对爆轰纳米金刚石周围水的氢键的原子见解：表面化学和溶解离子的影响
Atomistic insights into hydrogen bonds of water around detonation nanodiamonds: effects of surface chemistry and dissolved ions
摘要：
关于爆轰纳米金刚石（DND）的表面化学对水的氢键（HB）的影响的先前研究没有明确区分三大类HB：水位点HB（HB $^{(s)}$）、DND的水合层中的水-水HB（HB $^{(h)}$）和本体区域中的水-水HB（HB $^{(b)}$）。此外，尚未研究溶液中溶解的离子对上述HB的影响。在这项研究中，我们解决了这些问题，通过分子动力学模拟。研究中的每个系统都含有一个单一的DND，该DND用纯-H或用-H和-NH $_2$、-COOH或-OH基团之一的混合物官能化。然后，将产物溶解在0.1 M的KCl、NaCl、CaCl $_2$或MgCl $_2$盐中的任何一种的水溶液中。除DND-OH为电中性外，所有DND在溶液中均以带电或中性粒子的形式存在。而具有+56净电荷的DND-H诱导最强的HB $^{(h)}$，向DND-H添加+28电荷导致HB $^{(h)}$强度下降，并且变得与我们在DND-OH周围观察到的HB $^{(h)}$强度相同。仅考虑中性DND，HB $^{(h)}$强度按DND-H $\approx$ DND-COOH < DND-OH < DND-NH $_2$的顺序增加。对于带负电荷的DND-COOH的情况，虽然在NaCl或KCl溶液中的HB $^{(h)}$比HB $^{(b)}$稍弱，但与HB $^{(b)}$相比，对应于CaCl $_2$或MgCl $_2$溶液的HB $^{(h)}$强度增强。有趣的是，Mg $^{2+}$和在较小程度上在带电DND-COOH周围的Ca $^{2+}$与本研究中最强的HB $^{(s)}$相关。
英文摘要：
Prior studies on the effects of surface chemistry of detonation nanodiamonds (DNDs) on Hydrogen Bonds (HBs) of water have not unambiguously distinguished among three broad categories of HBs: water-site HBs (HB$^{(s)}$), water-water HBs in hydration layers of DNDs (HB$^{(h)}$), and water-water HBs in the bulk region (HB$^{(b)}$). Furthermore, the effects of dissolved ions in the solution on the aforementioned HBs have not been studied yet. In this study, we addressed these issues via Molecular Dynamics simulations. Each system under study contained a single DND that was functionalized either with purely -H or with a mixture of -H and one of -NH$_2$, -COOH, or -OH groups. Then, the product was dissolved in 0.1M aqueous solution of any of KCl, NaCl, CaCl$_2$, or MgCl$_2$ salts. All DNDs except for DND-OH, which was charge neutral, existed as either a charged or a neutral particle in the solution. Whereas DND-H with +56 net charges induced the strongest HB$^{(h)}$, the addition of +28 charges to DND-H led to a drop in HB$^{(h)}$ strength and became identical to what we observed for HB$^{(h)}$ strength around DND-OH. Considering only neutral DNDs, HB$^{(h)}$ strength increased in the sequence as DND-H $\approx$ DND-COOH < DND-OH < DND-NH$_2$. For the case of the negatively charged DND-COOH, while HB$^{(h)}$ in either NaCl or KCl solution was slightly weaker than HB$^{(b)}$, HB$^{(h)}$ strength corresponding to CaCl$_2$ or MgCl$_2$ solutions were enhanced compared to HB$^{(b)}$. Interestingly, Mg$^{2+}$ and to a lesser extent Ca$^{2+}$ around the charged DND-COOH were associated with the strongest HB$^{(s)}$in this study.
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