Ionic liquids (ILs) including ambient-temperature molten salts, which exist in the liquid state even at room temperature, have a long research history. However, their applications were once limited because ILs were considered as highly moisture-sensitive solvents that should be handled in a glove box. After the first synthesis of moisture-stable ILs in 1992, their unique physicochemical properties became known in all scientific fields. ILs are composed solely of ions and exhibit several specific liquid-like properties, e.g., some ILs enable dissolution of insoluble bio-related materials and the use as tailor-made lubricants in industrial applications under extreme physicochemical conditions. Hybridization of ILs and other materials provides quasi-solid materials, which can be used to fabricate highly functional devices. ILs are also used as reaction media for electrochemical and chemical synthesis of nanomaterials. In addition, the negligible vapor pressure of ILs allows the fabrication of electrochemical devices that are operated under ambient conditions, and many liquid-vacuum technologies, such as X-ray photoelectron spectroscopy (XPS) analysis of liquids, electron microscopy of liquids, and sputtering and physical vapor deposition onto liquids. In this article, we review recent studies on ILs that are employed as functional advanced materials, advanced mediums for materials production, and components for preparing highly functional materials.

Transcellular Mg2+ transport across epithelia, involving both apical entry and basolateral extrusion, is essential for magnesium homeostasis, but molecules involved in basolateral extrusion have not yet been identified. Here, we show that CNNM4 is the basolaterally located Mg2+ extrusion molecule. CNNM4 is strongly expressed in intestinal epithelia and localizes to their basolateral membrane. CNNM4-knockout mice showed hypomagnesemia due to the intestinal malabsorption of magnesium, suggesting its role in Mg2+ extrusion to the inner parts of body. Imaging analyses revealed that CNNM4 can extrude Mg2+ by exchanging intracellular Mg2+ with extracellular Na+. Furthermore, CNNM4 mutations cause Jalili syndrome, characterized by recessive amelogenesis imperfecta with cone-rod dystrophy. CNNM4-knockout mice showed defective amelogenesis, and CNNM4 again localizes to the basolateral membrane of ameloblasts, the enamel-forming epithelial cells. Missense point mutations associated with the disease abolish the Mg2+ extrusion activity. These results demonstrate the crucial importance of Mg2+ extrusion by CNNM4 in organismal and topical regulation of magnesium.

In situ SEM observation of a lithium deposition and dissolution process in an all-solid-state lithium metal battery using a sulfide-based solid electrolyte (SE) was carried out. We revealed visually that the morphology of lithium deposition varies with the operating current densities. At current densities higher than 1 mA cm(-2), local lithium deposition triggers large cracks, leading to a decrease in the reversibility of lithium deposition and dissolution. On the other hand, at a low current density of 0.01 mA cm(-2), its homogeneous deposition, which enables the reversible deposition and dissolution, hardly brings about the occurrence of unfavorable cracks. These results suggest that homogeneous lithium deposition on the SE and the suppression of the growth of lithium metal along the grain boundaries inside the SE are keys to achieve the repetitive lithium deposition and dissolution reaction without deterioration of the SE.

The authors report the expansion of the temperature range of cholesteric blue phases by doping nanoparticles. When spherical gold nanoparticles with a mean diameter of 3.7 nm were doped in a blue phase-exhibiting multi-component liquid crystal mixture, the temperature range of the cholesteric blue phase increased from 0.5 to 5 C, while the clearing temperature decreased by approximately 13 C. We believe that the mechanism stabilizing the cholesteric blue phase is similar to that of polymer-stabilized cholesteric blue phases: the nanoparticles accumulate in the lattice disclinations, stabilizing the overall cholesteric blue structure.

Reaction of 1-ethyl-3-methylimidazolium chloride ͑EMICl͒ and anhydrous hydrogen fluoride gives a nonvolatile, room temperature molten salt, EMIF•2.3HF. The elemental analysis, vibrational, and nuclear magnetic resonance spectroscopy suggests the presence of oligomeric anions, (HF) n F Ϫ in the salt. The liquid is stable in air and able to be handled in a Pyrex glass vessel. The specific conductivity is 100 mS cm Ϫ1 at 298 K, which is extremely high compared with other salts of this kind. The high conductivity is realized by its low viscosity ͑4.85 cP at 298 K͒. The liquid temperature ranges from 180 to 350 K, and electrochemical window is about 3.2 V when a vitreous carbon is used for the electrode material.

