Surface pressure versus molecular area (π-A) curves were measured on pure water as a subphase for a series of N,N′-diperfluoroalkanoyl-1,2(R,R)-diaminocyclohexanes. A molecule is denoted as RR-CFn, where n is the number of carbon atoms in a perfluoroalkanoyl chain (or n − 2 = the number of difluoromethylene units). The chain length was varied for n = 4, 5, 6, 8, 9, and 10. The results for n = 7 were reported previously. The effects of chain length and optical purity on film formation were investigated. The surface morphology of a film deposited onto a hydrophilic glass plate was observed using an atomic force microscope (AFM). For n = 4, 5, and 6, the floating films were already multilayered before compression and the deposited films were composed of rectangular or rod-like aggregates. For n = 7, 8, 9, and 10, monolayered films were formed and underwent structural transformation upon compression. From the AFM images, the films deposited after the transformation were composed of fiber-like aggregates. For a racemic mixture, no monolayer film was formed, and the film transfer was impossible irrespective of the chain length. p-Polarized infrared multiple angle incidence resolution spectrometry (pMAIRS) measurements were carried out on a film of RR-CF8 deposited onto a silicon wafer to determine the orientation of the composite molecules. The results were compared with the monolayer behavior reported for a compound having a single perfluoroalkyl chain. The relation to their gelation behavior is also discussed.
In recent years, artificial metalloenzymes (ArMs) have become a major research interest in the field of biocatalysis. With the ability to facilitate new-to-nature reactions, researchers have generally prepared them either through intensive protein engineering studies or through the introduction of abiotic transition metals. The aim of this review will be to summarize the major types of ArMs that have been recently developed, as well as to highlight their general reaction scope. A point of emphasis will also be made to discuss the promising ways that the molecular selectivity of ArMs can be applied to in areas of pharmaceutical synthesis, diagnostics, and drug therapy.
Understanding the requisite geometry of molecules and peripheral components is an essential step in endowing molecules with logical functions in quantum-dot cellular automata. To respond to the real problem of structural distortion from the ideal square cell configuration, a practical procedure is presented that simplifies the molecular shapes for device design with features that combine aspects of classical electrostatics and density functional theory calculations. By applying this method to a library of biferrocenium dimers with a three-input junction, it was demonstrated in theory that a covalently bonded parallelogram dimer responds precisely to six different patterns of nanoscale electric fields and works correctly as a device cell in both AND and OR logic gates. The counterintuitive usefulness of the non-square-shape is rationalized by four ferrocene-based orbital orientations and a functional group arrangement, equalizing the disadvantageous energy asymmetry between the states 0 and 1. The present procedure was applied to quasi-square tetrametallic Ru complexes and it was found that these complexes do not work as logic gates. This procedure expands the range of existing candidate molecules from squares to parallelograms and facilitates screening for implementation.
This account describes our quest for controlling the reactivity of organoiron species, and developing an iron catalyst that can efficiently activate a C–H bond of a substrate possessing a directing group, followed by reaction with nucleophiles (magnesium, zinc, boron, or aluminum reagents), electrophiles (alkyl halides, alkanol derivatives, allyl ethers, alkenes, alkynes, chloroamines), or with another C–H substrate (heteroarenes or electron-deficient arenes). Our forays into C–H activation using cobalt, manganese, and chromium catalysis are also briefly discussed.
The native water-soluble chlorophyll protein, CP663, extracted from Lepidium virginicum, consists of four subunits, each with one chlorophyll (Chl), and the four Chls form two dimers in an orthogonal arrangement. Accordingly, CP663 is considered to have three dimers, Chl a–Chl a (AA), Chl a–Chl b (AB), and Chl b–Chl b (BB), in a certain composition and to provide six excitonic transitions because each dimer gives rise to low (L)- and high (H)-energy transitions. To investigate the excitonic transitions and the dimeric composition, the absorption and circular dichroism spectra of CP663 were measured and the electronic transitions of the dimers were calculated by Zerner’s intermediate neglect of differential overlap method. On the basis of the experimental and calculated results, the Qy-absorption band was deconvoluted by the Gaussian fitting method. The resulting six Gaussian components were assigned to the individual transitions and the excitonic transition energy was found to increase in the order AAL, ABL, AAH, BBL, ABH, and BBH. From the spectral areas of the components, the composition of the dimers was calculated as AA:AB:BB = 0.52:0.34:0.14, indicating that CP663 accommodates the homodimers in preference to the heterodimer.
