物理化学学报 >> 1988, Vol. 4 >> Issue (05): 461-465.doi: 10.3866/PKU.WHXB19880505

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MINDO/3研究胞嘧啶异构体间异构化反应——Ⅲ. N3-氢-4-氨基-2-羰基胞嘧啶与异4-氨基-2-羟基胞嘧啶异构化反应

洪三国; 冯文林; 傅孝愿   

  1. 北京师范大学化学系
  • 收稿日期:1986-12-23 修回日期:1987-05-25 发布日期:1988-10-15
  • 通讯作者: 傅孝愿

MINDO/3 STUDY OF THE TAUTOMERIC REACTIONS OF THE TAUTOMERS OF CYTOSINE Ⅲ. THE TAUTOMERIC REACTION OF N3-H-4-NH2-2-OXO-CYTOSINE AND 4-NH2-2-OH-ISOCYTOSINE

Hong Sanguo; Feng Wenlin; Fu Xiaoyuan*   

  1. Quantum Chemistry Laboratory; Dept. of Chem. Beijing Normal University
  • Received:1986-12-23 Revised:1987-05-25 Published:1988-10-15
  • Contact: Fu Xiaoyuan

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摘要： 本文采用MINDO/3方法研究N_3-氢-4-氨基-2-羰基胞嘧啶与异4-氨基-2-羟基胞嘧啶异构化反应途径。对所研究的分子体系运用能量梯度法, 给出了计算优化的几何构型。用Powell法优化了过渡态几何构型, 并给出了该异构化反应的IRC。计算表明, 前者比后者在能量上稳定4.9 kcal mol~(-1), 正反应与逆反应的活化势垒分别为43.4和38.5kcal_mol~(-1)。本文对几个胞嘧啶异构化反应的物理实质也作了总结, 试图揭示该类反应的一致性规律。

Abstract: The molecular structures of 4-NH_2-2-OH-isocytosine (for short, iso-lactim) and N_3-H-4-NH_2-2-OXO-cytosine (for short, iso-lactam) have been optimized by MINDO/3. Iso-lactam is more stable than iso-lactim by ΔE=4.9kcal mol~(-1).
The geometric parameters of the transition state have been optimized by Powell's procedure which is contained in MINDO/3 program. The reaction pathway of the iso-lactam<=>iso-lactim has been studied by K. Fukui's IRC theory. The activation energies are 43.4 kcal mol~(-1) and 38.5 kcal mol~(-1) for the forward and backward reaction, respectively. An electron transfer scheme has been suggested to explain the nature of the tautomeric reactions of the tautomers of cytosine.