Billinghurst Brant E, Yeung Ralph, Loppnow Glen R
Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada.
J Phys Chem A. 2006 May 18;110(19):6185-91. doi: 10.1021/jp0609333.
5-Fluorouracil is an analogue of thymine and uracil, nucleobases found in DNA and RNA, respectively. The photochemistry of thymine is significant; UV-induced photoproducts of thymine in DNA lead to skin cancer and other diseases. In previous work, we have suggested that the differences in the excited-state structural dynamics of thymine and uracil arise from the methyl group in thymine acting as a mass barrier, localizing the vibrations at the photochemical active site. To further test this hypothesis, we have measured the resonance Raman spectra of 5-fluorouracil at wavelengths throughout its 267 nm absorption band. The spectra of 5-fluorouracil and thymine are very similar. Self-consistent analysis of the resulting resonance Raman excitation profiles and absorption spectrum using a time-dependent wave packet formalism suggests that, at most, 81% of the reorganization energy upon excitation is directed along photochemically relevant modes. This compares well with what was found for thymine, supporting the mass barrier hypothesis.
5-氟尿嘧啶是胸腺嘧啶和尿嘧啶的类似物，它们分别是在DNA和RNA中发现的核碱基。胸腺嘧啶的光化学性质很重要；DNA中胸腺嘧啶的紫外线诱导光产物会导致皮肤癌和其他疾病。在之前的工作中，我们曾提出胸腺嘧啶和尿嘧啶激发态结构动力学的差异源于胸腺嘧啶中的甲基作为质量屏障，将振动定位在光化学活性位点。为了进一步验证这一假设，我们测量了5-氟尿嘧啶在其267nm吸收带全波段波长下的共振拉曼光谱。5-氟尿嘧啶和胸腺嘧啶的光谱非常相似。使用含时波包形式对所得共振拉曼激发轮廓和吸收光谱进行自洽分析表明，激发时最多81%的重组能沿着光化学相关模式定向。这与胸腺嘧啶的情况非常吻合，支持了质量屏障假说。
