Copper-catalyzed cross-dehydrogenative coupling (CDC) reactions have been esteemed as a straightforward and efficient tool for C–C bonds formation. The single electron transfer (SET) process plays a vital role during the overall catalytic cycle. In the present density functional theory (DFT) study on the oxidation potential (Eox), which could reflect the SET occurring tendency from a thermodynamic respect as well as the substituent effects and structure-activity relationships for four classes of N-based compound substrates including THIQs, N,N-dimethylanilines, 3-benzylindoles, and N-phenylglycine esters derivatives have been fulfilled. Many quantitative structure-activity relationships between Eox and structural parameters, including HOMO energies, the Hammett substituent constant σ+ and so on were found. Furthermore, in the kinetics research section, we have performed four possible pathways of CDC reaction of N-aryl glycine esters with phenols in a CuBr/TBHP catalytic oxidation system. The results support the pathway wherein the formation of an iminium cation-type intermediate is involved would be more favorable. In addition, the solvent and substituent effects of two key steps including H-abstraction and C–C bond formation rate-determining step were explored, which could afford a total understanding of the mechanism regarding the Cu-catalyzed CDC reaction as well as the substrates and solvents screening.
A radical-mediated cyclopropanation tool for reactive alkenes including dehydroamino acids (DHAAs) has been developed based on directly photoexcitable borate generating iodomethyl radical under visible light irradiation. The borate at the excited state serves as a strong single electron reductant. Therefore, this photoexcitable borate offers a simple protocol for cyclopropanation of DHAAs to forge medicinally-important cyclopropane amino acids.
Chiral transcription from chiral inorganic nanoobjects to achiral organic molecules is a fascinating topic. In this study, chiral transcription was demonstrated using helically controlled Au nanowires (NWs) and achiral azobenzene derivatives with thiol moieties as the terminal group. The azobenzene derivatives mAZonSH can form a self-assembled monolayer on helical Au NWs through thiol-Au bonding. UV-Vis spectroscopy revealed that mAZonSH in the self-assembled monolayer forms H-aggregates. The self-assembled monolayers on the right- and left-handed Au NWs showed opposing circular dichroism (CD) signals derived from the azobenzene chromophore. This result indicates that chiral transcription from the helical Au NWs to the azobenzene derivatives was successfully accomplished by the self-assembly of achiral mAZonSH. Furthermore, we demonstrated that the CD responses of mAZonSH are independent of the tail (m) and spacer (n) alkyl lengths.
Newly synthesized B-site-disordered perovskites Ln2(FeTi)O6 (Ln = Pr and Nd) were found to show charge transfer between Fe and Ti ions, which was in contrast to the robust Fe3+/Ti3+ state in the isostructural Ln = La compound La2(Fe3+Ti3+)O6. The charge distribution for Ln = Pr and Nd can be expressed as Ln2(Fe3+0.8Ti3+0.8Fe2+0.2Ti4+0.2)O6 at room temperature, and the amount of Fe2+/Ti4+ increases with decreasing temperature. In addition, the charge transfer resulting in Ln-dependent valence states at the B site strongly affects magnetic properties, including the magnetic transition temperatures and the ground states.
The development of highly-functional visible light-driven hybrid catalysts (B12-Mn+/TiO2) prepared from B12 complexes (B12) derived from natural vitamin B12, earth-abundant metal ions (Mn+), and titanium oxide (TiO2) was reported. The metal ions, such as Cu2+, Ni2+, Fe2+, Zn2+, Mn2+, Al3+, and Mg2+, were modified on the surface of TiO2 (2.4 × 10−5–9.9 × 10−5 mol/g) to obtain effective response to visible light, and the B12 complex was also loaded (6.2 × 10−6–1.1 × 10−5 mol/g) to produce a highly-functional hybrid catalyst. Amide formations from dichlorodiphenyltrichloroethane (DDT) catalyzed by the B12-Mn+/TiO2 proceeded in up to 89% yields in the presence of triethylamine (NEt3) under visible light irradiation (λ ≧ 420 nm) in air at room temperature. These hybrid catalysts could be classified into two groups based on these reactivities, and it was found that the B12-Mg2+/TiO2 showed the most effective catalytic activities of all the prepared samples. The B12-Mg2+/TiO2 also catalyzed the syntheses of fine chemicals, such as N,N-diethyl-3-methylbenzeamide (DEET), and N,N-diethylcyanoformamide, from the corresponding trichloromethyl compounds (FG-CCl3) with about 80% yields.
