In this article, our recent results from practical optical resolution methods of disubstituted and tetrasubstituted [2.2]paracyclophane compounds and their transformations are described. The obtained enantiopure [2.2]paracyclophane compounds have been used as chiral building blocks to prepare optically active π-stacked molecules. π-Stacked molecules construct optically active second-ordered structures, such as V-, N-, M-, X-, triangle-shaped, and one-handed double helical structures, due to the orientation of stacked π-electron systems. They emit circularly polarized luminescence (CPL) by photo-excitation. [2.2]Paracyclophane-based chiral π-stacked molecules in this article emit brightly owing to good photoluminescence (PL) quantum efficiencies as well as large molar extinction coefficients. In particular, emission is of course CPL with a large disymmetry factor (glum value). It is basically difficult to achieve CPL with high brightness, high PL efficiency, and large glum value by using other chiral scaffolds; therefore, planar chiral [2.2]paracyclophane is an ideal scaffold to be an excellent CPL emitters.
Optimized pore size is essential for maximizing the encapsulation efficiency of molecules in solid supports. In this work, we prepared porous silica nanosheets with mesopore in the size range from several to dozens of nanometers, which may provide suitable spaces for loading of various molecules. Without any surface modification, the porous silica nanosheets show excellent immobilization capability (27 wt%) of enzymes with large molecular sizes (>10 nm). An enhanced activity of alcohol dehydrogenase (ADH) in the porous silica nanosheets was also achieved in compared with free ADH or ADH in mesoporous silica nanoparticles with average pore size of 12 nm. In addition, this ADH-silica nanosheets system showed effective catalytic performance not only with pure ethanol, but also alcohol drinks with complicated gradients or after relative harsh treatments. The efficient supporting of this inorganic porous structure to enzymes might also lead to its potentials for other biocatalysis, biosensing and enzymatic determination of alcohols etc.
Fine-tuning the physical and chemical properties of graphene and its derivatives is crucial for developing novel multi-functional graphene-based devices. Natural bio-surfaces with rich micro-nanostructures are inspirational for such schemes since they possess unique properties such as superhydrophobicity. In order to effectively acquire these bio-functions, graphene-related materials need to be structured into regularly arranged biomimetic structures. Laser-processing techniques, such as two beam laser interference lithography and femtosecond laser direct-writing, are powerful prototype techniques for their outstanding patterning ability. Herein, we briefly reviewed laser-structuring on graphene or graphene oxide to realize highly functional biomimetic surfaces.
Magnetic carboxylated multi-walled carbon nanotubes (Fe3O4-MWCNTs-COOH) have been prepared via in situ preparation. The Fe3O4-MWCNTs-COOH composite was characterized by transmission electron microscopy, X-ray diffraction and vibrating sample magnetometer, and then was successfully applied for the determination of caffeine in carbonated beverages coupled with high performance liquid chromatography. Compared with cetyltrimethylammonium bromide modified magnetic nanoparticles (Fe3O4/CTAB), chitosan modified magnetic carboxylated multi-walled carbon nanotubes (Fe3O4-MWCNTs-COOH/Chitosan), magnetic hydroxylated multi-walled carbon nanotubes (Fe3O4 enclosure MWCNTs-OH) and a hybrid which was composed of magnetic carboxylated multi-walled carbon nanotubes and magnetic hydroxylated multi-walled carbon nanotubes (Fe3O4 enclosure MWCNTs-OH-MWCNTs-COOH), the Fe3O4-MWCNTs-COOH composite exhibited better extraction efficiency for caffeine. The main parameters affecting the extraction efficiency were optimized in detail. Under the optimal conditions, satisfactory performance was obtained. The calibration curve was linear over the concentration range of 7.0 to 600.0 ng mL−1 with correlation coefficients (r) between 0.9993 and 0.9995. The limit of detection was 2.0 ng mL−1. The recoveries were between 97.5% and 101.2% with relative standard deviations ranging from 1.8% to 3.7%. Overall, the proposed method was an effectual pretreatment and enrichment procedure and could be utilized for the analysis of caffeine in complex matrices.
