We have systematically prepared three kinds of photosensitizing (PS) double layers on the surface of Pt-cocatalyst-loaded TiO2 (Pt-TiO2) nanoparticles by using four different phosphonate-functionalized Ru(II) polypyridine photosensitizers (Ru) and Zr4+ cation linkers to improve the photo-induced separation efficiency at the double-PS-layer and semiconductor interface. All three nanoparticles with double-PS-layer structure (Ru-Zr-Ru@Pt-TiO2) exhibited remarkably higher photocatalytic H2 evolution activity than that of single-PS-layer nanoparticles, Ru@Pt-TiO2 in low sacrificial electron donating (SED) L-ascorbic acid solution. The fine-tuning of emission energy of Ru(II) PS dye at the outer surface of Ru-Zr-Ru@Pt-TiO2 nanoparticle revealed that photoexcitation energy transfer from outer to inner Ru(II) PS dyes give a positive effect on the photocatalytic activity especially in the low SED concentration.
Synthesis of TiO2 photocatalysts with better activity via facile methods is desired to facilitate their applications. Here, we report a facile method to synthesize layered titanate/rutile heterojunction photocatalysts showing activity higher (up to twice) than that of a benchmark P25 TiO2 under irradiation with a solar simulator. In this method, a layered titanate (K0.8Ti1.73Li0.27O4) is treated with dilute HCl and dried under ambient conditions, resulting in the formation of rutile nanoparticles deposited on the outer particle surface of the protonated form of the layered titanate. The activity is identical to that of the prototype heterojunction synthesized by a similar method requiring a considerably longer time.
Understanding the mechanism of fluorescence enhancement of a fluorophore via anion addition is of critical importance for designing anion sensors. The distyrylpyrrole framework with cyano groups on olefin has a low rotation barrier in the excited state, which results in easy access to the conical intersection and, thus, fast non-radiative decay. In this study, it was proposed that the anion capture of a molecule with protons on the pyrrole and olefin moieties with a high anion affinity should induce fluorescence enhancement via restricted access to the conical intersection. It was revealed that the pyrrole derivative possessing cyano groups in the α-position of the pyrrole showed a strong enhancement in the fluorescence quantum yield up to 60% with an increasing concentration of anions in solution. NMR and X-ray single crystal diffraction revealed that the molecule formed a 1:1 complex with a chloride anion in solution and in the single crystal state. The fluorescence lifetime of the compound was prolonged via the addition of the chloride anion, indicating that fast non-radiative decay was suppressed by anion capture. The results support that the anion capture of the molecule can restrict access to the conical intersection to produce a fluorescence enhancement.
Here, we report a practical method for asymmetric synthesis of cyclopropane-fused GABA analogs. Starting from 2-furaldehyde, the cis-isomer (CAMP) was synthesized over 10 steps; (−)- and (+)-CAMP·HCl were synthesized by employing d- and l-menthol as the chiral auxiliary for total 2.5% and 1.3% yields, respectively. On the other hand, the trans-isomer (TAMP) was elaborated via double asymmetric induction, i.e. organocatalytic asymmetric cyclopropanation on chiral substrate. Thus, starting from l- and d-menthyl acrylate, in combination with quinidine-derived and quinine-derived organocatalysts, (−)- and (+)-TAMP·HCl were synthesized in total 6.6% and 3.7% yields, respectively, over 8 steps each. Configurational analysis of the synthetic intermediates based on 13C NMR is also reported. Preliminary oncological assays showed the weak but specific activities of CAMP and TAMP as the molecular basis of GABA analogs, which are still left unexplored.
The rich and stable interlayer porous biomass carbon sulfonic acids (SBCSAs) pillared by silica were prepared conveniently using bamboo powder and water glass as main raw materials and investigated by a series of characterization techniques. Additionally, the acid catalysis performances of SBCSAs were evaluated using the hydrolysis of sucrose, the esterification of oleic acid with methanol and the alkylation of toluene with benzyl chloride. The results showed that 0.05–0.025 M acidic silica sols could be efficiently and uniformly intercalated into the interlayers between bamboo carbon (BC) nanosheets, yielding the silica-pillared BC materials (SBCs) with rich interlayer slit-like pores after dehydration at 350 °C. Moreover, the porosity of SBCs could be very well kept after further sulfonation with concentrated sulfuric acid. The newly constructed SBCSA materials exhibited higher catalysis efficiency and better reusability for the above acid-catalyzed reactions than the non-pillared BCSA and commercial Amberlyst-15, which should be due to the overall improvements relating to their structure, porosity and acidity, as supported by BET, TGA, STEM-EDS and solid-state 31P MAS NMR spectra of adsorbed TMPO. This work opens up a new voyage for the fabrication of porous bio-based solid acids with good catalysis properties and extensive application prospect.
