Xie Min, Tsai Huei-Ru, Fujii Asuka, Lee Yuan-Pern
Department of Applied Chemistry and Institute of Molecular Science, National Chiao Tung University, 1001, Ta-Hsueh Road, Hsinchu 30010, Taiwan and MOE Key Laboratory of Laser Life Science & Institute of Laser Life Science, College of Biophotonics, Guangzhou Key Laboratory of Spectral Analysis and Functional Probes, South China Normal University, Guangzhou 510631, China.
Department of Applied Chemistry and Institute of Molecular Science, National Chiao Tung University, 1001, Ta-Hsueh Road, Hsinchu 30010, Taiwan.
Phys Chem Chem Phys. 2019 Jul 24;21(29):16055-16063. doi: 10.1039/c9cp03158h.
Three-electron two-center (3e-2c) hemi-bonds play important roles in the oxidation and electron transport of proteins and are implicated to be involved in some neurodegenerative diseases. Our previous investigations on infrared (IR) spectra of (CH3SH)2+ using vacuum-ultraviolet photoionization, infrared dissociation, and time-of-flight detection have shown that (CH3SH)2+ is (3e-2c)-bonded. To investigate the influence of the solvent molecules on the (3e-2c)-bonded (CH3SH)2+ in a supersonic jet, we added H2O or (CH3)2CO or NH3 or (CH3SH)n (n = 1-4) to (CH3SH)2+ and investigated their IR action spectra. The (3e-2c)-bonded (CH3SH)2+ ion core was maintained when a molecule of H2O or (CH3)2CO or CH3SH binds, indicating that the ion core is more stable than the hydrogen bond, whereas the (3e-2c)-bond became broken by a NH3 molecule because the proton transfer led to a more stable hydrogen-bonded structure. The spectral features of the SH-stretching modes of (CH3SH)n+ (n = 3-6) indicate that the (3e-2c)-bonded (CH3SH)2+ ion core is maintained and the first two additional CH3SH are H-bonded to the free SH groups of the ion core. For larger clusters with n = 5 and 6, the additional solvent molecules likely bind to the first solvation shell. These results show also that the (3e-2c)-bonded S∴S structure is more stable than the S∴O and S∴N structures in [(CH3SH)2-X]+ with X = H2O or (CH3)2CO or CH3SH or NH3.
三电子双中心（3e-2c）半键在蛋白质的氧化和电子传递中起着重要作用，并且被认为与某些神经退行性疾病有关。我们之前利用真空紫外光电离、红外解离和飞行时间检测对(CH3SH)2+的红外（IR）光谱进行的研究表明，(CH3SH)2+是以（3e-2c）键结合的。为了研究溶剂分子对超声速射流中以（3e-2c）键结合的(CH3SH)2+的影响，我们向(CH3SH)2+中添加了H2O或(CH3)2CO或NH3或(CH3SH)n（n = 1 - 4），并研究了它们的红外作用光谱。当一个H2O分子或(CH3)2CO分子或CH3SH分子结合时，以（3e-2c）键结合的(CH3SH)2+离子核心得以保持，这表明离子核心比氢键更稳定，而一个NH3分子会使（3e-2c）键断裂，因为质子转移导致形成了更稳定的氢键结构。(CH3SH)n+（n = 3 - 6）的SH伸缩模式的光谱特征表明，以（3e-2c）键结合的(CH3SH)2+离子核心得以保持，并且前两个额外的CH3SH通过氢键与离子核心的游离SH基团相连。对于n = 5和6的较大团簇，额外的溶剂分子可能会与第一溶剂化层结合。这些结果还表明，在[(CH3SH)2 - X]+中，其中X = H2O或(CH3)2CO或CH3SH或NH3，以（3e-2c）键结合的S∴S结构比S∴O和S∴N结构更稳定。
