Isoquinolines are ubiquitous structural motifs in a variety of bioactive compounds, including medicinal agents and natural products. The development of novel strategies for the preparation of isoquinolines using non-toxic organocatalysts is thus worthwhile. Herein, we report a simple amine-catalyzed protocol for the synthesis of isoquinolines from 1,5-yne-imines via the intramoleular migration of an N-aryl sulfonyl group to the carbon atom of the alkyne moiety.
Insights of environmental perturbation (an external electric field, EEF) are complicated but important in terms of experiments. In this paper, we report theoretical results of the effect of an EEF on olefin epoxidation by an Fe(IV)OCl–porphyrin complex using density functional theory. The EEF along the electron flow greatly affects the potential energy profile, and thereby affects the reaction mechanism and stabilization of the species. The results show that a negative EEF catalyzes ethylene epoxidation, whereas a positive EEF inhibits the reaction. Moreover, an EEF can exchange the ground state with the low-lying excited states. Therefore, the potential energy profile along the epoxidation reaction is mainly modified by the electron transfer from ethylene to the Fe(IV)OCl–porphyrin complex.
An ultrathin film was prepared by hybridizing a cationic Ir(III) complex with exfoliated nanosheets of clay minerals such as natural montmorillonite (denoted by MON) or synthetic saponite (denoted by SAP). The utilized Ir(III) complex with two long alkyl chains was [Ir(dfppy)2(dc9bpy)]+ (fppyH = 2-(2′,4′-difluorophenyl)pyridine; dc9bpy = 4,4′-dinonyl-2,2′-bipyridine) (denoted by DFPPY). Hybridization was performed at an air-water interface between a floating monolayer of the Ir(III) complex and the nanosheets exfoliated in an aqueous subphase. The hybrid floating film thus formed was transferred onto a hydrophilic quartz plate by a vertical dipping method. The emission from the deposited films exhibited rapid reversible change of intensity in response to the introduction or evacuation of oxygen gas in the pressure range of 0.1–101.3 kPa and the temperature range from 253 K to 313 K. The lifetime of the emission decay was measured as a function of oxygen pressure, confirming the occurrence of dynamic quenching of excited Ir(III) complexes by oxygen molecules.
A five-membered cyclic (amino)(ferrocenylene)carbene (CAFeC) ligand was developed as the counterpart of existing seven- and six-membered planar chiral CAFeC ligands to enrich the series. The novel CAFeC was subjected to carbene trapping experiments with sulfur and an iridium complex. The resulting sulfur adduct and Ir dicarbonyl complex were fully characterized by X-ray diffraction analysis, high-resolution mass spectrometry, and multinuclear NMR spectroscopy. The Tolman electronic parameter (TEP) of the Ir dicarbonyl complex revealed that the donor strength of the new CAFeC is high, as expected.
As part of our research over the past 20 years, we have designed sequence-specific DNA-binding ligands that are based on the chemical molecular recognition of bases in nucleic acids. The DNA minor groove-binding molecules, N-methylpyrrole (P), and N-methylimidazole (I) polyamides, have been developed to regulate the specific gene expression or high-order DNA structures and visualize specific DNA sequences in cells. The binding properties of PI polyamides were designed to target specific sequences for various chemical applications. The development of PI polyamides may be useful when applying the vast base sequence information obtained from recent genomic-level research.
Iron oxide (α-Fe2O3 and α-FeOOH)-based composite films were fabricated using an FeCl3·6H2O ethanol solution and transparent urethane resin. Iron oxide particles 50–90 nm in diameter were observed in the resulting composite films; analyses by Fourier transform infrared (FT-IR) spectroscopy and transmission electron microscopy confirmed the presence of iron oxide particles in the films. The films were initially yellowish-brown and turned greenish-gray upon UV irradiation. After UV irradiation of the films, their bandgap decreased (Bürstein–Moss effect). When the composite films (after UV irradiation) were placed in a dark room, their color and bandgap were restored to their initial states. Thus, the iron oxide-based composite films exhibited reversible photochromism.
Ultrasound has attracted much attention in recent years as an external stimulus capable of activating different types of nanomaterials for therapeutic application. One of the characteristics that makes ultrasound an especially appealing triggering stimulus for nanomedicine is its capacity to be non-invasively applied in a focused manner at deep regions of the body. Combining ultrasound with nanoparticles, different biological effects can be achieved. In this work, an overview of the four main types of inducible responses will be provided: inducing drug release, producing ultrasound-derived biological effects, modifying nanoparticle biodistribution and developing theranostic agents. Several examples of each one of these applications are presented here to illustrate the key concepts underlying recent developments in the discipline.
