Flow analysis preconcentration of Mg and Zn using emulsions for flame atomic absorption spectrometry

 A preconcentration method combining Water/ Oil/Water (W/O/W) emulsions with flow injection manifolds has been developed for determinations of Mg and Zn. The system consists of a mixing coil filled with Span 80 as a surfactant, palmitic acid or di(2-ethylhexyl) phosphate as an extractant, kerosene as a solvent in the oil phase, and HCl in the inner aqueous phase to form W/O emulsions, an extraction coil for the sample solution to form W/O/W emulsions, a phase separator to waste the outer aqueous phase, a dry bath to demulsify W/O emulsions with 2-ethylhexanol, a phase separator to waste the oil phase, and an air pump to deliver the concentrated sample solution to the flame atomic absorption spectrophotometer. This method proved to be excellent regarding the reproducibility, the rapidity, and the small quantity of sample, compared with the W/O/W emulsions method without the flow injection manifolds. The signal of flame atomic absorption spectrometry (FAAS) after preconcentration of Mg by this method was 2.4 times as large as that before preconcentration. Also, this method suppressed some interferences. The system was applied to FAAS determinations of Mg and Zn in duralumin alloys and Zn in commercial reagents. Received: 20 March 1996/Revised: 13 July 1996/Accepted: 20 July 1996     

Squalene‐Derived Triterpene Polyethers from the Red Alga Laurencia omaezakiana

In our continuing search on halogenated metabolites from species of the red algal genus Laurencia, a novel squalene‐derived triterpene polyether, named omaezakianol ( 2 ), was isolated from Laurencia omaezakiana Masuda along with 15,16‐anhydrothyrsiferol ( 3 ). Their structures were determined by spectral and chemical methods.     

Relation between electrophoretic behavior and molecular shapes of aromatic anions.

The capillary electrophoretic behavior of 44 aromatic organic ions was investigated. The observed ionic radii (r(obs0)) for the aromatic organic ions were obtained from the electrophoretic mobilities of sodium tetraborate (pH 9.2), potassium tetraborate (pH 9.2), ammonium borate (pH 9.2), and trisodium phosphate (pH 11.7) buffers with zero ionic strength. The linear relationships between the r(obs0)) values and the ionic radii (r(calc)), calculated by either the AM1 or PM3 method, were determined for benzyltrialkylammonium and aromatic sulfonate ions. However, the r(obs0)) values were constant for the aromatic carboxylate ions in buffers, in spite of the different r(calc) values. This indicates that aromatic carboxylate ions, such as benzenecarboxylate, pyridinecarboxylate, naphthalenecarboxylate, and anthracenecarboxylate ions, migrate as planar ions in buffers, whereas aromatic sulfonate ions could migrate as approximately spherical ions.     

Kinetic Studies on the Radiation-Induced Solution Polymerization of Tetrafiuoroethyiene

Abstract

Kinetic studies on the radiation-induced polymerization and postpolymerization of tetrafiuoroethyiene were carried out using chlorofluorohydrocarbons as the solvents. The mechanism of the radiochemical formation of radicals and the kinetics of the radical decay during in-source and postpolymerization are discussed. The remarkable post-polymerization is explained by the unusually slow rate of the bimolecular chain termination. The mechanism of chain transfer reactions is also discussed.     

Distribution of 137Cs and 134Cs in the North Pacific Ocean: impacts of the TEPCO Fukushima-Daiichi NPP accident

Impact of the TEPCO Fukushima-Daiichi NPP accident, FNPP1, to the North Pacific Ocean occurred through two pathways, namely direct release and atmospheric deposition to wide ocean surface. We collected more than 100 seawater samples in the North Pacific Ocean in April and May 2011 by seven commercial ships as VOS. Since the sample volume was 2 l each, we measured radiocaesium activity at Ogoya Underground Facility to obtain reliable activity. ¹³⁷Cs was detected at all stations and ¹³⁴Cs was detected at most of the stations in the North Pacific Ocean. The ¹³⁷Cs activity ranged from around 1 to 1,000 Bq m^?3 with activity ratios of ¹³⁴Cs/¹³⁷Cs close to 1 which is a signature of radiocaesium originated from the FNPP1 accident. At east of the International Date Line north of 40°N in the Pacific Ocean in April 2011, the ¹³⁴Cs activity ranged from 2 to 12 Bq m^?3.     

Conversion of a Disulfide Bond into a Thioacetal Group during Echinomycin Biosynthesis

Echinomycin is a nonribosomal depsipeptide natural product with a range of interesting bioactivities that make it an important target for drug discovery and development. It contains a thioacetal bridge, a unique chemical motif derived from the disulfide bond of its precursor antibiotic triostin A by the action of an S‐adenosyl‐L ‐methionine‐dependent methyltransferase, Ecm18. The crystal structure of Ecm18 in complex with its reaction products S‐adenosyl‐L ‐homocysteine and echinomycin was determined at 1.50 Å resolution. Phasing was achieved using a new molecular replacement package called AMPLE, which automatically derives search models from structure predictions based on ab initio protein modelling. Structural analysis indicates that a combination of proximity effects, medium effects, and catalysis by strain drives the unique transformation of the disulfide bond into the thioacetal linkage.     

Cubic phase of 4'-n-Hexadecyloxy-3'-cyanobiphenyl-4-carboxylic acid (ACBC-16)

The cubic phase structure of 4'-n-hexadecyloxy-3'-cyanobiphenyl-4-carboxylic acid (ACBC-16) was examined by X-ray diffraction. Unlike the octadecyloxy homologue showing an Im3m-type cubic phase, the cubic phase of ACBC-16 was of Ia3d type, both on heating and on cooling, similarly to the corresponding nitro-substituted analogue (ANBC-16). The lattice dimension a at 453 K was a = 11.0 nm, 2.5% larger than the value for ANBC-16 and rather close to the value of ANBC-17 or -18. It is expected that the appearance of the cubic phase type, as a function of the number of carbon atoms n in the alkoxy chain in the ACBC-n series, is essentially the same as in the ANBC-n series, but shifted towards shorter n by 1 or 2. In the latter ANBC-n series, the cubic phase type is Ia3d for 15≤n≤18, while an Im3m type is formed for 19≤n≤21, both on heating and on cooling.     

Synthesis of selenocystine derivatives from cystine by applying the transformation reaction from disulfides to diselenides

A stepwise conversion of a disulfide (SS) to a diselenide (SeSe) bond through the corresponding iodide intermediate was implemented and was applied to the synthesis of selenocystamine and l-selenocystine derivatives from cystamine and l-cystine, respectively, in moderate yields.