Shimalactone Biosynthesis Involves Spontaneous Double Bicyclo-Ring Formation with 8π-6π Electrocyclization

Shimalactones A and B are neuritogenic polyketides possessing characteristic oxabicyclo[2.2.1]heptane and bicyclo[4.2.0]octadiene ring systems that are produced by the marine fungus Emericella variecolor GF10. We identified a candidate biosynthetic gene cluster and conducted heterologous expression analysis. Expression of ShmA polyketide synthase in Aspergillus oryzae resulted in the production of preshimalactone. Aspergillus oryzae and Saccharomyces cerevisiae transformants expressing ShmA and ShmB produced shimalactones A and B, thus suggesting that the double bicyclo-ring formation reactions proceed non-enzymatically from preshimalactone epoxide. DFT calculations strongly support the idea that oxabicyclo-ring formation and 8π-6π electrocyclization proceed spontaneously after opening of the preshimalactone epoxide ring through protonation. We confirmed the formation of preshimalactone epoxide in vitro, followed by its non-enzymatic conversion to shimalactones in the dark.     

Selective wet air oxidation of diluted aqueous ammonia solutions over co-precipitated transition metal-aluminium catalysts

Catalytic wet air oxidation of ammonia over a co-precipitated transition metal-aluminium catalyst was investigated. Copper-aluminium (Cu-Al-O) catalyst exhibited the highest activity and N₂ selectivity among those prepared from Co, Fe, Mn, and Ni. 50% of 1500 ppm of ammonia could be removed from wastewater of pH 12 at 503 K under 2.0 MPa of air by using 4.0 g of catalyst without formation of toxic nitrogen containing compounds. Cu and Al ions were not found in solution after the reaction. It has been found that the catalytic performance of Cu-Al-O catalyst was strongly dependent on the preparation methods. The co-precipitated Cu-Al-O catalysts showed high N₂ selectivity. The presence of CuO is concluded to promote the reaction and CuAl₂O₄ in bulk phase is needed to stabilize the catalyst.     

Isolation of a new indoxyl alkaloid,Amoenamide B,from Aspergillus amoenus NRRL 35600: Biosynthetic implications and correction of the structure of Speramide B

A new prenylated indoxyl alkaloid, Amoenamide B (1), was isolated from Aspergillus amoenus NRRL 35600 along with Asperochramide A (2). Although many prenylated oxindole alkaloids, containing bicyclo[2.2.2]diazaoctane cores, have been isolated from the fungus of the genera Aspergillus and Penicillium to date, 1 is the fourth compound with the indoxyl unit containing the cores. During the structure elucidation of 1, we found that the planar structure matched to that of Speramide A (3), isolated from A. ochraceus KM007, but the reported structure of 3 was incorrect and turned out to be that of Taichunamide H (4), recently isolated from A. versicolor HDN11-84.     

Kinetic aspects associated with the lean reduction of no with C3H6 over well-structured pt nanocrystals

Summary Well-defined platinum nanocrystals (» 52% cubic), with an average diameter of 12 nm, were prepared by colloid method and then supported on alumina. The effect of the exposed Pt surface on lean de-NO_x reaction was investigated. The catalytic data free of transport effects were identified and then used to calculate the kinetic parameters of lean de-NOx reaction.     

Adsorbed state of nitrogen on ruthenium catalysts: TPD and isotopic study

The adsorbed state of nitrogen on Ru catalysts was studied by a TPD technique combined with an isotopic technique. (1) A molecular and an atomic species on Ru powder, (2) a molecular and three atomic species on Raney-Ru, and (3) two molecular and probably three atomic species on Raney-Ru/K were identified, respectively. Relations between the adsorbed states and those reactivities for an isotopic equilibration reaction of N₂ were discussed.     

Investigation of the morphology-catalytic reactivity relationship for Pt nanoparticles supported on alumina by using the reduction of NO with CH4 as a model reaction

The morphological evolution of large Pt nanoparticles supported on alumina in reaction conditions has a significant impact on the catalytic behaviour for the NO/CH4 reaction.     

Highly hydrophilic and nonionic poly(2-vinyloxazoline)-grafted silica: a novel organic phase for high-selectivity hydrophilic interaction chromatography

A new hydrophilic and nonionic poly(2-vinyloxazoline)-grafted silica (Sil-VOX _n ) phase was synthesized and applied for the separation of nucleosides and nucleobases in hydrophilic interaction chromatography (HILIC). Polymerization and immobilization onto silica were confirmed by using characterization techniques including ¹H NMR spectroscopy, elemental analysis, and diffuse reflectance infrared Fourier transform spectroscopy. The hydrophilicity or wettability of Sil-VOX _n was observed by measuring the contact angle (59.9°). The chromatographic results were compared with those obtained with a conventional HILIC silica column. The Sil-VOX _n phase showed much better separation of polar test analytes than the silica column, and the elution order was different. Differences in selectivity between these two columns indicate that the stationary phase cannot function merely as an inert support for a water layer into which the solutes are partitioned from the bulk mobile phase. To elucidate the interaction mechanism, the separation of dihydroxybenzene isomers was performed on both columns in normal-phase liquid chromatography. Sil-VOX _n was very sensitive to the dipole moments of the positional isomers of polycyclic aromatic compounds in normal-phase liquid chromatography. The interaction mechanism for Sil-VOX _n in HILIC separation is also described.