The molybdenum dioxo catalyst CNH/MoO2 is prepared via direct grafting of (dme)MoO2Cl2 (dme = 1,2-dimethoxyethane) onto the graphitic surfaces of carbon nanohorn (CNH) substrates. The structure of this heterogeneous catalyst was characterized by SMART-EM, XPS, and ICP, and is found to have single isolated MoO2 species on the surface as well as a few multi-Mo species. The CNH/MoO2 complex exhibits excellent catalytic activity for polyethylene terephthalate (PET) hydrogenolysis, N-oxide reductions, and reductive carbonyl coupling, representing an informative model catalyst for structural and mechanistic investigations.
To measure the direct electron transfer (DET) reaction of cytochrome c (Cytc) immobilized on a bare ITO electrode after removing the adsorbed molecules, automated solution exchange (ASE) processes were performed to induce their desorption. By fitting the absorbance decay curve observed at the Soret band peak position of Cytc at around 408 nm during the ASE processes with a double exponential equation, the final immobilized fraction was estimated to be 58.6% of the Cytc adsorbed on bare ITO electrodes under the experimental conditions. Cyclic voltammograms (CVs) of Cytc adsorbed on the bare ITO electrodes were measured for 60 min to elucidate the DET activity of immobilized Cytc. After repeated CV measurements, approximately 90% of immobilized Cytc was found to remain from the evaluation based on the coulombic amount of reduction and oxidation peaks. The scan rate dependent peak separation data from the immobilized Cytc between reduction and oxidation peaks in CVs produced 2.7 times larger DET reaction rate constant than that previously reported for the Cytc adsorbed on the bare ITO electrode.
[Ru(II)Cp((R)-Cl-Naph-PyCOOH)]PF6 ((R)-1) catalyzes the dehydrative cyclization of (E)-hept-2-ene-1,7-diol (2) to 2-vinyltetrahydro-2H-pyran (3) with a 97:3 S/R enantiomer ratio. Complex (R)-1 is in equilibrium between two diastereomers (R,RRu)-1 (AR) and (R,SRu)-1 (AS). A difference of turn over efficiency between the AS and AR cycles is thought to be the origin of the high enantioselectivity. The AS gives a major enantiomeric product (S)-3, according to the results of detailed mechanistic investigation via i) X-ray crystallographic analysis of related complexes, ii) NMR experiments using allylic alcohol 2, OH-lacking 2-mimic 4, d-labeled (S)-4-1d, enantiomerically enriched hept-6-ene-1,5-diol (6) as branched isomer of 2, and OH-lacking 6-mimic 5, iii) substrate structure/reactivity and selectivity relationships, iv) deuterium-labeling experiment, v) kinetics via calorimetric analysis, and vi) ligand structure/reactivity and selectivity relationships. AS captures 2 via hydrogen and halogen bonds. Oxidative addition in an H2Oin mode leads to a macrocyclic σ-allyl intermediate. Here, an efficient nC(7)OH/π*C(3)=C(2) trans-annular (TA) interaction facilitates an SN2′ nucleophilic addition of OH in an OHTA manner to furnish (S)-3. Contrary to the AS, AR cannot capture 2 using the halogen bond and slowly operates to give (R)-3. A conventional π-allyl-complex-involved mechanism is ruled out by a contradiction in the result of ii) and iii).
Chiral π-stacked molecules were prepared from planar chiral bis-(para)-pseudo-meta-type [2.2]paracyclophane. π-Electron systems were stacked to form a V-shaped structure with an angle of 120°. Optical and chiroptical properties were experimentally and theoretically investigated and compared with those of the V-shaped molecules comprising the same π-electron systems based on bis-(para)-pseudo-ortho-type [2.2]paracyclophane with an angle of 60°.
