Department of Chemistry and Biochemistry, University of Maryland, College Park, MD, 20742, USA.
Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA.
Nat Commun. 2021 Jan 12;12(1):310. doi: 10.1038/s41467-020-20587-1.
Molecular sieving may occur when two molecules compete for a nanopore. In nearly all known examples, the nanopore is larger than the molecule that selectively enters the pore. Here, we experimentally demonstrate the ability of single-wall carbon nanotubes with a van der Waals pore size of 0.42 nm to separate n-hexane from cyclohexane-despite the fact that both molecules have kinetic diameters larger than the rigid nanopore. This unexpected finding challenges our current understanding of nanopore selectivity and how molecules may enter a tight channel. Ab initio molecular dynamics simulations reveal that n-hexane molecules stretch by nearly 11.2% inside the nanotube pore. Although at a relatively low probability (28.5% overall), the stretched state of n-hexane does exist in the bulk solution, allowing the molecule to enter the tight pore even at room temperature. These insights open up opportunities to engineer nanopore selectivity based on the molecular degrees of freedom.
当两个分子竞争纳米孔时，可能会发生分子筛效应。在几乎所有已知的例子中，纳米孔都大于选择性进入孔的分子。在这里，我们通过实验证明了具有范德华孔径为 0.42nm 的单壁碳纳米管能够分离正己烷和环己烷-尽管这两种分子的动力学直径都大于刚性纳米孔。这一意外发现挑战了我们目前对纳米孔选择性的理解，以及分子如何进入紧密通道。从头分子动力学模拟表明，正己烷分子在纳米管孔内伸展近 11.2%。尽管在整体上发生的概率相对较低（28.5%），但在本体溶液中正己烷的伸展状态确实存在，这使得分子即使在室温下也能进入紧密的孔。这些见解为基于分子自由度来设计纳米孔选择性提供了机会。
