Decomposition mechanism of methylene blue caused by metallic iron-maghemite mixture

Decomposition mechanism of methylene blue (MB) caused by a mixture of metallic iron-maghemite (Fe⁰-γFe₂O₃) was investigated by means of ⁵⁷Fe-Mössbauer spectroscopy, X-ray diffractometry (XRD), Ultraviolet-Visible Absorption Spectroscopy (UV-vis) and electrospray-ionization mass spectroscopy (ESI-MS). Ten day-leaching test of 10 μmol L^???1 MB aqueous solution and Fe⁰-γFe₂O₃ mixture (mass ratio 3:7) showed a decrease in the concentration from 10.5 to 4.45 μmol L^???1 with first-order rate constant (k) of $1.5_{7} \times 10^{-1}$  day^???1. An ESI-MS study of Fe⁰-γFe₂O₃ mixture (3:7) after the leaching test revealed new peaks at m/z of 100, 110 and 137 due to fragmentation of MB, in addition to those observed at m/z of 284, 270 and 256 which were ascribed to MB, Azure B and Azure A, respectively. ⁵⁷Fe-Mössbauer spectra of Fe⁰-γFe₂O₃ mixture (3:7) resulted in a decrease in absorption area (A) for Fe⁰ (δ?=?0.00_±0.01 mm s^???1, H _int?=?33.0_±0.1 T) from 37.5 to 21.3, 9.7, 7.9, 7.0 and 4.5_±0.5 %, together with an increase in A from 0.0 to 5.0, 13.8, 17.2, 21.0 and 22.4_±0.5 % for octahedral (O _h) iron (Fe^II?+?Fe^III) of Fe₃O₄. XRD study of these samples indicated that the peak intensity at 2Θ of 44.7° being ascribed to Fe⁰ was decreased, while that of 35.6° due to Fe₃O₄ was almost constant; relative peak ratio of Fe $^{0}/\mathrm{Fe}_{3}$ O₄ was decreased from 26.3 to 2.76 after the leaching, indicating that Fe⁰ in the Fe⁰-γFe₂O₃ mixture was oxidized to Fe₃O₄. These experimental results suggest that Fe⁰-γFe₂O₃ mixture could be utilized for the cleaning or decomposition of toxic organic compounds like trichloroethylene.     

Stacked-Lamellar Structure in High-Speed Spun PET Fibers as Revealed by TEM

Morphological study of high-speed spun poly(ethylene terephthalate) (HSS-PET) fibers spun at 6 km/min was performed by a combination of alkaline etching, surface replica method, and transmission electron microscopy. In the two-stage replica of the alkaline-etched fiber, the stacked-lamella-like structure was observed, in which lamella-like striations were stacked in a direction leaning at about 40° away from the fiber axis. The spacing between the adjacent striations, namely the lamellar periodicity, was measured to be 10–30 nm. We have proposed that the stacked-lamellar structure, which is mainly composed of mosaic lamellar crystals and has the extended-chain crystals connecting the adjacently stacked lamellae, is an appropriate model for the fiber structure of HSS-PET fibers.     

In situ generation of active sites in olefin metathesis

The depth of our understanding in catalysis is governed by the information we have about the number of active sites and their molecular structure. The nature of an active center on the surface of a working heterogeneous catalyst is, however, extremely difficult to identify and precise quantification of active species is generally missing. In metathesis of propene over dispersed molybdenum oxide supported on silica, only 1.5% of all Mo atoms in the catalyst are captured to form the active centers. Here we combine infrared spectroscopy in operando with microcalorimetry and reactivity studies using isotopic labeling to monitor catalyst formation. We show that the active Mo(VI)-alkylidene moieties are generated in situ by surface reaction of grafted molybdenum oxide precursor species with the substrate molecule itself gaining insight into the pathways limiting the number of active centers on the surface of a heterogeneous catalyst. The active site formation involves sequential steps requiring multiple catalyst functions: protonation of propene to surface Mo(VI)-isopropoxide species driven by surface Br?nsted acid sites, subsequent oxidation of isopropoxide to acetone in the adsorbed state owing to the red-ox capability of molybdenum leaving naked Mo(IV) sites after desorption of acetone, and oxidative addition of another propene molecule yielding finally the active Mo(VI)-alkylidene species. This view is quite different from the one-step mechanism, which has been accepted in the community for three decades, however, fully consistent with the empirically recognized importance of acidity, reducibility, and strict dehydration of the catalyst. The knowledge acquired in the present work has been successfully implemented for catalyst improvement. Simple heat treatment after the initial propene adsorption doubled the catalytic activity by accelerating the oxidation and desorption-capturing steps, demonstrating the merit of knowledge-based strategies in heterogeneous catalysis. Molecular structure of active Mo(VI)-alkylidene sites derived from surface molybdena is discussed in the context of similarity to the highly active Schrock-type homogeneous catalysts.     

Complementary and synergistic roles in enzyme-catalyzed regioselective and complete hydrolytic deprotection of O-acetylated β-D-glucopyranosides of N-arylacetohydroxamic acids

An efficient chemoenzymatic synthesis of β-D-glucopyranosides of N-arylacetohydroxamic acids 3a-c was achieved by the chemoselective O-deacetylation of 1a-c under mild, neutral conditions, with no accompanying N-deacetylation. Lipase AS Amano from Aspergillus niger (LAS) and carboxylesterase from Streptomyces rochei (CSR) played complementary, synergistic roles in the O-deacetylation of 1a and its partially O-deacetylated intermediates. An intramolecular O-acetyl migration, which proceeded simultaneously, also accelerated the overall reaction rate. Under weakly acidic conditions at pH 5.0, where the intramolecular O-acetyl migration is markedly slower, LAS, CSR, and porcine liver esterase (PLE) exhibited different regioselective O-deacetylation activities. LAS and PLE showed regioselective 3-O-deacetylation and 2-O-deacetylation activity, respectively, for 1a and its tri-O-acetyl derivatives (4-7). CSR showed marked preferences for 3-O-deacetylation of 2,3,6-tri-O-acetyl intermediate 5 and 4-O-deacetylation of 2,4,6-tri-O-acetyl intermediate 6. In contrast, CSR showed almost no O-deacetylation activity toward the other tri-O-acetyl intermediates 4 and 7, which were efficiently O-deacetylated by LAS in a complementary manner. Using these enzyme-catalyzed regioselective O-deacetylation as well as chemical methods, we could synthesize all 14 partially O-acetylated intermediates (4-17) derived from 1a.     

