水溶液中碳酸向强碱直接质子转移的反应机理I：酸碱配位与电荷动力学
Reaction Mechanism for Direct Proton Transfer from Carbonic Acid to a Strong Base in Aqueous Solution I: Acid and Base Coordinate and Charge Dynamics.
作者信息
Daschakraborty Snehasis, Kiefer Philip M, Miller Yifat, Motro Yair, Pines Dina, Pines Ehud, Hynes James T
机构信息
Department of Chemistry and Biochemistry, University of Colorado , Boulder, Colorado 80309-0215, United States.
Department of Chemistry, Ben-Gurion University of the Negev , P.O. Box 653, Beer-Sheva 84105, Israel.
出版信息
J Phys Chem B. 2016 Mar 10;120(9):2271-80. doi: 10.1021/acs.jpcb.5b12742. Epub 2016 Mar 2.
Protonation by carbonic acid H2CO3 of the strong base methylamine CH3NH2 in a neutral contact pair in aqueous solution is followed via Car-Parrinello molecular dynamics simulations. Proton transfer (PT) occurs to form an aqueous solvent-stabilized contact ion pair within 100 fs, a fast time scale associated with the compression of the acid-base hydrogen-bond (H-bond), a key reaction coordinate. This rapid barrierless PT is consistent with the carbonic acid-protonated base pKa difference that considerably favors the PT, and supports the view of intact carbonic acid as potentially important proton donor in assorted biological and environmental contexts. The charge redistribution within the H-bonded complex during PT supports a Mulliken picture of charge transfer from the nitrogen base to carbonic acid without altering the transferring hydrogen's charge from approximately midway between that of a hydrogen atom and that of a proton.
通过Car-Parrinello分子动力学模拟，研究了水溶液中中性接触对中强碱甲胺（CH3NH2）被碳酸（H2CO3）质子化的过程。质子转移（PT）在100飞秒内发生，形成了一种由水溶剂稳定的接触离子对，这是一个与酸碱氢键（H键）压缩相关的快速时间尺度，而酸碱氢键压缩是一个关键反应坐标。这种快速的无势垒质子转移与碳酸-质子化碱的pKa差异一致，该差异极大地有利于质子转移，并支持了在各种生物和环境背景下，完整的碳酸作为潜在重要质子供体的观点。质子转移过程中氢键复合物内的电荷重新分布支持了Mulliken电荷转移图景，即电荷从氮碱转移到碳酸，而转移氢的电荷在氢原子和质子电荷的大约中间位置没有改变。
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