Institute of Organic Chemistry with Center of Phytochemistry , Bulgarian Academy of Sciences , 1113 Sofia , Bulgaria.
J Phys Chem B. 2019 Jan 24;123(3):622-630. doi: 10.1021/acs.jpcb.8b11316. Epub 2019 Jan 14.
Syn- and anti-conformers of four tautomer structures of inosine were studied in the gas phase and in solvent water to investigate the possibility of hydrogen bonding and tautomeric conversion. It was found that in the gas phase and in water solution the most stable is the syn-conformer of the 6-keto tautomer followed by its anti-conformer and syn-conformer of the 6-enol form. In the gas phase, the percent content of syn- and anti-conformers is 83.77 and 12.86%, respectively, whereas syn-enol tautomer is calculated to be 2.54%. However, in water solution the syn-conformer of the keto tautomer is 99.9%. The water-assisted proton transfer process in inosine was investigated using ab initio MP2 and SCS-MP2 quantum chemical approaches. Solute-solvent clusters containing an inosine molecule and five water molecules embedded in the "bulk" solvent treated as polarizable continuum (the CPCM/MP2/6-31+G(d,p) level of theory) were explored. The energy barrier of the water-assisted proton transfer reaction in inosine is found to be 12.9 kcal mol and the rate constant ( k = 6.68 × 101 s) is sufficiently large to generate the 6-enol tautomer. From the reaction profile of the proton transfer we can conclude that the process is realized through the asynchronous concerted mechanism.
在气相和溶剂水中研究了肌苷的四种互变异构体的顺式和反式构象，以研究氢键和互变异构转换的可能性。结果发现，在气相和水溶剂中，最稳定的是 6-酮互变异构体的顺式构象，其次是其反式构象和 6-烯醇形式的顺式构象。在气相中，顺式和反式构象的百分比含量分别为 83.77%和 12.86%，而烯醇互变异构体的计算值为 2.54%。然而，在水溶液中，6-酮互变异构体的顺式构象为 99.9%。使用从头算 MP2 和 SCS-MP2 量子化学方法研究了肌苷中的质子转移过程。探索了含有肌苷分子和五个水分子的溶剂-溶质簇，这些水分子嵌入“本体”溶剂中，被视为可极化连续体（CPCM/MP2/6-31+G（d，p）理论水平）。发现肌苷中质子转移的水辅助反应的能垒为 12.9 kcal/mol，速率常数（k=6.68×101 s）足够大，可以产生 6-烯醇互变异构体。从质子转移的反应轮廓可以得出结论，该过程是通过异步协同机制实现的。