Conducting composites consisting of carbon nanohorn (CNH), carbon dots (C-dots) and polyaniline (PA) or polypyrrole (PP) have been synthesized via in-situ polymerization and evaluated for performance as electrode materials for supercapacitors. The addition of C-dots to composites of CNH and conducting polymer showed a superior influence on supercapacitance properties in comparison with composites without C-dots. Incidentally, the specific capacitance was 1206 F/g and 538 F/g at a scan rate of 5 mV/s for composites of CNH with PA and PP, respectively, with addition of C-dots. These values were 1.6 and 2.3 times higher than values for composites without C-dots. Moreover, composites with C-dots exhibited high capacitance retention (94 and 93%, respectively). Thus, these results indicate that the addition of C-dots to composites of CNH with conducting polymers provides a significant enhancing effect as promising electrode materials for energy storage devices with high capacitance and stability.
Molecular crystals consist of an array of periodically arranged molecules in a three-dimensional space. Although nowadays we can routinely obtain crystal structures at the atomic level, the picture of how individual molecules gather together in an orderly manner and grow into crystals of visible size is still unresolved. Over the last decade, we focused on the mechanism of crystal nucleation, which is the initial step of crystallization—it plays a critical role in determining the crystal structure. We investigated the self-assembly mechanism of crystal nuclei of organic crystals and metal–organic frameworks using single-molecule-level electron microscopic imaging and bulk analysis. Statistical information on the size and structure of the individual prenucleation clusters, which cannot be investigated by conventional analytical methods, allowed us to study how the nucleating crystals acquire order and dimensionality in the nucleation process. We expanded understandings of the nucleation process to prepare submicrometer-sized amorphous particles of organic compounds from supersaturated solution by suppressing transition to crystalline nuclei, by external environment control. Further elucidation of the nucleation mechanism for various molecules will realize the controlled formation of crystals with desired structure and morphology, thus improving the efficiency of industrial processes, e.g., the production of pharmaceuticals and organic electronic devices.
Thermodynamic signatures accompanying ligand binding interactions with proteins and nucleic acids have great potential in drug discovery and help in deriving guidelines for rational drug design. Frequent discrepancies have been observed between the results obtained from routinely used fluorescence spectroscopy and direct high sensitivity isothermal titration calorimetry (ITC). These discrepancies lead to incorrect data analysis even though experiments are done with extensive care. We analyze these discrepancies and discuss possible causes by taking eleven examples from literature where the data on binding processes has been obtained both by fluorescence spectroscopy and ITC. Further, a protocol has been suggested to obtain accurate thermodynamic signatures so that the information resulting from studies of biologically important ligand binding reactions is complete and leads to correct direction. Results from fluorescence quenching data on drug binding interactions have frequently been analyzed incorrectly, many times without even establishing the nature of the quenching process. This results in incorrect proposals for mechanism of binding of drugs with the target biological macromolecules. Relatively lesser problems have been observed when isothermal titration calorimetry has been employed. The analysis and suggested protocol have implications in deriving accurate thermodynamic signatures focused on rational drug design and hence in target oriented drug discovery.
The effect of the head group on the oxidation of unsaturated phospholipids under low-level ozone was investigated. The phospholipids with head groups of glycerol and choline show different surface-pressure profiles but similar degradation kinetics of the C=C moieties was observed by heterodyne-detected sum frequency generation spectroscopy.
The alt-silylene-conjugated motif copolymers consist of one to three kinds of chromophores regioselectively arranged as part of the polymeric backbone and two adjacent chromophores are linked by a trtrahedral dialkylsilylene insulating spacer. These polymers are highly folded, and a bulkier alkyl substituent (such as the isopropyl group) on silicon may exert Thorpe-Ingold effect that can bring the adjacent chromophores to closer proximity resulting in changes of photophysical properties. Interactions between chromophores include ground state interaction, formation of charge transfer complex, through-space interaction between chromophores, observation of CT emission, and photoinduced electron transfer. Notably, the Marcus inverted region is observed in such silicon-containing polymers using aminostyrene donor and a range of acceptors with different −ΔG° values. Since polymer folding is crucially related to the photophysical properties, a series of small molecules (monomer to tetramer) having the same pair of chromophores as those of the polymer are synthesized. The properties of tetramer already behave similarly to those of the corresponding polymer. Replacement of silylene linkers in polymers with substituted methylene groups also demonstrates similar kinds of interactions among chromophores, but with different intensities.
