Evidence for an electric-dipole active continuum band of spin excitations in multiferroic TbMnO3

The wide range optical spectra on a multiferroic prototype TbMnO3 have been investigated to clarify the origin of spin excitations observed in the far-infrared region. We elucidate the full band structure, whose high energy edge (133 cm;{-1}) exactly corresponds to twice of the highest-lying magnon energy. Thus the origin of this absorption band is clearly assigned to two-magnon excitation driven by the electric field of light. There is an overlap between the two-magnon and phonon energy ranges, where the strong coupling between them is manifested by the frequency shift and transfer of oscillator strength of the phonon mode.     

Visible‐Light Sensitization and Photoenergy Storage in Quantum Dot/Polyoxometalate Systems

Recently, the process by which energy is transferred from photoexcited semiconductor nanocrystals, called quantum dots (QDs), to other semiconductors has attracted much attention and has potential application in solar energy conversion (i.e., QD‐sensitized solar cells). Sensitization of wide band gap polyoxometalates (POMs) to visible light by using CuInS₂ QDs dispersed in an organic solution is demonstrated herein. Photoluminescence quenching and lifetime studies revealed efficient electron transfer from the CuInS₂ QDs to POMs, such as SiW₁₂O₄₀ and W₁₀O₃₂, that were hybridized with a cationic surfactant. CuInS₂ QDs function as an antenna that absorbs visible light and supplies electrons to the POMs to enable certain photocatalytic reactions, including noble‐metal‐ion reduction. The photoenergy storage capabilities of the QD‐POM system, in which electrons photogenerated in QDs by visible‐light excitation are trapped and accommodated by POMs to form reduced POM, are also demonstrated. Electrons stored in the POM can be later discharged through reductive reactions, such as oxygen reduction, in the dark.     

Syntheses of chiral homoazacalix[4]arenes incorporating amino acid residues: molecular recognition for racemic quaternary ammonium ions

Chiral calixarene analogues incorporating amino acid residues into the macrocyclic rings were prepared from the cyclization reactions of bis(chloromethyl)phenol-formaldehyde tetramer with amino acid methyl ester in moderate yields. The macrocycles form a chiral concavity, which is induced by the chiral transmission from the point chirality of the amino acid residues to the phenol-formaldehyde tetramer unit. The macrocycles have the cavity pi-basic enough to include the quaternary ammonium ion due to the cation-pi interaction and can serve as a shift reagent for racemic ammonium ions during 1H NMR analysis.     

Polymerization of vinyloxyaluminum and formation of syndiotactic poly(vinyl alcohol)

The polymerization of diisobutylvinyloxyaluminum, CH₂?CHOAl(i-Bu)₂, and diethylvinyloxyaluminum, CH₂?CHOAlEt₂, did not take place in the presence of typical radical or cationic initiators. The polymerization was realized at 60°C by the addition of tetrahydrofuran (THF) or tetrahydropyran, no conventional initiator being required. Diethyl ether, glyme, and dioxane were not effective on the polymerization. At Dry Ice–acetone temperature, polymerization did not take place, even in the presence of tetrahydrofuran, but did take place in the presence of both THF and SnCl₄. The role of cyclic ethers in the polymerization was studied. Polymers were converted into poly(vinyl alcohol) (PVA) by solvolysis. All the resulting PVA was syndiotactic; particularly polymers obtained at ?78°C showed syndiotactivity of 89%, which is the highest value ever reported.     

Synthetic noncyclic ionophores with multiple carboxylate groups for alkaline earth metal cations

A series of synthetic ionophores containing two carboxylic acid groups were synthesized as carriers for alkaline earth metal cations. Among them, the lipophilic derivative having a trimenthylene bridge and multiple quinaldate moieties selectively transported barium ion from the basic aqueous phase to the acidic aqueous phase through the bulk dichloromethane liquid membrane. The cation selectivity was explained by considering the fit of the cation diameter with the pseudocyclic cavity.     

