Phosphorus-modified AFX zeolite was synthesized by the hydrothermal conversion of FAU zeolite, which was impregnated with tetraethylphosphonium hydroxide (TEPOH). For the optimization of the introduced phosphorus, we investigated the influence of the loaded amount of TEPOH on FAU zeolite and tested the combination of the starting materials, composed of phosphorus-free and TEPOH-impregnated FAU zeolites. The synthesis system, employing the combined starting materials, effectively incorporated phosphorus into AFX zeolite while the TEPOH-impregnated FAU zeolite was not effective as a solo starting material. X-ray diffractometry, N2 adsorption, and elemental analysis were employed to confirm the high purity of the AFX zeolite, obtained from the utilization of combined starting materials. Moreover, 13C and 31P magic angle spinning (MAS) NMR spectroscopy further revealed the modification of phosphorus in which the phosphorus species interacting with the zeolite framework was formed via the decomposition of tetraethylphosphonium (TEP) by calcination.
Hydrogen energy is considered a competitive and environmentally friendly carrier owing to its high calorific value, abundant reserves, carbon-free emission, and renewability. Water splitting for sustainable production of hydrogen from water via sunlight or clean energy derived electricity has attracted paramount attention. Photocatalytic water splitting provides a clean solution to produce hydrogen by taking advantage of abundant solar power. Due to their unique physico-chemical properties, metal/metal oxide based composite electrospun semiconductor photocatalysts show great potential to supplant some of the non-oxide photocatalysts and other nanostructures in water splitting. The key issues to the commercialization and scale-up production remain on the fabrication, modification and performance of photocatalysts. In this review article, we showcase recent significant progress in the fabrication of semiconductor photocatalysts toward water splitting based on versatile electrospinning. The modification and performance improving strategies for a wide range of metal/metal oxide (single, mixed, metal/carbon cocatalysts) electrospun semiconductors including the structure and compositional engineering are presented. Furthermore, we also discuss the challenges and future perspectives of electrospinning toward the rational design and facile fabrication of photocatalysts.
Carbazole-fused azaborines were synthesized via a Buchwald-Hartwig amination followed by a Pd-catalyzed C-H activation-cyclization reaction. These azaborines exhibited red-shifted absorptions and photoluminescence emissions compared to those of dibenzoazaborines, suggesting the efficient HOMO-LUMO energy gap decrease by the carbazole-annulation. The carbazole-fused azaborines showed improved electrochemical stability compared with the previously reported dibenzoazaborine derivatives.
In nature, molecular recognition is crucial to induce functions as living systems. Bioinspired molecular recognition chemistry has been intensively studied for more than half a century since the discovery of crown ethers. Chemical sensors are a concrete representative example of the application of artificial molecular recognition materials. The sensors have the ability to visualize the recognition phenomena and provide quantitative information on an analyte. However, developing chemical sensors that fully meet the requirements for practical application is still challenging. To this end, the author has focused on a cross-hierarchical and comprehensive development of chemical sensors based on molecular recognition chemistry and supramolecular chemistry. Through the efforts with bottom-up and top-down approaches, the author has contributed to the progress of practical supramolecular analytical chemistry which allows identification of target chemical species in real samples, and realization of sensor devices for on-site detection. This account summarizes the author’s recent achievements for chemical sensors including the design of artificial receptors, optical chemosensor arrays, and organic field-effect transistors.
Electronic structures and direct observation of adlayers on Au(111) of triangular expanded hemiporphyrazines that can be classified into azaporphyrinoids and which can trap three transition metal ions are reported. The electronic structure was examined by electronic absorption and magnetic circular dichroism (MCD) spectroscopies and interpreted in conjunction with molecular orbital (MO) calculations. Both metal-free and metallated compounds were 30 π-electron systems with n = 7 in 4n + 2 aromaticity. In addition, calculations of the anisotropy of the induced current density (ACID) and nucleus-independent chemical shift (NICS) were performed. The inner core region of the metal-free compound was weakly anti-aromatic or nonaromatic, but after metal insertion, this region increased aromatic character. The direct observation of adlayers of one of their cobalt and nickel complexes on Au(111) by scanning tunneling microscopy (STM) revealed that these three ions are arranged specifically in the shape of a triangle.
