Martinez-Fernandez L, Fahleson T, Norman P, Santoro F, Coriani S, Improta R
Istituto di Biostrutture e Bioimmagini-CNR, Via Mezzocannone 6, I-80134 Napoli, Italy.
Photochem Photobiol Sci. 2017 Sep 13;16(9):1415-1423. doi: 10.1039/c7pp00105c.
The excited electronic states of 2-thiouracil, 4-thiouracil and 2,4-dithiouracil, the analogues of uracil where the carbonyl oxygens are substituted by sulphur atoms, have been investigated by computing the magnetic circular dichroism (MCD) and one-photon absorption (OPA) spectra at the time-dependent density functional theory level. Special attention has been paid to solvent effects, included by a mixed discrete/continuum model, and to determining how our results depend on the adopted DFT functional (CAM-B3LYP and B3LYP). Whereas including solvent effects does not dramatically impact the MCD and OPA spectra, though improving the agreement with the experimental spectra, the performances of CAM-B3LYP and B3LYP are remarkably different. CAM-B3LYP captures well the effect of thionation on the uracil excited states and provides spectra in good agreement with the experiments, whereas B3LYP shows some deficiency in describing 2-TU and 2,4-DTU spectra, despite being more accurate than CAM-B3LYP for 4-TU.
尿嘧啶的类似物2-硫尿嘧啶、4-硫尿嘧啶和2,4-二硫尿嘧啶的羰基氧被硫原子取代，通过在含时密度泛函理论水平上计算磁圆二色性（MCD）和单光子吸收（OPA）光谱，对其激发电子态进行了研究。特别关注了溶剂效应，采用混合离散/连续介质模型来考虑，以及确定我们的结果如何依赖于所采用的密度泛函理论（DFT）泛函（CAM-B3LYP和B3LYP）。虽然考虑溶剂效应不会显著影响MCD和OPA光谱，尽管能改善与实验光谱的一致性，但CAM-B3LYP和B3LYP的表现却显著不同。CAM-B3LYP很好地捕捉到了硫代作用对尿嘧啶激发态的影响，并提供了与实验结果高度一致的光谱，而B3LYP在描述2-硫尿嘧啶（2-TU）和2,4-二硫尿嘧啶（2,4-DTU）光谱方面存在一些不足，尽管对于4-硫尿嘧啶（4-TU）比CAM-B3LYP更准确。
