Thione-thiol tautomerization is biologically and synthetically significant proton transfer reaction. Current study analyses the effect of protic solvents on this reaction involving heterocyclic thiocarbonyl compounds having potent bioactivities such as 1,3-dihydroimidazole-2-thione, 2-thiohydantoin and 2-thiouracil. The computed catalytic effect of polar protic solvents water and methanol is explained by the favorable lone pair – antibonding orbital interactions which facilitates the required proton transfer. Microhydration study up to six water molecules has been carried out to get more insight into the explicit water-solute interaction. It has been concluded that four water molecules are enough to model explicit water-solute interaction that favorably affects the tautomerism of heterocyclic thiocarbonyl compounds. Moreover, the thione formation step of the equilibrium gets relatively more facilitated by the polar protic solvents. The results are further validated by considering a reported thiol-thione conversion in enzymatic decarboxylation reaction of 4'-phosphopantothenoylcysteine.

亚硫醇互变异构是生物学和合成上重要的质子转移反应。当前的研究分析了质子溶剂对该反应的影响，该质子溶剂涉及具有有效生物活性的杂环硫代羰基化合物，例如1,3-二氢咪唑-2-硫酮，2-硫代乙内酰脲和2-硫尿嘧啶。极性质子溶剂水和甲醇的催化作用的计算结果可通过有利的孤对-抗键轨道相互作用来解释，该相互作用促进了所需的质子转移。进行了多达六个水分子的微水化研究，以更深入地了解水与溶质之间的显式相互作用。已经得出结论，四个水分子足以模拟显式的水-溶质相互作用，从而有利地影响杂环硫代羰基化合物的互变异构现象。而且，极性质子溶剂使平衡的硫酮形成步骤相对更加容易。通过考虑报道的4'-磷酸蒽二甲酰基半胱氨酸的酶促脱羧反应中的硫醇-硫酮转化，可以进一步验证该结果。