Speciation analysis of aluminium(III) in natural waters and biological fluids by complexing with various catechols followed by differential pulse voltammetry detection

The biological effects of aluminium have received much attention in recent years. Speciation of Al is of basic relevance as it concerns its reactivity and bioavailability. A differential pulse voltammetry (DPV) procedure is proposed for speciation analysis of Al(III) in natural waters and biological fluids using six catechols (L-dopa, dopamine, epinephrine, norepinephrine, caffeic acid and o-benzenediol) as electroactive ligands. The decrease of the DPV anodic peak current for each catechol ligand is linear with the increase of Al concentration. This speciation analysis idea is based on the measurement of the complexation capacity, namely, different affinities of Al(III) for catechols and organic ligands under two pH conditions. The labile monomeric Al fraction (mainly inorganic aluminium) is determined at pH 4.6, while the total monomeric Al fraction is determined at pH 8.5. The principle for Al(III) speciation analysis by an electrochemical method is discussed. This sensitive and simple fractionation method is successfully applied to the speciation analysis of Al in natural waters and the results agree well with those of Driscoll's method. The speciation analysis of Al in biological fluids is also explored and the results are compared with those obtained by ultrafiltration and dialysis. Compared with other speciation protocols the electrochemical method possesses some remarkable advantages: rapidity, high sensitivity, cheap instrumentation and a simple operation procedure.     

Separation and identification of Taxifolin 3-O-glucoside isomers from Chamaecyparis obtusa (Cupressaceae)

Taxifolin 3-O-glucoside isomers, [(2R, 3R)-, (2R, 3S)-, (2S, 3R)- and (2S, 3S)-] were isolated from leaves of Chamaecyparis obtuse (Cupressaceae). Their structures were elucidated on the basis of UV, MS, CD, 1H- and 13C-NMR spectral data, including 2D shift correlation. It was found that the compounds could be distinguished by the use of 1H- and 13C-NMR spectral data.     

Palladium-catalyzed homocoupling reactions between two Csp(3)-Csp(3) centers

[reaction: see text] A novel palladium-catalyzed coupling reaction between two Csp(3)-Csp(3) centers has been investigated. This protocol is initiated by the oxidative addition of an alpha-halo carbonyl compound to a palladium(0) species, followed by the double transmetalation. The key dialkyl palladium intermediate undergoes reductive elimination to form the desired coupling product.     

Analysis of olive and hazelnut oil mixtures by high-performance liquid chromatography-atmospheric pressure chemical ionisation mass spectrometry of triacylglycerols and gas-liquid chromatography of non-saponifiable compounds (tocopherols and sterols)

We analysed the triacylglycerol, tocopherol and sterol composition of hazelnut oil, olive oil and their mixtures (90% olive oil with 10% hazelnut oil, 70% olive with 30% hazelnut oil and 50% olive oil with 50% hazelnut oil). The main triacylglycerols were 1,2,3-trioleylglycerol, 2,3-dioleyl-1-palmitoylglycerol, 2,3-dioleyl-1-linoleylglycerol and 2,3-dioleyl-1-stearoylglycerol. Non-saponfiable compounds (tocopherols and sterols) were derivatised as O-trimethylsilyl ethers. Alpha-tocopherol was the main vitamin E isomer in all samples; however, small amounts of beta-tocopherol and gamma-tocopherol were also found. Beta-sitosterol and delta5-avenasterol were the principal sterols in all samples; campesterol and stigmasterol were minor sterol compounds in all samples. Obtusifoliol, which was a major sterol in olive oil and oil mixtures, was not found in hazelnut oil. The discriminant analysis showed that hazelnut oil, olive oil and oil mixtures were clearly separated according to their triacylglycerol composition.     

A novel synthesis of racemic and enantiomeric forms of prostaglandin B1 methyl ester

3-(Dimethoxyphosphorylmethyl)cyclopent-2-enone was converted into (+/-)-prostaglandin B1 methyl ester in two steps involving regioselective alkylation at C(2) with methyl 7-iodoheptanoate and subsequent Horner-Wittig reaction with dimer of 2-hydroxyheptanal (42% overall yield). The use of (R)- and (S)-2-(tert-butyldimethylsilyloxy)heptanal for the Horner olefination reaction gave, after deprotection of the hydroxy group, the enantiopure forms of the title compound in 28% overall yield.     