Reaction of some N-alkylimidazolium chlorides with anhydrous hydrogen fluoride ͑HF͒ gave nonvolatile room temperature molten salts ͑room temperature ionic liquids͒, RMImF•2.3HF where RMIm ϭ 1,3-dimethylimidazolium ͑DMIm͒, 1-ethyl-3-methylimidazolium ͑EMIm͒, 1-methyl-3-propylimidazolium, 1-butyl-3-methylimidazolium, 1-methyl-3-pentylimidazolium, and 1-hexyl-3-methylimidazolium. Vacuum stable salts at room temperature exhibited similar stoichiometry regardless of the type of cation. In the differential scanning calorimetry ͑DSC͒ curve, DMImF•2.3HF exhibited both the freezing and melting on the cooling and heating process, respectively, while EMImF•2.3HF showed the glass transition on the cooling process and devitrification and melting on the heating process. The other salts show only the glass transition on the DSC curves. High specific conductivities, 110 and 100 mS cm Ϫ1 , were observed at 298 K for DMImF•2.3HF and EMImF•2.3HF, respectively. Introduction of the longer alkyl side chains to the imidazolium cation increased the viscosity and decreased the conductivity. These salts were stable in air and did not etch a Pyrex glass container at ambient conditions. The dissociation pressures of HF from the salts were negligibly small at ambient condition. The electrochemical windows of these salts was about 3 V.Since the discovery of the moisture stable room temperature molten salt ͑RTMS, sometimes called room temperature ionic liquid, RTIL͒, 1-ethyl-3-methylimidazolium tetrafluoroborate in 1992, 1 many RTMS have been reported by the combinations of alkylimidazolium cations and inorganic and organic fluoroanions. 2-8 The number of reports of the alkylimidazolium RTMS containing the remarkably stable bis͓͑trifluoromethyl͒sulfonyl͔ amide anion have been increasing in the last five years. These salts are single salts containing only one kind of cation and anion. The order of conductivity ranges 10 Ϫ1

The chemical and electrochemical behavior of titanium was examined in the Lewis acidic aluminum chloride-1-ethyl-3methylimidazolium chloride (AlCl 3 -EtMeImCl) molten salt at 353.2 K. Dissolved Ti͑II͒, as TiCl 2 , was stable in the 66.7-33.3% mole fraction ͑m/o͒ composition of this melt, but slowly disproportionated in the 60.0-40.0 m/o melt. At low current densities, the anodic oxidation of Ti͑0͒ did not lead to dissolved Ti͑II͒, but to an insoluble passivating film of TiCl 3 . At high current densities or very positive potentials, Ti͑0͒ was oxidized directly to Ti͑IV͒; however, the electrogenerated Ti͑IV͒ vaporized from the melt as TiCl 4 (g). As found by other researchers working in Lewis acidic AlCl 3 -NaCl, Ti͑II͒ tended to form polymers as its concentration in the AlCl 3 -EtMeImCl melt was increased. The electrodeposition of Al-Ti alloys was investigated at Cu rotating disk and wire electrodes. Al-Ti alloys containing up to ϳ19% atomic fraction ͑a/o͒ titanium could be electrodeposited from saturated solutions of Ti͑II͒ in the 66.7-33.3 m/o melt at low current densities, but the titanium content of these alloys decreased as the reduction current density was increased. The pitting potentials of these electrodeposited Al-Ti alloys exhibited a positive shift with increasing titanium content comparable to that observed for alloys prepared by sputter deposition.

A characteristic of negligible vapor pressure that a room temperature ionic liquid (RTIL) possesses enables us to introduce RTILs in the apparatus requiring vacuum conditions for material production and analyses. This combination creates a path toward development of new techniques under vacuum conditions. As for material production, especially metal nanoparticle synthesis, those are magnetron sputtering onto RTILs, plasma reduction in RTILs, physical vapor deposition onto RTILs, and electron beam and γ-ray irradiation to RTILs. Interestingly, the nanoparticles prepared in RTILs without any stabilizing agent do not aggregate in the RTILs. Also, we can introduce RTILs in analytical instruments requiring vacuum conditions such as X-ray photospectroscopy (XPS), matrix-assisted laser desorption/ionization mass spectroscopy (MALDI-MS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The fact that the RTIL is not charged under irradiation by quantum beams enables us to establish new analytical techniques. Furthermore, homogeneous conditions that are obtainable by dissolving a substance in a RTIL are quite useful for conducting analyses using the instruments described above, for example, MALDI-MS, with high reproducibility.