Flow Synthesis of Plasmonic Gold Nanoshells via a Microreactor

Gold nanoshells with tunable surface plasmon resonances are a promising material for optical and biomedical applications. They are produced through seed‐mediated growth, in which gold nanoparticles (AuNPs) are seeded on the core particle surface followed by growth of the gold seeds into a shell. However, synthetic gold nanoshell production is typically a multistep, time‐consuming batch‐type process, and a simple and scalable process remains a challenge. In the present study, a continuous flow process for the seed‐mediated growth of silica–gold nanoshells is established by exploiting the excellent mixing performance of a microreactor. In the AuNP‐seeding step, the reduction of gold ions in the presence of core particles in the microreactor enables the one‐step flow synthesis of gold‐decorated silica particles through heterogeneous nucleation. Flow shell growth is also realized using the microreactor by selecting an appropriate reducing agent. Because self‐nucleation in the bulk solution phase is suppressed in the microreactor system, no washing is needed after each step, thus enabling the connection of the microreactors for the seeding and shell growth steps into a sequential flow process to synthesize gold nanoshells. The established system is simple and robust, thus making it a promising technology for producing gold nanoshells in an industrial setting.     

Enantioselective Single-Crystal-to-Single-Crystal Photodimerization of Coumarin and Thiocoumarin in Inclusion Complexes with Chiral Host Compounds

An intermolecular enantioselective photoreaction by a single-crystal-to-single-crystal transformation has been carried out for the first time, as is evident from X-ray structure analysis and X-ray powder diffractometric studies. This reaction, the dimerization of the title compound to cyclobutane derivative 1 (X=O, S), provides a good example for studying the mechanism of topochemical reactions in the crystal.     

The influence of chloro-substituent sites of hexachlorobiphenyl on the respiration of rat liver mitochondria.

The actions of three hexachlorobiphenyls (HCBs) 2,3,4,2',3',4'-, 2,3,4,3',4',5'- and 3,4,5,3',4',5'-HCBs, on the respiration of rat liver mitochondria with succinate as the substrate were compared, and the effect of chloro-substitution sites in HCB on the respiration was examined. 2,3,4,2',3',4'-HCB strongly inhibited both state 3 and 2,4-dinitrophenol (DNP)-stimulated respiration with 50% inhibition dose of 52 and 54 microM for state 3 and DNP-stimulated respiration, respectively. The inhibitory action of 2,3,4,3',4',5'-HCB on both respiration was approximately half as potent as that of 2,3,4,2',3',4'-HCB. On the other hand, 3,4,5,3',4',5'-HCB did not inhibit any respiration at all. These results indicate that both inside (ortho) and outside (meta or para) positions in each phenyl ring of the biphenyl molecule should be replaced with chlorines for HCB to be an effective inhibitor. Either the actual position of chloro-substituent or steric conformation caused by its substitution or both can be considered as factors affecting the inhibition. On the basis of the conformational energy, calculated by AM1 (Austin model 1) method, with increases in chlorine number in ortho position, HCB molecule became angulated. Furthermore, calculated probability of the conformation distribution for HCB indicated that the probability of nonplanarity was higher for effective HCB than for less effective HCB. These structural features suggest the significance of steric conformation as well as chloro-substituent sites in determining the inhibitory ability of HCB.(ABSTRACT TRUNCATED AT 250 WORDS)     

ortho-Selective ethylation of phenol with ethanol catalyzed by bimetallic mesoporous catalyst, CoAl-MCM-41

CoAl-MCM-41 (X) catalysts with X = n_Si/(n_Co + n_Al) various ratios were synthesized and ethylation of phenol with ethanol was studied in vapor-phase at temperatures between 250 and 450 °C. The products obtained were O-alkylated product (ethyl phenyl ether), C-alkylated products (2-ethylphenol and 4-ethylphenol), and C-/O-alkylated products (ethyl ethylphenyl ether). The phenol conversion increased significantly with reaction temperature over all the catalysts. The activity of the catalysts followed the order CoAl-MCM-41 (20) > CoAl-MCM-41 (50) > CoAl-MCM-41 (80). Selectivity between the C-alkylation and the O-alkylation depended on the factors such as acidity of the catalyst and the reaction temperature. CoAl-MCM-41 (20) catalyst displayed a phenol conversion of 40% and a selectivity of more than 80% for 2-ethylphenol under the optimized reaction condition. The ethanol to phenol ratios and the reactant flow rate are also influential for both activity and selectivity of CoAl-MCM-41 catalysts.     

Optically active N-acetyldopamine dimer of the crude drug "Zentai," the cast-off shell of the Cicada, Cryptotympana sp

Two optically active N-acetyldopamine dimers together with four phenolic monomers were isolated from the crude drug "Zentai," a cast-off shell of the cicada of Cryptotympana sp. (Cicadidae). The former two were 2-(3',4'-dihydroxyphenyl)-1,4-benzodioxane derivatives carrying substituents at the 3 and 6 (or 7) positions, which are known to be components of sclerotized insect cuticles. Their structures including absolute configurations were determined on the basis of NMR and circular dichroism (CD) spectroscopic data.     

Ultramicrodetermination of nitrogen in organic compounds: I. Application of interpolation in the sealed tube method

A method is described for the decimilligram determination of nitrogen in organic compounds based on measuring by interpolation the volume of nitrogen collected in a capillary tube. The blank value is determined indentically.     

One-pot multistep synthesis of 4-acetoxy-2-amino-3-arylbenzofurans from 1-aryl-2-nitroethylenes and cyclohexane-1,3-diones

[reaction: see text] A novel method for synthesizing 4-acetoxy-2-amino-3-arylbenzofurans (4) from 1-aryl-2-nitroethylenes (1) and cyclohexane-1,3-diones (2) is described. The method features one-pot operation of a solution of 1 and 2 in THF with catalytic Et3N (rt, 12 h) followed with Ac2O, Et3N, and DMAP (rt, 5 h), although the process consists of 13 elementary reactions.     

Synthesis of o-benzoquinones derived from [2.2]- and [3.3]paracyclophanes

Oxidation of [2.2]- and [3.3]paracyclophanols with benzeneseleninic anhydride readily afforded the corresponding cyclophane-o-quinones which showed the intramolecular charge-transfer interactions.     

Metabolism of methylated arsenic compounds by arsenic-resistant bacteria (Klebsiella oxytoca and Xanthomonas sp.)

Two bacteria exhibiting resistance to toxic arsenic were isolated. These had been contaminated with arsenic in a Chlorella sp. culture medium containing arsenic. The two bacteria were identified as Klebsiella oxytoca and Xanthomonas sp., and grew well in a peptone medium at neutral pH at 30°C, reaching the stationary phase in ca 100h and 70h, respectively. The growth of the bacteria was not affected by arsenic(V) concentrations in the medium as high as 1000mg dm^?3. The bacteria bioaccumulated arsenic, a part of the arsenic being methylated. The bioaccumulation exhibited its peak around the turing point from the log phase to the stationary phase. The relative content of methylated arsenic in the excrement was greater than that in the bacterial cells. Adaptation treatment of inorganic arsenic caused an increase in the bioaccumulation of inorganic arsenic by K. oxytoca. Such a situation was not observed in the case of Xanthomonas sp. The bacteria also bioaccumulated methylated arsenic compounds, and demethylation of these species was observed. When the bacteria were killed by ethanol, arsenic was not taken up by the cells.