This work reports the fabrication of mesoporous Al2O3-TiO2 composites with various contents of TiO2 and their utilization as adsorbents for molybdenum anions with potential application in medical radioisotope production. The increase of TiO2 promotes the deposition of more TiO2 nanoparticles on the surface of the Al2O3 support without altering the original morphology. Furthermore, alumina samples loaded with smaller amounts of TiO2 (Al2O3-2.5% Ti (20.01 mass% TiO2) and Al2O3-5% Ti (34.55 mass% TiO2)) are amorphous in nature. However, at a high loading (Al2O3-10% Ti (63.97 mass% TiO2)), anatase TiO2 becomes the dominant phase, suggesting the extensive coverage of the Al2O3 surface by TiO2 NPs. The TiO2 modification is also observed to greatly increase the surface area from 177 m2 g−1 for pristine γ-Al2O3 to as high as 982 m2 g−1 for Al2O3-5% Ti sample. When employed for molybdenum adsorption, the Al2O3-5% Ti sample displays a higher Mo adsorption capacity (44.5 mg g−1) than Al2O3-2.5%Ti (39.0 mg g−1), Al2O3-10%Ti, (40.5 mg g−1), and pristine γ-Al2O3 (37.1 mg g−1) samples. The larger surface area and presence of additional hydroxyl groups for attracting the molybdenum anions contribute to the enhanced adsorption capacities of the Al2O3-TiO2 composites compared to that of pristine γ-Al2O3.
The room temperature ionic liquid, 1-methyl-3-octylimidazolium tetrafluoroborate, abbreviated as [C8mim]BF4, has been known as a good glass-former, which can be cooled or heated at normal scanning rates without any phase transition. However, after cooling to 183 K, just below the glass transition temperature, 190 K, followed by heating to 223 K, Tg + 33 K, a novel phase transition from the supercooled liquid to a partially ordered phase was observed by X-ray diffractometry during a slow isothermal annealing at that temperature. The XRD profiles showed that the ordered phase is not crystal, but a smectic-A phase of a bilayer structure as seen in typical lamellar phases of surfactant solutions or lipid polymers. It is remarkable that the liquid phase still remains even after the existence of the ordered SmA phase for more than 90 hours, which is supposed to be the coexistence, or partial ordering, of the liquid and liquid crystalline. This cannot be seen in conventional one-component systems, such as ordinary molecular liquids. The ionic liquid structure is expected to be very stable due to the original mesoscopic order, which is predicted by MD simulation, Raman spectroscopy and neutron scattering.
This account highlights the development of efficient methods for generation of alkyl radicals from organosilicon peroxides and their applications in selective alkylation reactions. Compared with commonly used organic peroxides, a more diverse range of organosilicon peroxides can be prepared as bench-stable alkyl radical precursors, and their use in combination with transition metal catalysts allows for generation of alkyl radicals under mild conditions. Consequently, these methods have opened up a new way for the formation of various carbon–carbon and carbon–heteroatom bonds, affording highly functionalized carbon skeletons in chemoselective or asymmetric manners.
