We propose a new algorithm that can be practically applied for searching molecular conformations without specifying the explicit reaction coordinates in advance. The basic idea is to introduce repulsive interactions among all the sampling structures (walkers) to spread the walker distributions. By increasing the strength of the repulsive interactions, walkers trapped in a local potential minimum overcome the potential barrier and can flow into other potential areas. Using this method, called the GLobal Area Search (GLAS) approach, all the walkers are optimized in parallel like a conventional geometrical optimization procedure, but in which only the repulsive force is added to the total gradient like an extra restraint term. We tested the GLAS method using simple molecules, i.e., ethane and glycine, and we could show that their conformers are properly generated. As the GLAS method has the following advantages: (i) computational time is the order of the geometrical optimizations, (ii) parallel exclusion is possible, and (iii) some GLAS trajectories are very close to the minimum energy path, the GLAS approach will be quite useful to search for stable conformations and reactivity especially for uncharacterized molecules.
The zeolitic imidazolate frameworks (ZIFs) ZIF-8 and ZIF-67 are well-known as belonging to the series of metal-organic frameworks. Using different types of metal ions in them, such as Zn2+ and Co2+ simultaneously, brings both advantages and disadvantages with respect to the carbonization process. For tailoring their properties, we suggest that the best approach involves control of the bimetallic ZIF-derived carbon nanoarchitecture, which is hybridized through the synergistic effects of each metal ion. In this study, the bimetallic ZIFs were designed by controlling the molar ratio of zinc (Zn2+) and cobalt (Co2+) ions, and the carbon nanoarchitecture was subsequently formed by a facile heat treatment and acid leaching. We demonstrate this approach to achieve tailored ZIF derived carbon nanoarchitectures with different pore sizes, surface areas, and degree of graphitization. These pave the way to finding the optimal carbon nanoarchitecture for specific applications such as Li-O2 air cell.
A facile one-pot, phosgene-free method for the synthesis of N-phenylcarbamates is developed. Using this method, various aromatic carbamates could be prepared from aromatic amines, CO2 and metal alkoxides. Aniline reacted with titanium methoxide (Ti(OMe)4) in the presence of CO2 (5 MPa) to give methyl N-phenylcarbamate in 85% yield, in 20 min. Titanium residue could be regenerated by reaction with dimethyl carbonate at 220 °C for 16 h.
Competitive binding of binary mixed counterions to the headgroups of adsorbed surfactant films has been investigated at solution surfaces by total reflection X-ray absorption fine structure (XAFS) spectroscopy. The obtained extended XAFS χ spectra for bromide counterions are linear combinations of the spectra of fully hydrated bromide ions (free Br) and partially dehydrated bromide ions bound to the headgroups of the surfactant ions (bound Br). From the fraction of bound Br in counterion mixed systems, two series of the relative strengths of counterion binding are proposed for the trimethylammonium (TA+) and 3-methylimidazolium (MIM+) headgroups: (a) TA–SO4 < TA–Cl < TA–Br < TA–BF4 and (b) MIM–Br < TA–Br < TA–BF4 < MIM–BF4. For the TA headgroup, matching the hydration of the headgroups and counterions gives series (a) according to Collins’ law, which states that the tendency of contact ion pair formation becomes larger when the absolute values of the hydration enthalpies of the ions match. For the MIM headgroup, the number of binding sites of hydrogen bonds between the MIM headgroup and counterion is essential, which leads to series (b) because of competition between the counterion and water for interaction with the MIM headgroup.
PtNi alloy nanoparticles prepared by unique nanocapsule method exhibited high oxygen reduction reaction activity in alkaline media. The catalytic activity was dependent much on the alloy composition. At the optimum composition (ca. 50 atom% of Ni), the mass activity was more than twice as high as that of pure Pt nanoparticles.
Absorption properties of 13 bisazomethine dyes in a crystalline state were studied by optical waveguide spectroscopy. Their solid-state absorption spectra were found to shift bathochromically relative to those in solution with no remarkable change in a spectral shape. The observed spectral shifts were characterized in terms of two intermolecular interactions, conformational change and exciton interaction, on the basis of the crystal structure. Solid-state fluorescence properties of the diethylamino derivatives were also examined for their electronic characterization. The characteristic two-dimensional staircase structure, one of the proposed structures of J-aggregates, was found to play a significant role in the bathochromic spectral shift of all the bisazomethine derivatives.
Concerning a series of naphthalimide-based fluorescence dyes in which the π-system is extended with oligothiophene units, it has been revealed that the absorption and fluorescence maxima can be tuned over ca. 100 nm and ca. 180 nm range by extending π-conjugation, respectively. The effects of the solvent on the fluorescence quantum yield depend on the conjugation length. For the same series but with an electron-donating moiety (push-pull type dyes), the absorption and fluorescence maxima are less dependent on the conjugation length. The fluorescence quantum yields of the push-pull type dyes are large in toluene (>0.3) but extremely low in DMSO. These results will be a guide for the design of naphthalimide-based sensors and probes.