Silver nanoparticles are known to have strong antibacterial activity and constitute a novel material to treat infectious diseases caused by pathogenic bacteria. The antimicrobial activity of silver nanoparticles is influenced by two important factors, their high dispersion stability and their release of silver ions. In this study, silver nanoparticles were treated with gold ions. The resultant Ag/Au nanoparticles were a hollow-shaped alloy made of silver and gold atoms. The antibacterial activity of the Ag/Au nanoparticles against the pathogenic bacteria S. Typhimurium was stronger than the original silver nanoparticles. Additionally, the release of silver ions from the hollowed Ag/Au nanoparticles was higher than the original silver nanoparticles. The existence of gold atoms on the silver metal and chloride ions in the medium likely enhanced the release of silver ions from the nanoparticles. The gold treatment of silver nanoparticles is an effective method to improve their antimicrobial activity.
In addition to ketene dithioacetal monoxides that were specially designed and have been used so far, general alkenyl sulfoxides of moderate reactivity have now become applicable as substrates in the trifluoroacetic anhydride-mediated annulation with phenols for the shorter-step and transition-metal-free synthesis of benzofurans having diverse substituents. The improved method enabled concise formation of furan-fused complex polycyclic skeletons, which culminates in the two-step synthesis of dioxahelicene. The modest reactivity of alkenyl sulfoxides has allowed isolation of dihydrobenzofurans as intermediates, which unveiled two interesting phenomena: (i) the initial cyclization reflects the stereochemistry and steric environment of alkenyl sulfoxides and (ii) the aromatization by the departure of alkanethiol is the rate-determining step.
In this account we describe the various morphologies of crystalline structures called supracrystals of 5 nm Au nanocrystals used as building blocks. The Au nanocrystals are coated with dodecanthiol, except when it is mentioned in the text. It is shown that traces of water molecules markedly change the average distance between nanocrystals. Similarly, the way to solvent evaporation, solvent vapor pressure and excess of coating agents induces a transition from films to shaped supracrystals. Furthermore, segregation between single domain and polycrystalline 5 nm Au nanocrystals takes place during the supracrystal formation. By mixing single domain Au and Co nanocrystals, vicinal surfaces are produced. A mechanism of such spontaneous formation of high index planes in Au single domain nanocrystal superlattices is proposed.
Canonical peptide nucleic acid (PNA), in which naturally occurring nucleobases (A, G, C, and T) are bound to a poly(N-(2-aminoethyl)glycine) backbone, forms a stable duplex with single-stranded complementary DNA. However, this PNA hardly forms stable complexes with double-stranded DNA. We here show that, when some of the A and T groups therein are replaced with pseudo-complementary nucleobases (2,6-diaminopurine and 2-thiouracil), even only one strand of this partially pseudo-complementary PNA efficiently invades double-stranded DNA. This single-strand invasion spontaneously occurs at 25–50 °C, indicating its promising applicability to versatile purposes both in vivo and in vitro. The promotion by 2,6-diaminopurine is primarily attributed to the formation of an additional hydrogen bond with T in one of the two DNA strands, whereas the 2-S atom in 2-thiouracil promotes stacking interactions with adjacent nucleobases. Furthermore, the present new methodology is successfully employed to site-selective scission of double-stranded DNA, in which the single-stranded portion, formed upon the single-strand invasion, is preferentially hydrolyzed by CeIV/EDTA complex.
A phytochemical investigation of the leaves of Solanum capsicoides resulted in the isolation and characterization of five new withanolide-type steroids, capsisteroids G–K (1–5), along with three known analogues (6–8). Their structures were identified by interpretation of the NMR and HRESIMS data as well as by spectral data comparison with known analogues. The isolated steroids were found to be not cytotoxic against a limited panel of cancer cell lines. The ability of the isolated steroids to suppress superoxide anion generation and elastase release in N-formyl-methionyl-leucyl-phenylalanine/cytochalasin B (fMLF/CB)-induced human neutrophils was also evaluated and displayed variable activities.
In this paper, development and application of iridium catalysts for dehydrogenative reactions including (1) dehydrogenative oxidation of alcohols into carbonyl compounds, (2) hydrogen storage systems based on the reversible interconversion between saturated N-heterocycles and unsaturated aromatic N-heterocycles by catalytic dehydrogenation and hydrogenation, and (3) efficient hydrogen production from methanol-water solution under very mild conditions, are reported. The key point of the study described in this paper is designing a series of catalysts based on the cooperation of a metal center and a functional ligand, which is based on reversible transformation of two catalytically active species (an iridium species bearing α-pyridonate-based functional ligand and an iridium species bearing α-hydroxypyridine-based functional ligand). Various novel iridium catalysts have been synthesized and a number of catalytic dehydrogenative reactions have been developed. In addition to providing new methods for organic synthetic chemistry, these investigations would contribute to the fields of environmental chemistry and sustainable energy research.
