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采用密度泛函B3LYP方法,在6-311G(d,p)基组水平上对6-巯基嘌呤质子转移引起的硫酮式与硫醇式互变异构反应机理进行了计算研究,获得了互变异构过程的反应焓、活化能、活化吉布斯自由能和质子转移反应的速率常数等参数。计算结果表明,6-巯基嘌呤无论是孤立分子还是一水合物,其硫酮式TP2是最稳定的异构体。计算结果同已有实验结果相符。由硫酮式通过分子内质子转移向硫醇式异构化找到4条反应通道(P1,P2,P3,P4),各通道的活化能分别为114.0,133.9,128.0,95.1 kJ·mol~(-1)。当水分子参与反应以双质子转移机理异构化时,活化能垒显著降低,各通道的活化能依次降为51.2,63.0,70.5,42.8 kJ·mol~(-1),可见,水助催化有利于硫酮式向硫醇式转变。计算结果还表明,氢键的强弱对TP2一水合物的稳定性会有一定的影响。
The pyrothione-thiol tautomerization reaction mechanism caused by the proton transfer of 6-mercaptopurine was studied at the 6-311G (d, p) basis by density functional B3LYP method. Reaction enthalpy, activation energy, rate constant of Gibbs free energy and proton transfer reaction in the variation process. The calculated results show that 6-mercaptopurine is the most stable isoform of thioketal TP2, both as an isolated molecule and as a monohydrate. The calculation results are consistent with the experimental results. The four reaction channels (P1, P2, P3 and P4) were found by the intramolecular proton transfer and thiolation of thioketone. The activation energies of the channels were 114.0, 133.9, 128.0 and 95.1 kJ · mol ~ ( -1). When the water molecule is isomerized by the bipyridine transfer mechanism, the activation energy barrier decreases significantly, and the activation energy of each channel decreases to 51.2, 63.0, 70.5 and 42.8 kJ · mol -1 in turn, showing that water-assisted catalysis Conducive to the conversion of thiol to thiol. The calculation results also show that the strength of hydrogen bonds will have a certain impact on the stability of TP2 monohydrate.