Alternating copolymerization of ethylene with maleic anhydride

The copolymerization of ethylene with maleic anhydride was carried out with γ-radiation and a radical initiator, i.e., 2,2′-azobisisobutyronitrile and diisopropyl peroxydicarbonate under pressure at various reaction conditions. The homopolymerization of neither monomer was observed in this system. In the γ-ray-initiated copolymerization the G value (polymerized monomer molecules per 100 e.v.) was shown to be between 10³ and 10⁴. It was found that the dose rate exponent of the rate is approximately unity, and the rate is proportional to the amount of ethylene monomer. Apparent activation energies of 1.8 and 27.5 kcal./mole were obtained for γ-ray-initiated and AIBN-initiated copolymerization, respectively. Since the composition of copolymer is independent of monomer molar ratio and the molar ratio of ethylene to maleic anhydride in the polymer is approximately unity, the monomer reactivity ratios were obtained as r_E ? 0 and r_M ? 0 for γ-ray-initiated polymerization at 40°C. Alternating copolymerization was, therefore, concluded to occur. Infrared analysis of the copolymer is almost consistent with this. The copolymer in the solid state is amorphous. It is soluble in water, cyclohexane, and dimethylformamide and insoluble in lower alcohols, ether, and aromatic hydrocarbons. The aqueous solution of polymer gave a strong acid.     

Visible-light-responsive photocatalytic reaction on tetrahedrally-coordinated chromium oxide moieties loaded on ZSM-5 zeolites and HMS mesoporous silica: partial oxidation of propane

Chromium oxide (Cr-oxide) moieties loaded on ZSM-5 zeolites and HMS mesoporous silica molecular sieves were prepared by an impregnation method and characterized by various spectroscopic methods (XRD, XAFS, UV-Vis, photoluminescence) and their photocatalytic reactivities for partial oxidation of propane under visible light irradiation were investigated. The local structure of Cr-oxide species depended to a large extent on the zeolite types and Si/A1 ratios of zeolites. Tetrahedrally-coordinated isolated Cr-oxide moieties can be loaded on HMS and ZSM-5 having the higher Si/A1 ratios. On these catalysts, in the presence of propane and O₂, a partial oxidation proceeded under visible light irradiation to produce acetone with high selectivity. The charge-transfer excited state of the tetrahedral Cr-oxide moieties plays a significant role in the selective photocatalytic reactions under visible light irradiation.     

Initiation and propagation in γ-radiation-induced polymerization of ethylene

The initiation and propagation reaction in γ-ray-induced polymerization of ethylene was studied by the two-stage irradiation method, i.e., a first stage in which initiation and propagation occur at a high dose rate, and a second stage where only the growth of polymer radical occurs. The rate of initiation is calculated from the amount of polymerized monomer and the degree of polymerization as the rate of increase in the number of polymer chains. The initiation rate is shown to be proportional to the ethylene density in the reactor and dose rate. G_R of radical formation is found to be about 1.6 at 30°C. at a dose rate of 2.5 × 10⁴ rad/hr. and is almost independent of ethylene density but decreases slightly with increasing irradiation dose rate. The lifetime of the growing polymer chain radical is shown to be long at normal temperature. The absolute propagation rate is proportional to the square of ethylene fugacity and depends on dose rate to some extent. For chain growth, irradiation of low dose rate is necessary. The apparent activation energy for the propagation reaction is ?9 kcal./mole.     

A novel fluorescent indicator for Ba2+ in aqueous micellar solutions

The highly selective and sensitive fluorescence detection of Ba(2+) among alkali metal and alkaline earth metal cations was successfully achieved in aqueous media by the combination of a novel monoazacryptand type of fluorophore and micelles of Triton X-100.     

Two-stage irradiation study on propagation and termination in the γ-radiation-induced polymerization of ethylene in liquid carbon dioxide

The propagation and termination reaction in the γ-radiation-induced ethylene polymerization in liquid carbon dioxide were investigated by a two-stage irradiation. After irradiation at high dose rate, the polymerization occured at a considerable rate under the extremely low dose rate without initiation. The absolute propagation rate was determined in the second stage to be proportional to the square of ethylene fugacity and depended slightly on dose rate. The apparent activation energy for the propagation reaction is ?9 kcal./mole. From these observations which are the same as those in bulk polymerization, it is concluded that carbon dioxide acts as a diluent of ethylene monomer in the propagation reaction. Also, carbon dioxide was shown to be inactive to the growing radicals without irradiation, but oxygen which is produced by the radiolysis of carbon dioxide at high dose terminates the growing radicals with formation of carbonyl in the polymer.