Citrinadin A, a novel pentacyclic alkaloid from marine-derived fungus Penicillium citrinum

[structure: see text] A novel pentacyclic alkaloid, citrinadin A (1), was isolated from the cultured broth of the fungus Penicillium citrinum, which was separated from a marine red alga, and the structure was elucidated by spectroscopic data. The relative stereochemistry of the pentacyclic core was assigned on the basis of NOESY data and (1)H-(1)H coupling constants, and the presence of an N,N-dimethyl-L-valine residue in 1 was determined by chiral HPLC analysis of the hydrolysate.     

Cationic grafting from carbon black. VIII. Cationic ring-opening polymerization and copolymerization of oxepane initiated by acylium perchlorate groups on carbon black

The cationic ring-opening polymerization of oxepane was found to be initiated by carbon black having acylium perchlorate (CO⁺CIO) groups, which were introduced by the reaction of acyl chloride groups with silver perchlorate. It was confirmed that polyoxepane, i.e., poly(oxyhexamethylene), was propagated from CO⁺CIO groups on carbon black and effectively grafted on the surface. The rate of the polymerization and the percentage of grafting of poly(oxyhexamethylene) remarkably increased by the addition of epichlorohydrin (ECH) as a promoter: the percentage of grafting in the presence of ECH increased to about 100% with an increase in conversion. Furthermore, CO⁺CIO groups on carbon black have an ability to initiate the cationic ring-opening copolymerization of oxepane with ECH to give poly(oxepane-co-ECH) with various composition. The ring-opening copolymerization of oxepane with phthalic anhydride was also initiated by CO⁺CIO groups to give polyether ester, i.e., poly(hexamethylene phthalate) containing poly(oxyhexamethylene) sequence. In the copolymerization, polyether or polyether ester was effectively grafted from carbon black based on the propagation of these polymers from CO⁺CIO groups.     

Effects of heating rate (1–300° h−1) on the non-isothermal thermogravimetry of CuSO4 · 5 H2O

The course of the reaction CuSO₄ · 5 H₂O ? CuSO₄ · H₂O + 4 H₂O was studied by non-isothermal thermogravimetry with various heating rates ranging from 1 to 300° h^?. The measurements were made either in static air, in a dry nitrogen stream, or in water vapor at a reduced pressure (9 mm Hg). In static air, the shape of the TG curve changed drastically at a heating rate of 13 to 15° h^?, and this change was explained by considering the nature of the plateaus and inflections present. In a dry nitrogen stream, the dehydration is made much easier at slow heating rates and occurs almost in one step at 2° h^?; in water vapor at 9 mm Hg, on the other hand, a very distinct two-step curve is obtained at 1° h^?. This can reasonably be compared with the phase diagram of copper sulfate.     

Radical polymerization of methyl methacrylate initiated by an enolizable ketone–carbon black system

The polymerization of methyl methacrylate (MMA) initiated by an enolizable ketone (R₁? CO? CH₂? CO? R₂)-carbon black system was investigated. Although enolizable ketone itself could not do so, the polymerization of MMA was initiated by enolizable ketone in the presence of carbon black. In addition, a chloranil-enolizable ketone system was able to initiate the polymerization of MMA. It was found that the enol form of the ketone and quinonic oxygen groups on the carbon black surface played an important role in the initiation system; namely, it was considered that the polymerization was begun by the ketone radical (R₁? CO? CH? CO? R₂) formed by a one-electron transfer reaction from enolate ion to quinonic oxygen groups. The effect of solvent on the process was also studied. The rate of the polymerization increased, depending on the solvent used, in the following order: benzene < 1,4-dioxane < dimethyl sulfoxide < N,N-dimethylformamide < N-methyl-2-pyrrolidone. Furthermore, it became apparent that during the polymerization poly(methyl methacrylate) was grafted onto the carbon black surface (grafting ratio was ca. 40% when benzene was used as solvent) and the carbon black obtained gave a stable colloidal dispersion in organic solvent.     

Catalytic asymmetric synthesis of 2,2-disubstituted terminal epoxides via dimethyloxosulfonium methylide addition to ketones

Catalytic asymmetric Corey-Chaykovsky epoxidation of ketones with dimethyloxosulfonium methylide 2 using an LLB 1a + Ar3P O complex proceeded smoothly at room temperature, and 2,2-disubstituted terminal epoxides were obtained in high enantioselectivity (91-97%) and yield (>88-99%) from a broad range of methyl ketones with 1-5 mol % catalyst loading. The use of achiral additive Ar3P O 5i was important to achieve high enantioselectivity.     

