Campetella Marco, Montagna Maria, Gontrani Lorenzo, Scarpellini Eleonora, Bodo Enrico
Chemistry Department, University of Rome "La Sapienza", Piazzale A. Moro 5, 00185, Rome, Italy.
Phys Chem Chem Phys. 2017 May 17;19(19):11869-11880. doi: 10.1039/c7cp01050h.
We have explored by means of ab initio molecular dynamics two ionic liquids based on the combination of a choline cation with deprotonated cysteine and aspartic acid anions. While the combination of the strong base choline with various other amino-acids leads to the formation of a highly ionized medium where proton transfer is negligible, the presence of additional protic functions on the SH and COOH groups leads to an unexpected and interesting behavior and to a sizable migration of their acidic protons onto the NH basic terminals. As far as we know this is the first time that such proton migration, which in water leads to the well-known zwitterionic form of aminoacids, is observed to take place in their ionized, anionic form. We analyze in detail such dynamical effects using accurate ab initio molecular dynamics computations validated through comparison with X-ray scattering data.
我们通过从头算分子动力学方法研究了两种离子液体，它们是由胆碱阳离子与去质子化的半胱氨酸和天冬氨酸阴离子组合而成。强碱胆碱与其他各种氨基酸结合会形成高度电离的介质，其中质子转移可忽略不计，但SH和COOH基团上额外的质子功能会导致意想不到且有趣的行为，以及它们的酸性质子大量迁移到NH碱性末端。据我们所知，这是首次观察到这种质子迁移现象，而在水中这种迁移会导致氨基酸形成众所周知的两性离子形式，此次是在其离子化的阴离子形式中发生。我们通过与X射线散射数据比较验证的精确从头算分子动力学计算，详细分析了这种动力学效应。
