Enzymatic kinetic resolution of racemic 4-tetrahydropyranols by Candida rugosa lipase

Enzymatic kinetic resolution of (±)-hydroxytetrahydropyrans has been achieved for the first time by means of lipase-mediated transesterification to afford optically active (2S,4R)-tetrahydropyranyl acetates and (2R,4S)-tetrahydropyranols in excellent yields with high enantioselectivity. Absolute configurations of the tetrahydropyranyl acetates were assigned as (S) by chemical correlation.     

Chemosensors for the marine toxin saxitoxin

Eleven anthracylmethyl crown ethers have been synthesized and evaluated as fluorescence sensors for the marine toxin saxitoxin. Fluorescence enhancement data are consistent with a 1:1 binding complex for all crowns. The binding constants are in the range of 10(4) M(-)(1) in ammonium phosphate buffer (pH 7.1) in 80% ethanol solvent. Selectivity for sensing saxitoxin versus several organic analytes has been demonstrated for the first time. Possible modes of binding are presented, and relevance to saxitoxin monitoring programs are discussed.     

Spectrophotometric studies on the zirconium complex of 2-(3,6-disulfo-8-hydroxynaphthylazo)-1,8-dihydroxynaphtualene-3, 6-disulfonic acid

Summary A chromotropic azo dye, DSNADNS, prepared from chromotropic acid and 1-amino-8-naphthol-3,6-disulfonic acid has been found to produce quantitative precipitation of zirconium in acid medium. The blue-violet complex formed is insoluble in all organic solvents commonly used for solvent extraction work, but is soluble in a number of liquid organic bases and solutions of ammonium salts in water showing pink to violet colouration. Spectrophotometric studies as to the nature of the complex in pyridine, triethanolamine ammonium acetate, oxalate and carbonate solutions and the analytical possibility of these solutions have been made. The complex appears to decompose in pyridine, ammonium acetate and ammonium oxalate solutions, but it is fairly stable in ammonium carbonate and triethanolamine solutions. The absorbance peaks of the dye in these solutions occur at 500 and 520 nm respectively, while the complex in triethanolamine and ammonium carbonate both shows absorbance maxima at 540 nm. The solution of the complex in these two solvents obeys Beer's law within a concentration range 4 to 25 mg of zirconium per litre. The molar absorbance coefficients of the complex in triethanolamine and ammonium carbonate are respectively 686 and 823, which indicate poor sensitivity. The solution of the complex in the former solvent is more stable than that in the latter and an analytical procedure for the spectrophotometric determination of zirconium, with little interference from foreign ions, may be developed with ease in the triethanolamine solution.

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Zusammenfassung Ein Azofarbstoff der Chromotropsäure, DSNADNS, der aus Chromotropsäure und 1-Amino-8-naphthol-3,6-disulfonsäure dargestellt werden kann, ergibt mit Zirkonium in saurer Lösung eine quantitative Fällung. Der blauviolett gefärbte Komplex ist in allen üblichen organischen Lösungsmitteln unlöslich, löst sich jedoch in einigen flüssigen organischen Basen sowie wäßrigen Lösungen von Ammoniumsalzen mit rosa bis violetter Färbung. Die Lösungen des Komplexes in Pyridin, Triäthanolamin sowie in Ammoniumacetat, -oxalat und -carbonatlösungen und ihre analytische Verwendbarkeit werden spektrophotometrisch untersucht. In Pyridin sowie in Ammoniumacetat und -oxalatlösungen scheint sich der Komplex zu zersetzen, während er in Triäthanolamin und Ammoniumcarbonatlösungen ziemlich beständig ist. Das Absorptionsmaximum des Farbstoffs in diesen beiden Lösungsmitteln liegt bei 500 bzw. 520 nm, der Komplex weist in beiden Fällen ein Maximum bei 540 nm auf. Das Beersche Gesetz wird in beiden Lösungsmitteln von 4–25 mg Zr/l erfüllt. Der molare Absorptionskoeffizient beträgt 686 bzw. 823. Die Lösung des Komplexes in Triäthanolamin ist stabiler als in Ammoniumcarbonatlösung. Eine spektrophotometrische Bestimmung von Zirkonium, die nur wenig von Fremdionen gestört wird, könnte daher gut in Triäthanolaminlösung durchgeführt werden.