Affinity-based elimination of aromatic VOCs by highly crystalline multi-walled carbon nanotubes

Carbon nanotubes (CNTs) are capable of adsorbing pollutant chemicals. Their adsorptive capacities and adsorbing mechanisms, however, are not fully understood. As-grown CNTs often contain both crystalline and amorphous carbon, and the ratio of carbon types can affect adsorption. In this study, highly crystalline multi-walled carbon nanotubes (HC-MWCNTs) were used as the adsorbent for volatile organic compounds (VOCs) in contaminated air samples. Air containing 23 added VOCs (1,1-dichloroethylene, dichloromethane, trans-1,2-dichloroethylene, cis-1,2-dichloroethylene, chloroform, 1,1,1-trichloroethane, carbon tetrachloride, 1,2-dichloroethane, benzene, trichloroethylene, 1,2-dichloropropane, bromodichloromethane, cis-1,3-dichloropropene, toluene, trans-1,3-dichloropropene, 1,1,2-trichloroethane, tetrachloroethylene, dibromochloromethane, m-xylene, p-xylene, o-xylene, bromoform, and p-dichlorobenzene) was used for model samples. Adsorptive experiments were carried out by passing the air samples through a cartridge packed with HC-MWCNTs. Initial results showing high selectivity and high affinity for adsorbing aromatic VOCs (benzene, toluene, m-xylene, p-xylene, o-xylene, and p-dichlorobenzene) have provided new insight into the adsorption mechanisms. Data suggest that the HC-MWCNTs, unlike conventional carbon materials, adsorb aromatic compounds according to Fukui's frontier theory, which is based on the interactions between the HOMO and LUMO of the aromatic VOCs and those of the HC-MWCNTs.     

Syntheses and properties of tetraaza‐, diaza‐, tetraoxa‐, and dioxa‐metacyclophanes

Metacyclophanes were prepared by cyclization reactions between bis(chloromethyl) compounds and piperazine, primary amines, or ethylene glycol. The ¹H nmr relaxation time (T₁) measurements indicated that the macrocycles feature the up and down motion of the aromatic units around the XCH₂Ar (X = N, O) methylene moieties as the axes. Metacyclophanes incorporating piperazine units showed high complexation ability for alkaline metal cations.     

π-conjugated columnar polyacetylenes prepared with Rh complex catalysts

Highly stereospecific polymerization of monosubstituted acetylenes was carried out using the Rh complex, [Rh(norbornadiene)Cl]₂ catalysts. The resulting polyacetylenes were characterized in detail by ¹HNMR, ESR, laser Raman, diffuse reflective UV, and wide angle X-ray diffraction methods. The data showed that the Rh complex were the preferred catalyst to selectively yield the corresponding cis-transoid polymers even at room temperature when alcohol, triethylamine or water was used as the polymerization solvent. Additionally, the resulting cis polyacetylenes were found to have a helical form whose polymer is amorphous or composed of pseudohexagonal structures called π-conjugated columnar as self-assembly or super structure. Further compression of the amorphous cis polymers resulted in cis to trans isomerization at room temperature under vacuum, breaking rotationally the cis C=C bonds giving π-radicals called solitons as the origin of a polymer magnet. On the other hand, the π-conjugated columnar was also found to show an extremely longer wavelength absorption compared with that of the amorphous one, although the absorption maximum was shifted to a shorter wavelength when the columnar was destroyed by the compression. Therefore, the formation of the π-conjugated columnar can be considered as a new and quite useful control method concerning color of such conjugated polymers, i.e., a new concept concerning the color of conjugated polymers.     

Optical properties of InGaN/GaN double quantum wells with varying well thickness

The optical properties and recombination kinetics of the InGaN/GaN double quantum well (DQW) structures with different well thickness (L_w) have been studied by means of photoluminescence (PL), time-resolved PL, and cathodoluminescence (CL) measurements. With increasing quantum well thickness up to 4 nm, the PL emission energy decreases and the blueshift of the PL emission energy increases with increasing excitation density. On the other hand, the PL emission energy of the DQWs with L_w=16 nm is higher than that of the DQWs with L_w=4 nm, and is independent of the excitation density. With increasing L_w from 1 to 4 nm, the PL decay times increase. In contrast, the decay times of 16 nm DQWs are faster than those of 4 nm DQWs. These different results for 16 nm DQWs such as the blueshift of the emission energy, the decrease of the excitation density dependence, and the increase of recombination rate can be ascribed to the relaxation of the piezoelectric field. We also observed the inhomegeneity in the CL spectra of the DQWs with L_w=1 nm on 1 μm scale.     

High‐temperature ethylene/α‐olefin copolymerization with a zirconocene catalyst: Effects of the zirconocene ligand and polymerization conditions on copolymerization behavior

Copolymerizations of ethylene and α‐olefin with various zirconocene compounds at a high temperature were carried out to study the relationship between the ligand structure of zirconocene compounds and the copolymerization behavior. All of the indenyl‐based zirconocene compounds in combination with dimethylanilinium tetrakis(pentafluorophenyl)borate/triisobutylaluminum produced only low molecular weight copolymers at a high temperature, regardless of the substituents and bridged structures of the zirconocene compounds. However, zirconocene compounds with a fluorenyl ligand gave rise to a significant increase in the activity and molecular weight of the copolymers by the selection of a diphenylmethylene bridge structure even at a high temperature. Ethylene/1‐hexene copolymers obtained with the fluorenyl‐based catalysts contained inner double bonds accompanied by the generation of hydrogen, presumably because of a C H bond activation mechanism. The contents of the inner double bonds were significantly influenced by the polymerization conditions, including the 1‐hexene feed content, polymerization temperature, and ethylene pressure. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4641–4648, 2000