Bis(oxazoline)–ligand-mediated asymmetric [2,3]-Wittig rearrangement of benzyl ethers: reaction mechanism based on the hydrogen/deuterium exchange effect

We have investigated the mechanism of chiral induction in the asymmetric [2,3]-Wittig rearrangement of allyl benzyl ether in the presence of a bis(oxazoline) chiral ligand [(S,S)-Box–tBu] by comparing the reaction of both enantiomers of monodeuterated benzyl ether 1a–d. As a result, we found that chirality was induced via enantioselective deprotonation followed by efficient chirality transfer of the resulting chiral benzyl carbanion with the inversion of stereochemistry. It was revealed that the chiral ligand facilitates selective deprotonation as well as prevents the chiral carbanion from racemization. Moreover, we examined the effect of the o-methoxy substituent on the benzene ring.     

Structure-activity studies on the fluorescent indicator in a displacement assay for the screening of small molecules binding to RNA

A series of xanthone and thioxanthone derivatives with aminoalkoxy substituents were synthesized as fluorescent indicators for a displacement assay in the study of small-molecule-RNA interactions. The RNA-binding properties of these molecules were investigated in terms of the improved binding selectivity to the loop region in the RNA secondary structure relative to 2,7-bis(2-aminoethoxy)xanthone (X2S) by fluorimetric titration and displacement assay. An 11-mer double-stranded RNA and a hairpin RNA mimicking the stem loop IIB of Rev response element (RRE) RNA of HIV-1 mRNA were used. The X2S derivatives with longer aminoalkyl substituents showed a higher affinity to the double-stranded RNA than the parent molecule. Introduction of a methyl group on the aminoethoxy moiety of X2S effectively modulated the selectivity to the RNA secondary structure. Methyl group substitution at the C1' position suppressed the binding to the loop regions. Substitution with two methyl groups on the amino nitrogen atom resulted in reducing the affinity to the double-stranded region by a factor of 40%. The effect of methyl substitution on the amino nitrogen atom was also observed for a thioxanthone derivative. Titration experiments, however, suggested that thioxanthone derivatives showed a more prominent tendency of multiple binding to RNA than xanthone derivatives. The selectivity index calculated from the affinity to the double-stranded and loop regions suggested that the N,N-dimethyl derivative of X2S would be suitable for the screening of small molecules binding to RRE.     

Rhenium-catalyzed regioselective synthesis of multisubstituted pyridines from β-enamino ketones and alkynes via C-C bond cleavage

A new method is described for the regioselective synthesis of multisubstituted pyridine derivatives. Treatment of N-acetyl β-enamino ketones with alkynes in the presence of the rhenium catalyst, Re(2)(CO)(10), gives multisubstituted pyridines regioselectively. In this reaction, the N-acetyl moieties are important for the selective formation of the multisubstituted pyridines. This reaction proceeds via insertion of alkynes into a carbon-carbon single bond of β-enamino ketones, intramolecular nucleophilic cyclization, and elimination of acetic acid.     

Peripherally ethynylated carbazole-based core-modified porphyrins

Peripherally ethynylated carbazole-based core-modified porphyrins were synthesized by sequential metal-catalyzed coupling and annulation reactions. Experimental results and DFT calculations both confirm that the π-conjugated networks of the resulting porphyrins effectively delocalize over the entire macrocycle, including the ethynyl substituent groups.     

Electronic structure analysis of Mn- and Fe-codoped In2O3 by photoemission yield measurements

The valence band electronic structures of Mn- and/or Fe-doped In₂O₃, i.e., In₂O₃:Mn, In₂O₃:Fe, and In₂O₃:(Mn, Fe), are investigated by photoemission yield measurements. Significant changes are observed in the threshold energy of photoemission, depending on the doped magnetic ions, which indicates that an additional occupied band appears above the top of the valence band of In₂O₃ owing to doping with Mn and/or Fe ions. It is confirmed that the order of the threshold energies of photoemission, E_PET, is E_PET(In₂O₃:Mn)<E_PET(In₂O₃:(Mn, Fe))<E_PET(In₂O₃:Fe)<E_PET(In₂O₃). To gain a better understanding of these results, first-principles molecular orbital calculations are also carried out, which successfully explain the observed changes in the photoemission threshold energies.     

Specific uptake of aromatic compounds from aqueous solution by montmorillonite modified with tetraphenylphosphonium

Montmorillonite (MT) modified with tetraphenylphosphonium (TPP·MT) had specific uptake behavior for aromatics in aqueous solution. This is attributed to the extent of π–π stacking interactions between the benzene rings of intercalated TPP⁺ and the benzene rings of aromatics with different electronic states. The uptake order of aromatics by TPP·MT was in contrast to that by layered double hydroxide (LDH) intercalated with 2,7-naphthalene disulfonate. The selective uptake of target aromatic compounds from aqueous solution can be achieved by combining appropriate inorganic layered compounds and modified aromatic ions.