Single cell analysis has been the main focus of studies among scientists in recent decades for its outstanding contribution to medical treatment. An alternative method has been developed using a centrifugal microfluidic device to trap single cells, conduct immunostaining, and measure the cell surface receptor fluorescence intensity. The ratio of the fluorescence intensity can be used to profile the cell differentiation and the archived images can be useful in further analysis of the obtained data points. This could provide information on the morphological condition and receptor protein distribution on the surfaceome of the cells. To demonstrate the utility of the device, THP-1 and Jurkat Cells were tested and profiled with CD3, CD13, and CD31 markers. The results show that the device has performance similar to Fluorescence-activated cell sorting method (FACS) using relatively small sample volume and low cell suspension concentration. The utility of this device can be proven in identifying new surface markers and insight into basic biology.
The selective oxidation of CH4 using O2 is one of the most attractive subjects as an elusive target reaction. Ohkubo and Hirose recently reported that chlorine dioxide radical (ClO2•), which is generated by mixing NaClO2 and HCl in an aqueous solution, acts as an efficient oxidant in the oxidation of CH4 to CH3OH and HCOOH under photoirradiation in the two-phase system of perfluorohexane and water (Angew. Chem., Int. Ed. 2018, 57, 2126). The reaction system gives CH3OH and HCOOH without further oxidation products. They proposed that methoxy radical (CH3O•) plays an important role as an intermediate in the oxidation of CH4. In the present work, we focus on the reactivity of CH3O• to CH4 in detail to propose a reasonable radical mechanism for the oxidation of CH4 using DFT calculations at the M06-2X/6-311+G** level of theory and UCCSD(T)/6-311+G** calculations. Our reaction analysis suggests that the reaction of CH3O• with CH4 and the disproportionation of CH3O• take place as CH4 + CH3O• → CH3• + CH3OH and 2CH3O• → CH3OH + HCHO, respectively. In contrast, the isomerization from CH3O• to CH2•(OH), suggested by Ohkubo and Hirose, is unlikely to occur under ambient conditions, due to the high activation barrier for this reaction. A better understanding of the well-controlled radical chain reactions is useful for reaction design of the hydroxylation of methane.
We propose a strategy to prepare luminescence materials via simple and organic solvent-free fashion by mixing an anionic luminescent complex with an anion exchanging support. As a proof-of-concept, we employed the heptaanionic TbIII complex Tb3TCAS2 (TCAS = thiacalixarene-p-tetrasulfonate) and QAE Sephadex A-25, a dextran support bearing anion exchanging groups. By stirring a mixture of TCAS and dextran (1.0 µmol Tb3TCAS2/50 mg dextran), 99.8% of Tb3TCAS2 was successfully immobilized within 2 h. The electrostatic interactions were strong enough to irreversibly bind Tb3TCAS2 to the dextran. The material exhibited TbIII-centered luminescence upon excitation of the TCAS center. The luminescent lifetime and quantum yield were 1.18 ms and 45.5%, respectively. When the amount of Tb3TCAS2 immobilized on the dextran was reduced to 1.0 nmol/50 mg dextran, the lifetime increased to 1.32 ms, suggesting concentration quenching above 1.0 µmol Tb3TCAS2/50 mg dextran. On the other hand, the luminescence quantum yield decreased to 3.1%, suggesting that the absorption of excited light by the support was not negligible. Preparation of the materials in D2O resulted in increases in the lifetime and quantum yields to 1.32 ms and 44%, respectively.
Molecules exhibiting cold crystallization, an exothermic phenomenon in heating following supercooling, can be used as a heat storing material. On the other hand, examples in non-polymers are still few. A chiral Schiff-base nickel(II) complex, which had a characteristic methyl group and long alkyl chains, exhibited complicated thermal behavior including cold crystallization. The methyl group was a steric barrier to dimerization and molecular stacking, leading to the supercooled state. In addition, the thermal behavior of enantiomer was different from that of racemate.
Crystalline alumina is a significant inorganic solid that has been utilized as a high-surface-area catalyst support. However, it has been in fact difficult to obtain alumina having high interior porosity and adequate crystallinity in their powder forms because complete crystallization of pore walls (alumina frameworks) is generally suppressed by the porous structures. Here, we report an aerosol-assisted synthesis of highly porous alumina using asymmetric polystyrene-b-poly(ethylene oxide) (PS-b-PEO) type diblock copolymers, and summarize it as an effective strategy to achieve quick optimization of the synthetic conditions. Extra-large pores (∼40 nm using PS35000-b-PEO17000 and ∼200 nm using PS58500-b-PEO37000) were architected in the aerosol-assisted particles successfully. The alumina frameworks can be adequately crystallized to its γ-phase through calcination at high temperature (e.g., 1000 °C) with the retention of initial porous structures. In addition, surface propertis of the alumina frameworks were changed from hydrophilic to hydrophobic with the crystallization degree, being a significant insight for tuning functions through the porous materials design.
