Synthesis, X-ray structural analysis, redox behavior, and morphological features of π-extended macrocyclic oligothiophene heptamer and tetradecamer are reported. Due to nanophase separation between inner and outer domains, butyl-substituted π-extended macrocyclic oligothiophenes exhibit marked ringsize effects in the solid state. Among macrocycles with the same composition formula, heptamer has a round shape-persistent structure to produce crystals, whereas the corresponding tetradecamer shows morphological diversity to form single crystals, rods, ovals, and balls. The surface structures of small rods, ovals, and balls were investigated by absorption spectra and PXRD analysis. By cyclic voltametric analysis, heptamer and tetradecamer exhibit reversible two-step redox behavior reflecting moderate donor ability, and the first oxidation potentials of heptamer and tetradecamer are roughly consistent with their HOMO levels.
α-Aryl-α-isocyanoacetoamide derivatives were synthesized through palladium-catalyzed nucleophilic isocyanation. Diethylphosphates derived from N,N-disubstituted mandelamide derivatives reacted with trimethylsilyl cyanide in the presence of a catalytic amount of Pd(OAC)2 to afford the titled isonitriles (13 examples) in moderate to high yield. The silyl cyanopalladate complex formed in situ was a proposed catalyst, which behaved as a Lewis acid promoting elimination of the phosphate group and also the N-nucleophilic cyanide reagent. The isocyanation was applied to a gram-scale reaction with 0.2 mol% of the catalyst. The obtained isocyanoacetoamide was employable for the further transformation into the trisubstituted oxazole without any purification procedure. DFT calculation suggested that the neighboring group effect of the carbonyl moiety in the substrate amide group assisted the elimination of phosphate and stabilized the carbocation intermediate. A plausible reaction mechanism of the isocyanation is also described.
A protocol for blood sampling, storage and digestion for subsequent determination of Br, Cl and I by inductively coupled plasma mass spectrometry (ICP-MS) was proposed. The blood sampling was performed by a protocol known as dried blood spot (DBS). Their characteristics make it a perfect couple with microwave-induced combustion in disposable vessels (MIC-DV) for trace elements determination. Strategies for controlling the blood volume or mass collected in the DBS paper were evaluated. Operational conditions of MIC-DV such as the time of vessel purging with O2, suitable absorbing solutions, and blood mass were evaluated. Results for Br, Cl and I determination by ICP-MS after MIC-DV in three venous samples were compared with reference values obtained by analyte determination by ICP-MS and MIC. The limits of quantification achieved combining DBS/MIC-DV/ICP-MS were 0.23 µg g−1 for Br, 66 µg g−1 for Cl, and 27 ng g−1 for I, which were considered fit for purpose. After MIC-DV optimization, a protocol for Br, Cl and I determination in blood was proposed and applied for blood analysis from ten volunteers. The analyte concentration ranged from 1.79 to 3.57 µg g−1 for Br, 2634 to 3113 µg g−1 for Cl and 0.033 to 0.060 µg g−1 for I.
Radial distribution functions are commonly used to represent the structures of solutions, which represent the probability of finding another atom in the shell at a distance r from the atom of interest. This method has been used to study the structures of many non-crystalline materials. However, the information gained in this method is microscopic, and is limited to the first or second nearest neighbors from the featured atom. The present author proposed a completely different method to describe the solution structure by expressing the inhomogeneity in distribution of atoms and molecules and in concentration as “density fluctuation” and “concentration fluctuation”, respectively; namely the structure of a solution is described in terms of the “mixing state” or “mixing scheme.” This paper introduces density fluctuation and concentration fluctuation, as well as Kirkwood-Buff Integrals. Fluctuations of solutions become more pronounced in the mesoscale region. The relationship with solution thermodynamics, which represents the macroscopic limit, is also discussed. The features and cautions of experiments to measure the fluctuations are described. Finally, as analytical examples, temperature and concentration dependences of mixing schemes for two solution systems with upper critical and lower critical solution temperatures are presented.
This account describes recent aspects of the polyketone-based synthesis of functional molecules. Polyketones are rope-like compounds that combine conformational flexibility with reaction diversity. Although natural-type polyketones, bearing a repeating 1,3-diketone sequence, are difficult to handle as synthetic components owing to complex tautomerism and rapid intramolecular cyclization, the recent development of 1,3- and 1,4-diketone hybrid sequences has enabled access to stable, discrete polyketones for further synthetic functionalization. Various molecular structures with functional properties can be generated from the polyketone chains through rope manipulations, such as bending and coiling. Herein, we introduce their synthesis and structures, focusing on the functionality derived from π-conjugation and metal ion coordination with polyketone derivatives, such as solid-state photo emission, metal-ion conduction, and adsorption.