     

Ir-catalyzed C-H activation in the synthesis of borylated ferrocenes and half sandwich compounds

The complex generated from 1/2[Ir(OMe)(cod)]2 and 4,4'-di-tert-butyl-2,2'-bipyridine catalyzes the regioselective borylation of ferrocenes, CpMn(CO)3 and CpMo(CO)3CH3 with a stoichiometric amount of B2pin2.     

Analyses of carcinogenic aromatic amines released from harmful azo colorants by Streptomyces SP. SS07

Extracellular fluid protein (ECFP) of Streptomyces species SS07 has been used to reduce water soluble azo dyes and the carcinogenic amines released have been compared with that from chemical reduction. The effect of temperature, pH and contact time on the recovery of amines using ECFP was studied. The ECFP releases carcinogenic amines at a pH of 9.2 and a temperature of 37 degrees C for a contact period of 24 h. The reduction products were analyzed with HPLC and their structures confirmed by LC-MS and GC-MS. It was observed that both the ECFP and chemical reduction methods released similar type of amine products. In the case of dye samples, compared to chemical reduction, 5-20% increase in the release of carcinogenic amines by ECFP was observed. The percentage of amine products released by chemical reduction was higher for leather garment samples compared to ECFP treatment.     

Extraction—spectrophotometric determination of rhenium with 5,6-diphenyl-2,3-dihydro(asym)triazine-3-thione

The reagent 5,6-diphenyl-2,3-dihydro(asym)triazine-3-thione produces a green complex with perrhenate in hydrochloric acid medium in presence of stannous chloride. The complex on extraction in chloroform shows a peak at 685 nm. The system obeys Beer's law from 2–10 p.p.m. of rhenium and its molar absorptivity is 1.53-l0^-4. It tolerates the presence of a large number of ions, including Mo^XXX and W^XXX. Job's and molar ratio methods suggest that rhenium and the reagent are present in the ratio 1:2 and the isolated complex is of the same composition, i.e. ReO(C₂₅H₁₀N₃S)₂.     

Ternary complexes of copper(II), nickel(II) and zinc(II) with nitrilotriacetic acid as a primary ligand and some phenolic acids as secondary ligands

Summary The formation of ternary complexes of the MAL^3– type [where M = Cu^II, Ni^II and Zn^II ; A = nitrilotriacetic acid (NTA); L = 1-hydroxy-2-naphthoic acid (1,2 HNA) and 2-hydroxy-1-naphthoic acid (2,1 HNA)] have been studied potentiometrically in 50% v/v aqueous — ethanol (25° and µ = 0.1). Under identical conditions the binary complexes of the 1,2- and 2,1-HNA ligands have also been examined. The values of mixed ligand formation constants K_MAL have been found to be lower than K_ML (first step formation constant of binary complexes) and even less than (second step formation constant of binary complexes).     

Separation of xylidine isomers by micellar electrokinetic chromatography

Xylidines are important precursors for the production of dyes, drugs, and various other products. Because of the high carcinogenic nature of some xylidine isomers it becomes very essential and relevant to develop suitable analytical procedures to separate isomers as well as enhance detection at very low concentrations. Micellar electrokinetic chromatography has been standardized at various influencing parameters such as pH, ionic strength, and micelle modifiers, and the optimum conditions have been ascertained for the best separation and sensitivity of standard mixtures. The applicability of the procedure in environmental samples is studied.     

A class of exact solutions for doubly anharmonic oscillators

The solution of a difference equation in the form of an infinite continued fraction is used to obtain a class of exact solutions for the eigenfunctions and eigenvalues of doubly anharmonic oscillators described by potentials of the type (1/2)²x²+(1/4)x⁴+(1/6)x⁶, n>0, provided certain constraints on the couplings are satisfied. The class is denumerably infinite but not complete.