Optimization of NH3 Decomposition by Control of Discharge Mode in a Rotating Arc

In this study, the characteristic behavior of a rotating arc was investigated. Various modes, depending on the electric power supplied, can be observed in a rotating arc. Each mode produces different discharge characteristics and thermal environments and, accordingly, chemical processes hosted in the plasma reaction volume can be controlled differently in each mode. General thermal to non-thermal transitions observed in a gliding arc are based on the longitudinal expansion of the arc column. In a rotating arc, the reverse transition or non-thermal to thermal transition can be hosted by controlling the reactor geometry. The reverse transition can be achieved by self-adjustment of the arc column where longitudinal expansion of the arc column is confined. The reverse transition enhances the conversion efficiency of electric power to thermal energy. Then, optimization of thermal activation was obtained by controlling the mode of operation, and it was verified using the NH₃ decomposition reaction.     

Flavusides A and B, antibacterial cerebrosides from the marine-derived fungus Aspergillus flavus

Flavusides A (1) and B (2), two new antibacterial cerebroside derivatives, and the previously described phomaligol A (3), kojic acid (4), methyl kojic acid (5), and dimethyl kojic acid (6) have been isolated from the extract of a marine isolate of the fungus Aspergillus flavus. The structure and absolute stereochemistry of two cerebrosides were assigned on the basis of NMR and Tandem FAB-MS/MS experiments. Compounds 1, 2, and 3 exhibited a mild antibacterial activity against Staphylococcus aureus, methicillin-resistant S. aureus, and multidrug-resistant S. aureus. The minimum inhibitory concentration (MIC) values for each strain are as follows: compounds 1 and 2 showed 15.6 μg/ml for S. aureus and 31.2 μg/ml for methicillin-resistant S. aureus and multidrug-resistant S. aureus, and compound 3 exhibited 31.2 μg/ml for S. aureus and methicillin-resistant S. aureus and 62.5 μg/ml for multidrug-resistant S. aureus.     

Facile nucleophilic fluorination reactions using tert-alcohols as a reaction medium: significantly enhanced reactivity of alkali metal fluorides and improved selectivity

Although protic solvents are generally not preferred for nucleophilic displacement reactions because of their partial positive charge and hydrogen-bonding capacity that solvate the nucleophile and reduce its reactivity, we recently reported a remarkably beneficial effect of using tertiary alcohols as a reaction media for nucleophilic fluorination with alkali metal fluorides, as well as fluorine-18 radiolabeling with [18F]fluoride ion for the preparation of PET radiopharmaceuticals. In this work, we investigate further the influence of the tert-alcohol reaction medium for nucleophilic fluorination with alkali metal fluorides by studying various interactions among tert-alcohols, the alkali metal fluoride (CsF), and the sulfonyloxy substrate. Factors such as hydrogen bonding between CsF and the tert-alcohol solvent, the formation of a tert-alcohol solvated fluoride, and hydrogen bonding between the sulfonate leaving group and the tert-alcohol appear to contribute to the dramatic increase in the rate of the nucleophilic fluorination reaction in the absence of any kind of catalyst. We found that fluorination of 1-(2-mesyloxyethyl)naphthalene (5) and N-5-bromopentanoyl-3,4-dimethoxyaniline (8) with Bu(4)N(+)F(-) in a tert-alcohol afforded the corresponding fluoro products in much higher yield than obtained by the conventional methods using dipolar aprotic solvents. The protic medium also suppresses formation of byproducts, such as alkenes, ethers, and cyclic adducts.     

Synergistic induction of cancer cell migration regulated by Gβγ and phosphatidylinositol 3-kinase

Phosphatidylinositol 3-kinase (PI3K) is essential for both G protein-coupled receptor (GPCR)- and receptor tyrosine kinase (RTK)-mediated cancer cell migration. Here, we have shown that maximum migration is achieved by full activation of phosphatidylinositol 3,4,5-trisphosphate-dependent Rac exchanger 1 (P-Rex1) in the presence of Gβγ and PI3K signaling pathways. Lysophosphatidic acid (LPA)- induced migration was higher than that of epidermal growth factor (EGF)-induced migration; however, LPA-induced activation of Akt was lower than that stimulated by EGF. LPA-induced migration was partially blocked by either Gβγ or RTK inhibitor and completely blocked by both inhibitors. LPA-induced migration was synergistically increased in the presence of EGF and vice versa. In correlation with these results, sphingosine-1-phosphate (S1P)-induced migration was also synergistically induced in the presence of insulin-like growth factor-1 (IGF-1). Finally, silencing of P-Rex1 abolished the synergism in migration as well as in Rac activation. Moreover, synergistic activation of MMP-2 and cancer cell invasion was attenuated by silencing of P-Rex1. Given these results, we suggest that P-Rex1 requires both Gβγ and PI3K signaling pathways for synergistic activation of Rac, thereby inducing maximum cancer cell migration and invasion.     

Characterization of Xyn10J,a Novel Family 10 Xylanase from a Compost Metagenomic Library

A gene encoding an extracellular xylanase was cloned from a compost metagenomic library. The xylanase gene, xyn10J, was 1,137 bp in length and was predicted to encode a protein of 378 amino acid residues with a putative signal peptide of 27 amino acid residues. The molecular mass of the mature Xyn10J was calculated to be 39,882 Da with a pI of 6.09. Xyn10J had a motif GVKVHFTEMDI characteristic of most members of glycosyl hydrolase family 10. The amino acid sequence of Xyn10J showed 60.0% identity to that of XynH, a xylanase from an uncultured soil bacterium and 55% identity to XylC of Cellvibrio mixtus. Site-directed mutagenesis of the expected active site based on the sequence analysis indicated that an aspartic acid residue (Asp207), in addition to the identified catalytic residues Glu165 and Glu270, plays a crucial role for the catalytic activity. The purified Xyn10J had a mass of about 40 kDa and was optimally active at pH 7.0 and 40 °C. Xyn10J hydrolyzed beechwood xylan > birchwood xylan > oat spelt xylan > arabinoxylan. Xyn10J hydrolyzed xylotetraose and xylohexaose exclusively to xylobiose, xylopentaose, and xylotriose mainly to xylobiose with transglycosylation activity. The saccharification of reed (Phragmites communis) powder by commercial enzymes was significantly increased by the addition of a small amount of Xyn10J to the commercial preparation. Xyn10J is the first xylanase screened directly from a compost metagenomic library, and the enzyme has the potential to be used in the conversion of biomass to fermentable sugars for biofuel production.