Supramolecular self-assembly in two-dimensional (2D) spaces on solid surfaces is the subject of intense current interest because of perspectives for various applications in nanoscience and nanotechnology. At the liquid/graphite interface, we found by means of scanning tunneling microscopy molecules with a rigid triangular core, a twelve-membered phenylene-ethynylene macrocycle called dehydrobenzoannulene (DBA), substituted by six flexible alkoxy chains self-assembled to form hexagonal porous 2D molecular networks via van der Waals interactions between interdigitated alkyl chains as the directional intermolecular linkages. Factors that affect the formation of the porous 2D molecular networks including alkyl chain length, solvent, solute concentration, and temperature were elucidated through a systematic study. Because DBA molecules are versatile for chemical modification, they turned out to be highly adaptive for on-surface supramolecular chemistry with respect to (i) pore size control by changing the chain length, (ii) study of parity effect due to even or odd number chains, (iii) generation of supramolecular chirality on surfaces by introducing stereocenters, (iv) chemical modification of the pore interior for selective co-adsorption of guest molecules by introducing functional groups. Additionally, formation of superlattice structures on surfaces was incidentally observed by mixing DBAs of different alkoxy chain parity or by addition of guest molecules via an induced-fit mechanism. These results made significant contribution to advancement of supramolecular chemistry in 2D space.
It is highly probable that the first impression that organic chemists would have of fluorine, F, is that it is “dangerous”. Elemental fluorine, F2, is a gas that reacts with all elements quickly and violently. The oxidation power of F2 is extraordinarily strong and even the noble gases such as Kr and Xe react with F2 forming the corresponding fluorides. Fortunately, the receptiveness to fluorine chemistry by synthetic chemists has gradually changed in the late 20th century with the development of shelf-stable reagents for fluorination and trifluoromethylation reactions. In this account, I introduce our recent contributions to the development of shelf-stable reagents for the synthesis of organofluorine compounds. Electrophilic reagents for fluorination, mono-, di-, and trifluoromethylation, and trifluoromethylthiolation are discussed. Nucleophilic reagents for monofluoromethylation are also described including enantioselective reactions.
Caged compounds, (3-benzazolyl-2-hydroxy-5-methylphenyl) methyl acetate (HBO-Ac, HBT-Ac, HBI-Ac) were synthesized and their photocleavage reaction were investigated by means of determination of quantum yield of photocleavage reaction as well as absorption and fluorescence spectroscopy and DFT calculation. These compounds are expected to exist as three conformations anti-enol (a), anti-enol (b) and syn-enol and exhibited fluorescence emission due to the tautomer produced by intramolecular hydrogen-atom transfer in anti-enol (a) form. The compounds HBT-Ac and HBI-Ac underwent photocleavage reaction in CH3Cl, CD3OD and aqueous CD3OD, while HBO-Ac underwent photocleavage reaction in CD3OD and aqueous CD3OD but almost no reaction in CDCl3. The photocleavage reaction may take place from anti-enol (a), which is in accordance to the results of DFT calculation and the experimental results that the relative efficiency of photocleavage reaction increased with decreasing the energy level of anti-enol (a) vs. syn-enol in the ground state calculated by DFT. The results obtained in this study suggest that the efficiency of photocleavage reaction depends on the solvent properties and hydrogen-bonding properties of light-absorbing chromophore of caged compounds which control the stability of conformation causing photocleavage reaction.
The copolymerization of 3-hexylthiophene (3HT) and triphenylamine (TPA) was carried out by using FeCl3. The incorporation of TPA and 3HT into the resultant polymer main chain was clarified by NMR and MALDI-TOF MS spectrometry. Thermogravimetric analysis suggests that the copolymers show excellent thermal stability.
An improved synthesis for easy access to the natural product inspired chromenopyrrolizine and chromenoindolizine scaffolds is delineated. The strategy involves controlled thermal activation of diverse salicylaldehyde tethered dipolarophiles having the strategically stationed activating substituents with proline/pipecolic acid for the facile [3+2] cycloaddition of the in situ generated azomethine ylides and concomitant oxidation of the resulting cycloadducts to arrive at diverse chromenopyrrolizine or pyrrolizine analogs of aza-medicarpin and chromenoindolizines embodying the tetracyclic core isomeric to lamellarin alkaloids, in good yields under base and metal free condition.
Porphyrin-appended gold nanoparticles with different chain lengths were synthesized to examine the control over photosensitization. The efficiencies evaluated by singlet-oxygen generation were adjusted by the average number of porphyrins on one gold nanoparticle and the particle size regardless of the linker chain length between porphyrin site and gold core.
Hetero nuclear bimetallocene compounds, ferrocenylruthenocene (FcRc), ferrocenylosmocene (FcOc), ruthenocenylosmocene (RcOc) and 1-ferrocenyl-4-ruthencoenylbenzene (FcPhRc) were synthesized by Suzuki–Miyaura coupling or Negishi coupling reaction. When these compounds were oxidized with I2, mixed-valence compounds, [(C5H5)FeII(C5H4-C5H4)OsIV-I(C5H5)]I3 (1), [(C5H5)RuII(C5H4-C5H4)OsIV-I(C5H5)]I3 (3) and [(C5H5)FeIII(C5H4-Ph-C5H4)RuIV-I(C5H5)](I3)2 (4), were obtained. The valence state was investigated by using 57Fe Mössbauer spectroscopy and variable-temperature 1H NMR spectroscopy. FcOc was also oxidized by [(C5H5)2RuIV-Cl]PF6, and the ferrocenylosmocenium-Cl adduct [(C5H5)FeII(C5H4-C5H4)OsIV-Cl(C5H5)]PF6 (2) was obtained. The valence detrapping described as FeII-OsIV ⇌ FeIII-OsIII was observed by 1H NMR measurement in high-temperature solution. The valence detrapping was also observed in solid state by 57Fe Mössbauer spectroscopy.
