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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >UV-induced generation of rare tautomers of 2-thiouracils: A matrix isolation study
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UV-induced generation of rare tautomers of 2-thiouracils: A matrix isolation study

机译：紫外线诱导的2-硫尿嘧啶罕见互变异构体的生成：基质分离研究

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Unimolecular photoisomerization reactions were studied for 2-thiouracil, 6-aza-2-thiothymine, 1-methyl-2-thiouracil, and 3-methyl-2-thiouracil isolated in low-temperature Ar matrixes. The IR spectra have revealed that before UV irradiation all the matrix-isolated compounds adopted exclusively the oxo-thione tautomeric form. Upon UV (lambda > 320 nm) irradiation of the matrixes, two oxo-thiol photoproducts were generated for monomeric 2-thiouracil as well as for monomeric 6-aza-2-thiothymine. Generation of these products corresponds to transfer of a proton from either the N(1)-H or N(3)-H group to the sulfur atom of the C(2)=S thiocarbonyl moiety. The first of the above reactions was photoreversible. As a consequence, after prolonged UV irradiation most of the material was transformed into the oxo-thiol-N(1)H form. The hydroxy-thiol tautomers of 2-thiouracil and 6-aza-2-thiothymine were also photogenerated as minor products. For 1-methyl-2-thiouracil and 3-methyl-2-thiouracil, thione -> thiol phototautomeric reactions yielded the oxo-thiol isomers of the compounds. Since these reactions were photoreversible, the final stages of the photoinduced processes corresponded, for both methylated 2-thiouracils, to photostationary states. All the products of the investigated photoreactions were identified by comparison of their IR spectra with the spectra calculated at the DFT-(B3LYP)/6-311++G(2d,p) level.
机译：研究了在低温Ar基质中分离的2-硫尿嘧啶，6-氮杂-2-硫胸腺嘧啶，1-甲基-2-硫尿嘧啶和3-甲基-2-硫尿嘧啶的单分子光异构化反应。红外光谱表明，在紫外线照射前，所有与基质分离的化合物均采用氧代-硫酮互变异构形式。在对基质进行紫外线（λ> 320 nm）照射后，生成了两个2-硫氧嘧啶单体以及6-氮杂-2-硫胸腺嘧啶单体的氧代硫醇光产物。这些产物的产生对应于质子从N（1）-H或N（3）-H基团转移至C（2）＝ S硫代羰基部分的硫原子。上述反应中的第一个是光可逆的。结果，长时间的紫外线照射后，大多数材料都转变为氧代硫醇-N（1）H形式。 2-硫尿嘧啶和6-氮杂-2-硫胸腺嘧啶的羟基-硫醇互变异构体也作为次要产物被光生。对于1-甲基-2-硫尿嘧啶和3-甲基-2-硫尿嘧啶，硫酮→硫醇光互变异构反应产生化合物的氧代-硫醇异构体。由于这些反应是光可逆的，因此对于甲基化的2-硫尿嘧啶，光诱导过程的最后阶段对应于光平稳状态。通过比较其红外光谱与在DFT-（B3LYP）/ 6-311 ++ G（2d，p）水平上计算的光谱，可以确定所研究的光反应的所有产物。

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