Donor-acceptor triads composed of tetrathiafulvalene (TTF) and benzoquinone (BQ) fused by a benzene-spacer (3, 4) were successfully synthesized. In the cyclic voltammetry, the bis[(2-ethyl)hexylthio]-4 (4e) exhibited five-pairs of one-electron transfer waves corresponding to the formation of both reduction and oxidation states from −1 to +4. The 3/Li cell exhibited high discharge energy density exceeding 700 mWh g−1.
Archival storage in DNA is one of the most challenging themes in rapidly growing information technology. In addition, its practical applications are more difficult due to complicated data analysis, instability of long and linear DNA strands (>1000 nt), and other factors. In the present study, we have developed a simple and eminent DNA-based storage system in which small DNA rings are employed as memory units. Compared with previous approaches, this methodology has advantages of robustness, low cost, convenience and so on. In high density, Chinese language was directly stored in a pool of 76-nt-long single-stranded DNA rings (designated as “Info-Store”), in which each ring memorized the index number and five Chinese characters (or marks). During “Read-Out”, all the ssDNA rings in the pool were simultaneously amplified by hyper-branched rolling cycle amplification (HRCA), and their sequences were accurately determined by a portable MinION sequencer aided by a personal computer. Then, the original Chinese text was precisely and smoothly decoded by simple data analysis.
Incorporating soft and dynamic elements into crystalline porous materials with hard and static structures can be of immense utility. To this end, herein, the design of functional porous materials and their dynamic properties are described. Dynamic molecular elements were incorporated in porous coordination polymers (PCPs)/metal-organic frameworks (MOFs) to realize responsive and high-performance porous systems. The dynamic nature of the PCPs/MOFs was directly visualized in real-time via atomic-force microscopy. Additionally, by combining the concepts of soft matter dynamics and porous material chemistry, a new class of porous materials, possessing both fluidity and porosity, could be fabricated. By focusing on the dynamic properties of materials, functional nanoporous systems could be designed, leading to the development of next-generation porous materials.
Boehmite nanomaterials have been researched for use in applications such as separation media, fillers for resins, and catalyst support. This study investigates the relationship between structural density and mechanical and thermal performance of boehmite nanofiber-polymethylsilsesquioxane (PMSQ) composite aerogels. Tri-functional organosilicon alkoxide methyltrimethoxysilane (MTMS) was added to a boehmite nanofiber aqueous dispersion; the colloidal nanofibers were coated and bonded with polymethylsilsesquioxane, to produce transparent to translucent wet gel monoliths. Low bulk density aerogel panels were prepared by CO2 supercritical drying of the wet gel monoliths before their mechanical properties and thermal conductivity were investigated. As the amount of the MTMS in the starting composition increased, the fibrillar monolith skeleton coated with PMSQ thickened. Correspondingly, the Young's modulus of the monoliths increased, and the thermal conductivity decreased. When the amount of MTMS added was small, it was possible to deform the translucent panels by uniaxial compression. After 30% uniaxial compression of the panel, the thermal conductivity was suppressed by 19%. The thermal conductivity response to compressive deformation of fibrous aerogels, after fabrication, may inform future insulation material development.
In order to control a crystal configuration of MAPbBr3 (MA = CH3NH3+) perovskite ultra-thin layers, the Au(100) single-crystal, the self-assembled monolayer (SAM) of 4-aminothiophenol (4-ATP), and the layer-by-layer alternating immersion were employed as a substrate, a linker between the perovskite thin layer and gold substrate, and a preparation method, respectively. Structure and crystal configuration of the constructed MAPbBr3 perovskite ultra-thin layers on 4-ATP SAM modified Au(100) were investigated by X-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM), and grazing incidence surface X-ray diffraction (GISXRD). As a result, we succeeded to construct the structure-controlled MAPbBr3 perovskite ultra-thin layers on the 4-ATP SAM modified Au(100) surface with an atomic dimension.
