Gomez Axel, Thompson Ward H, Laage Damien
PASTEUR, Department of Chemistry, École normale supérieure, PSL University, Sorbonne Université, CNRS, Paris, France.
Department of Chemistry, University of Kansas, Lawrence, KS, USA.
Nat Chem. 2024 Nov;16(11):1838-1844. doi: 10.1038/s41557-024-01593-y. Epub 2024 Aug 20.
The transport of excess protons in water is central to acid-base chemistry, biochemistry and energy production. However, elucidating its mechanism has been challenging. Recent nonlinear vibrational spectroscopy experiments could not be explained by existing models. Here we use both vibrational spectroscopy calculations and neural-network-based molecular dynamics simulations that account for nuclear quantum effects for all atoms to determine the proton transport mechanism. Our simulations reveal an equilibrium between two stable proton-localized structures with distinct Eigen-like and Zundel-like hydrogen-bond motifs. Proton transport follows a three-step mechanism gated by two successive hydrogen-bond exchanges: the first reduces the proton-acceptor water coordination, leading to proton transfer, and the second, the rate-limiting step, prevents rapid back-transfer by increasing the proton-donor coordination. This sequential mechanism is consistent with experimental characterizations of proton diffusion, explaining the low activation energy and the prolonged intermediate lifetimes in vibrational spectroscopy. These results are crucial for understanding proton dynamics in biochemical and technological systems.
水中过量质子的传输是酸碱化学、生物化学和能量产生的核心。然而，阐明其机制一直具有挑战性。最近的非线性振动光谱实验无法用现有模型解释。在这里，我们使用振动光谱计算和基于神经网络的分子动力学模拟，对所有原子考虑核量子效应，以确定质子传输机制。我们的模拟揭示了两种具有不同类本征和类尊德尔氢键基序的稳定质子局域结构之间的平衡。质子传输遵循由两个连续氢键交换控制的三步机制：第一步减少质子受体水的配位，导致质子转移，第二步是限速步骤，通过增加质子供体配位来防止快速反向转移。这种顺序机制与质子扩散的实验表征一致，解释了振动光谱中低活化能和延长的中间寿命。这些结果对于理解生化和技术系统中的质子动力学至关重要。
