Micciarelli Marco, Valadan Mohammadhassan, Della Ventura Bartolomeo, Di Fabio Giovanni, De Napoli Lorenzo, Bonella Sara, Röthlisberger Ursula, Tavernelli Ivano, Altucci Carlo, Velotta Raffaele
Department of Physics, University of Naples Federico II , Via Cintia, 26, 80126 Napoli, Italy.
J Phys Chem B. 2014 May 15;118(19):4983-92. doi: 10.1021/jp4115018. Epub 2014 May 2.
The photophysical and photochemical properties of 5-benzyluracil and 5,6-benzyluracil, the latter produced by photocyclization of the former through irradiation with femtosecond UV laser pulses, are investigated both experimentally and theoretically. The absorption spectra of the two molecules are compared, and the principal electronic transitions involved are discussed, with particular emphasis on the perturbation induced on the two chromophore species (uracil and benzene) by their proximity. The photoproduct formation for different irradiation times was verified with high-performance liquid chromatography and nuclear magnetic resonance measurements. The steady-state fluorescence demonstrates that the fluorescence is a distinctive physical observable for detection and selective identification of 5- and 5,6-benzyluracil. The principal electronic decay paths of the two molecules, obtained through TDDFT calculations, explain the features observed in the emission spectra and the photoreactivity of 5-benzyluracil. The order of magnitude of the lifetime of the excited states is derived with steady-state fluorescence anisotropy measurements and rationalized with the help of the computational findings. Finally, the spectroscopic data collected are used to derive the photocyclization and fluorescence quantum yields. In obtaining a global picture of the photophysical and photochemical properties of the two molecules, our findings demonstrates that the use of 5-benzyluracil as a model system to study the proximity relations of a DNA base with a close-lying aromatic amino acid is valid at a local level since the main characteristics of the decay processes from the excited states of the uracil/thymine molecules remain almost unchanged in 5-benzyluracil, the main perturbation arising from the presence of the close-lying aromatic group.
研究了5-苄基尿嘧啶和5,6-苄基尿嘧啶的光物理和光化学性质，后者是前者通过飞秒紫外激光脉冲照射光环化产生的，进行了实验和理论研究。比较了这两种分子的吸收光谱，并讨论了主要的电子跃迁，特别强调了两个发色团（尿嘧啶和苯）由于其接近而引起的扰动。用高效液相色谱和核磁共振测量验证了不同照射时间下光产物的形成。稳态荧光表明，荧光是检测和选择性鉴定5-和5,6-苄基尿嘧啶的独特物理可观测量。通过TDDFT计算得到的两种分子的主要电子衰变路径解释了发射光谱中观察到的特征以及5-苄基尿嘧啶的光反应性。通过稳态荧光各向异性测量得出激发态寿命的数量级，并借助计算结果进行了合理化解释。最后，收集的光谱数据用于推导光环化和荧光量子产率。在获得这两种分子的光物理和光化学性质的全局图时，我们的研究结果表明，使用5-苄基尿嘧啶作为模型系统来研究DNA碱基与紧邻芳香族氨基酸的接近关系在局部水平上是有效的，因为尿嘧啶/胸腺嘧啶分子激发态衰变过程的主要特征在5-苄基尿嘧啶中几乎保持不变，主要扰动来自紧邻芳香族基团的存在。
