A strategy for designing chiral Brønsted base organocatalysts through noncovalent modification of a chiral dibasic molecule with an achiral phosphoric acid diester is introduced for the first time. Such a molecular modification concept utilizing acid-base interactions may facilitate the on-demand design of asymmetric organocatalysts, as preliminarily demonstrated in this work.
The effects of isotope-labelled NADH and CO2 on formate dehydrogenase from Candida boidinii (CbFDH)-catalyzed CO2 reduction activity were investigated. It was found that the rate of CO2 reduction to formate with CbFDH decreased by using deuterium-labelled NADH (NADH-d4) as a co-enzyme. In contrast, the rate of CbFDH-catalyzed CO2 reduction to formate was unchanged in the use of 13CO2 as a substrate. In the substrate 12CO2 and 13CO2 is mixed, however, curious phenomenon on CbFDH-catalyzed CO2 reduction activity decrease was observed.
The joining of dissimilar materials such as resin and metal has been attracting attention as a means of reducing the weight of automobiles. It is necessary to ensure that the dissimilar material joints are sufficiently strong and durable over time for practical use. Additionally, it is necessary to clarify the mechanisms that produce these properties. We fabricated direct joints of glass fiber-reinforced polyphenylene sulfide (GFRP) and unreinforced pure polyphenylene sulfide (PurePPS) that were injection molded onto aluminum (Al) with nanometer-scale surface irregularities. We used synchrotron microbeam X-ray diffraction to visualize the residual strain distribution at the jointed interface in a nondestructive, micrometer-resolution manner. While the GFRP-Al joint has a lower average tensile residual strain than the PurePPS-Al joint, its strain distributions are quite different. The residual strain distribution of the GFRP-Al joint was comparable to the orientation of glass fibers. The change in the strain distribution when tensile loading was applied in the elastic region was measured, indicating that the tensile strain at the jointed interface increased for PurePPS-Al. Our in situ microbeam X-ray diffraction method helps evaluate the strain at the interface, which is related to joint reliability.
We demonstrate that apparent pKa of extractant impregnated in a polymer phase varies with the cross-linking degree and the coexistence of other extractants, which induces a change in the hydrophobicity of the polymer phase. The results presented herein will be beneficial for the development of novel solid-extraction adsorbents.
K-ion batteries (KIBs) are a widely attractive alternative to Li-ion batteries. While avoiding scarce/toxic elements in their construction, the low standard electrode potential of K+/K allows a low cut-off potential of the negative electrode and high operation voltages that are competitive with those observed in LIBs. Because of the wide operating potential range, developing improved non-aqueous electrolytes with higher oxidation stability and the ability to passivate low-potential negative electrodes is one of the major challenges of high-voltage KIB production. This account primarily covers our recent studies on non-aqueous electrolytes design based on potassium salt and solvent properties. We also discuss remaining/emerging challenges and provide our perspective on non-aqueous electrolytes for high-voltage KIBs.
Magnetite nanoparticles of 9 nm size were synthesized by co-precipitation, hybridized with carbon dots by in situ hydrothermal treatment, and chemically bound on an acid-treated carbon nanohorn through carbon dots. Separately, magnetite nanoparticles were in situ deposited on an acid-treated carbon nanohorn. Both composites were well dispersed in aqueous medium and displayed magnetism. These composites were examined for drug (doxorubicin and gemcitabine) loading/release and, additionally, a carbon dot-immobilized composite exerted the influence of the photodynamic/photothermal effects under laser light emission on gemcitabine release. The release of gemcitabine from magnetite-bound composite was completed when the hyperthermia procedure was conducted together under a magnet. Thus, the magnetite- and carbon dot-including composites possess possible simultaneous usage in phototherapy and thermotherapy including hyperthermia beside chemotherapy.
Optically active V-shaped molecules were synthesized by exploiting chemoselective Sonogashira-Hagihara coupling using planar chiral pseudo-meta- and pseudo-ortho-disubstituted [2.2]paracyclophane scaffolds. In these scaffolds, different para-phenylene-ethynylene π-electron systems were stacked. The synthesized molecules emitted circularly polarized luminescence (CPL) with relatively high dissymmetry factors (glum values) at the order of 10−3. The CPL behaviors are controlled by the stacking angle, position, and manner of the two π-electron systems.
The design of the precursor for intramolecular oxidative coupling is a key to construct novel polycyclic compounds. Fold-in type oxidative fusion reactions of heteroaromatic necklace-like molecules have been proved to be a powerful method to afford heteroatom-embedded circulenes and helicenes. The scope and limitation of this unique transformation as well as the intriguing properties of the particular products have been summarized.