Graphene oxide (GO) contains various types of oxygen functional groups (e.g., C–OH, C–O–C, C=O, and O=C–OH groups), which provide superior functions such as proton conductivity, catalytic activity, and selective absorption. In contrast, the complex structure of GO complicates control over its function; therefore, GO with a simple and/or uniform structure is desired. In this study, we demonstrated that monolayer GO, in which surface oxygen functional groups are controlled as epoxy groups, was successfully prepared by exfoliating graphite oxide prepared using Brodie’s method. The monolayer ratio of GO reached 99.2%, and the nanosheets were stable in water for 1 month. Fourier transform infrared, X-ray photoelectron spectroscopy, and temperature-programmed desorption analyses indicated that most oxygen functional groups on GO were epoxy groups. Further, it was determined that GO had structural regularity over a wide range and small amounts of lattice defects despite being oxidized. This means that the developed GO can potentially advance considerably GO studies by replacing previous GO.
Charge-discharge performance at −30 °C was studied by using low-viscosity ester solvents (propyl acetate (PA), propyl propionate (PP), and ethyl propionate (EP)) as electrolyte for improving the low-temperature performance of lithium-ion rechargeable batteries. Among the studied ester, PA based electrolyte shows the most superior cycle stability, and it was found that EC-PA based electrolyte increased the discharge capacity of the cell at −30 °C by 6% compared to the EC-DEC based electrolyte. Although the cell capacity at low temperature was increased, favorable solid electrolyte interface (SEI) may not be formed and the cycle stability was decreased in the cell using PA component as the electrolyte. By using an electrolyte additive for SEI formation in combination with PA based electrolyte, the low temperature discharge capacity and cycle stability were much increased which is strongly demanded for electric vehicle application.
Hydrophobic silicone macroporous materials prepared in an aqueous solution by the sol–gel method have been considered for various applications such as separation media, heat insulators, and liquid nitrogen adsorbents. In the conventional preparation process, surfactants are used to suppress phase separation to obtain a uniform bulk material. However, a large amount of solvent and time is required to remove them before drying, which hinders industrial-scale synthesis. By copolymerizing tetra-, tri-, and bifunctional organosilicon alkoxides in an aqueous acetic acid–urea solution, flexible macroporous silicone monoliths were successfully obtained. The marshmallow-like monoliths recovered their original shape even after 80% uniaxial compression and significant bending and water repellency. The thermal conductivity of those materials was ∼0.035 W m−1 K−1 and did not increase even under 60% uniaxial compression. This characteristic property can be used for thermal insulation on surfaces with various shapes and in confined spaces under harsh conditions.
Highly strained cyclic xanthene dimers, which serve as models for reduced graphene oxide (RGO), were synthesized by Ni(0) mediated homo-coupling reactions. The dimers are obtained as highly stable colorless solids. X-ray crystallographic analysis of a tetra-tert-butyl derivative demonstrates that it possesses a highly strained structure with an extremely short non-bonded O•••O distance (2.5662(44) Å). The results of variable temperature NMR experiments show that no signal broadening occurs even at 398 K, indicating that conformational flipping requires considerably high energy.
In this account, we provide an overview of unique anisotropic hydrogels comprising uniaxially aligned lamellar bilayers embedded in amorphous gel matrix. Owing to their unique structures, the lamellar gels exhibit many unique functions that cannot be obtained from conventional hydrogels featuring amorphous and isotropic structures. For example, the periodical multilayer structure having interlayer spacing of several hundreds of nanometers imparts beautiful structural colors to the gel that respond sensitively to mechanical and chemical stimuli, the water-impermeable nature of the bilayers imparts one-dimensional swelling and diffusion, and the hydrophobic association of the bilayers serves as sacrificial bonds to impart high mechanical strength and toughness during deformation. This work demonstrates the significant potential of hydrogel materials fabricated by introducing anisotropic ordered structures.
Organic compounds with an open-shell electronic structure, in which unpaired electrons remain in the molecule, have attracted much attention in recent years due to their high reactivity and unique physical and functional properties. This paper presents my recent studies on the investigation of the properties of organic radical species through a structural organic chemistry approach to synthesize molecules with new frameworks. In particular, this paper focuses on (1) elucidation of the electronic structure of singlet biradicals and exploration of the properties characterized by the unique electronic structure, (2) molecular interpretation of the strange magnetic state of graphene nanoribbons, and (3) elucidation of the new association mode of organic radical species.