We report simultaneous detection of tumor marker proteins using a molecularly imprinted polymer-based fluorescence sensing system, in which prostate-specific antigen (PSA) recognition cavity, labeled with Alexa Fluor 594, and α-fetoprotein (AFP) recognition cavity, labeled with Alexa Fluor 647, exist together in the polymer matrix. The individually fluorescent-labeled PSA- and AFP-imprinted polymer was prepared by a dual imprinting method, followed by multi-step post-imprinting modifications (PIM). A polymerizable group, conjugated with PSA or AFP via a disulfide bond, was prepared and immobilized on a phenylboronic acid moiety-introduced substrate by the formation of cyclic diester between phenylboronic acid and glycans on proteins. The polymer matrix was prepared using surface-initiated atom transfer radical polymerization. After the reduction of the disulfide bond and hydrolysis of the cyclic diester, PSA- and AFP-imprinted nano-cavities were generated simultaneously. In multi-step PIM, thiol-reactive fluorescent dyes were introduced via a dynamic protection procedure using the target protein, which yielded dual fluorescence-labeled imprinted nano-cavities. Fluorescence signaling abilities were assessed, and each AFP and PSA-imprinted nano-cavity was confirmed to transduce the protein binding events into specific fluorescence signals, with lower values of limit of detection (<2.0 ng/mL). Therefore, the proposed methodology could be a novel platform for the simultaneous detection of multiple proteins.
Strategies for regioselective C-H trifluoromethylation of heteroaromatic compounds are summarized herein. This review article consists of four sections: (1) Introduction; (2) C-H trifluoromethylation of five-membered heteroaromatic compounds; (3) C-H trifluoromethylation of six-membered heteroaromatic compounds; and (4) Conclusion. Each section is categorized by the reaction sites.
This study investigated the relationship between the air–water interfacial dilational viscoelasticity and foam properties in mixed anionic surfactant aqueous solutions of sodium bis(2-ethylhexyl)sulfosuccinate (AOT), sodium n-dodecylsulfate (C12AS), sodium n-tetradecylsulfate (C14AS), and sodium n-hexadecylsulfate (C16AS). The surfactants used here differ only in hydrophobic chains. The air–water interfacial viscoelasticity of AOT aqueous solutions mixed with C12AS or C14AS was similar to that of AOT single aqueous solutions at the same constituent concentration of AOT. On the other hand, the air–water interfacial viscoelasticity of mixed aqueous solutions of AOT and C16AS was intermediate between the respective single aqueous solutions. The foam properties of these mixed aqueous solutions were evaluated by a modified Ross–Miles method and it was shown that foam stability is correlated with the maximum value of viscoelastic modulus in mixed aqueous solutions of AOT and AS.
Genetic code manipulation enables the ribosomal synthesis of peptide libraries bearing diverse nonproteinogenic amino acids, which can be applied to the discovery of bioactive peptides in combination with screening methodologies, such as mRNA display. Despite a tremendous number of successes in incorporation of l-α-amino acids with non-proteinogenic sidechains and N-methyl-l-α-amino acids into nascent peptide chains, d-, β-, and γ-amino acids have suffered from low translation efficiency. This obstacle has been hindering their integration into such peptide libraries. However, the use of engineered tRNAs, which can effectively recruit EF-Tu or/and EF-P, has recently made possible significant improvement of their incorporation efficiency into nascent peptides. This article comprehensively summarizes advances in such methodology and applications to the discovery of peptide ligands against target proteins of interest.
Symmetry is found all around us. It is a fundamental concept in the arts as well as in the sciences. In chemical reactions, the use of reagents and catalysts with rotational symmetry decreases the number of transition states, a situation that may lead to increased selectivity. The presence of symmetry facilitates strucure determinations, and symmetry arguments may be helpful for elucidating mechanisms and for gaining insight into dynamic molecular processes.
Hierarchical porous carbon materials with high surface area and large porosity derived from biomass are desired for the sustainable development of low-cost electrode materials for advanced energy storage devices. Here, we report the electrochemical supercapacitance performance of washnut seed-derived nanoporous carbon materials in aqueous electrolyte (1 M H2SO4) on a three-electrode system. Potassium hydroxide (KOH) activation of the pre-carbonized Washnut seed powder at high temperatures (800–1000 °C) under nitrogen atmosphere yielded nanoporous carbons with hierarchical micro- and mesoporous structure with well-developed porosity. The surface areas and pore volumes are found in the range of 2005 to 2185 m2 g−1 and 1.370 to 2.002 cm3 g−1, respectively. The as-prepared materials showed outstanding electrochemical energy storage performance achieving a high specific capacitance of 288.7 F g−1 at a current density of 1 A g−1 followed by a high rate capability sustaining 67.2% capacitance even at a high current density of 50 A g−1 with only a small capacity loss (<2%) after 10,000 charging/discharging cycles. This work demonstrates novel insights into low-cost high-performance carbon materials design using natural biomass for the sustainable development of electrode materials for advanced supercapacitor applications.
