Jin Peipei, Wang Xueli, Pan Haifeng, Chen Jinquan
State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200241, China.
Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, Shanxi 030006, China.
Phys Chem Chem Phys. 2022 Jan 4;24(2):875-882. doi: 10.1039/d1cp04811b.
Selenium nucleic acids possess unique properties and have been demonstrated to have a wide range of applications such as in DNA X-ray crystallography and novel medical therapies. However, as a heavy atom, selenium substitution may easily alter the photophysical properties of a nucleic acid by red-shifting the absorption spectra and introducing effective intersystem crossing to triplet excited states. In present work, the excited state dynamics of a naturally occurring selenium substituted uracil (2-selenuracil, 2SeU) is studied by using femtosecond transient absorption spectroscopy as well as quantum chemistry calculations. Ultrafast intersystem crossing to the lowest triplet state (T) and effective non-radiative decay of this state to the ground state (S) are demonstrated in the neutral form 2SeU. However, the triplet lifetime of the deprotonated form 2SeU is found to be almost one order of magnitude longer than that in the neutral one. Quantum chemistry calculations indicate that the short triplet lifetime in 2SeU is due to excited state population decay through a crossing point between T and S. In the deprotonated form, shortening the N1-C2 bond length makes the structural distortion more difficult and brings a larger energy barrier on the pathway to the T/S crossing point, resulting in one order of magnitude increase of the triplet state lifetime. Our study reveals one key factor to regulate the triplet lifetime of 2SeU and sets the stage to further investigate the photophysical and photochemical properties of 2SeU-containing DNA/RNA duplexes.
硒核酸具有独特的性质，并已被证明有广泛的应用，如在DNA X射线晶体学和新型医学疗法中。然而，作为一种重原子，硒取代可能很容易通过使吸收光谱红移并引入有效的系间窜越到三重激发态来改变核酸的光物理性质。在本工作中，通过使用飞秒瞬态吸收光谱以及量子化学计算，研究了天然存在的硒取代尿嘧啶（2-硒尿嘧啶，2SeU）的激发态动力学。在中性形式的2SeU中，证明了超快系间窜越到最低三重态（T）以及该态到基态（S）的有效非辐射衰变。然而，发现去质子化形式的2SeU的三重态寿命比中性形式的几乎长一个数量级。量子化学计算表明，2SeU中短的三重态寿命是由于通过T和S之间的交叉点的激发态布居衰变。在去质子化形式中，缩短N1-C2键长使结构畸变更困难，并在通往T/S交叉点的途径上带来更大的能垒，导致三重态寿命增加一个数量级。我们的研究揭示了调节2SeU三重态寿命的一个关键因素，并为进一步研究含2SeU的DNA/RNA双链体的光物理和光化学性质奠定了基础。