Extraction behavior of U(VI) in biphasic systems consisting of an aqueous layer and an ionic liquid (IL) layer has been investigated. The ILs used are bis(trifluoromethylsulfonyl)amide ([Tf2N]−) salts of N,N,N-trimethyl-l-alaninium ([HAbet]+), N,N,N-trimethyl-l-valinium ([HVbet]+), N,N,N-trimethyl-l-leucinium ([HLbet]+), or N,N,N-trimethyl-l(+)-isoleucinium ([HIbet]+). The present ILs resulted in higher extractability of U(VI) compared with that of the N,N,N-trimethylglycinium ([HGbet]+) system studied by us previously. This improvement can be explained in terms of hydrophobicity of ILs, because hydrophobicity of the present ILs is higher than that of [HGbet][Tf2N] as demonstrated by logarithmic partitioning coefficients (log Pow) of the [Tf2N]− salts of [HGbet]+ (−0.54), [HAbet]+ (−0.15), [HVbet]+ (−0.09), [HLbet]+ (1.4) and [HIbet]+ (1.8). Uranium(VI) was also selectively extracted from aqueous solutions containing other metal ions such as Na(I), Ca(II), Al(III), Fe(II), Co(II) and Ni(II). In addition, extracted U(VI) species were easily separated as precipitates by adding 30 wt % H2O2. After removal of the U(VI) precipitate, ILs were also collected. The recovery yield of IL was enhanced with an increase in hydrophobicity of its cationic component. Therefore, highly hydrophobic betainium is preferable for both high U(VI) extractability and recyclability of ILs.
A Simulated Annealing (SA) algorithm is combined with our recently developed conformational search technique, Outlier FLOODding (OFLOOD) method [J. Comput. Chem. 2015, 36, 97], to avoid a slow convergence in finding a global minimum by the conventional SA (CSA). This method is referred to as SA-OFLOOD and designed for an efficient SA algorithm that robustly detects global minimum states in the protein-folding problems. As a demonstration, SA-OFLOOD was applied to reproduce the folding process of Trp-cage from a fully extended to the native states in implicit solvent. Through the demonstration, SA-OFLOOD successfully predicted the native state of Trp-cage within errors of 0.6 ± 0.2 Å Cα root mean square deviation (RMSD) with only 200 ns simulation time. In contrast, both CSA with sufficiently slow temperature scheduling and canonical MD simulations at room temperature (300 K) failed to find the native state (more than 3.0 Å Cα RMSD), indicating the strength of SA-OFLOOD on the protein-folding problem. As an application to a realistic system, SA-OFLOOD was applied to the folding of Trp-cage in explicit solvent, and the native state was also sampled within Cα RMSD of 1.0 Å through a nanosecond-order simulation time.
New dicarboxylic acids were synthesized from ricinoleic acid in 3–8 steps in good overall yields, and they were found to be effective as an electrolyte in aluminum electrolytic capacitors. These types of dicarboxylic acids show good heat-resistance and higher withstand voltage than conventional electrolytes.
Reactions between acetylenes and a stable digermyne bearing 4-t-Bu-2,6-[CH(SiMe3)2]2-C6H2 (Tbb) groups afforded the corresponding stable 1,2-digermabenzenes together with the respective 1,4-digermabarrelenes. The properties of the obtained products and the reaction mechanism are discussed on the basis of experimental and theoretical results. Especially, the aromaticity of the newly obtained 1,2-digermabenzene has been discussed on the detailed calculations, revealing its aromatic character to some degree.
A representative gold(III) complex ion ([AuCl4]−), successively hydrolyzes to form [AuCl4−n(OH)n]− (n = 0–4) in aqueous solution as the pH increases and, finally, precipitates. It has been referred to as “gold(III) hydroxide” for the past fifty years. However, whether the precipitate is gold(III) hydroxide (Au(OH)3) or hydrous gold(III) oxide (Au2O3·nH2O) has remained uncertain. Few studies have been conducted to determine its chemical and physical properties. The aim of this investigation is to identify the precipitate and to determine its solubility. The precipitate was X-ray amorphous. Based on the transmission electron microscopy (TEM) observation, the shape was spherical and the particle diameter was approximately 9 nm. From the results of 197Au Mössbauer spectroscopy, Au L3-edge X-ray absorption (XA) spectroscopy and thermogravimetry/differential thermal analysis (TG/DTA) measurements, the precipitate composition was estimated to be Au(OH)3. Based on the composition, its structure was proposed to be a linear polymer. Moreover, its solubility at 298 K was determined to be 0.00120 g/100 g of H2O. This chemical and physical properties information of Au(OH)3 is essential for gold chemistry, for example, for preparing supported gold catalyst.
Carbazole-, quinoline-, benzothiazole-, and stilbene-containing fluorescent gelators are synthesized by connecting gelation-driving segments, and their gelation abilities are studied with 13 solvents. Fibrous thin-layer films are prepared on quartz plates from the solutions or gels, and they are studied as chemosensors for explosives. Fluorescence quenching of the films upon exposure to saturated TNT or RDX vapor is used to evaluate the abilities of the films to detect explosives. The relationship between the thickness of the thin-layer film and the quenching efficiency upon exposure to TNT is studied. The morphologies of the thin-layer films are observed by dynamic force mode scanning probe microscopy and discussed with regard to their fluorescence quenching. The interactions among chromophores in the gels, thin-layer films, and solutions are studied by variable-temperature spectroscopy. The mechanism of TNT detection is discussed from the viewpoint of the HOMO and LUMO energy levels.