Deprotection of dithioacetals with 30% hydrogen peroxide catalyzed by tantalum(V) chloride–sodium iodide or niobium(V) chloride–sodium iodide

The reaction of dithioacetals with 30% hydrogen peroxide in the presence of catalytic amounts of tantalum(V) and iodide ion effectively produced carbonyl compounds in high yields. Dithioacetals also can be deprotected using the niobium(V) catalyzed oxidation of iodide ion by hydrogen peroxide under mild conditions.     

Preparation of metal adsorbent from poly(methyl acrylate)-grafted-cassava starch via gamma irradiation

Metal adsorbent containing hydroxamic acid groups was successfully synthesized by radiation-induced graft copolymerization of methyl acrylate (MA) onto cassava starch. The optimum conditions for grafting were studied in terms of % degree of grafting (Dg). Conversion of the ester groups present in poly(methyl acrylate)-grafted-cassava starch copolymer into hydroxamic acid was carried out by treatment with hydroxylamine (HA) in the presence of alkaline solution. The maximum percentage conversion of the ester groups of the grafted copolymer, % Dg=191 (7.63 mmol/g of MA), into the hydroxamic groups was 70% (5.35 mmol/g of MA) at the optimum condition. The adsorbent of 191%Dg had total adsorption capacities of 2.6, 1.46, 1.36, 1.15 and 1.6 mmol/g-adsorbent for Cd²⁺, Al³⁺, UO₂²⁺, V⁵⁺ and Pb²⁺, respectively, in the batch mode adsorption.     

Terpendole E,a Kinesin Eg5 Inhibitor,Is a Key Biosynthetic Intermediate of Indole-Diterpenes in the Producing Fungus Chaunopycnis alba

1. Download : Download high-res image (212KB)
2. Download : Download full-size image

Highlights? The terpendole biosynthetic gene cluster was isolated ? Terpendole E is a key biosynthetic intermediate of indole-diterpenes ? Terpendole E was overproduced by gene knockout of the bispecific enzyme TerP ? Indole-diterpene biosynthetic pathways can be classified into two groups     

Theoretical Study of the Cycloaddition Reaction of a Tungsten‐Containing Carbonyl Ylide

The [3+2] cycloaddition reaction of a tungsten‐containing carbonyl ylide with methyl vinyl ether and the insertion reactions of the nonstabilized carbene complex intermediates produced have been investigated through the use of B3LYP density functional theory. The [3+2] cycloaddition reaction of the tungsten‐containing carbonyl ylide has been proven to proceed concertedly, reversibly, and with high endo selectivity. The intermolecular Si? H insertion reactions of the carbene complex intermediates have been proven to be favored over the intramolecular C? H insertion, in good agreement with experimental results. Moreover, the kinetic endo/exo ratio of the [3+2] cycloaddition reaction has been shown to determine the endo/exo selectivity of the Si? H insertion products. In addition, secondary orbital interactions involving the benzene ring and the carbonyl ligand on the metal center have turned out to strongly influence the high endo selectivity of the [3+2] cycloaddition reaction with methyl vinyl ether.     

Antibacterial metal implant with a TiO2‐conferred photocatalytic bactericidal effect against Staphylococcus aureus

Photocatalysis with anatase Titanium dioxide (TiO₂) under ultraviolet A (UVA) has a well recognized bactericidal effect. There have been a few reports, however, on the effects of photocatalysis on bio‐implant‐related infections. The purpose of present study was to evaluate the photocatalytic bactericidal effects of anatase TiO₂ on Staphylococcus aureus (S. aureus) associated with surgical site infections. TiO₂ films were synthesized on commercially pure titanium substrates and SUS316 stainless steel using a plasma source ion implantation method followed by annealing. The chemical composition of the surface layers was determined using GXRD and XPS. The disks were seeded with cultured S. aureus and exposed to UVA illumination from black light. The bactericidal effect of the TiO₂ films was evaluated by counting the survived colonies statistically. A structural gradient anatase type TiO₂ layer formed on all substrates. The viability of the bacteria on the photocatalytic TiO₂ film coated on titanium was suppressed to 7.0% at 30 minutes and 5.5% at 45 minutes, whereas that on a similarly coated stainless steel was suppressed to 45.8% at 30 minute and 28.6% at 45 minutes (ANOVA: p < 0.05). Complete bacterial inactivation was achieved after 90 minutes on titanium and after 60 minutes on stainless steel. The photocatalytic bactericidal effect of TiO₂ is useful for sterilizing the contaminated surfaces of bioimplants. Copyright © 2008 John Wiley & Sons, Ltd.     

