Department of Physical and Quantum Chemistry, Faculty of Chemistry, Wrocław University of Science and Technology, Wybrzeże Wyspiańskiego 27, 50-370 Wrocław, Poland.
Department of Astronomy, Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138, United States.
J Phys Chem Lett. 2021 Jul 22;12(28):6707-6713. doi: 10.1021/acs.jpclett.1c01384. Epub 2021 Jul 14.
Substitution of exocyclic oxygen with sulfur was shown to substantially influence the properties of RNA/DNA bases, which are crucial for prebiotic chemistry and photodynamic therapies. Upon UV irradiation, thionucleobases were shown to efficiently populate triplet excited states and can be involved in characteristic photochemistry or generation of singlet oxygen. Here, we show that the photochemistry of a thionucleobase can be considerably modified in a nucleoside, that is, by the presence of ribose. Our transient absorption spectroscopy experiments demonstrate that thiocytosine exhibits 5 times longer excited-state lifetime and different excited-state absorption features than thiocytidine. On the basis of accurate quantum chemical simulations, we assign these differences to the dominant population of a shorter-lived triplet nπ* state in the nucleoside and longer-lived triplet ππ* states in the nucleobase. This explains the distinctive photoanomerziation of thiocytidine and indicates that the nucleoside will be a less efficient phototherapeutic agent with regard to singlet oxygen generation.
用硫取代环外氧被证明会极大地影响 RNA/DNA 碱基的性质，而这些性质对前生物化学和光动力疗法至关重要。在紫外线照射下，硫代核苷碱基被证明能有效地进入三重激发态，并能参与特征光化学反应或生成单线态氧。在这里，我们表明，核苷的存在，即核糖，会极大地改变核苷碱基的光化学反应。我们的瞬态吸收光谱实验表明，硫代胞嘧啶的激发态寿命比硫代胞嘧啶核苷长 5 倍，激发态吸收特征也不同。基于精确的量子化学模拟，我们将这些差异归因于核苷中短寿命的三重 nπ态的主要分布和核苷碱基中长寿命的三重ππ态。这解释了硫代胞嘧啶的独特光异构化，并表明核苷在生成单线态氧方面将是一种效率较低的光疗试剂。