Sortase A is used for the post-translational modification of proteins in vitro and in cell, and it is known that amino acid residues involved in Ca2+ binding are important for the enzymatic reaction. In this study, the effects of various conditions and mutations on the transpeptidase activity of Sortase A were investigated. We also examined the effect of exogenous metal ions on the enzymatic reaction. The results showed that the transpeptidase activity was maintained over a wide range of Ca2+ concentrations and temperatures. Moreover, amino acid residues E108 and N114, possibly involved in Ca2+ binding, were found essential for enzyme activity. Furthermore, the results showed that Lewis basicity, amino acid side chains, and steric effects were closely related to Ca2+ binding and enzyme activity. In contrast to previous results, we found that Mg2+, an ion homologous to Ca2+, reduced the transpeptidase reactivity of Sortase A to a level comparable to that of the apo form. This study provides fundamental insights into the structure and function of Sortase A, which may be useful for the development of artificial functional Sortase A enzymes.
Multi-metallic inorganic alloy materials have attracted great attention recently. Additionally, molecule-based materials have wide designability in terms of their structures and electronic states. These are two different ideas. Here, we report the mixing of Pd(III) and Au(III) ions into a bromide-bridged molecular chain compound [Ni(chxn)2Br]Br2 (chxn: 1R,2R-diaminocyclohexane) to form an average formula of [Ni0.853Pd0.142Au0.005(chxn)2Br]Br2, which was synthesized by an electrochemical oxidation method. This trimetallic material is revealed to be a Mott–Hubbard state semiconductor with a one-dimensional electronic system like that of [Ni(chxn)2Br]Br2, whereas it shows a smaller activation energy for conductivity than that of pristine [Ni(chxn)2Br]Br2. This work represents a fusion of the concepts of multi-metallic and molecule-based materials using a 1D compound.
E,E-1,4-bis(2-trifluoromethylstyryl)benzene (2CF3) can form two types of crystals—one emitting purple-blue (vF-2CF3) and the other emitting green (gF-2CF3)—by simply drop-casting its solution onto polydimethylpolysiloxane. Subjecting vF-2CF3 to a N2 laser excitation causes it to exhibit amplified spontaneous emission with a low threshold of 6.8 µJ cm−2.
To develop a fast synthesis method for organic-modified single-nanosized zirconium oxide (zirconia) particles dispersed in a solvent, the effects of temperature (300–400 °C), simultaneous modification with carboxylic acids, and precursors on the solvothermal synthesis with benzyl alcohol as a solvent were investigated. The formation of zirconia nanoparticles in this study occurred much faster than in a typical solvothermal condition (250 °C), and nanoparticles (2.6–3.4 nm) were successfully obtained at 2–5 min. The combination of TG and FT-IR analysis for the sample treated with benzoic acid at 400 °C confirmed that benzoic acid was chemically modified on the nanoparticles. In addition, the carbon number of the alkyl group of the zirconia precursor is an important factor that determines the size of zirconia.
Electron doping is an essential process for developing n-type organic thermoelectric materials, and thus the search for efficient n-type dopants is critically important. By replacing the central 1-methylpyrrole ring in 2,5-bis((2,6-diphenyl-4H-pyran-4-ylidene)methyl)-1-methylpyrrole (1) with electron-rich 3,4-ethylenedioxythiophene and 2,2′-bis(3,4-ethylenedioxythiophene) moieties, we synthesized new candidate molecules (2 and 3, respectively) as n-type dopants. The single-crystal X-ray analyses of 1 and 3 elucidated that 3 has a totally planar π-conjugated structure over the whole molecule, whereas 1 has a non-planar structure. Although the energy levels of the highest occupied molecular orbitals of 1–3 evaluated by the electrochemical measurement in solution were not significantly different, the work function of 3 thin film evaluated by the Kelvin probe method was slightly higher than those of 1 and 2. Furthermore, 3 was capable of electron-doping to an n-type semiconducting polymer, poly(benzimidazobenzophenanthroline) (BBL), and the resulting doped BBL showed decent thermoelectric characteristics with the power factor of 1.25 × 10−3 µW m−1 K−2, which was higher by one order of magnitude than those of 1- and 2-doped BBL thin films. These results imply that the high planarity of 3 can contribute to electron-doping ability, which could be useful information for further development of n-type dopants for organic thermoelectric applications.
