• 关键词：胸腺嘧啶  溴化1-烷基-3-甲基咪唑类离子液体  氢键  π-π⁺堆积作用

• 基金项目：浙江省自然科学基金（No.LY16B070006）；国家自然科学基金（No.21177098）

• 曹建平
• 温州医科大学, 药学院, 温州 325035

• 余德观
• 1. 温州医科大学, 药学院, 温州 325035;2. 温州市人民医院, 药学部, 温州 325000

• 陈媛媛
• 温州医科大学, 药学院, 温州 325035

• 黄罗仪
• 温州医科大学, 药学院, 温州 325035

• 王朝杰
• 温州医科大学, 药学院, 温州 325035

• 摘要：溴化咪唑类离子液体的生物小分子作用机制亟待探索.本文采用M06-2X/6-311++G（2d，p）/PCM/water理论方法计算了研究胸腺嘧啶（T）与溴化1-烷基-3-甲基咪唑类离子液体（[C_nmim]Br，n=2、4、6、8、10）相互作用形成的T-[C_nmim]⁺、T-Br^-、T-[C_nmim]Br和T-2[C_nmim]Br体系的结构和能量学特征.结果表明T与阴阳离子间形成典型构型的稳定顺序是：共面 < 垂直 < 堆积（T-[C_nmim]⁺），top < front（T-Br^-），T-[C_nmim]⁺ < T-Br^- < T-[C_nmim]Br < T-2[C_nmim]Br.T与Br^-之间的氢键作用与咪唑阳离子伴随弱氢键的堆积环境更有利，阳离子烷基链长影响不明显.在堆积构型中胸腺嘧啶与咪唑阳离子以π-π⁺色散吸引为主，并伴随C-H…O和C-H…π弱氢键作用，部分碱基电子转移至阳离子（π→π⁺），其NBO分析显示稳定化能主要来自π→π^+*（ΣE_π→π+*²）轨道作用的贡献；T与Br^-之间以静电吸引为主，溴离子向胸腺嘧啶转移电子，稳定化能源于lp_Br→σ_N-H^*.

• Abstract：The known information on the genotoxic mechanism about 1-alkyl-3-methylimidazolium bromide ionic liquids ([C_nmim]Br) is as yet limited. With the aim of exploration of the preferred interaction sites and arrangements of thymine with the imidazolium cations and bromine anion, we have performed a systematic study of geometries, energetics, and electronic structures of the ionized thymine (T) clusters by means of the M06-2X/6-311++G(2d, p) theoretical calculation with the Polarizable Continuum Model (PCM, ε=78.4). The binding (E_bind) and interaction (E_int) energies show the same trend for the arrangements of thymine with cations (T-[C_nmim]⁺):stacking > perpendicular > coplanar, and the Br^- anion (T-Br^-):front > top. For the most stable ionization of thymine with ion (or pairwise), the stacking model between thymine and[C_nmim]⁺ cations accompanying by weaker hydrogen bonds (HBs) which are always far less favorable than the HB interaction between the nucleobase and Br^- anion (T-[C_nmim]⁺ -). These results are in concordance with the trends obtained for the clusters, irrespective of with the growing size, or increasing alkyl chains in the imidazolium cation. Analyzing the topological features of electronic density at critical points, the sum of electronic densities calculated at bond and cage critical points (Σρ_BCP and Σρ_CCP) between thymine and π⁺ are greater than the C-H…O or C-H…π H-bonds interaction, indicating that the π-π⁺ dispersion interaction is stronger than the weak ionic HBs in T-[C_nmim]⁺. The ρ_BCP for the N-H…Br bond between thymine and Br^- anion shows the dominating electrostatic attraction in nature. Natural bond orbital analysis combined with natural population atoms reveals that the more electron donation occurs from the lone pair of the Br^- anion to the N-H σ^* orbital (lp_Br→σ_N-H^*), and the charge transfer is from the anion to thymine, while the ΣE² values of π^*←π⁺ interaction are less than those of π→π^+*, and the charge transfer occurs primarily from the neutral π system to the positive π⁺ cation.

• Key words：thymine  1-alkyl-3-methylimidazolium bromide  hydrogen bonds  π-π⁺ stacking

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