The Co2(CO)8-catalyzed reaction of acetals with hydrosilanes and CO under mild reaction conditions (an ambient temperature under an ambient CO pressure), leading to the production of vicinal diols is reported. A siloxymethyl group can be introduced via the cleavage of one of two alkoxy groups in the acetal. The effects of the types of hydrosilanes, acetals, solvents, and reaction temperatures on the yield of siloxymethylation products were examined in detail. The reactivity for hydrosilanes is as follows; HSiMe3 > HSiEtMe2 > HSiEt2Me > HSiEt3. Hemiacetal esters are more reactive than dimethyl acetals. The polarity of the solvent used also has a significant effect on both the course of the reaction as well as the reaction rate. The site-selective siloxymethylation can be achieved in the case of cyclic acetals such as tetrahydrofuran (THF) and tetrahydropyrane (THP) derivatives, depending on the nature of the oxygen substituent attached adjacent to the oxygen atom in the ring. When 2-alkoxy THF or THP derivatives are used as substrates, the siloxymethylation takes place with cleavage of the ring C-O bond. In contrast, the reaction of 2-acetoxy THF or THP derivatives results in siloxymethylation with the cleavage of C-OAc bond. The ring-opening siloxymethylation of lactones was also examined.
The calculation speed of the ab initio fragment molecular orbital (FMO) method can and must be increased by applying approximations to the environmental electrostatic potential (ESP) and the dimer electrostatic potential (dimer-es). These approximations were previously implemented by introducing the Cholesky decomposition with adaptive metric (CDAM) method to the FMO (Okiyama et al., Chem. Phys. Lett. 2010, 490, 84). In this study, a distributed memory algorithm of CDAM was introduced to reduce the necessary memory size. The improved version of CDAM was applied to the ESP approximation and was shown to give sufficiently precise energy values while halving the calculation time.
Biological events of proteins are too infrequent to observe with molecular dynamics (MD) simulations, though they are strongly related to the biological functions. To detect such rare events, several enhanced sampling methods have been proposed. Recently, as one of the enhanced sampling methods, we have developed parallel cascade selection molecular dynamics (PaCS-MD). PaCS-MD performs short-time MDs repeatedly from initial structures selected by a given rule as a function of arbitrary reaction coordinates. In the present study, the conventional PaCS-MD is extended as UCHMZ-PaCS-MD, where water coordinates are rearranged before restarting the short-time MDs, which perturb a given system by generating a variety of initial configurations. The restart of short-time MDs from the perturbed systems enables us to further enhance the conformational search. As a demonstration, UCHMZ-PaCS-MD was applied to folding of Chignolin and efficiently identified several metastable states including the intermediate, the misfolding, and the native ones. Furthermore, as a demonstration for globular proteins, large-amplitude domain motions of T4 lysozyme and adenylate kinase were efficiently detected with UCHMZ-PaCS-MD. Additionally, the generated transition pathways were analyzed with Markov state models (MSMs), enabling us to calculate broader free energy landscapes compared with the conventional PaCS-MD.
For enhancing the photocatalytic performance of anatase TiO2, proper control of the reactive facets and its molecular-level understanding are crucial. This experimental and theoretical study clarifies the facet dependence of the photocatalytic reaction at the anatase TiO2 surface. The 〈112〉-oriented anatase TiO2 layer is deposited on a Ru(0001) substrate at 360 °C by low-pressure chemical vapor deposition. The deposition rate is three times higher than that of the multi-orientation layer on the Pyrex glass. The photocatalytic activity induced by ultraviolet (UV) irradiation around 365 nm in methylene blue aqueous solutions is significantly high, and the rate constant is 6.1 × 10−1 min−1, which is two orders of magnitude greater than that on the multi-orientation TiO2. The density functional theory (DFT) calculations using the constrained DFT method and the hybrid functionals show that the (112) surface stabilizes the adsorbed water molecule most strongly. The photogenerated hole is stably trapped not at the bare surface but at the hydroxylated surface, especially at the hydroxyl group of the hydroxylated (112) and (001) surfaces. The experimental and theoretical findings consistently indicate the high photocatalytic activity at the anatase TiO2(112) surface.