Chitin is an abundant marine biomass that contains nitrogen atoms in its monomer units. Therefore, it is an attractive feedstock for the production of renewable organonitrogen compounds. The hydrolytic hydrogenation of chitin produces 2-acetamide-2-deoxysorbitol (ADS), which is a potential platform chemical in chitin-based biorefinery. In this work, we report the catalytic conversion of ADS to oxazolidinones named 2,3-OX and 1,2-OX. Of the two isomers, 2,3-OX possesses specific chirality suited for the application of antibiotic agents, naturally derived from ADS. This work demonstrates that a ubiquitous base catalyst, KHCO3, selectively gives 2,3-OX in 84% yield, 12 times more preferential than 1,2-OX under kinetic control. DFT calculations show that inner-molecular hydrogen bonds formed in the transition states specifically reduce the energy barrier for the 2,3-OX formation, thus giving this isomer selectively. We also found that the addition of boron compounds slightly shifts the selectivity towards 1,2-OX.
Large surface area hierarchically nanoporous activated carbons are prepared by KOH activation and high temperature carbonization of agricultural waste, Phoenix dactylifera (date) seeds. The nanoporous activated carbon obtained by this method has excellent surface porosity with very large surface area, typically 2383.2 m2 g−1, and large pore volume (1.76 cm3 g−1) due to their interconnected micro- and mesoporous structure. The hierarchically nanoporous material of this activated carbon leads to excellent electrochemical charge storage capability for their application as supercapacitor electrode materials. In a three-electrode cell, an optimum carbon sample exhibited high specific capacitance ca. 386 F g−1 at a current density of 1 A g−1 with excellent retention of specific capacitance (63%) at a very high current density of 50 A g−1. Cyclic stability is also excellent with 98% specific capacitance retention after 10,000 charge-discharge cycles. These hierarchical nanoporous activated carbons derived from agricultural waste materials have sufficient potential for use as electrode materials in commercial, and advanced supercapacitors.
Hansen solubility parameters (HSP) are useful for understanding the solubility and dispersibility of substances in liquids. This study aims at utilizing HSP to describe the affinity between solutes and solid surfaces in solutions. For this purpose, we designed the index “H” based on the HSP theory for predicting the adsorption behavior. In this study, the adsorption index H was used to estimate the desirable solvent compositions for preparing samples for laser desorption/ionization mass spectrometry (LDI-MS). The compositions for obtaining a high-intensity signal of analytes were estimated by selecting an appropriate H value from the relationship between the H and the solubility of the analytes predicted from the HSP. Four different pesticides (analytes) adsorbed on an organosilica film (LDI-MS substrate) were detected with high-intensity signals using the estimated solvent compositions. This study shows that the H is a useful parameter in the design of sample solutions for obtaining high-intensity signals in LDI-MS. Moreover, it is potentially useful for other applications that utilize molecular adsorption on solid surfaces.
Development of an efficient method for the analysis and identification of the target proteins with which biologically active glycosides directly interact is highly desirable in many research fields. In this article, we report an efficient strategy for the preparation of chemical probes of biologically active glycosides using a reaction sequence of i) a boron-mediated aglycon delivery (BMAD) with an N3-functionalized 1,2-anhydroglucose donor, ii) deprotection, and iii) strain-promoted azide-alkyne cycloaddition. Using the synthesized chemical probes, we successfully demonstrated that the target proteins of a cardiac glycoside, lanatoside C (1), can be visualized and identified in human colon cancer HCT116 cells.
Self-assembled aggregates of bacteriochlorophyll(BChl)-c/d/e pigments play key roles in major light-harvesting antenna systems of photosynthetic green bacteria. Herein, we report the self-assembly of a lipophilic zinc BChl-d model with an N,N-didodecylamide in the 17-substituent. The present model formed two types of J-aggregates, which formed under kinetic and thermodynamic controls.
Nano-magnetic CoFe2O4 materials with excellent crystallization and high saturation magnetization were synthesized by solvothermal method using Fe(NO3)3·9H2O and Co(NO3)2·6H2O as raw materials and ethanol solution as solvent, respectively. The effects of solvent ratio, reaction temperature and reaction time on the composition and properties of these nanomaterials were explored. The phase, morphology and magnetism of the CoFe2O4 were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and vibrating sample magnetometry (VSM). The specific surface area of CoFe2O4 was measured by N2 adsorption-desorption isotherm and calculated by the Brunauer-Emmett-Teller (BET) method. The results showed that the structure and magnetic properties of the prepared materials were greatly dependent on the synthesis conditions. Under optimal prepared conditions, i.e., reaction temperature of 200 °C, reaction time of 20 h and pure ethanol (EtOH) solvent, favorable CoFe2O4 material with high purity, small particle size, larger specific surface area and outstanding saturation magnetization was obtained. Importantly, this method with the advantages of easy-operation, environment-friendliness, and without the introduction of any precipitant or surfactant exhibits promise for the industry-scale production of nano-magnetic CoFe2O4 material.