The effect of an external magnetic field on the supercapacitor performance of cobalt oxide/magnetic graphene composites has been investigated. The composites were prepared via the hydrothermal reaction of cobalt nitrate with iron oxide-incorporated magnetic graphene. Cobalt oxide nanoparticles were deposited on the graphene sheets and contributed to enhancing the electrochemical capacitance, since the cobalt oxide could work as pseudocapacitance material different from the graphene sheet with the electric double-layer capacitance effect. Further enhancement was observed upon applying the external magnetic field, which was increased via a home-made electric circuit. The specific capacitances of the composite materials under the external magnetic field of 1191 Gauss were found to be a maximum of 11 times higher than those without the magnetic field. It was also suggested that the increase in specific capacitance under the magnetic field follows the power law of the magnetic field due to a magnetohydrodynamic effect. These results demonstrate the importance of the external magnetic field to develop new technologies on energy-related applications of magnetic materials.
Noncovalent interactions are important for determining the assembling modes of materials. Electronically neutral π-systems form stacking structures based on π–π interactions, which are mainly derived from dispersion forces. Introducing charges into π-systems would affect the interaction, owing to the increased contribution from electrostatic forces. This unique interaction, which we have proposed as iπ–iπ interaction, can provide ion pairs that form assembled structures. The number of possible combinations of ion pairs can be obtained as the product of the number of components being paired. As π-electronic ions, especially anions, are more reactive than electronically neutral π-systems, their stabilization is required. We have recently focused on porphyrins as platforms to stabilize π-electronic ions by charge delocalization over their large π-systems. In addition, the facile structural modifications of porphyrins enable tuning of the assembly modes and functionalization of the ion-pairing assemblies. In this account, progress of charged porphyrin derivatives and their ion-pairing assembly behaviors is summarized.
This paper discusses a method for the synthesis of ionic liquids which are mixtures of oligomeric silsesquioxanes (OSS) of polyhedral structure and their analogs with open chains containing aprotic cationic ionic groups with different lengths of alkyl substituents and reactive hydroxyl groups in the organic shell (OSS-ILs). This method includes the quaternization reaction of OSS with tertiary amine and primary and secondary hydroxyl groups by n-bromopropane or n-bromodecane. Obtained compounds were amorphous with glass transition temperature below 0 °C. The ionic conductivity of OSS-ILs increases with decreasing the alkyl substituent length and reaches 1.4·10−3 S/cm at 120 °C.
Dynamic light scattering reveals that the length of alkyl substituent of OSS-ILs affects the assembly behavior in aqueous solutions. According to atomic force microscopy images, the surface morphology of the film of OSS-IL with short substituents showed disk-like flat micelles with an average diameter of 229 ± 92 nm and height of 2 nm. OSS-IL with long substituents formed polydisperse micellar morphologies, of which a majority showed elongated, worm-like structures with an average height of 2 nm. The ability to endow ionic conductivity and to tune morphology makes these materials promising as potential polymer electrolytes for various electrochemical applications, in particular ionic sensors and energy storage devices.
Gold nanoparticle assemblies significantly enhance optical fields and have been applied for nano-optical devices, biosensing, and chemical reactions. The optical properties of the assembly are, however, less controllable once the assemblies are fabricated on a solid substrate. An assembly prepared at the water-organic solvent interface overcomes this restriction and provides flexible photochemical reaction fields. Additionally, the physical and chemical properties of the assembly can be controlled by modification of the nanoparticle surface. In this study, we investigated the optical properties of the assembly using two-photon-induced photoluminescence and surface-enhanced Raman scattering, and demonstrated that the optical field enhancement and chemical environment near the gold nanoparticle assembly can be finely controlled by surface-modification of the gold nanoparticles.
Assembled molecular gels exhibit dynamic properties and have been developed as functional soft materials with self-healing ability, stimuli responsiveness, and other such properties. Nevertheless, dynamicity is not essential to molecular assemblies. We created static and robust hydrogels composed of self-assembled cello-oligosaccharide networks. In fact, the novel gels are solvent-exchangeable from water even to nonpolar organic solvents, reflecting extremely low stimuli responsiveness. This Account summarizes our recent research progress on cello-oligosaccharide gels, from their production to applications that exploit the unique properties of these crystalline oligosaccharide assemblies. Our findings suggest that statically assembled molecular gels have unconventional applications.
