Kameta Naohiro, Ding Wuxiao, Dong Jiuchao
Nanomaterials Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan.
ACS Omega. 2017 Sep 30;2(9):6143-6150. doi: 10.1021/acsomega.7b00838. Epub 2017 Sep 26.
By means of a two-step self-assembly process involving three components, including short poly(ethylene glycol) (PEG) chains, we produced two different types of molecular monolayer nanotubes: nanotubes densely functionalized with PEG chains on the outer surface and nanotubes densely functionalized with PEG chains in the nanochannel. Turbidity measurements and fluorescence spectroscopy with an environmentally responsive probe suggested that the PEG chains underwent dehydration when the nanotubes were heated above 44-57 °C and rehydration when they were cooled back to 25 °C. Dehydration of the exterior or interior PEG chains rendered them hydrophobic and thus able to effectively extract hydrophobic amino acids from the bulk solution. Rehydration of the PEG chains restored their hydrophilicity, thus allowing the extracted amino acids to be squeezed out into the bulk solutions. The nanotubes with exterior PEG chains exhibited selectivity for all of the hydrophobic amino acids, whereas the interior PEG chains were selective for hydrophobic amino acids with an aliphatic side chain over hydrophobic amino acids with an aromatic side chain. The higher selectivity of the latter system is attributable that the extraction and back-extraction processes involve encapsulation and transportation of the amino acids in the nanotube channel. As the result, the latter system was useful for separation of peptides that differed by only a single amino acid, whereas the former system showed no such separation ability.
通过一个涉及三个组分的两步自组装过程，包括短聚乙二醇（PEG）链，我们制备了两种不同类型的分子单层纳米管：外表面密集功能化有PEG链的纳米管和纳米通道中密集功能化有PEG链的纳米管。浊度测量以及使用环境响应探针的荧光光谱表明，当纳米管加热到44 - 57°C以上时，PEG链会发生脱水，而当冷却回到25°C时会重新水化。外部或内部PEG链的脱水使其具有疏水性，从而能够有效地从本体溶液中提取疏水性氨基酸。PEG链的重新水化恢复了它们的亲水性，从而使提取的氨基酸能够被挤出到本体溶液中。具有外部PEG链的纳米管对所有疏水性氨基酸都表现出选择性，而内部PEG链对具有脂肪族侧链的疏水性氨基酸比对具有芳香族侧链的疏水性氨基酸更具选择性。后一种体系的较高选择性归因于提取和反萃取过程涉及纳米管通道中氨基酸的包封和运输。结果，后一种体系可用于仅相差一个氨基酸的肽的分离，而前一种体系没有这种分离能力。
