Excited State Lifetimes of Sulfur-Substituted DNA and RNA Monomers Probed Using the Femtosecond Fluorescence Up-Conversion Technique
Excited State Lifetimes of Sulfur-Substituted DNA and RNA Monomers Probed Using the Femtosecond Fluorescence Up-Conversion Technique
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DOI：
10.3390/molecules25030584
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发表时间：
2020-02-01
期刊：
影响因子：
4.6
通讯作者：
Crespo-Hernandez, Carlos E.
中科院分区：
文献类型：
--
作者：
Brister, Matthew M.;Gustavsson, Thomas;Crespo-Hernandez, Carlos E.
硫取代的DNA和RNA核碱基衍生物（a.k.a.，硫代碱基）是生物分子的重要家族。它们在医疗环境中用作前药和化疗剂，并在结构生物学应用中用作光交联剂分子。值得注意的是，用紫外到近可见光激发硫碱基导致在数百飞秒的时间尺度上的长寿命和反应性三重态的种群，并且具有接近统一的产率。这种有效的非辐射衰变途径解释了文献中硫代碱基的荧光产率和荧光寿命的稀缺性。在这项研究中，我们报告的荧光寿命为12硫代碱基衍生物，无论是在水溶液中，在生理pH值和乙腈。在267和362 nm处进行激发，而在380、425、450、525或532 nm处检测荧光发射。所有研究的硫代碱基揭示的荧光寿命，衰减在几百飞秒和幅度依赖于和敏感的位置和程度的硫原子取代和溶剂环境。然而，有趣的是，三种硫代嘧啶衍生物（即，2-硫代胞苷、2-硫代尿苷和4-硫代胸苷）在水溶液中也表现出几皮秒的小幅度荧光成分。此外，硫代碱基的N-糖基化形成DNA或RNA核苷类似物被证明影响其荧光寿命。在水溶液中，在267 nm激发的荧光衰减信号等于或慢于在362 nm激发收集的荧光衰减信号。然而，在乙腈中，在267 nm激发时记录的荧光衰减信号在所有情况下都快于在362 nm激发时测量的荧光衰减信号。与文献值的比较表明，虽然DNA和RNA核碱基和硫碱基衍生物都表现出亚皮秒荧光寿命，但核碱基单体中的（1）pi pi* 激发态群体主要衰减回基态，而它主要在硫碱基单体中占据长寿命和反应性三重态。
Sulfur-substituted DNA and RNA nucleobase derivatives (a.k.a., thiobases) are an important family of biomolecules. They are used as prodrugs and as chemotherapeutic agents in medical settings, and as photocrosslinker molecules in structural-biology applications. Remarkably, excitation of thiobases with ultraviolet to near-visible light results in the population of long-lived and reactive triplet states on a time scale of hundreds of femtoseconds and with near-unity yields. This efficient nonradiative decay pathway explains the vanishingly small fluorescence yields reported for the thiobases and the scarcity of fluorescence lifetimes in the literature. In this study, we report fluorescence lifetimes for twelve thiobase derivatives, both in aqueous solution at physiological pH and in acetonitrile. Excitation is performed at 267 and 362 nm, while fluorescence emission is detected at 380, 425, 450, 525, or 532 nm. All the investigated thiobases reveal fluorescence lifetimes that decay in a few hundreds of femtoseconds and with magnitudes that depend and are sensitive to the position and degree of sulfur-atom substitution and on the solvent environment. Interestingly, however, three thiopyrimidine derivatives (i.e., 2-thiocytidine, 2-thiouridine, and 4-thiothymidine) also exhibit a small amplitude fluorescence component of a few picoseconds in aqueous solution. Furthermore, the N-glycosylation of thiobases to form DNA or RNA nucleoside analogues is demonstrated as affecting their fluorescence lifetimes. In aqueous solution, the fluorescence decay signals exciting at 267 nm are equal or slower than those collected exciting at 362 nm. In acetonitrile, however, the fluorescence decay signals recorded upon 267 nm excitation are, in all cases, faster than those measured exciting at 362 nm. A comparison to the literature values show that, while both the DNA and RNA nucleobase and thiobase derivatives exhibit sub-picosecond fluorescence lifetimes, the (1)pi pi* excited-state population in the nucleobase monomers primarily decay back to the ground state, whereas it predominantly populates long-lived and reactive triplet states in thiobase monomers.