Solid crystal materials with selective ion channel function based on crown ether

Ion channels of biomembrane are the passive transport channels of inorganic ions across the membrane Through the inflow and outflow of charged ions, the ion channel can change the voltage inside and outside the cell membrane, which makes the cell react to the external stimulation instantaneously In recent years, many scientists have prepared some porous materials with ion channel function by artificial synthesis, such as porous coordination polymers, zeolites and supramolecular aggregates However, the channels of these materials are limited to the transport and exchange of water molecules and neutral organic molecules Therefore, the selectivity of the synthetic channel has been unable to match the ion channel of the biofilm Figure 1 Structure of crystal material 1 and schematic diagram of ion exchange process (picture source: angel Chem Int ed.) recently, Professor Sadafumi Nishihara, Department of chemistry, Hiroshima University, Japan reported a solid crystal material Li 2 ([18] crown-6) 3 [Ni (dmit) 2] 2 (H 2O) 4 (1) based on crown ether (Figure 1) The material can selectively exchange potassium ions, and its physical properties change greatly before and after ion exchange The crystal material is mainly composed of two parts, one is the main compound 18-crown-6, the other is the common building unit [Ni (dmit) 2] - in the molecular magnet Through the combination of the two, we have successfully prepared the crystal materials with selective ion exchange properties This achievement was published in German Applied Chemistry (DOI: 10.1002 / anie 201813709) under the title of "selective ion exchange induced by supramolecular channel in crystal state" Fig 2 Infrared spectrum of crystal materials 1, 1-k and 1-na (picture source: angelw Chem Int ed.) Firstly, the author preliminarily studied the exchange performance of crystal materials for potassium and sodium ions (Fig 2) The positions of C-O-C bond vibration peaks in crown ethers will vary with their binding to alkali metal ions Therefore, the infrared spectra of crystal materials (1-k, 1-na) soaked in the same concentration of potassium chloride and sodium chloride solution are compared The results show that the C-O-C vibration peak of crystal material 1-k soaked in potassium ion solution moves from 1104cm-1 to 1114cm-1, and its peak shape changes from double peak to single peak In addition, the O-H peak of water molecules in the crystal structure will change obviously after ion exchange However, 1-na does not show similar changes, which indicates that the crystal material may only exchange potassium ions selectively Figure 3 EPMA analysis of 1-k and 1-na crystal materials soaked in potassium chloride and sodium chloride solution (picture source: angelw Chem Int ed.), followed by electron probe microanalysis (EPMA) and inductively coupled plasma atomic emission spectroscopy (ICP-AES) ）The ion exchange properties of crystal materials are analyzed in detail EPMA results show that after soaking in the corresponding solution for one day, the K / Ni ratio in the crystal material 1-k is almost 1, while the Na / Ni ratio in 1-na is 0 (Fig 3) More accurate ICP-AES results show that the K / Ni ratio in 1-k is very close to 1, and no signal of lithium ion is detected in 1-k, which shows that 1 can exchange potassium ion selectively and has high efficiency Fig 4 After ion exchange of crystal material 1 under different conditions (picture source: angelw Chem Int ed.), the author optimized the ion exchange conditions and explored the ion exchange of crystal material in the presence of potassium, sodium and lithium ions (Fig 4) The results show that no matter the concentration of sodium ion, when the concentration of potassium ion is more than 0.1 M, the crystal material can exchange it 100%; when the concentration of potassium ion is less than 1 mm, neither potassium ion nor sodium ion can enter the crystal material Similarly, when the solution contains both potassium and lithium ions, the crystal materials only exchange potassium ions selectively In addition, when the concentration of potassium ion is 10 mm, only part of the potassium ion in the solution is exchanged Different from ordinary porous materials, this kind of crystal material has obvious boundary in its structure after insufficient exchange, and the boundary is perpendicular to the direction of ion channel In addition, after ion exchange, the physical properties of the crystal also changed obviously, such as the increase of cell size, the decrease of magnetic interaction and the decrease of ionic conductivity Highlights of the paper: a solid crystal material was prepared by crown ether and [Ni (dmit) 2] - the crystal material can selectively exchange potassium ions, and its physical properties changed significantly before and after exchange Full text author: Katsuya Ichihashi, Daisuke Konno, Kseniya Yu Maryunina, Katsuya Inoue, Kazuhiro Toyoda, Shogo Kawaguchi, Yoshiki Kubota, Yoko tatewaki, Tomoyuki Akutagawa, Takayoshi Nakamura and Sadafumi Nishihara.