title: Photophysical and photochemical properties of 4-thiouracil: time-resolved IR spectroscopy and DFT studies.
abstract: 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-nucleic 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 (5-4)/(6-4) pyrimidine-pyrimidone product. In the presence of O2 under aerobic conditions, the triplet 4-TU acts as an energy donor to produce singlet oxygen (1)O2 by triplet-triplet energy transfer. The highly reactive oxygen species (1)O2 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 (1)O2, which has profound implications for photo cross-linking, DNA photodamage, as well as photodynamic therapy studies.
authors.affiliation: State Key Laboratory of Molecular Reaction Dynamics, Beijing National Laboratory for Molecular Sciences (BNLMS), Institute of Chemistry, Chinese Academy of Sciences , Beijing 100190, China.
authors.forename: Xiaoran
authors.initials: X
authors.lastname: Zou
authors.forename: Xiaojuan
authors.initials: X
authors.lastname: Dai
authors.forename: Kunhui
authors.initials: K
authors.lastname: Liu
authors.forename: Hongmei
authors.initials: H
authors.lastname: Zhao
authors.forename: Di
authors.initials: D
authors.lastname: Song
authors.forename: Hongmei
authors.initials: H
authors.lastname: Su
mesh_terms: D008027:Light; D008958:Models, Molecular; D010100:Oxygen / Q000737:chemistry; D011789:Quantum Theory; D026082:Singlet Oxygen / Q000737:chemistry; D013055:Spectrophotometry, Infrared; D013889:Thiouracil / Q000031:analogs & derivatives* / Q000737:chemistry
chemical_list: D026082:Singlet Oxygen; C114719:4-thiouracil; D013889:Thiouracil; D010100:Oxygen