The synthesis of helical complexes is attracting increased attention because their chiral properties lead to a variety of functional applications. In this work, a series of neutral, dinuclear M(III) (M = Al, Ga, or In) triple-stranded helicates were prepared using a tetradentate bisiminopyrrole ligand (H2L). An X-ray crystallographic analysis revealed that both right- (P) and left-handed (M) helical structures exist in the solid state for Al2L3, Ga2L3, and In2L3. The enantiomers were successfully resolved by chiral column chromatography, and the chiroptical properties of the complexes were characterized by circular dichroism, circularly polarized emission spectroscopy, and time-dependent density functional theory calculations.
The anisotropic properties of one-dimensional (1D) supramolecules have generally been the sole way to input molecular information along a structure of high density. Although the chain reaction of a synthetic polymer (e.g., in radical polymerization) does realize anisotropic polymer elongation, it has remained challenging to induce such properties in artificial 1D self-assembling systems. Herein, by employing J-aggregate nanofibers of TPPS — a sort of self-assembling porphyrin — as a model, we describe a system in which linear momentum of laminar flow facilitates directional supramolecular elongation of the flowing nanofibers. In situ fluorescence and linear dichroism (LD) measurements revealed that the elongation of the J-aggregate nanofibers could be accelerated only when they were oriented in the flow direction. Moreover, linear transport of the oriented nanofibers along the stream disrupted the isotropic reactivity at their two termini; one terminus could be activated selectively, resulting in directional nanofiber elongation. The shear rate gradient of the laminar flow induced collisions of the TPPS monomer units at the end of one terminus of the nanofibers. This strategy should be applicable more generally to supramolecular 1D elongation (supramolecular polymerization) of various functional molecules, regardless of their chemical properties, thereby extending the frontiers of supramolecular chemistry.
The selective reduction of α,β-unsaturated carbonyl compounds was achieved to produce saturated carbonyl compounds with aqueous HI solution. The introduction of an aryl group at an α or β position efficiently facilitated the reduction with good yield. The reaction was applicable to compounds bearing carboxylic acids and halogen atoms. Through the investigation of the reaction mechanism, it was found that Michael-type addition of iodide occurred to produce β-iodo compounds followed by the reduction of C-I bond via anionic and radical paths.
Herein, a continuous-flow deuteration methodology for various aromatic compounds is developed based on heterogeneous platinum-catalyzed hydrogen-deuterium exchange. The reaction entails the transfer of a substrate dissolved in a mixed solvent of 2-propanol and deuterium oxide into a catalyst cartridge packed with platinum on carbon beads (Pt/CB). Pt/CB could be continuously used without significant deterioration of catalyst activity for at least 24 h. Deuteration proceeded within 60 s of the substrate solutions being passed through the Pt/CB layer in the Pt/CB-packed cartridge.
The isopropylation of naphthalene (NP) over USY zeolite (FAU06, SiO2/Al2O3 = 6) gave all eight possible diisopropylnaphthalene (DIPN) isomers: β,β- (2,6- and 2,7-), α,β- (1,3-, 1,6-, and 1,7-), and α,α- (1,4- and 1,5-). The catalyses are operated under kinetic and/or thermodynamic controls depending on the reaction temperatures because the cavities of FAU topology are wide enough to form all DIPN isomers. Enhanced selectivities for β,β-DIPN were observed at the early stages at 200, 250, and 300 °C although the selectivities decreased with the increasing periods, accompanying the increase in α,α- and α,β-DIPN. The enhancement occurs under new types of thermodynamic controls through thermodynamically preferred transition states to β,β-DIPN. Triisopropylnaphthalene (TriIPN) isomers are also formed in the isopropylation. Unstable α,α,β-TriIPN (1,4,6- and 1,3,5-) is predominantly formed at lower temperatures; however, decreased with the increase of stable α,β,β-TriIPN (1,3,6- and 1,3,7-) at higher temperatures. The predominant formation of 1,4,6-TriIPN was also observed in the initial stages in the range of 200, 250 and 300 °C, as reaction period was increased, while the selectivity for the isomer was decreased with concomitant increase in the selectivities for the other isomers. These changes of the selectivities operated under kinetic and/or thermodynamic controls. Large cavities of the zeolite allow the formation of all TriIPN isomers without steric restriction.