Designing polymers experimentally is a time-consuming task. Quantitative structure-property relationship analysis can help speed the development of new polymers. The authors hypothesized the ideal mixture model, with which polymers are represented by composition-weighted descriptors of monomers. In this study, we pursued a new polymer that had the desired properties from an industrial dataset. We first constructed a partial least squares (PLS) model and random forest with five descriptor sets. The PLS model with fragment counts, which was the most appropriate model for prediction, was used to optimize the compositions. Subsequently, the authors identified the important substructures of monomers using least absolute shrinkage and selection operator (LASSO). The important substructures were used to select seed structures of monomers for structure generation. Another PLS model with distributed representation, called mol2vec, was constructed, because the ordinary fragment counts are unavailable for extrapolation. The PLS model estimated the polymer target property for screening novel structures. The major novelties of this study are to identify important substructures to the polymer target property and to apply mol2vec to design of network polymers. Eventually, we found a novel desired polymer through the composition optimization and demonstrated that virtual screening of monomers with distributed representation worked.
Multicomponent sepiolite/magnetite/Prussian blue (PB) were prepared following the nanoarchitectonics approach by incorporating PB pigment to sepiolite fibers previously assembled with magnetite, being later encapsulated within in situ formed calcium alginate beads. These composites were characterized by diverse physicochemical techniques, showing homogeneous dispersion of the assembled nanoparticles (NP) on the surface of sepiolite fibers, the formed Ca-alginate beads exhibiting stability and superparamagnetic response. Based on the affinity of PB toward cesium ions, these beads were tested as selective adsorbent to remove Cs+ from water under different experimental conditions. The maximum adsorption capacity of the beads for Cs+ ions determined by Langmuir equation was around 130 mg/g. The resulting beads maintain a constant adsorption capacity over a large domain of pH, i.e. from 4 to 11. The mechanism of Cs+ removal could be mainly ascribed to the complexing ability of PB, although in minor extent also to cation-exchange properties of sepiolite as well as to interactions with residual carboxylic groups from the alginate biopolymer matrix. The resulting multicomponent composite can be considered as an efficient, economic, ecologic and easily recoverable adsorbent for the removal of Cs+ ions from solution, including radioactive 137Cs, and therefore contributing to environmental remediation of pollution caused in nuclear plants.
The design of advanced carbon-based electrodes with unique electronic, electrical and textural properties is crucial for the development of high-performance energy storage devices. Here, we report on the fabrication of ordered mesoporous fullerene/carbon hybrids through nanotemplating approach by mixing the fullerene precursor in chloronaphthalene with different amount of sucrose using SBA-15 as a template. The characterization data reveal that the prepared materials exhibit an ordered structure with much better textural parameters than pure mesoporous fullerene. The surface properties can be controlled with the simple adjustment of the sucrose molecules in the synthesis mixture. The prepared materials are used as electrodes for supercapacitance and Li-ion battery applications. The optimized sample offers the specific capacitance of 213 F/g at 0.5 A/g which is much higher than that of activated carbon, MWCNT, ordered mesoporous carbon and mesoporous C60. The same sample also delivers the discharge capacities of 1299 mAh/g at 0.1 A/g, demonstrating the best Li-ion battery performance. These data reveal the importance of carbon coating on the mesoporous fullerene for energy storage devices as it facilitates the easy electron transport between the fullerene molecules and further supports the accessibility and diffusion of the electrolytes due to high specific surface area.