Molecular probes are useful chemical tools that are widely applied in life science research, including in molecular biology and drug discovery. However, the preparation of molecular probes often requires considerable time and effort even if the synthesis is conducted by well-trained organic chemists. This is mostly due to the complex structure of the target molecules or their precursors, which typically contain sensitive functional moieties. Furthermore, the synthetic route to probes must frequently be modified from that of the original compounds because the functional moiety of the probe should be preferably introduced into the molecule at a late stage of the synthesis. To address these issues, we propose a new concept that we named a “molecular renovation strategy” that can expedite the synthesis of molecular probes. This approach involves direct transformation of the original bioactive compounds to the probe precursors, followed by the introduction of a functional moiety. This account describes our recent efforts to realize this concept, particularly made for expeditious preparation of imaging probes for positron emission tomography (PET) via transition metal-catalyzed borylation reactions via cleavage of stable chemical bonds and transition metal-mediated deborylative radiolabeling reactions with PET nuclides.
The dialkylgermylene Trp*2Ge: (Trp*: peripherally extended sterically demanding alkyl groups based on the triptycyl (Trp) framework), was obtained from the reaction of Trp*Li with GeCl2·dioxane. The structure of Trp*2Ge: was unequivocally determined by NMR and UV-vis spectroscopy, mass spectrometry, and a single-crystal X-ray diffraction analysis. Moreover, the reactivity of Trp*2Ge: was examined.
The synthesis of C-arylcalixpyrogallolarene sulfonic acid derivatives and their application as an organocatalyst material for biodiesel production were investigated. The C-arylcalixpyrogallolarene derivatives were prepared in high yields through a two-step reaction: condensation between pyrogallol and aromatic aldehydes (i.e. benzaldehyde, 4-hydroxy-3-methoxybenzaldehyde and 4-ethoxy-3-methoxy benzaldehyde) and then followed by a sulfonation reaction with sulfuric acid. They were evaluated as the organocatalyst for the esterification reaction of palmitic acid with methanol as a representation of biodiesel production. Using 4 mol% of C-4-hydroxy-3-methoxyphenylcalixpyrogallolarene sulfonic acid, methyl palmitate was generated in up to 91.9% yield after 4 h at 65 °C, making it similarly efficient to sulfuric acid that is used as the catalyst in the conventional reaction under similar conditions. However, different from sulfuric acid, the C-4-hydroxy-3-methoxyphenylcalixpyrogallolarene sulfonic acid could be recovered by using a simple filtration technique making it better than sulfuric acid from industrial and environmental points of view. These results demonstrate that the C-arylcalixpyrogallolarene sulfonic acid derivatives are a novel and potential organocatalyst for methyl palmitate biodiesel production.
The ET•+ molecules in a charge-transfer salt (ET)Ag4(CN)5 form a three-dimensional diamond spin-lattice with S = 1/2 (ET: bis(ethylenedithio)tetrathiafulvalene), where a geometrical spin-frustration is expected when an appropriate spin interaction is realized. A metallic nature has been proposed for this salt based on both band calculation and electron paramagnetic resonance measurements. We studied the crystal and band structures, optical spectra, resistivity, magnetic, and NMR measurements and found the salt to be a three-dimensional monomer Mott insulator with a resistivity of 1.8 × 102 Ω cm at room temperature (// c), though the calculated band structure showed a Dirac-like semimetallic dispersion. 1H NMR and magnetic susceptibility measurements reveal an antiferromagnetic spin ordering at TN = 102 K, above which characteristic temperature insensitive behaviors of T1−1 and spin susceptibility are observed. A weak ferromagnetism is detected below TN with a spin canting angle of ∼0.01°, possibly arising from a Dzyaloshinskii-Moriya interaction due to a lowering of the crystal symmetry. This is the first example of a weak ferromagnetic three-dimensional diamond spin-lattice among the organic charge-transfer solids.
Efficient conversion of crystalline cellulose to useful chemicals is a grand challenge in biorefining. In this work, we report that amorphization and semi-dry conversion of crystalline cellulose to oligosaccharides is achieved by impregnated H3PO4. Specifically, the impregnation of crystalline cellulose with H3PO4 under 5 MPa of He and subsequent drying at room temperature produces amorphous cellulose. The impregnated H3PO4 likely permeates bulk phase cellulose by dissociating the hydrogen bonding network of cellulose during the treatment. The resulting swollen solid is depolymerized to oligosaccharides in 40% yield with 72% selectivity by heat-treatment at 100 °C with no solvent. The analysis of obtained oligosaccharides using nuclear magnetic resonance and mass spectroscopy reveals that the products are oligomers of glucose linked by various kinds of glycosidic bonds that may be useful as prebiotics.
