是什么驱动离子在水溶液中纳米金刚石表面的吸附？
What drives adsorption of ions on surface of nanodiamonds in aqueous solutions?
摘要：
尚不清楚是什么驱动了爆轰纳米金刚石（DND）上的离子吸附，这在其靶向治疗应用中对化疗药物在DND表面上的装载（卸载）起关键作用。此外，还没有研究吸附离子对不同表面化学性质的DND周围水的水合层的影响。通过一系列的分子动力学模拟，我们发现，水亲和力匹配规律一般很好地解释了离子在DND表面官能团上的吸附模式。取决于离子的水亲和力是否与表面官能团的水亲和力匹配，前者主要与后者形成接触离子对（CIP）或溶剂共享离子对（SIP）。在这方面，Na $^{+}$和Mg $^{2+}$分别具有与${-}$ COO $^{-}$官能团形成CIP和SIP缔合的最高倾向。然而，在DND ${-}$ COOH上有84个${-}$ COO $^{-}$基团的极端情况下，我们观察到很少的Mg $^{2+}$ ${-}$ COO $^{-}$ CIP缔合，对此我们提出了基于熵增益的假设。此外，Mg $^{2+}$和在较小程度上Ca $^{2+}$与带电荷的DND ${-}$ COOH表面上的${-}$ COO $^{-}$官能团合作导致水在DND的第一水合层中相对高的停留时间。这项研究还提供了第一手的分子水平上的洞察力，在附近的带正电的DND ${-}$ H，在先前的实验研究尚未达成共识的水的优先取向。
英文摘要：
It is not yet clear what drives the adsorption of ions on detonation nanodiamonds (DNDs), which plays a critical role on the loading (unloading) of chemotherapeutic drugs on (from) the surface of DNDs in their targeted therapy applications. Furthermore, effects of adsorbed ions on the hydration layers of water around DNDs with different surface chemistries have not been studied yet. Through a series of Molecular Dynamics simulations, we found out that the law of matching water affinity generally explains well the adsorption patterns of ions onto the surface functional groups of DNDs. Depending on whether the water affinity of the ion matches with that of the surface functional group or not, the former predominantly forms either Contact Ion-Pair (CIP) or Solvent-shared Ion-Pair (SIP) with the latter. In this regard, Na$^{+}$ and Mg$^{2+}$ have the highest tendencies to form, respectively, CIP and SIP associations with ${-}$COO$^{-}$ functional groups. In the extreme case of 84 ${-}$COO$^{-}$ groups on DND${-}$COOH, however, we observed few Mg$^{2+}$${-}$COO$^{-}$ CIP associations, for which we have proposed a hypothesis based on the entropy gains. Furthermore, Mg$^{2+}$ and to a lesser extent Ca$^{2+}$ in cooperation with ${-}$COO$^{-}$ functional groups on the surface of charged DND${-}$COOH lead to relatively high residence times of water in the first hydration layer of DND. This study also provides a firsthand molecular level insight about the preferential orientation of water in the vicinity of positively charged DND${-}$H, on which prior experimental studies have not yet reached a consensus.
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