Magnetically recoverable osmium catalysts for dihydroxylation of olefins

We prepared magnetically recoverable osmium catalysts by use of magnetite, quaternary ammonium salts, and potassium osmate(VI), and applied them to the dihydroxylation of olefins. By employing 2 mol% of the magnetic osmium catalyst, the dihydroxylation reaction proceeded smoothly to provide the corresponding vicinal diol in a good chemical yield. The osmium catalyst was readily recovered by use of an external magnet, and was reused repeatedly.     

Effect of thermal treatment on the photocatalytic degradation of ethylene,trichloroethylene, and chloroform

The thermal treatment of TiO₂ pellets prepared by the sol–gel method decreased the photocatalytic activity. The activity divided by the specific surface area of the pellets for the complete mineralization of ethylene or chloroform was maximized at the firing temperature of 400°C. For the photocatalytic degradation of trichloroethylene (TCE), most of them were converted to chlorinated by-products, such as dichloroacetic acid, chloroform, and phosgene, and the stoichiometric ratio of [CO₂]_formed/[TCE]_degraded showed a maximal value at 400°C. The electron spin resonance (ESR) spin-trapping with 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) in the flow injection system indicated that firing at 400°C gave the highest signal intensity of DMPO–OH adducts. These findings indicated that the OH radical was produced most effectively on the TiO₂ fired at 400°C, which would be related to the content of anatase and rutile. Concerning the formation of chlorinated by-products from TCE, more dichloroacetic acid (DCAA) were detected and less CHCl₃ and COCl₂ were formed at lower firing temperatures, suggesting that the branching ratio of chloroethoxy radicals to the formation of DCAA or CHCl₃ and COCl₂ by C–C bond scission depended on the firing temperature.     

Enantiomer separation of hydrophobic amino compounds by high-performance liquid chromatography using crown ether dynamically coated chiral stationary phase

CROWNPAK CR(+) column, which is powerful for the separation of amino acid enantiomers, must be used at a column temperature below 50°C and a mobile phase containing less than 15% methanol, because the chiral crown ether moiety of the stationary phase is dynamically coated on an ODS matrix. The second peak of the enantiomers of alanine-β-naphthylamide (Ala-β-NA) appeared at 204 min (k₂=148) by using ordinary mobile phase, that is, a mixture of 10 mM perchloric acid and 15% methanol. In this study, enantiomer separations of Ala-β-NA and 1-(1-naphthyl)ethylamine (1-NEA), both of which are hydrophobic amino compounds, were investigated through the modification of the mobile phase. Addition of crown ether, cyclodextrins (CDs), cations, etc., affected the stability of the complex between an analyte and the chiral moiety, leading to fast separation. The second peak of the enantiomers of Ala-β-NA appeared at 68 min (k₂=49) through the addition of 10 mM β-CD, or at 61 min (k₂=44) using potassium dihydrophosphate as a buffer component. This method was applied for the optical purity testing of -Ala-β-NA, which is used as one of the chiral derivatization reagents for carboxylic compounds. Validations such as reproducibility and linearity were also demonstrated and this method was found to be sufficient as a quality control method for the optical purity testing of -Ala-β-NA. As little as 0.05% -form in -Ala-β-NA could be determined.