The ice-templating (IT) approach has become a popular way to prepare macroporous monoliths due to environmental friendliness and low cost, as well as the controllability of the macroporosity and exterior structures. In particular, a directional freezing process induces the formation of aligned ice-crystals that afford a brand-new material genre: aligned macroporous monoliths (AMMs). This short review gives an overview of the IT technique and the preparation of AMMs, with a subsequent unfolding of two representative AMMs, i.e., aligned micro-honeycomb monoliths and aligned micro-lamellar monoliths. These AMMs are characterized with their structural anisotropy and regularity, which imparts potentials towards various applications. We particularly highlighted the utilization of these AMMs in the context of thermal insulation, filtration, energy storage and structural engineering. Finally, future directions within this research field are also discussed.
Chiral supramolecular polymers were constructed through the host-guest complexation of an octaphosphonate biscavitand and a chiral diammonium guest. Isothermal titration calorimetry determined that host-guest complexation was enthalpy- and entropy-favored with high binding constants. Diffusion-ordered NMR spectroscopy and viscometry of the host-guest solution revealed that supramolecular polymerization occurred, which most likely followed a ring-chain mechanism. The cyclic oligomers and the supramolecular polymer chains were visualized by atomic force microscopy. Circular dichroism was observed when the octaphosphonate biscavitand and the chiral diammonium guest were mixed, which suggested that chirally twisted supramolecular polymers were formed.
Two kinds of thia- and selenacalixdithienoselenophene, a cyclic dithieno[3,2-b:2′,3′-d]selenophene (DTS) oligomers bridged with divalent chalcogen atoms (S or Se), were successfully prepared via a one-pot cyclization protocol. A palladium-catalyzed coupling of dibromo DTS derivative and (Bu3Sn)2Ch (Ch = S or Se) afforded the cyclic compounds in moderate yield. We have also developed a preparation strategy for the starting DTS derivatives in multi-gram quantity. X-ray analysis revealed that these macrocyclic compounds have different conformations depending on the linker atoms. Thiacalix derivatives form an annular geometry consisting of two sets of vertical and horizontal DTS pairs, while selenacalix derivatives forms a highly symmetrical alternate arrangement of DTS units. The latter macrocycle gave a channel framework to form cavity assembled porous material. Cyclic voltammetry and differential pulse voltammetry measurements for these macrocycles indicated lower redox potentials compared to those of dithienothiophene analogues reported before. Both compounds form a 1:2 complex with C60 in the solid state through face-to-face and S•••π interactions between DTS and C60. Two guest C60 molecules were captured in the identical space formed by a symmetrical 1,3-alternate conformer.
An efficient, one-pot protocol for the synthesis of highly functionalized cyclopentenols has been accomplished starting from vinylethylene carbonates and bissulfonylmethanes. This protocol proceeds via sequential palladium-catalyzed decarboxylative allylation and oxidative cyclization in an operationally simple manner. A wide range of substrates is well-accommodated to afford diverse cyclopentenols in moderate to good yields with excellent selectivity. Further control experiments demonstrated that the selective formation of the isolatable (Z)-allyl alcohols (up to Z/E = >19:1) underlies the success of the subsequent cascade oxidation-cyclization.
Among the various types of photochromic compounds, diarylethenes have good fatigue resistance, but further improvement is required. In this study, we investigated photochromic reaction behavior and fatigue resistance by inclusion in cyclodextrin (CD), which is a cyclic host molecule with three different pore sizes. A water-soluble diarylethene (DE1) synthesized in this work exhibited reversible photochromism in water. Continuous irradiation with UV light resulted in the formation of its byproduct. The addition of αCD showed no improvement of fatigue resistance. However, the addition of βCD and γCD suppressed a side reaction to result in the improvement of fatigue resistance. Especially, the addition of γCD gave a large improvement. To clarify the relationship between fatigue resistance of DE1 and the pore size of CD, the host-guest interaction between DE1 and CD was investigated using NOESY spectra. The results indicate that the depth of DE1 included in CD shows a large effect on suppression of the side reaction of DE1.
Mechanophores, which change their chemical structure in response to mechanical stimuli, are widely used to develop mechanoresponsive materials, and their reactivity is greatly affected by the surrounding environment. Here, we focus on the effect of electrostatic interactions on the activation of mechanophores. A series of radical-type mechanophores with ionic functional groups, as well as mixed systems of these radical-type mechanophores with dicarboxylic acid groups and divalent ions were prepared, and their mechano-responsiveness in the bulk was investigated via ball-milling and subsequent electron paramagnetic resonance spectroscopy measurements. The results revealed that the mechano-responsiveness is governed by the introduction of electrostatic interactions into the mechanophores.
The title polycyclic aromatic hydrocarbons were synthesized by Pd-catalyzed Heck-type cyclotrimerization of 2-bromoaceanthrylene derivatives. X-ray analysis of the 2,4,6-trimethylphenyl substituted derivative revealed that molecules took a propeller-shaped aromatic framework. The barrier to propeller inversion of this derivative was determined to be 81 kJ mol−1 by a dynamic NMR method.
We have developed carbon-bridged oligo(phenylenevinylene)s (COPVs), in which the molecular structure of the phenylenevinylenes is constricted via intramolecular bridging by carbon atoms, or more specifically, substituted methylene groups. COPVs are characterized by their rigid planar molecular structure, which is ideal for the expansion of π-conjugation, and leads to excellent functionality and high stability. Most importantly, COPVs exhibit some phenomena at room temperature that conventional molecules only demonstrate at cryogenic temperatures. In this account, the features of COPVs will be outlined together with research background on structural control using carbon bridges.
