We employed the generalized energy-based fragmentation (GEBF) approach to investigate the gas-phase structures of B-DNA double-helices up to 10 base pairs at several theoretical levels. By comparing the results obtained using the M06-2X functional and other methods (including the B3LYP, B3LYP-vdW, and TPSS functionals), we found that the absence of stacking interactions could lead to the enlargement of the vertical distance between adjacent bases. The magnitude of this enlargement of the vertical distance quickly decreases as the length of the double-helix increases. The gas-phase stabilization of the double-helical structure of B-DNA is a cooperative effect, in which hydrogen bonding plays a more important role than stacking interaction does up to 10 base pairs.%采用密度泛函理论,将基于能量的分子片方法(GEBF)应用于气相中优化B型脱氧核糖核酸(碱基对数目N=2,5,10)双螺旋构型的结构。通过比较M06-2X泛函和其他方法(B3LYP、B3LYP-vdW和TPSS泛函)的结果,发现不考虑碱基之间的π-π堆积作用将会导致碱基之间的纵向距离拉长。随着体系双螺旋链长的增加,没有考虑碱基堆积作用而导致的相邻碱基纵向距离拉长的程度快速衰减。计算表明,气相中B-DNA双螺旋结构的稳定性来源于其作用力(主要是氢键和π-π堆积作用)的协同性,对不多于10组碱基对的体系而言,其氢键的贡献明显大于碱基堆积作用。
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