Ring-structured DNA and RNA exhibit a variety of unique features in chemistry, biology, medicine, material science, and so on, which cannot be accomplished by their non-cyclic counterparts. In this review, both naturally occurring DNA/RNA rings and artificially synthesized ones have been comprehensively covered, mainly to bridge these two growing fields. In the first part, the structures and functions of naturally occurring DNA/RNA rings (extrachromosomal circular DNA, circulating cell-free DNAs, cyclic RNAs, and others) are described. Their roles as biomarkers for disease diagnosis are especially noteworthy. The second part mainly presents recent methods to synthesize DNA/RNA rings selectively and efficiently from oligonucleotide fragments. DNA/RNA rings of desired sequences and sizes are successfully prepared in large amounts for versatile applications. Production of RNA rings in cells using autocatalytic transcripts is also described. Lastly, practical applications of DNA/RNA rings are briefly reviewed. Critical significance of the cooperation of these two areas for further developments, as well as strong potential for interdisciplinary studies, have been emphasized.
Reversible water molecule-induced spin state inter-conversion for the mononuclear cobalt(II) complex [Co(terpy)2]I2·2H2O (1, terpy = 2,2′:6′,2′′-terpyridine) is reported along with its co-crystallization with 1,3,5-triiodo-2,4,6-trifluorobenzene (TITFB) to yield three types of halogen bonded frameworks, [Co(terpy)2][(TITFB)I2] (2), [Co(terpy)2][(TITFB)2I2] (3) and [Co(terpy)2][(TITFB)4(MeOH)I2] (4) (TITFB = 1,3,5-triiodo-2,4,6-trifluorobenzene). The magnetic properties of 1–4 have been investigated. While 1 exhibits gradual spin crossover (SCO) behavior, de-solvated [Co(terpy)2]I2 (1′) exhibits abrupt SCO behavior (T1/2 = 120 K) attributed to a change in its intermolecular interactions on dehydration. The crystal structures as well as the magnetic properties of 1 and 1′ can be switched reversibly via single-crystal to single-crystal (SCSC) transformations via hydration/dehydration processes. Co-crystallization of [Co(terpy)2]I2 with TITFB resulted in three types of halogen-bonded frameworks (2–4). While 2 exhibits incomplete abrupt spin transition (T1/2 = 56 K), 3 and 4 show incomplete gradual SCO behavior (attributed to stabilization of the LS state). The observed SCO behaviors are in accord with the structural distortions occurring in the respective [Co(terpy)2]2+ cations and resulting from their intermolecular interactions with the surrounding frameworks. These results illustrate the manner by which co-crystallization leading to halogen-bonded co-crystals in the present study can result in spin state modulation in SCO complexes.
We have prepared a new donor MTDT-TTP (bis(methylthio)dithio-tetrathia-pentalene) and obtained β-(MTDT-TTP)2BF4, which undergoes structural transition by ordering of the bis(methylthio) groups at 190 K. A crystal structure analysis indicated that the BF4 salt is in a charge-ordered (CO) state at room temperature (RT), although it shows a metallic behavior above 260 K. The CO pattern at RT has a four-molecular cycle. The BF4 salt has also the CO state below the transition temperature, but the CO pattern is changed by the structure change.