In this study, the yield of nanosheets fabricated through the exfoliation of Li(Ni0.33Co0.33Mn0.34)O2 in aqueous solution was enhanced by performing an additional chemical oxidation step. The lateral dimensions and thickness of the obtained nanosheets were estimated via atomic force microscopy, and their chemical composition was determined using thermogravimetry, chemical composition analysis, and X-ray absorption near edge structure measurements, while their local crystal structure was examined using Raman spectroscopy and X-ray absorption fine structure techniques. In addition, the electrode properties of the restacked nanosheets in aqueous KOH solution were compared with those of the layer-structured bulk material.
In contrast to methyl and isobutyl phenyl sulfone, condensing under basic conditions higher alkyl sulfones and trans-2,3-epoxy-butanol 13c (or its O-benzyl and O-silyl derivatives) proved unfeasible, a difficulty that was overcome by using mono ethers of trans-2,3-epoxy-butane-1,4-diol 35c as the electrophilic reagents. Thus, adding excess BuLi to a mixture of the benzyl ether 35b and sulfone ent-12a, a stereodiad sulfone prepared in pure state from the R-Roche ester, via the O-trityloxy-sulfone ent-12c (X-ray), gave, after elimination by column chromatography of the side-formed regioisomer, a diol-sulfone that was next converted to sulfone 20 by means of conventional functional-group modifications. Reacting likewise this sulfone with the parent O-PMB derivative 35a, and then proceeding to the same purification process and function adjustment, delivered the title fragment in virtually pure state.
A combination of iron(III) fluoride and 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene (SIPr) catalyzes the high-yielding cross coupling of an electron-rich aryl chloride with an alkyl Grignard reagent, which cannot be attained using other iron catalysts. A variety of alkoxy- or amino-substituted aryl chlorides can be cross-coupled with various alkyl Grignard reagents regardless of the presence or absence of β-hydrogens in the alkyl group. A radical probe experiment using 1-(but-3-enyl)-2-chlorobenzene does not afford the corresponding cyclization product, therefore excluding the intermediacy of radical species. Solution-phase X-ray absorption spectroscopy (XAS) analysis, with the help of density functional theory (DFT) calculations, indicates the formation of a high-spin (S = 2) heteroleptic difluorido organoferrate(II), [MgX][FeIIF2(SIPr)(Me/alkyl)], in the reaction mixture. DFT calculations also support a feasible reaction pathway, including the formation of a difluorido organoferrate(II) intermediate which undergoes a novel Lewis acid-assisted oxidative addition to form a neutral organoiron(IV) intermediate, which leads to an FeII/FeIV catalytic cycle, where the fluorido ligand and the magnesium ion play key roles.
Self-assembling peptides have been explored as building blocks to construct functional materials that can be used in a broad range of biomedical applications. This account gives an overview of the materials built from biomolecules and summarizes the cell culture and drug delivery applications of nanofibrous and hydrogel materials formed via self-assembly of peptides. The design flexibility of materials composed of calcium ion-responsive peptides, which offer a wide range of applications from cell culture scaffolds to drug releasing devices, is highlighted.
Recently, thermoelectric (TE) conversion has attracted strong interests toward converting waste heat to electrical potential for applications such as portable and wearable electronic devices. Among a number of different candidates including inorganic and polymeric materials, single-walled carbon nanotubes (SWCNT) are particularly attractive due to their non-toxicity, material abundance, solution processability, remarkable electrical conductivity and so on. Here, progress in TE research based on SWCNT sheets is reviewed mainly for air stabilization of n-type SWCNT sheets and the TE properties of semiconducting SWCNT sheets.
Synthesis and dynamic nature of molecular and macromolecular systems controlled by rotaxane molecular switches are discussed. Rotaxane molecular and macromolecular switches including those working without solvent were synthesized mainly using sec-ammonium salt/crown ether couples. A linear polymer possessing a crown ether/sec-ammonium salt-type rotaxane moiety at the chain terminal was prepared by the rotaxane-linking of single polymer chain, and applied to the linear polymer–cyclic polymer topology transformation. Successful synthesis of macromolecular rotaxane (M2R) possessing single polymer axle and one crown ether wheel made possible a variety of unique applications such as development of topology-transformable polymers and rotaxane cross-linked polymers (RCPs) by connecting polymer chains to the components of M2R. The pronounced dynamic nature of these polymer systems is quite interesting and is expected to afford much useful information for designing novel stimuli-responsive molecules, polymers, and polymer materials.
