论文标题
水辅助质子运输在受限的纳米通道中
Water Assisted Proton Transport in Confined Nanochannels
论文作者
论文摘要
疏水性限制下的水合过量质子是纳米多孔材料和生物分子系统中电荷转运行为和反应性的关键组成部分。 Herein excess proton confinement effects are computationally investigated for sub-2 nm hydrophobic nanopores by varying the diameters (d = 0.81, 0.95, 1.09, 1.22, 1.36, 1.63, and 1.90 nm), lengths (l ~3 and ~5 nm), curvature, and chirality of cylindrical carbon nanotube (CNT) nanopores.还探索了具有不同直径段组合的CNT。限制下水分子的空间分布依赖于直径。然而，始终发现质子溶剂化和运输发生在孔壁附近的水层中，显示出水合过量质子氢氢氢的结构的“两亲性”特征。随着纳米孔直径的增加，质子传输的自由能屏障也显着降低，并且在d> 1 nm纳米孔中，质子转运几乎无屏障。在所研究的纳米孔中，Zundel阳离子（$ {H_ {5} O_ {2}}}}^{+} $）仅在D = 0.95 nm CNT（7,7）Nanopore中填充。 CNT（7,7）纳米孔内的水合过量质子和$ k^{+} $的存在分别诱导水密度增加40％和20％。 $ k^{+} $通过CNT纳米孔的传输在自由能屏障中的运输量也比质子传输始终高。有趣的是，多余的质子电荷缺陷分布的演变揭示了d = 0.81 nm cnt（6,6）纳米孔（或段）中的“冷冻”单线构型（或段），该水合只能通过Grotthuss机制穿梭过多的质子。车辆扩散与“平坦”自由能区域和较宽的纳米孔中的质子传输有关，质子主要不主要沿轴向沿轴向方向穿梭。
Hydrated excess protons under hydrophobic confinement are a critical component of charge transport behavior and reactivity in nanoporous materials and biomolecular systems. Herein excess proton confinement effects are computationally investigated for sub-2 nm hydrophobic nanopores by varying the diameters (d = 0.81, 0.95, 1.09, 1.22, 1.36, 1.63, and 1.90 nm), lengths (l ~3 and ~5 nm), curvature, and chirality of cylindrical carbon nanotube (CNT) nanopores. CNTs with a combination of different diameter segments are also explored. The spatial distribution of water molecules under confinement are diameter-dependent; however, proton solvation and transport is consistently found to occur in the water layer adjacent to the pore wall, showing an "amphiphilic" character of the hydrated excess proton hydronium-like structure. The proton transport free energy barrier also decreases significantly as the nanopore diameter increases and proton transport becomes almost barrierless in the d > 1 nm nanopores. Among the nanopores studied, the Zundel cation (${H_{5}O_{2}}^{+}$) is populated only in the d = 0.95 nm CNT (7,7) nanopore. The presence of the hydrated excess proton and $K^{+}$ inside the CNT (7,7) nanopore induces a water density increase by 40 and 20%, respectively. The $K^{+}$ transport through CNT nanopores is also consistently higher in free energy barrier than proton transport. Interestingly, the evolution of excess protonic charge defect distribution reveals a "frozen" single water wire configuration in the d = 0.81 nm CNT (6,6) nanopore (or segment), through which hydrated excess protons can only shuttle via the Grotthuss mechanism. Vehicular diffusion becomes relevant to proton transport in the "flat" free energy regions and in the wider nanopores, where protons do not primarily shuttle in the axial direction.
