Q000031:analogs & derivatives / Q000737:chemistry* / Q000378:metabolism / Q000528:radiation effects*; D014466:Ultraviolet Rays; D014498:Uracil / Q000737:chemistry* / Q000378:metabolism / Q000528:radiation effects*
chemical_list: D014498:Uracil; D004247:DNA; D013941:Thymine