Mechanism of stereoregular polymerization of butadiene by homogeneous Ziegler-Natta catalysts. I. Effects of the species of transition metals

Butadiene was polymerized by catalysts of the type: metal acetylacetonate (metal: Ti to Ni in the periodic table)–triethylaluminum–aluminum halide, with various ratios of triethylaluminum to aluminum halide. The minimum cis content was observed with vanadium catalyst in all cases, while the minimum polymer yields were observed with the iron and the manganese catalysts. These transition metal effects are discussed in terms of the crystal field theory, and it is suggested that the electrostatic interaction between the nearly nonbonding electrons of transition metal atom and a butadiene molecule or a growing end of the polymeric chain plays an important role in the stereoregular polymerization of butadiene by homogeneous Ziegler-Natta catalysts.     

Extraction—photometric determination of trace amounts of nitrite in waters

Traces of nitrite in river water can be determined by extraction spectrophotometry. Nitrite in 100 ml of sample water at pH 1.5–3.0 diazotizes p-aminoacetophenone, which is then coupled with m-phenylenediamine at the same pH. The 2,4-diamino-4'-acetyl-azobenzene formed is extracted into 5 or 10 ml of toluene at pH 9 and the absorbance is measured at 450 nm. The molar absorptivity is about 2.3·lO⁴ l mol^?1 cm^?1. The ions normally present in river water do not interfere. The nitrite contents in river waters in Okayama Prefecture, Japan, are 1–30 P.P.b.     

Validation of the CALUX bioassay for the screening of PCDD/Fs and dioxin-like PCBs in retail fish

The chemical-activated luciferase expression (CALUX) assay is a reporter gene assay that detects dioxin-like compounds based on their ability to activate the aryl hydrocarbon receptor (AhR) and thus expression of the reporter gene. In this paper, the CALUX assay was examined for its application in the screening of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and dioxin-like polychlorinated biphenyls (dioxin-like PCBs) in retail fish. The sample extracts were cleaned up on a sulfuric acid-silica gel column followed by an activated carbon column, and the AhR activity of the separated PCDD/F and dioxin-like PCB fractions was determined using the assay. The quantitative limit for 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) was 0.98 pg ml(-1) (0.19 pg assay(-1) in the standard curve, corresponding to 0.16 pg g(-1) of CALUX-based toxic equivalency (2,3,7,8-TCDD equivalents) in the tested sample. Recovery tests in which dioxins were added to fish samples resulted in acceptable recoveries (77-117%). The CALUX assay performed well in the analysis of dioxins in fish samples and a comparative study revealed a strong correlation between the CALUX assay and high-resolution gas chromatography-high-resolution mass spectrometry analysis for the determination of PCDD/Fs (r = 0.89) and dioxin-like PCBs (r = 0.91) in retail fish (n = 22). These data revealed that the CALUX assay would be a useful screening method for PCDD/Fs and dioxin-like PCBs in retail fish.     

The Cauchy problem for hyperbolic systems with Hölder continuous coefficients with respect to time

We discuss the local existance and uniqueness of solutions of certain nonstrictly hyperbolic systems, with Hölder continuous coefficients with respect to time variable. We reduce the nonstrictly hyperbolic systems to the parabolic ones, then we shall prove them by use of Tanabe-Sobolevski’s method.     

Rhodium-catalyzed asymmetric 1,4-addition of sodium tetraarylborates to β,β-disubstituted α,β-unsaturated esters

A rhodium-catalyzed 1,4-addition of sodium tetraarylborates to β,β-disubstituted α,β-unsaturated esters has been developed. Highly efficient asymmetric catalysis has also been described to create quaternary carbon stereocenters at the β-position of esters by tuning the ester group of substrates and employing a readily available chiral diene ligand.     

Structure elucidation of AK-toxins,host-specific phytotoxic metabolites produced by alternaria kikuchiana tanaka

The structures of two host-specific phytotoxic metabolites, AK-toxin I and II, isolated from culture broth of Alternaria kikuchiana Tanaka (the fungus causing black spot disease of Japanese pear) were determined to be the ester consisting of N-acetyl-β-methyl-phenylalanine and 9,10-epoxy-8-hydroxy-9-methyl-2E, 4Z, 6E-decatrienoic acid ($\text{1}$) and its β-demethyl derivative ($\text{2}$).     

Nickel-catalyzed asymmetric grignard cross-coupling of dinaphthothiophene giving axially chiral 1,1'-binaphthyls

Asymmetric cross-coupling of dinaphtho[2,1-b:1',2'-d]thiophene with ArMgBr (Ar = Ph, 4-MeC6H4, 4-MeOC6H4) proceeded with high enantioselectivity in THF at 20 degrees C in the presence of 3 mol % of a nickel catalyst generated from Ni(cod)2 and a chiral oxazoline-phosphine ligand to give high yields of axially chiral 2-mercapto-2'-aryl-1,1'-binaphthyls, whose enantiomeric excesses are over 93%. The mercapto group in the chiral binaphthyl was converted into iodo, boryl, and phosphino groups without racemization.