The conceptual difference between RS-stereoisomerism and stereoisomerism as well as between RS-stereogenicity and stereogenicity is discussed according to Fujita’s stereoisogram approach (S. Fujita, Mathematical Stereochemistry; De Gruyter: Berlin, 2015). Enumeration of [2.2]paracyclophanes is conducted to clarify hierarchy of stereoisomerism, i.e., under the point group D2 (individual derivatives), the point group D2h (enantiomerism), the RS-stereoisomeric group (RS-stereoisomerism), the stereoisomeric group (stereoisomerism). Stereoisograms for characterizing RS-stereoisomerism are discussed briefly for the purpose of examining nomenclature of [2.2]paracyclophane derivatives. Global and local RS-stereogenicities as well as global and local RS-stereoisomerism are discussed on the basis of two kinds of handedness. Nomenclature for global RS-stereogenicity and that for local RS-stereogenicity are discussed after two modes of numbering of skeletal carbons are determined explicitly.
Thermal stability and effect of hydration were studied for calcium oxide cluster ions, CanOm+, using gas-phase thermal desorption spectrometry. Near stoichiometric CanOn+, CanOn+1+, and CanOn+2+ clusters were formed in the gas phase at 300 K, and the more oxygen-rich clusters, CanOn+2+ (n = 3, 5, 7, 9), released O2 to form CanOn+, when heated to a higher temperature. The stability and the propensity of O2 release were well explained in terms of the formal oxidation states of the atoms in the clusters. Reaction of CanOn+ and CanOn+1+ (n = 4, 6, 9) with a water molecule forms CanOn+1H2+ and CanOn+2H2+, respectively. Density functional theory (DFT) calculations on the stable geometries of Ca4O5H2+ and Ca4O6H2+ suggested that an O–H bond of H2O was activated upon reaction and di-hydroxides, Ca4O3(OH)2+ and Ca4O4(OH)2+, were formed via exothermic processes. Upon heating, OH and O2H were released from Ca4O3(OH)2+ and Ca4O4(OH)2+, respectively, to form Ca4O3(OH)+. For other clusters (n = 3, 5, 7 and 8), OH release and O2H release were not observed by the simple heating of CanOn−1(OH)2+ and CanOn(OH)2+. Nevertheless, solvation of gas phase CanOm+ by multiple water molecules was found to generate hydrated CanOn−1(OH)+.
A transparent bacterial cellulose/atactic polypropylene (BC/at-PP) composite film was prepared by a very facile “sandwich” hot-press method. The resulting BC/at-PP composite film exhibited good transparency, hydrophobicity, and significantly enhanced mechanical properties, indicating its tremendous potential as transparent film for food packaging and optoelectronics applications.
Quantum mechanical (QM) calculation in solution is becoming a popular and useful tool in chemistry. We have developed a hybrid method between QM and reference interaction site model (RISM). To combine RISM with QM calculations, we have to employ charge fitting approaches. By introducing constrained spatial electron density distribution (cSED) in the fitting, we developed a new generation of RISM self-consistent field (SCF). Our method (RISM-SCF-cSED) overcame the instability of the original RISM-SCF calculations. We extended RISM-SCF-cSED by coupling a variety of QM approaches. We applied our method to tautomerization reactions of cytosine, 6-chloro-2-pyridone, and isonicotinic acid in water and Stokes shift calculation of indole and 5-cyanoindole. Our method correctly evaluated relative free energy differences in the reaction and the Stokes shift change along the polarity of solvent.
The novel layered zinc glycolate (LZG) with a lamella structure was successfully synthesized from zinc acetate by solvothermal reactions in ethylene glycol (EG) without water. The octahedral-shaped zinc glycolate (OZG) particles were formed in EG containing 1% water. LZG and OZG are crystal polymorphs with the same composition, Zn(OCH2CH2O). At 5% water content, the uniform and spherical particles of ZnO were formed. EG moieties in LZG were partially exchanged with Mn acetate complex in Mn acetate solution and the interlayer spacing of LZG was increased from 1.09 nm to 1.42 nm. ZnO and ZnMn2O4 were formed by heating the exchanged LZG at 600 °C. Acetate ions in the exchanged LGZ were exchanged with salicylic ions. EG moieties in OZG were mainly exchanged with OH in Mn acetate solution to form an amorphous phase.
X-ray structure analysis of (DM-TTP)2X (X = PF6, AsF6 and SbF6) was successfully performed. The arrangement of DM-TTP molecules was classified as β20-type. A tight-binding band calculation suggested these salts had a quasi-one-dimensional Fermi surface. (DM-TTP)2SbF6 exhibited metallic conductivity down to 10 K with σ⊥ = 1.4 S cm−1 at room-temperature.
A spin-coating method has been employed to prepare crystalline nanostructured zinc oxide (ZnO) thin films. The CdS nanoparticles are then deposited on the surface via a successive ion adsorption and reaction (SILAR) method. Three different concentrations (15, 30, and 50 mM) are used to investigate the effect of various CdS loading on the photocatalytic activity of the hybrid ZnO-CdS hybrid thin films. The transparent crack-free thin films possess fine nanostructures on the top surface, with a fine dispersion of CdS nanoparticles. The highest photocatalytic activity is realized when the concentration is 30 mM. ZnO-CdS hybrid thin films with high surface area, crystalline wall, and low band gap have a great potential as a high-performance material for absorption and degradation of harmful dye molecules such as methylene blue (MB).