A new tetracopper(I) complex containing a cuboidal Cu4S4 core, [Cu4(dap)4], where dap− is dibenzodiazepinethiolate(1–), has been synthesized and structurally characterized by single-crystal X-ray diffraction analysis. The monoanionic iminothiolate ligand dap− renders the cluster framework exceptionally stable to retain the tetranuclear structure in solution, which allows us to examine for the first time the solution properties of this class of clusters, including UV-vis and NMR spectroscopy and cyclic voltammetry.
The palladium-catalyzed reaction of 4-iodo-2-quinolones with diarylacetylenes in the presence of Ag2CO3 as a base in N,N-dimethylformamide (DMF) at 100 °C afforded unprecedented polyfused 2-quinolones via sequential [2+2+1] spirocyclization/arene C–H activation. A plausible mechanism is suggested based on control experiments and density functional theory (DFT) calculations.
The use of hole-transporting materials (HTMs) is crucial in achieving high photovoltaic performance in perovskite solar cells (PSCs). Considering the high-cost, difficult synthesis, and/or the device stability issues of the commonly used HTMs such as spiro-OMeTAD, PTAA, and PEDOT:PSS, the development of low-cost and highly-efficient HTMs for stable PSCs has received intense attention. In this Account, we summarize the recent advances of the design and synthesis of new organic HTMs with a pyrene backbone for efficient and stable PSCs, including small molecular HTMs, electropolymerized films as dopant-free HTMs, and a pyrene-cored sulfur-rich molecule as an interfacial layer of PSCs. Among the devices with these materials, the best power conversion efficiency of over 20% has been achieved.
Enantioselective C-H addition is one of the most straightforward and efficient approaches towards the synthesis of optically active molecules from readily available arenes. The most significant feature of these reactions is that the nucleophilic aryl metal species is generated catalytically in situ via C–H bond activation. These reactions typically proceed without requirement of either strongly basic or acidic conditions, thus with good functional group compatibility. In this review, recent progress on transition-metal-catalyzed enantioselective direct C-H addition to polar unsaturated bonds is summarized. The intramolecular C-H additions to carbonyls enabled by Ir(I) or Rh(III) catalyst provided an access to chiral alcohol scaffolds with high efficiency. Planar chiral 1,2-substituted ferrocenes were afforded by C-H addition of ferrocenes to acrylates by an Ir/chiral diene catalyst. In addition, the asymmetric hydroarylation reactions of Michael acceptors including acrylates, α, β-unsaturated esters and nitroolefins were also described. Moreover, the enantioselective conjugate additions of aromatic and benzylic C-H bonds to α, β-unsaturated ketones catalyzed by Cp*M(III)/chiral acid hybrid catalyst (M = Rh, Co) were presented. These enantioselective C-H additions provided a straightforward access to structurally diverse and valuable chiral fragments. Meanwhile, the reaction mechanisms are also introduced.