To investigate local electron transfer in metal-organic frameworks (MOFs), we synthesized a new MOF structure composed of zinc cations and 1,4-naphthalenedicarboxylate (14ndc) linker anions. The crystal structure was determined by single crystal X-ray diffractometry and the optical properties were investigated by measurements of luminescence and excitation spectra. [Zn4(ndc)3(OH)2](C2H5OH)(1.4H2O) crystallizes in space group P-1 and contains ZnO4 and ZnO6 coordination spheres linked by the naphthalenedicarboxylate (ndc, C12H6O42−) units. Under UV irradiation, the MOF shows violet luminescence, which is probably due to energy transfer involving two different systems in the structure. The MOF shows good stability in a water/ethanol mixed solvent (approximately 3:5 ratio by volume that is consistent with the solvent used for sample preparation).
High-performance, low molecular weight gelators can be used as stimuli-responsive functional materials and soft templates for shape-controlled metal nanomaterials. In previous work, we reported that double-helical Au nanowires (NWs) can be synthesized in semi-transparent hydrogels prepared by addition of LiCl to aqueous solutions of d-12-hydroxystearic acid (HSA) and a long-chain amidoamine derivative (C18AA). In this work, we report the effect of three components, i.e., C18AA, HSA, and LiCl, on the fluidity and thermal properties of the hydrogel and the morphological structure of the gelator consisting of C18AA and HSA. We also demonstrate that gelation-degelation regulation and the gel–sol transition temperature can be controlled by tuning the concentrations of LiCl and C18AA, respectively. Further, the degelation behavior affords a gentle removal of the hydrogel soft template from double-helical Au NWs simply by washing with water.
Chemical doping of graphene is necessary to generate a band gap that is valuable for a range of applications. Chemical doping of graphene with elements like nitrogen and boron gives rise to useful properties. In this context, recent studies of borocarbonitrides, BxCyNz, comprising carbon, and the two elements on either side of it, are of significance. While uniformly homogeneous compositions of borocarbonitrides may be hard to generate, there have been efforts to synthesize them by solid state as well as gas phase routes. The products obtained show evidence for the presence of B-C and C-N bonds besides B-N and C-C bonds (but no N-N bonds), and possible occurrence of random BCN networks in addition to graphene and BN domains. Properties of borocarbonitrides depend on the composition, and the method of synthesis, enabling one to traverse from the insulating BN to the conducting graphene. In this account, we present important features of borocarbonitrides including synthesis, characterization, properties and potential applications. Surface oxygen functionalities and amine-groups of borocarbonitrides have been quantitatively determined by the fluorescence labeling of surface species (FLOSS) technique. Typical applications are in gas adsorption and energy devices such as supercapacitors and fuel cells as well as electrochemical sensors. Performance of borocarbonitrides as a HER catalysts is impressive, showing electrochemical activity close to that of Pt. It is possible to covalently link a BCN layer to other 2D nanosheets and the materials obtained by such cross-linking with layers of C3N4, MoS2 and MoSe2 show outstanding HER performance and other useful characteristics. Interestingly, heterostructures of BCN with nanosheets of MoS2 and other 2D materials can be formed reversibly by supramolecular means, which show good visible-light driven photochemical hydrogen evolution activity.
Thermal lens spectrometry was realized under an optical microscope by controlling the chromatic aberration of the objective lens system. This thermal lens microscope (TLM) is ultrasensitive to non-fluorescent molecules and detection at even the yoctomole level in a liquid was confirmed. The TLM is widely applicable, almost the same as spectrophotometry, but its specificity for the analyte species is similarly poor. During development of the TLM equipment, a microchannel fabricated on a glass substrate was used as a sample vessel, which then became a microchemical chip. The generalized microchemical chip design method, micro unit operation (MUO) and continuous flow chemical processing (CFCP) was proposed and a variety of complex chemical processes for analyses, syntheses, and biomedical experiments could be integrated onto the microchemical chip. Therefore, the development of microchemical chips realized significant expansion of the field of microfluidics. Microchemical chips are also suitable devices for separation chemistry, and combination of the TLM and microchemical chips could compensate for the poor selectivity of TLM. These innovative methods will not only impact analytical chemistry but also microfluidics and most certainly other research fields such as biology and medicine. This account of The Chemical Society of Japan Award for Creative Work 2006 introduces these achievements.