Due to increasing environmental pollution, benign responsive materials are of great importance in the field of oil/water separation. Here, a fluoride-free UV-responsive material for oil/water separation material and dye degradation was prepared. Environmentally friendly and low cost cellulose, silicon dioxide (SiO2), titanium dioxide (TiO2) and stearic acid (SA) were used to fabricate the superhydrophobic coating. The coated cotton fabric can be obtained by simple dip-coating, and its wettability can transition from superhydrophobic to superhydrophilic under UV irradiation. The responsive surface of the coated cotton fabric can be applied for the effective separation of heavy or light oil/water mixtures, water-in-oil emulsions and oil-in-water emulsions. In addition, the UV-responsive coated cotton fabric can realize the degradation of methyl blue after UV irradiation, which may provide a new prospect for the development of intelligent materials.
Four-electron oxygen reduction reaction (4e−-ORR) is the foundation of both natural and artificial energy conversion systems. Mechanism studies and catalysis improvements of 4e−-ORR are important research for the actualization of a sustainable society. In this study, we present a dinuclear cobalt complex containing mono-deprotonated forms of 6,6′-dihydroxy-2,2′-bipyridine (6DHBP-H+), [Co2(OH)2(6DHBP–H+)2(btpyxa)](PF6)2 (2) is a highly active 4e−-ORR catalyst in a low acid concentration solution. When ferrocene (Fe(Cp)2) was used as a reductant in PhCN containing a low concentration of perchloric acid (1.0 mmol L−1), 2 showed higher selectivity (99%) and reaction rate (kcat = 6.0 × 103 M−1 s−1) for 4e−-ORR than the bpy analog 1 (kcat = 6.2 × 10 M−1 s−1) and 4DHBP analog 3 (kcat = 1.5 × 102 M−1 s−1). A high catalytic current in the cyclic voltammetry (CV) of 2 indicates a high reaction rate for electrochemical ORR under low acid concentration conditions. Moreover, X-ray crystallography of the corresponding monomeric analog [Co(OH2)(6DHBP–2H+)(trpy)](PF6) (4, 6DHBP–2H+: a doubly deprotonated form of 6DHBP) suggests that OH groups of 2 can form hydrogen bonds with a μ-O2 ligand. Hydroxy groups at the 6,6′-position of bpy would deliver protons to the μ-O2 ligand of the intermediate, thereby promoting O–O bond cleavage in the proton-coupled electron transfer (PCET) process.
An excimer is an excited dimer complex made of two π-conjugated fluorophore molecules such that one is in the ground, and the other in the excited state. In the solid state, the intensity of the excimer emission, which is mainly caused by the formation of the excited dimer, heavily depends on the movability of the excited π-conjugated molecule. In this study, we report that organic salts composed of disulfonic acid with a common π-conjugated molecule, 2,2′-bithiophene (BT), can act as functional excimer moieties, while linear alkylamines may be used as arrangement-controlling moieties. Furthermore, we found that the intensity of the excimer emission can be drastically changed by fixing the BT moiety, which can be achieved via the interaction of the alkyl groups (i.e., the anchor effect). The experimental relationship between the movability of the π-conjugated molecule and the intensity of the excimer emission was revealed without changing the structure and arrangement of the functional organic molecules in the solid state.
Useful bioactive polycyclic natural products are important targets in academic research, wherein their mechanisms of action and total syntheses are commonly investigated. In addition, polycyclic compounds that exhibit highly selective biological activities through multipoint recognition are valuable as biochemical reagents and lead compounds for pharmaceuticals. However, when such compounds are difficult to obtain, their supply depends on appropriate chemical preparations. Unfortunately, polycyclic natural products pose difficult synthetic problems, such as the construction of distorted ring structures, contiguous stereogenic centers, and quaternary asymmetric carbon atoms in their fused ring moieties. Moreover, since polycyclic natural products have a large number of bonds, their total syntheses inevitably become multi-step procedures, and when enantioselective total synthesis is required, the number of steps tends to increase, since such routes require the use of commercially available chiral compounds. Hence, their efficient total synthesis is challenging. In our group, we have demonstrated the preparation of chiral synthetic intermediates, especially those bearing a quaternary stereogenic center, through novel asymmetric catalysis procedures, as well as the incorporation of logically designed cascade reactions to reduce the number of transformations. This route can ultimately lead to the efficient enantioselective total syntheses of useful bioactive polycyclic natural products.