The rhodium (III) complexes supported by a di-deprotonated o-phenylenediamido ligand, ([Cp*RhIII(C6H4N2tBu2Ph22−)] ([Cp*RhIII(L2−)], 1), and one-electron and two-electron oxidized ligands, [Cp*RhIII(C6H4N2tBu2Ph2•−)(CN)] ([Cp*RhIII(L•−)(CN)], 2) and [Cp*RhIII(C6H4N2tBu2Ph20)(CN)]+ ([Cp*RhIII(L0)(CN)]+, 3) (H2L = H2C6H4N2tBu2Ph2 = N,N-di-(3,5-di-tert-butylphenyl)benzene-1,2-diamine)), have been synthesized and characterized by 1H NMR, ESI–mass, EPR, UV-vis spectroscopic methods, and cyclic voltammetry as well as single-crystal structure analysis. In complexes 2 and 3, a cyanide ion coordinates to each rhodium(III) center to stabilize the six-coordinate structures. Catalytic activity of these complexes has been examined in the intramolecular C–H amination of trisylazide (2,4,6-triisopropylphenylsulfonyl azide) to find that complex 2 shows the highest activity. The result suggests that single-electron transfer takes place from the anion radical ligand C6H4N2tBu2Ph2•− of 2 to trisylazide to form a nitrene radical bound rhodium(III) active species for the C–H amination.
Organotellurium chain transfer agents (CTAs) used for organotellurium-mediated radical polymerization (TERP) are highly photosensitive and generate radicals by carbon-tellurium bond homolysis upon absorbing UV-vis light at approximately 350–500 nm. The controlled radical polymerization of various vinyl monomers takes place in the presence of organotellurium CTAs under photoirradiation. The use of low-intensity light is important to attain structural control because of the need to maintain a low radical concentration. Photo-TERP not only preserves the synthetic advantages of TERP under thermal conditions, as exemplified by its high versatility in polymerizable monomer families, but also attains new benefits, including decreasing the amount of dead polymers, increasing the control of the macromolecular structure, lowering the polymerization temperature, and providing temporal control. In contrast, irradiation of a polymer prepared by TERP in the presence of dienes and styrenes with high-intensity light selectively gives the dimer via a polymer-end radical coupling reaction. Various symmetrical telechelic and mid-chain-functionalized polymers and ABA-triblock copolymers can be synthesized. Due to the mild conditions for both photo-TERP and the coupling reaction, unique macromolecular structures, and high structural control, these methods provide a new method in macromolecular engineering for fabricating functional polymer materials with improved and/or new functions.
Selective hydroxylation of arylboronic acids was achieved through PVP (polyvinylpyrrolidone)-stabilized nanogold catalyzed in situ generated H2O2 formed by the oxidation of an alcoholic solvent under aerobic conditions. The synthetic application of in situ generated H2O2 was investigated through aerobic epoxidation of (E)-chalcone.
In a catalyst ink for polymer electrolyte fuel cells (PEFCs), some of the ionomer is adsorbed on the carbon-supported Pt catalyst (Pt/C), which enhances the ink stability, while the rest is dispersed in the solvent as a nonadsorbed ionomer. To clarify the effect of nonadsorbed ionomer on the ink viscosity, the amount of nonadsorbed ionomer in the catalyst ink was evaluated by small-angle neutron scattering (CV-SANS). At high-shear viscosity, the nonadsorbed ionomer was found to act as ionomer solution described by the Huggins equation. Moreover, comparison with the CV-SANS results revealed that the conventional filtration method overestimates the amount of nonadsorbed ionomer in a catalyst ink.
Fujita’s stereoisogram approach (S. Fujita, Mathematical Stereochemistry; De Gruyter: Berlin, 2015) has been applied to the discussion on the stereochemistry of twistane derivatives. In addition to chirality as the first kind of handedness, RS-stereogenicity is emphasized as the second kind of handedness, where an R-twistane skeleton and an S-twistane skeleton are recognized to be a pair of RS-diastereomers as a result of RS-stereogenicity. The contrast between global/local chirality and global/local RS-stereogenicity is clearly demonstrated by introducing the names, R-twistane and S-twistane, which are based on the globality of RS-stereogenicity. Among the five types of stereoisograms (type I to type V) as the full repertoire, there appear only type-I and type III stereoisograms during the discussions on twistane derivatives. Combinatorial enumeration of twistane derivatives are discussed on the basis of Fujita’s proligand method (S. Fujita, Combinatorial Enumeration of Graphs, Three-Dimensional Structures, and Chemical Compounds; University of Kragujevac, Faculty of Science: Kragujevac, 2013).