Cytochrome (cyt) c is a multifunctional water-soluble heme protein. It transfers electrons from the cyt bc1 complex (Complex III) to cyt c oxidase (Complex IV) in the respiratory chain of mitochondria, and can trigger apoptosis as well. Although cyt c has been studied for more than a century, its new aspects are still being elucidated. For example, we found that cyt c molecules can form oligomers and polymers by 3D domain swapping (3D-DS), where the C-terminal α-helix is exchanged between molecules. 3D-DS is observed in other c-type cyts—although the swapping regions may differ—indicating that 3D-DS is a common feature for c-type cyts. 3D-DS of c-type cyt can occur during protein folding and expression in cells. The electron transfer ability of cyt c decreases by 3D-DS, due to the dissociation of Met80 from the heme iron, whereas the peroxidase activity increases. The cyt c electron transfer partners, Complex III and Complex IV, are embedded in the inner mitochondria membrane, whereas positively charged cyt c interacts with negatively charged cardiolipin (CL) molecules at the inner mitochondrial membrane. We have recently elucidated the CL-interaction site of cyt c at atomic level by NMR spectroscopy using CL-containing bicelles. The membrane interaction site of cyt c is relatively wide and similar to the interaction site for Complex III and Complex IV, indicating that cyt c interacts with lipid membranes and partner proteins in a similar way. When cyt c interacts strongly with CL, Met80 dissociates from the heme iron and the peroxidase activity of cyt c increases. We have shown that the proton concentration at the CL-containing membrane is higher than that in the bulk solution, which may enhance the peroxidase activity of cyt c. The Met80-dissociated cyt c has been shown to oxidize CL, increasing the permeability of cyt c through the membrane. We found that when Met80 is dissociated from the heme iron in cyt c, Met80 can be oxidized to methionine sulfoxide by the peroxidase reaction of the heme of cyt c or its reaction with molecular oxygen under reduced conditions. Met80-oxidized cyt c depicts a higher peroxidase activity compared to that of unmodified cyt c; thus Met80 oxidation may enhance lipid oxidation and eventually apoptosis. These new findings not only help in understanding the structure-function relationships of multifunctional cyt c but also show that there are still hidden properties in well-studied proteins.
The traditional preparation of non-fullerene acceptors (NFAs) via Knoevenagel condensation reaction (KCR) of aldehyde and active methylene leaves vulnerable and reversible exocyclic vinyl bonds in structures, which undermine the intrinsic chemo- and photostability of NFAs. In this work, we demonstrate a new access to acceptor-donor-acceptor (A-D-A) NFAs via Stille coupling between new electron deficient groups and classic donor core in over 90% yield, wherein the robust carbon-carbon bonds, replacing the exocyclic double bonds from traditional KCR, result in stable A-D-A acceptors, Q1-XF (X representing 0, 2 and 4 fluorine atoms, respectively). Among the three studied examples, Q1-4F exhibits improved optoelectronic and electron transport properties, leading to the best photovoltaic performance with optimal charge kinetics for Q1-4F based OSCs. Overall, this strategy can lead to a new way for developing stable photovoltaic materials.
A distinct difference between the three-center halogen bond and the analogous three-center coordinative bond of silver is demonstrated by computational, X-ray crystallographic and solution NMR spectroscopic investigations of their complexes with a bidentate Lewis base. Iodine(I) preferentially forms an entropically favored monomeric complex, whereas silver(I) forms enthalpically favored dimeric complexes. Counterion coordination considerably influences the structure of the silver complexes in the solution and solid state, whereas it does not have notable effect on the analogous halogen bond.
This account describes our work concerning the application of alkylboranes to addition reactions to unsaturated compounds, with catalysis by copper. Alkylboranes are readily obtained from standard alkene hydroboration reactions, which is an advantage of these processes. The substrates can contain a wide range of functional groups. The reactions described herein include the formation of alkylcopper(I) species via the catalytic B/Cu transmetallation of alkylboranes and subsequent addition to unsaturated carbon–carbon bonds or carbon dioxide.
The lability, dynamics of the first solvation shell, and structure breaking effect properties of Cs+ in liquid ammonia have been evaluated using Quantum Mechanical Charge Field Molecular Dynamics (QMCF-MD) simulation. The system was conducted in a simulation box containing 593 ammonia molecules with a density of 0.690 g/cm3. The Hartree-Fock level of theory was employed to calculate the interaction of the particles in the QM region using LANL2DZ-ECP and DZP (Dunning) basis set for ion and ligands, respectively. The two solvation regions were observed, and the non-single coordination number confirmed a labile solvation structure. The first solvation shell predominantly by [Cs(NH3)9]+ and the angular distribution function (ADF) confirmed a distorted capped square antiprism geometry. The mean residence time of 1.57 ps and reverse sustainability of 3.1 are more dynamic than the “self-solvation” of ammonia, indicating structure breaking effect by Cs+.