Spectrophotometric determination of osmium based on its catalytic effect on the oxidation of carminic acid by hydrogen peroxide

A highly sensitive spectrophotometric method is described for the determination of trace amounts of osmium(VIII), based on its catalytic effect on the oxidation of carminic acid by hydrogen peroxide. The reaction was monitored spectrophotometrically by measuring the decrease in absorbance of carminic acid at 540 nm after 3 min of mixing the reagents. The optimum reaction conditions were 1x10(-4) mol l(-1) carminic acid, 0.013 mol l(-1) hydrogen peroxide and pH 10 at 25 degrees C. By using the recommended procedure, the calibration graph was linear from 0.1 to 1.5 ng ml(-1) of osmium; the detection limit was 0.02 ng ml(-1); the RSD for five replicate determinations of 0.2-1.4 ng ml(-1) was in the range of 1.8-4.7%. The influence of several foreign ions on osmium determination were studied and the effect of interfering ions were removed by extracting osmium into isobuthyl methyl ketone and back extracting into sodium hydroxide solution.     

Fluorinated tetrathiafulvalenes with preserved electron-donor properties and segregated fluorous bilayer structures based on F...F nonbonded interactions

The synthesis of the fluorinated 4,5-(2,2'-difluoropropylenedithio)-1,3-dithiol-2-one heterocycle with DAST allows for the preparation of several symmetrical and unsymmetrical di- and tetrafluoro-substituted tetrathiafulvalenes with accessible oxidation potentials (0.6 < E1(1/2) < 0.85 V vs SCE) despite the presence of the electron-withdrawing CF2 groups. The flexibility of the fluorinated seven-membered ring identified from room-temperature NMR data has been thoroughly investigated by temperature-variable 1H and 19F NMR experiments, allowing for the identification of two independent folding processes, whose coalescence temperatures (Tc) and activation energies (deltaGdouble dagger) were determined (Tc = -15 degrees C, deltaGdouble dagger = 50.2 kJ mol(-1) and Tc = 47 degrees C, deltaGdouble dagger = 51.1 kJ mo(-1)). The analysis of the X-ray crystal structures of three of those fluorinated TTF demonstrates the efficiency of the nonbonded fluorine exclusion interactions for the stabilization of layered structures with fluorous bilayers, together with S...S van der Waals interactions and C-H...F hydrogen bonds.     

Acid-base equilibria in gamma-butyrolactone studied by use of pH-ISFETs

pH-ISFETs were used in the study of acid-base equilibria in gamma-butyrolactone (GBL). After the spectrophotometric determination of the pK(a) value of 3,5-dichloropicric acid, the pK(a) values and homo-conjugation constants of various acids (including the conjugate acids of bases) were determined potentiometrically using a Ta(2)O(5)-type pH-ISFET. The values of pK(a) in GBL were in a linear relation with those in propylene carbonate (PC) and 1.0 units smaller on average. The difference in pK(a) between GBL and PC was mainly attributable to the difference in proton solvation. The autoprotolysis constant of GBL, roughly estimated by a rapid titration with a Si(3)N(4)-ISFET, was about 30 on the pK(SH) scale. A comparative study was made of the response speeds of the Ta(2)O(5)- and Si(3)N(4)-type pH-ISFETs and a conventional pH-glass electrode. The result was Si(3)N(4)-ISFET > Ta(2)O(5)-ISFET > glass electrode. Because GBL is not stable against acids and bases, the use of pH-ISFETs was much more convenient than the use of the conventional glass electrode.     

EFFECT OF MOLYBDENUM PROMOTER ON THE Cu-Co BASED CATALYSTS

The synthesis of mixed alcohols (C1-C5) from syngas has been studied at 6. 0 MPa over modified Co/CuLaZr catalysts. The molybdenum addition enhanced greatly the activity and the selectivity to alcohols. The improvement of hydrogenation capacity of the system via a reversible spillover effect of hydrogen could explain this effect, together with a great capacity of CO insertion, illustrated by the effect of C2H4 addition as a probe to syngas. Under our experimental conditions, a mixed alcohol production of 147.1g/kg. cat/h containing a proportion of 33. 1% of higher alcohols (C2 OH) was obtained with a selectivity to ROH of 52. 8%.