Photophysical and Photochemical Properties of 4-Thiouracil: Time-Resolved IR Spectroscopy and DFT Studies

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• 作者：Xiaoran Zou ; Xiaojuan Dai ; Kunhui Liu ; Hongmei Zhao ; Di Song ; Hongmei Su
• 刊名：Journal of Physical Chemistry B
• 出版年：2014
• 出版时间：June 5, 2014
• 年：2014
• 卷：118
• 期：22
• 页码：5864-5872
• 全文大小：439K
• 年卷期：v.118,no.22(June 5, 2014)
• ISSN：1520-5207

文摘

Intensified research interests are posed with the thionucleobase 4-thiouracil (4-TU), due to its important biological function as site-specific photoprobe to detect RNA structures and nucleic acid鈥搉ucleic acid contacts. By means of time-resolved IR spectroscopy and density functional theory (DFT) studies, we have examined the unique photophysical and photochemical properties of 4-TU. It is shown that 4-TU absorbs UVA light and results in the triplet formation with a high quantum yield (0.9). Under N₂-saturated anaerobic conditions, the reactive triplet undergoes mainly cross-linking, leading to the (5鈥?)/(6鈥?) pyrimidine鈥損yrimidone product. In the presence of O₂ under aerobic conditions, the triplet 4-TU acts as an energy donor to produce singlet oxygen ¹O₂ by triplet鈥搕riplet energy transfer. The highly reactive oxygen species ¹O₂ then reacts readily with 4-TU, leading to the products of uracil (U) with a yield of 0.2 and uracil-6-sulfonate (U^SO3) that is fluorescent at 390 nm. The product formation pathways and product distribution are well rationalized by the joint B3LYP/6-311+G(d,p) calculations. From dynamics and mechanistic point of views, these results enable a further understanding for 4-TU acting as reactive precursors for photochemical reactions relevant to ¹O₂, which has profound implications for photo cross-linking, DNA photodamage, as well as photodynamic therapy studies.