Catalytic dissymmetrization of meso-2-imidazolidinones: alternative route to chiral synthons for 1,2-diamines

The chiral functionalization of a simple heterocycle, 1,3-dihydro-2-imidazolone, was achieved by the highly enantioselective monodeacylation of meso-1,3-diacetyl-2-imidazolidinones via an oxazaborolidine-catalyzed borane reduction. This kinetically controlled dissymmetrization is sufficiently effective to provide a synthetic route to either enantiomer of (4S, 5S)- or (4R, 5R)-4,5-dimethoxy-2-imidazolidinone derivatives, which serve as chiral synthons for threo-1,2-diamines.     

Extraction-spectrophotometric determination of nickel in steels and aluminium metal with 3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine and ethyl tetrabromophenolphthalein

Nickel ions react with 3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine in aqueous solution at pH 6.8 to form a red 1:3 complex cation which can be extracted at pH 6.3 into 1,2-dichloroethane with ethyl tetrabromophenolphthalein anion as an ion association compound having an absorption maximum at 610 nm. The apparent molar absorptivity is 2.21 × 10⁵ l mol^?1 cm^?1 and a linear calibration graph is obtained in the range 0–0.05 μg ml^?1 (0?8.52 × 10^?7 M) nickel in aqueous solution. The r.s.d, is 1.5%. This method can be applied to the determination of traces of nickel in steels and aluminium chips.     

Single-crystal Al(18)B(4)O(33) microtubes

Aluminum borate microtubes were prepared in excellent yield by annealing the Al(2)O(3)-NaBH(4)-NiCl(2) starting materials at 1050 degrees C under N(2)(H(2)) atmosphere. The tubes are usually open at each end with the outer diameters narrowly distributed at ca. 1 microm. XRD results and TEM analysis identified the composition of these tubes as single-crystal orthorhombic Al(18)B(4)O(33). These newly discovered ceramic microtubes with open ends have a variety of promising applications such as being filled with other materials for protection or for the fabrication of novel composites or filtering media.     

Study of the parameters controlling the enantio-differentiating ability of asymmetrically modified solid catalysts for the hydrogenation of γ-ketoesters

The enantio-differentiating hydrogenation of γ-ketoesters was carried out over asymmetrically modified solid catalysts. The parameters affecting the enantiomer excess (ee) were investigated and the results were compared with those of the hydrogenation of methyl acetoacetate and 2-octanone reported in the literature. The highest value of enantiomer excess of 51% was attained for the hydrogenation of methyl 4-oxopentanoate over a tartaric acid (TA)-NaBr-modified reduced nickel catalyst prepared from nickel oxide. The amount of NaBr in the modification solution needed to be optimized according to the manufacturers of the nickel oxides. The addition of an appropriate amount of carboxylic acid to the reaction media increased the enantiomer excess of the hydrogenated products.     

DNA charge transport leading to disulfide bond formation

Here, we show that DNA-mediated charge transport (CT) can lead to the oxidation of thiols to form disulfide bonds in DNA. DNA assemblies were prepared possessing anthraquinone (AQ) as a photooxidant spatially separated on the duplex from two SH groups incorporated into the DNA backbone. Upon AQ irradiation, HPLC analysis reveals DNA ligated through a disulfide. The reaction efficiency is seen to vary in assemblies containing intervening DNA mismatches, confirming that the reaction is DNA-mediated. Interestingly, one intervening mismatch near the thiols promotes an increase in efficiency, which we attribute to increased base dynamics. Hence, here, where the reaction is on the backbone rather than within the base stack, stacking perturbations do not necessarily lead to an inhibitory effect on DNA CT.     

Advancement of flow-based analysis with alternative chemical reactions and new devices for environmental and biological samples.

This review includes our researches and other methodologies related to flow-based techniques, such as flow injection analysis (FIA) and sequential injection analysis (SIA). The methods will demonstrate semi-and full automated FIA and SIA, including liquid-liquid and liquid-solid extraction. FIA using alternative chemical reactions in the aqueous solution was applied to the trace analysis of metals in biological and environmental samples. For durable liquid-liquid extraction, several phase separators were designed. Moreover, multi-channel FIA with newly designed flow cells and SIA with lab-on-valve devices have been used for the simultaneous and successive determination of metals and organic compounds. On-line solid phase extraction (SPE) has also been proposed for highly sensitive analysis of organic and inorganic compounds.     

Synthesis and lithium ion insertion/extraction properties of hollandite-type MnO2 prepared by acid digestion of Mn2O3

Single-phase specimens of α-MnO₂ (hollandite-type) and β-MnO₂ (rutile-type) were synthesized by the acid digestion of Mn₂O₃ under reflux conditions. The type of polymorph of MnO₂ products was strongly dependent on the reaction temperature, type of acid used, and its concentration. The pH titration curve of α-MnO₂ displayed a monobasic acid behavior toward Li⁺, but β-MnO₂ showed a poor ion-exchange property. In contrast, both α-MnO₂ and β-MnO₂ acted as a rechargeable active material in a liquid organic electrolyte lithium cell. The initial discharge capacities of both electrodes exceeded 200 mAh/g (cut-off voltage: 2 V). After discharge–charge repetition, the α-MnO₂ structure was still retained without structure collapse, although the β-MnO₂ structure was destroyed. These findings show that Li⁺ ions can be inserted only into the hollandite-type tunnels in α-MnO₂ and cannot diffuse the rutile-type linkages in α-MnO₂ as well as those in β-MnO₂ without structure collapse.     

Consolidation of hydrogenation–disproportionation–desorption–recombination processed Nd–Fe–B magnets by spark plasma sintering

We have successfully consolidated hydrogenation–disproportionation–desorption–recombination (HDDR) processed Nd–Fe–Co–Zr–B–Ga powder by spark plasma sintering (SPS). The field compacted samples were sintered at different temperatures (T_S) from 550 to 600 °C with compressive pressure of 80 MPa for 20 min. Microstructural investigations by transmission electron microscopy indicated that the sintered specimen exhibits Nd₂Fe₁₄B grains of ~300 nm with Nd-rich grain boundary phase. The optimum magnetic properties of B_r: 1.22 T, H_c: 928 kA/m, _BH_c: 600 kA/m, (BH)_max: 210 kJ/m³ were obtained in the sample sintered at 550 °C. The strategy for further improving the coercivity and remanence is discussed based on the microstructure-property relationships.     

Catalytic flow-injection determination of sub-ppb copper(II) using the redox reaction of cysteine with iron(III) in the presence of 2,4,6-tris(2-pyridyl)-1,3,5-triazine.

A kinetic-catalytic spectrophotometric flow-injection method was developed for the rapid and sensitive determination of trace amounts of copper(II). The method is based on the catalytic effect of copper(II) on the redox reaction of cysteine with iron(III). Iron(II) produced by the catalytic reaction reacts with 2,4,6-tris(2-pyridyl)-1,3,5-triazine (TPTZ) to form the iron(II)-TPTZ complex (lambda(max) = 593 nm). By measuring an absorbance of the complex, one could determine 0.05-8 ppb copper(II) with the relative standard deviations (n = 10) of 1.6%, 1.3%, and 0.8% for 0.5 ppb, 1 ppb, and 2 ppb copper(II), respectively. The limit of detection (S/N = 3) was 0.005 ppb. The sample throughput was 30 h(-1). The proposed method was successfully applied to the determination of copper in natural water and serum samples.