The 1,2-rearrangement of o-quinols has been a long-standing unsolved problem since 1958. Although the rearrangement is expected to be useful for syntheses of catechol derivatives, it is hampered by many competing reactions and has not been developed as a useful methodology. Here, we succeeded in settling this problem by a first systematic thorough investigation, establishing the 1,2-rearrangement as a cascade reaction with a retro Diels-Alder reaction from o-quinol dimers. This is a useful strategy for syntheses of substituted catechols used as synthetic building blocks for bioactive compounds and material molecules. o-Quinol dimers were synthesized by improved oxidative hydroxylation of substituted phenols followed by spontaneous Diels-Alder reaction. The dimers then underwent the retro Diels-Alder reaction to regenerate the o-quinols followed by 1,2-rearrangement under neutral heating conditions at an appropriate temperature depending on the migratory substituent, furnishing substituted catechols in good yields. The competing reactions such as an elimination of a substituent or α-ketol rearrangement were minimized by controlling the reaction temperature.
Large-Angle X-ray scattering (LAXS) and Sc K X-ray absorption near-edge structure (XANES) measurements are made at room temperature on a 1 M (= mol dm−3) Sc(NO3)3 aqueous solution. The X-ray interference function is subjected to an empirical potential structure refinement (EPSR) modeling to extract the site-site pair correlation functions, the coordination number distribution, and the spatial density functions (three-dimensional structure). The LAXS analysis combined with EPSR reveals that Sc3+ is surrounded by six or seven water molecules and one oxygen atom of NO3− with an Sc3+-Ow (H2O) and Sc3+-ON (NO3−) distance of 2.14 Å. NO3− has a weak solvation shell with a broad distribution of coordination numbers with the highest population of nine at an N-Ow distance of 3.66 Å. Solvent water forms the tetrahedral network structure. The XANES spectrum is compared with simulated spectra on various coordination geometries of an ScO7 moiety with a discrete variational Xα (DV-Xα) molecular orbital (MO) method. A distorted monocapped trigonal prism structure of Sc3+ best reproduced the experimental pre-peak due to the Sc 1s → 3d transition in the XANES spectrum.
A neutral radical crystal with a two-dimensional network, namely Co(Pc)Br2 (Pc: phthalocyanine) was synthesized. Additionally, intermolecular contacts between the two-dimensional sheets, leading to isotropic semiconducting behavior, were observed. Furthermore, previously reported Co(Pc)Cl2 was revealed to have a three-dimensional network with isotropic nature and exhibited a metallic nature at 8 GPa.
Among synthetic models of nitrogenases, iron–dinitrogen complexes with an Fe–C bond have attracted increasing attention in recent years. Here we report the synthesis of square-planar iron(I)–dinitrogen complexes supported by anionic benzene-based PCP- and POCOP-type pincer ligands as carbon donors. These complexes catalyze the formation of ammonia and hydrazine from the reaction of dinitrogen (1 atm) with a reductant and a proton source at −78 °C, producing up to 252 equiv of ammonia and 68 equiv of hydrazine (388 equiv of fixed N atom) based on the iron atom of the catalyst. Anionic iron(0)–dinitrogen complexes, considered an essential reactive species in the catalytic reaction, are newly isolated from the reduction of the corresponding iron(I)–dinitrogen complexes. This study examines their reactivity using experiments and DFT calculations.
Cancer stem cells (CSCs) are a small subpopulation of cells within the cancer tissue that play major roles in metastasis, drug resistance, and recurrence. Synthetic ligands capable of recognizing the specific DNA sequences are believed to be promising in targeted disruption of transcription factor-DNA interaction, which can achieve regulatory control over tumor-susceptible signaling pathways. Herein, we report a sequence-specific cyclic pyrrole-imidazole polyamide capable of targeting Gli-mediated transcription and inhibiting the hedgehog pathway which is implied to play a major role in cancer stem cell proliferation. The DNA binding affinities of cyclic polyamides were superior to corresponding hairpin polyamides. Mechanistically, the cyclic PIPs blocked the Gli function, which was confirmed by qRT-PCR and luciferase assay. Furthermore, combinatorial treatment of cyclic PIPs and temozolomide (TMZ) to glioblastoma and brain cancer stem cells showed increased cell death compared to TMZ alone. Taken together, cyclic PIPs targeting Gli-mediated transcription can be a promising strategy in suppressing the CSCs.
We designed and synthesized a new series of NHCs with a sulfoxide moiety as a hemilabile ligand. We investigated the catalytic activities of Au(I)-NHC complexes in the strong oxidant-free cross-coupling of iodoarenes with 1,3,5-trimethoxybenzene. We ascertained that the sulfoxide moiety is critical for the Au(I)/(III) catalytic cycle.