NaOH水溶液中浓度依赖的质子转移机制：从受主驱动到供体驱动及返回,The Journal of Physical Chemistry Letters

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NaOH水溶液中浓度依赖的质子转移机制：从受主驱动到供体驱动及返回
The Journal of Physical Chemistry Letters ( IF 4.8 ) Pub Date : 2016-08-11 00:00:00 , DOI: 10.1021/acs.jpclett.6b01448
Matti Hellström ₁ , Jörg Behler ₁

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质子转移过程在化学的许多领域中都起着重要的作用。在稀碱性水溶液，从水分子的质子转移到氢氧根离子是由“presolvation”的帮助下，即，修改绕质子接收OH的氢键性环境的热波动^-离子变得更类似于中性H的_2个O分子。然而，特别是在高浓度下，对潜在机理尤其是抗衡离子的作用了解甚少。作为一个典型案例，我们使用分子动力学模拟研究NaOH水溶液，该分子动力学模拟采用了由密度泛函理论参考数据构建的反应性高维神经网络电位。我们发现，随着浓度是“受驱动”，主要的质子转移机制的转变，即由OH的presolvation治理^-以“捐助方驱动”，即通过H的presolvation管辖₂ O，和背到受受体驱动的接近室温的19 mol / L的溶解度极限，这对应于仅包含约一个H ₂的极度缺乏溶剂的系统每个离子O分子。具体来说，我们鉴定，其中质子传递速率大多受OH浓度范围^-失去一个公认的氢键，OH ^-形成捐赠氢键，H ₂ ö形成一个公认的氢键，或H ₂ ö失去协调的Na ⁺。预溶剂化还表现为Na ⁺ -OH ₂距离的缩短，因为Na ⁺ “推动”了H ₂ O质子之一。

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Concentration-Dependent Proton Transfer Mechanisms in Aqueous NaOH Solutions: From Acceptor-Driven to Donor-Driven and Back

Proton transfer processes play an important role in many fields of chemistry. In dilute basic aqueous solutions, proton transfer from water molecules to hydroxide ions is aided by “presolvation”, i.e., thermal fluctuations that modify the hydrogen-bonding environment around the proton-receiving OH^– ion to become more similar to that of a neutral H₂O molecule. In particular at high concentrations, however, the underlying mechanisms and especially the role of the counterions are little understood. As a prototypical case, we investigate aqueous NaOH solutions using molecular dynamics simulations employing a reactive high-dimensional neural-network potential constructed from density functional theory reference data. We find that with increasing concentration the predominant proton transfer mechanism changes from being “acceptor-driven”, i.e., governed by the presolvation of OH^–, to “donor-driven”, i.e., governed by the presolvation of H₂O, and back to acceptor-driven near the room-temperature solubility limit of 19 mol/L, which corresponds to an extremely solvent-deficient system containing only about one H₂O molecule per ion. Specifically, we identify concentration ranges where the proton transfer rate is mostly affected by OH^– losing an accepted hydrogen bond, OH^– forming a donated hydrogen bond, H₂O forming an accepted hydrogen bond, or H₂O losing a coordinated Na⁺. Presolvation also manifests itself in the shortening of the Na⁺–OH₂ distances, in that the Na⁺ “pushes” one of the H₂O protons away.

更新日期：2016-08-11

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