Bashkir State University, Department of Chemistry, Chair of Physical Chemistry and Chemical Ecology, 32 Zaki Validi Str., Ufa 450074, Russia; Institute of Petroleum Refining and Petrochemistry, Laboratory of Quantum Chemistry and Molecular Dynamics of the Department of Chemistry and Technology, 12 Initsiativnaya Str., Ufa 450065, Republic of Bashkortostan, Russia.
Bashkir State University, Department of Chemistry, Chair of Physical Chemistry and Chemical Ecology, 32 Zaki Validi Str., Ufa 450074, Russia; Ufa Institute of Chemistry, Russian Academy of Sciences, Laboratory of Chemical Physics, 69 Prospekt Oktyabrya, Ufa 450054, Russia; Institute of Petroleum Refining and Petrochemistry, Laboratory of Quantum Chemistry and Molecular Dynamics of the Department of Chemistry and Technology, 12 Initsiativnaya Str., Ufa 450065, Republic of Bashkortostan, Russia.
J Mol Graph Model. 2018 Jan;79:65-71. doi: 10.1016/j.jmgm.2017.11.007. Epub 2017 Nov 11.
Relative stabilities of the N1/N3/О5/О6 anions of 42 substituted uracils in gas phase and aqueous solutions have been theoretically studied using approximation IEFPCM (SMD) - TPSS/aug-cc-pVTZ. The specific solvation of uracil and its anions has been simulated with the first hydrate shell made up with 5 water molecules. The nonspecific solvation has been accounted in terms of the SMD model. We have found a series of relative stability under conditions of both specific and nonspecific hydration. The series is ranked according to the increase of the relative stability of the N3 anion. In gas phase, the N1 anion is significantly more stable than its N3 counterpart: the ΔG values vary in the range from 19.54 (5OH6СНU) to 83.14 (5NO6NHU) kJ/mol that is caused by a more effective delocalization of the excess charge through the uracil framework in the N1 anion. The hydration pronouncedly diminishes ΔG to the range from -0.02 (5OH6СНU) to 38.16 (5Br6NOU) kJ/mol due to the fact that the polar solvent is prone to stabilize more polar anionic states of uracils. Therefore, less polar uracil anions are more stable. We have defined the main factor influencing the N1/N3/О5/О6 distribution of anions, viz. the presence of the substituents in 5 and 6 positions of the pyrimidine ring. Herewith, the most favorable mechanism of the influence of 5-substituents has been previously defined as resonant whereas, as we found in this work, the inductive mechanism is more pronounced in the case of 6-substituents.
已使用近似IEFPCM（SMD）-TPSS/aug-cc-pVTZ 理论研究了 42 种取代尿嘧啶在气相和水溶液中 N1/N3/О5/О6 阴离子的相对稳定性。使用由 5 个水分子组成的第一水合壳模拟了尿嘧啶及其阴离子的特殊溶剂化作用。非特异性溶剂化作用根据 SMD 模型进行了计算。我们在特定和非特定水合的条件下找到了一系列相对稳定性。该系列根据 N3 阴离子相对稳定性的增加进行排序。在气相中，N1 阴离子明显比其 N3 对应物更稳定：ΔG 值的范围为 19.54（5OH6CHU）至 83.14（5NO6NHU）kJ/mol，这是由于 N1 阴离子中过剩电荷通过尿嘧啶骨架更有效地离域化所致。由于极性溶剂易于稳定尿嘧啶的更极性阴离子态，因此水合作用将 ΔG 明显降低至-0.02（5OH6CHU）至 38.16（5Br6NOU）kJ/mol 的范围。因此，极性较小的尿嘧啶阴离子更稳定。我们已经确定了影响阴离子 N1/N3/О5/О6 分布的主要因素，即嘧啶环 5 和 6 位上取代基的存在。在此，以前将 5-取代基的影响的最有利机制定义为共振，然而，正如我们在这项工作中发现的那样，6-取代基的诱导机制更为明显。