My research target can be described as “Next Generation Multifunctional Nano-Science of Advanced Metal Complexes with Quantum Effect and Nonlinearity”. My work encompasses four important key areas: (1) inorganic-organic hybrid systems, (2) nano-size and nano-space, (3) bottom-up and self-assembly, and (4) nonlinearity and quantum effect. Among them, nonlinearity and quantum effect are the most important for nano-science of advanced metal complexes. I have been working on these two topics (nonlinearity and quantum effect) simultaneously for more than 40 years. As for quantum effect, I have focused on Haldane gap systems, single-chain magnets (SCMs), single-molecule magnets (SMMs), Kondo resonance on SMMs, photo-switchable SMMs, metallic conducting SMMs, SMMs encapsulated into single-walled carbon nanotube (SWCNT), and metal-organic framework (MOF)-spintronics for spin qubits, for pursuing high-density memory devices and quantum computing. As for nonlinearity, I have focused on quasi-one-dimensional halogen-bridged metal complexes (MX-Chains; M = Pt, Pd, and Ni; X = Cl, Br, and I) with nonlinear excitons such as solitons and polarons, strongly electron-correlated Ni(III) complexes with gigantic third-order optical nonlinearity, and phase transitions and charge fluctuations between Pd(III) averaged states (= Mott insulator) and Pd(II)-Pd(IV) mixed-valence states (= charge density wave states), for pursuing optical communication, optical switching, and optical computing. In this review article, I will describe the above main topics (quantum effect and nonlinearity) according to my research history of more than 40 years, respectively. Finally, I will propose future perspectives for the two topics.
Metal homoenolates represent uniquely useful organometallic intermediates in synthetic chemistry, allowing umpolung synthesis of β-functionalized carbonyl compounds. While siloxycyclopropanes had been established as reliable precursors to homoenolates, often stoichiometric, for diverse carbon–carbon bond forming reactions, unprotected cyclopropanols have emerged as alternative and attractive precursors to homoenolates, often catalytically generated, in carbon–carbon and carbon–heteroatom bond-forming reactions. This review article provides an overview of the development of such homoenolate transformations, as classified with respect to the metals involved in the cyclopropane ring opening.
The planar trigonal structure of 1,3,5-trisubstituted benzene, named phenine, has been adopted as basic units of polygonal networks to shape nanometer-sized curved organic π-molecules. The phenine design allows for concise syntheses of large carbonaceous molecules reaching 4 kDa by stitching geodesic lines with aryl coupling reactions. In this Account, the development of the defective nanocarbon molecules, i.e., geodesic phenine frameworks, is summarized to overview unique structural/electronic features.
A monocationic Zn(II) acetate complex of a C2-chiral bisamidine-type sp2N bidentate ligand (LR) possessing two dioxolane oxygen n orbitals in the reaction site catalyzes, without the use of an external base, a highly efficient asymmetric 1,3-dipolar cycloaddition (1,3-DC) of tridentate α-substituted α-imino esters with acrylates, attaining up to >99:1 enantiomeric ratio with perfect regio- and diastereo-selectivities. A catalyst loading of 0.1 mol% is generally acceptable to furnish various chiral multi-substituted prolines. Both (S)-α-imino ester and the R enantiomer show a high level of enantioselectivity. An overall picture of the present 1,3-DC has been revealed via analyses of substrate structure/reactivity/selectivity relationships, NMR, MS, X-ray diffraction, 12C/13C isotope effects, rate law, and kinetics. The first success in the high performance 1,3-DC is ascribed to i) a Brønsted base/Lewis acid synergistic effect of [Zn(OAc)LR]OTf (R cat); ii) the existence of the n orbital, which determines the position of the intermediary N,O-cis-Zn enolate (dipole) by an n-π* non-bonding attractive interaction between the oxygen atom in LR and the C=N moiety of the dipole; and iii) utilization of chelatable α-imino esters capturing Zn(II) as a tridentate ligand. A 12C/13C analysis has clarified that a stepwise 1,3-DC mechanism is operating.