A helicene compound called AIBTh, wherein two azulene units are fused with isobenzothiophene, has been prepared and characterized by spectroscopic and crystallographic methods. The enantiomers of AIBTh were resolved by HPLC, exhibiting stable optical activity. AIBTh showed two reversible oxidation and one irreversible reduction waves with a HOMO-LUMO gap of 2.07 eV. Upon one-electron oxidation of AIBTh, its air-stable cation radical was isolated and analyzed by EPR as well as X-ray crystallography. Based on the EPR spectrum, the crystal structure, and DFT calculation, it is suggested that favorable resonance structures including aromatic tropylium cation forms and wide delocalization of electronic spin are dominating in the electronic structure of the cation radical.
In view of the key roles played by noncovalent or weak interactions in biological processes, it is important to understand them at the molecular level. Based on the results of the thermodynamic, spectroscopic and X-ray structural studies on ternary Cu(II) complexes, as platform molecules for ligand-ligand interactions, the presence of π-π interactions between aromatic rings (phenyl, phenol and indole) of amino acids and aromatic rings of imidazole, diamines have been shown. We carried out systematic theoretical studies using different DFT functionals (pure-GGA, meta-GGA, hybrid-GGA and meta-hybrid-GGA) with triple-ζ (def2TZVP) basis set for the experimentally determined structure of [Cu(hista)(Phe)]ClO4, to obtain the most suitable method. We gained reliable insight into the geometry, electronic structure and noncovalent interactions for different ternary complexes, [Cu(hista)(AA)]ClO4 (AA = Phe, Tyr, Trp, Leu, Ile, Ala, Met, Val) by applying the most accurate method (PW91/def2TZVP/CPCM). The calculated stability constants (logK) were in good agreement with the experimental results. We obtained knowledge of the differences in noncovalent interactions and excited states among the ternary Cu(II) complexes containing Phe, Tyr, and Trp by the Non-Covalent Interaction (NCI) and TDDFT methods.
Molecular architectonics has its essence in custom design and engineering of molecular assemblies by judicious exploitation of the noncovalent forces to construct ordered architectures with novel properties and functions. The art of mastering the programmed molecular assemblies is a challenging task owing to complex factors that govern recognition events at the molecular level. In this context, biomolecules with in-built information for molecular recognition are capable of guiding the molecular architectonics to construct nano, micro, and macro-architectures with functional properties and applications. In particular, amino acids and peptides are attractive auxiliaries to guide the controlled molecular self-assembly, coassembly, heterostructures and living assembly systems of functional molecules in the scheme of molecular architectonics. Use of these exquisite biomolecular auxiliaries to master the art of engineering the molecular assembly of functional aromatic units viz., arylenediimides has been a continuous effort in the emerging field of molecular architectonics. In this accounts article, we outline the amino acid and peptide functionalized arylenediimide-based designer molecular systems as functional modular units developed by our group and others with an objective to demonstrate the concept of molecular architectonics to construct functional nano, micro and macroarchitectures with wide range of properties and applications.
We have designed and synthesized three kinds of diisopropylaminoboranes substituted with two electron-donating π-conjugated systems, 2a: bis(phenothiazinyl) 2b: bis(N-phenyldihydrophenazinyl), and 2c: bis(phenoxazinyl) derivatives, and investigated their structures and electronic properties including those of oxidized species. The structural analyses of 2a–c and 2a–c•+ indicated that the π-electronic systems composed of boron and three nitrogen atoms showed unique structural deformation by one-electron-oxidation. The structures of the neutral compounds were almost C2-symmetrical, indicating that the two donor π-electronic systems are almost identical. In contrast, the radical cationic compounds were not C2-symmetrical structures because the charges of the radical cations were localized on one of the electron donors. In addition, the B–N bonds directly bound to the radical cations were elongated; also, perpendicular arrangements between the p-orbital of boron and π-conjugated orbitals of the radical cations were observed. We also succeeded in observing the triplet state of 2b2(•+), which was categorized as a heteroatom analogue of the trimethylenemethane (TMM) π-electronic system, by means of electron-spin resonance (ESR) spectroscopy.
The energy-representation theory of solutions is developed to address the dissolution of a molecule in homogeneous fluid as well as the partitioning into such nanoscale structures as micelle and lipid membrane and the physisorption onto gas-liquid and solid-liquid interfaces in a unified manner as solvation in an extended sense. The present review describes the formulation of the solution theory with illustrative applications to the peptide configuration in lipid membrane, the water dissolution into polymer, and the physisorption on urea crystal in contact with liquid water. The solution theory in the energy representation is a density-functional scheme formulated by adopting the solute-solvent pair interaction energy as a one-dimensional coordinate for distribution functions and provides an approximate functional for the solvation free energy in terms of energy distribution functions in the reference-solvent and solution systems of interest. Each of the solute and solvent molecules is treated as a single unit as a whole, and due to this feature, a species with intramolecular flexibility and a solvent system with nano-scale inhomogeneity or interface can be analyzed in a common framework. The role of water is pointed out in determining the configuration of a peptide in lipid membrane, and the dissolution of water into polymer medium is described at chemical accuracy. Some directions of future developments are also discussed.