新型鸟嘌呤类似物y-鸟嘌呤及其异构体电子光谱性质的理论研究

荧光核酸碱基类似物的设计合成是众多研究领域的热点课题. 本文利用密度泛函理论(DFT)和含时密度泛函理论(TDDFT)考察了新型鸟嘌呤类似物y-鸟嘌呤(yG-t1) 及其五个异构体(yG-t2到yG-t6)的结构性质、电子性质和光谱性质, 同时考察了甲醇溶剂和碱基配对对其光谱性质的影响. 研究表明, 气相中y-鸟嘌呤的标准结构并不是最稳定的结构, 其具有三个能量相近的异构体, y-鸟嘌呤最有可能以这三种形式存在. 光谱性质研究表明y-鸟嘌呤的最大吸收波长比天然鸟嘌呤大得多, 人们可以对其进行选择性激发. y- 鸟嘌呤的标准结构与其异构体显示出不同的光谱特性, 因此可以利用其电子光谱指纹对它们进行区分. 研究发现甲醇溶剂将使y-鸟嘌呤标准结构的最大吸收波长和荧光发生蓝移, 而使其他异构体相应值发生红移; 与胞嘧啶配对将使yG-t1, yG-t2, yG-t5 和yG-t6的最大吸收波长和荧光波长发生蓝移, 表明y-鸟嘌呤的电子光谱性质受环境影响较大.

Theoretical study on the photophysical properties of the newly designed guanine analog y-guanine and its tautomers

Recently, newly created unnatural fluorescent nucleobase analogs have gained increasing attention. In the present work, a comprehensive theoretical study on the structural, electronic, and excited-state properties of y-guanine (yG-t1) and its five possible tautomers (yG-t2, yG-t3, yG-t4, yG-t5 and yG-t6) is performed. Tautomerization analysis reveals that the canonical form of yG is not the most stable tautomer in the gas phase since it has three tautomers with the same stabilities. The spectroscopic properties are investigated: It is found that these tautomers have different absorption spectra, and so we can distinguish them by their spectroscopic signatures. In addition, effects of methanol solution and hydrogen bonding with cytosine on the absorption and emission spectra are examined. The methanol solution is found to red-shift both the absorption and emission maxima of the studied bases except for yG-t1, for which the absorption and emission maxima have blue-shifts after solvation. On the other hand, hydrogen bonding with cytosine is found to are blue-shifted both the absorption and emission maxima of yG-t1, yG-t2, yG-t5, and yG-t6. Theoretical predictions here are helpful for the investigation of the tautomerism of yG and the optical properties of yDNA.