In the realm of supramolecular chemistry, the development in synthetic receptors for harmful analytes has attracted substantial attention in recent decades due to the fact that a huge number of chemical and biological processes involve molecular recognition of these species. It is therefore important to develop methods/techniques for sensing such analytes. To design and develop a chemical sensor, one or more urea/thiourea fragments are incorporated in acyclic, cyclic, or polymeric frameworks that are directly attached to the signaling units as well as spacers. Being a good hydrogen bond donor, urea/thiourea has an excellent binding affinity for anionic and neutral species. In our research, we designed and developed urea/thiourea based novel receptors decorated with finely tuned signaling units and spacers for the detection of fluoride, cyanide, and tabun (first nerve agent). The developed chromogenic and fluorogenic hosts instantaneously detect these toxic anions and analytes with exceptional selectivity over other interfering agents. Inspired by the multianalyte detection approach, we further aimed to explore novel chromo-fluorogenic receptors that not only detect these analytes but also differentiate from one another. Urea/thiourea motifs have been extensively used in the chemosensing of anionic and neutral analytes, supramolecular catalysis, and supramolecular medicinal chemistry. In this Account, these studies have also been briefly summarized.
We herein summarize our recent results on the design and application of metal complexes that bear N-phosphine-oxide-substituted imidazolylidenes (PoxIms), in which the volume and shape of the reaction space around the carbene atoms can be drastically changed via the rotation of the N-phosphinoyl groups; this phenomenon is discussed in detail based on experimental and theoretical results. We also discuss the application of PoxIms to implement the frustration revival strategy via the synthesis of external stimuli-responsive Lewis acid–base adducts that are comprised of PoxIms and B(C6F5)3, as well as to the phosphinoylation of CO2 and carbonyl compounds. The results presented in this Account have expanded the frontiers of multifunctional N-heterocyclic carbenes, which had previously been employed mainly as multidentate ligands for metal complexes.
In this account, we summarized our recent efforts to develop molecular transformations under Brønsted base catalysis on the basis of our own guiding principles for designing reaction systems, that include “the generation and application of anionic species which are difficult to utilize in conventional reaction systems” and “the employment of organosuperbases possessing much higher basicities than conventional organic bases as a catalyst”. In particular, we discussed reactions involving the generation of carbanions of less acidic compounds through the formal umpolung process from carbonyl compounds and formal [3+2] cycloadditions involving the generation of the synthetic equivalent of a 1,3-dipole through epoxide opening.
We here describe our various concepts and achievements for material science, which have been introduced through liquid-crystalline (LC) and polymer chemistry. They have resulted in the development of new classes of functional organic, polymer, and hybrid materials. Supramolecular LC complexes and polymers with well-defined structures were found to be built through complimentary hydrogen bonding between carboxylic acid and pyridine. Since then, a variety of intermolecular interactions such as hydrogen bonding, ionic interactions, ion-dipolar interactions, and halogen bonding were used for the formation of supramolecular liquid crystal organic materials and polymers. The nanosegregation in molecular assemblies in liquid crystals leads to the various 1D, 2D and 3D self-assembled nanostructures. These strategy and material designs lead to the development of new dynamically functional materials, which exhibit stimuli-responsive properties, photoluminescence, transport of charge, ions, and molecules, electro-optic properties, and templates. We also show new hybrid liquid crystals, biomineral-inspired nanorod and nanodisk liquid crystals. These nanomaterials form colloidal LC solutions, which exhibit stimuli-responsive properties.