We successfully fabricated a novel sensing platform, a Membrane-type Surface stress Sensor (MSS) coated with copper(I) complex bearing phen and BINAP ligands, [Cu(phen)((±)-BINAP)]PF6 (1, phen = 1,10-phenanthroline, BINAP = 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl), for specific molecular sensing. Based on the transduction of mechanical stresses derived from sorption-induced deformation of Cu(I) complex, the detection performance of various volatile organic compounds (VOCs) has been investigated. The fabricated sensor devices showed selective responses to methanol over a wide range of VOCs. In addition, distinct MSS signals upon exposure to methanol were observed for mixing samples of methanol in n-hexane and gasoline with clear discrimination of ethanol mixtures. In fact, gasoline vapor with 1% methanol exhibited much higher MSS responses than 20% ethanol containing gasoline samples. Methanol contamination in gasoline and related petroleum samples is a world-wide common problem in the automobile and fuel sectors where detection of methanol contaminants with portable devices by easy procedures is required. The current research results will contribute to fulfilling these social demands.
We present the Generalized Root Mean Square Deviation (G-RMSD) method. G-RMSD is an optimization method to calculate the minimal RMSD value of two atomic structures by optimal superimposition. G-RMSD is not restricted to systems with an equal number of atoms to compare or a unique atom mapping between two molecules. The method can handle any type of chemical structure, including transition states and structures which cannot be explained only with valence bond (VB) theory (non-VB structures). It requires only Cartesian coordinates for the structures. Further information, i.e. atom- and bond types can also be included. Applications of G-RMSD to the classification of α-d-glucose conformers and 3D partial structure search using a dataset containing equilibrium (EQ), dissociation channel (DC), and transition state (TS) structures are demonstrated. We find that G-RMSD allows for a successful classification and mapping for a wide variety of molecular structures.
This Account summarizes our work in the area of organoiron chemistry during the last two decades, with special emphasis on iron catalyzed C-C-bond formation. Specifically, it is shown that iron catalysts can emulate reactivity more befitting noble metals in that they allow various cross coupling, cycloaddition and cycloisomerization reactions to be carried out with surprising ease. At the same time, this base metal opens opportunities for the discovery of genuinely new transformations.
The role of surfaces in materials properties is significantly pronounced when the materials are designed in nanoscopic dimensions. Recent developments of nanomaterials chemistry have led researchers to modify properties as well as impart new functions by the surface modification of various nanomaterials. In this review article, grafting reactions (covalent attachments of functional units) for the surface modification of oxide based nanomaterials are summarized with the emphasis on layered solids, and the preparation and the nanoarchitectures of the products.
Organocatalysts activate substrates through mild noncovalent and covalent interactions, and their cooperative actions at multiple catalytic sites are essential even in intrinsically rapid organic reactions such as intramolecular cyclizations. The enzyme-like catalytic system is effective for recognizing specific molecular conformations of substrates, which continually change under reaction conditions, through multipoint interactions, thereby leading to high stereoselectivity. On the basis of this concept, we developed a range of organocatalytic asymmetric synthetic reactions, which are challenging using other categories of catalysts. The proposed catalysis was applied to various manners of asymmetric induction including those accompanied by not only facial selectivity but also by kinetic resolution (KR), dynamic kinetic resolution (DKR), desymmetrization, and dynamic kinetic asymmetric transformation (DYKAT). They enabled various asymmetric transformations through intramolecular hetero-Michael addition, construction of axial chirality, and α,β-unsaturated acylammonium catalysis, which advanced the methods for asymmetric heterocycle synthesis, construction of tetrasubstituted chiral carbons, enantioselective synthesis of axially chiral compounds, and asymmetric library synthesis of pharmaceutically potential compounds. This study also expanded the chemistry of bifunctional organocatalysis. This review provides a comprehensive account of our achievements regarding multipoint recognition of molecular conformations with organocatalysts for asymmetric synthetic reactions.
The diverse and complex structures of polyketide natural products have stimulated the imagination of synthetic chemists for decades. Captivated by their often impressive biological activities and their dazzling array of stereochemically-rich motifs, we have been motivated to achieve their efficient and stereocontrolled total synthesis. This review captures snapshots from our thirty-year foray into the total synthesis of 18 polyketide natural products, detailing the unique challenges, discoveries and revelations made en route to eventual success. Notably, crucial to each of these campaigns was the judicious application of highly selective aldol reactions to iteratively configure the densely oxygenated stereoclusters that characterise this fascinating class of bioactive natural products.