The significance of NIR light-absorbing and/or emitting materials is growing day by day in industrial applications as well as research fields because of intrinsic versatility of NIR light. The unique properties of NIR light, such as invisibility to human eyes, high permeability and transmissibility, are readily applicable to novel functional devices for detection sensors, optical communications, imaging probes and photomedical therapy. However, there are several problems to be overcome especially for obtaining efficient NIR-emissive materials, and therefore development of new skeletons which can present efficient NIR emission is still challenging. Herein, we demonstrate molecular design strategies and recent results for preparing the NIR-emissive materials based on element-block π-conjugated polymers. By focusing on the isolated lowest molecular orbital (LUMO), selective perturbation of one frontier molecular orbital (FMO) is accomplished, leading to narrow-energy-gap materials without expanding π-conjugated systems. As another example, it is shown that hypervalent bonds of main group elements are also effective for narrowing energy gap to generate emission in the NIR region. It can be said that the combination of the inherent element features with π-conjugated polymeric systems is expected to be one solution to overcome these problems. On the basis of this strategy, we obtained a variety of π-conjugated polymers showing light-absorption and/or emission in the NIR region with versatile functions. Our approaches presented in these recent studies could be new tactics for developing next-generation optical materials with NIR-light absorption and/or emission.
Detonation nanodiamonds (DNDs) have attracted considerable attention, in particular, in the field of nanomedicine due to their biocompatibility as well as various functionalities imparted by surface modification. Meanwhile, boron neutron capture therapy (BNCT) is an advanced cancer treatment utilizing nuclear fission reaction of 10B upon neutron irradiation. Recently, quite a few boron-containing nanoparticles have been investigated to deliver 10B atoms into cancer tissue selectively and retentively. In this study, we explored boronic acid functionalized DNDs as an anticancer agent for BNCT. Phenylboronic acid (PBA) moiety was introduced to polyglycerol (PG) modified DNDs (DND-PG) through multistep organic transformation, giving percent order of boron atoms. The process is scalable and reliable by simple covalent chemistry and the resulting product is well dispersed, and stable chemically and physically under physiological conditions. In the in vivo experiments, the resulting material was accumulated in the tumor to exert BNCT efficacy upon neutron irradiation. These results demonstrate that the PBA functionalized DNDs are a promising candidate as an anticancer nanodrug for BNCT.
Although various lanthanide clusters with different shapes and connections have been synthesised, more rules are still needed to guide their further serial expansion and directed structural modification. Herein, we used the multidentate chelating ligand N′2,N′9-bis((E)-2-hydroxy-3-methoxybenzylidene)-1,10-phenanthroline-2,9-dicarbohydrazide (H4L) to react with Dy(NO3)3·6H2O under EtOH/CH3CN conditions to obtain an example of a nonanuclear dysprosium cluster, i.e., [Dy9(L)2(μ2-OH)(μ3-OH)6(NO3)12(H2O)3]·5CH3CN·H2O (1). The structural framework of cluster 1 contains 2 (L)4− ligands, 1 μ2-OH−, 6 μ3-OH−, 12 NO3−, and 3 H2O. Each ligand (L)4− chelates five Dy(III) ions, and its coordination mode is μ5-η1:η2:η1:η2:η1:η1:η2:η1:η2:η1. Cluster 1 has many different connection modes of NO3−, such as μ5-η2:η2:η2, μ2-η1:η1, and μ2-η1:η2. Notably, we only changed the metal salt to Dy(OAc)3·6H2O and obtained an example of a trinuclear dysprosium cluster, i.e., [Dy3(H2L)(OAc)7]·CH3CN·3H2O (2). The structure of cluster 2 contains three Dy(III) ions, one (H2L)2− ion, one μ3-η2:η2-bridged OAc− and six end-coordinated OAc−. The coordination mode of ligand (H2L)2− is μ3-η1:η1:η2:η1:η1:η1:η2:η1. More notably, we only changed the solvent to MeOH/CH3CN, and under the same reaction conditions, we got an example of a dodeca-nucleus dysprosium cluster, i.e., [Dy12(L)4(μ2-OH)2(OAc)14(H2O)8]·4C2H3O2·2H2O (3). In cluster 3, ligand (L)4− adopts the μ5-η1:η2:η1:η2:η1:η1:η2:η1:η2:η1 coordination mode, and the four ligands (L)4− are connected to each other forming the grid structure. Twelve Dy(III) ions are “embedded” in the chelating sites of the ligand and bridged by multiple OAc− ions. A large cavity is formed in the centre of the ‘well’ in cluster 3. The test results of variable temperature AC magnetic susceptibility show that clusters 1–3 all exhibit single-molecule magnet behaviour. To the best of our knowledge, this study is the first to describe that an out-to-in growth mechanism has been manipulated by anions and solvents to realise the synthesis of a series of completely differently connected dysprosium clusters. In addition, this mechanism is also one of the rare examples of anion and solvent co-induced assembly to form lanthanide clusters with completely different shapes and connections.