High-throughput analysis of human serum for selected polychlorinated biphenyls (PCBs) by gas chromatography-isotope dilution time-of-flight mass spectrometry (GC-IDTOFMS)

A method for the high-throughput analysis of human serum for the 38 most prevalent polychlorinated biphenyls (PCBs) based on the use of fast gas chromatography-isotopic dilution time-of-flight mass spectrometry (GC-IDTOFMS) is presented. The chromatographic separation time was 8 min. The separation of the congeners was carried out either chromatographically or analytically using the mass spectral deconvolution capability of the TOFMS. The instrument and the method limits of detection (LODs) were 0.5 pg microL(-1) and 20 pg microL(-1), respectively, which is not as good as the one achieved using high resolution mass spectrometry (HRMS) but allows the detection and quantification of the prevalent PCBs present in real human serum samples. The dynamic range covered 3 orders of magnitude. The comparison with the high resolution mass spectrometry (HRMS) reference method (28 min) was good and some separation improvements have been observed. This method allows the analysis of 100 samples per day per instrument.     

Messkette zur direkten potentiometrischen Bestimmung des Enantiomerenüberschusses von 1-Phenyläthylmmonium-Ionen

Cell Assembly for the Potentiometric Determinatin of the Enantiomeric Excess of 1-Phenylethylammonium-Ions A cell assembly with two membranes containing each one enantiomer of the ionophor N,N,N′,N′,N″,N″,N?,N?-octabutyl-1,4,7,10,16-hexaoxacyclooctadecane-2,3,11,12-tetracarboxamide is used for the direct potentiomewtirc determination of the enantiomeric excess ee of 1-phenylethylammonium ions in aqueous solutions. The preference for the (R)-over the (S)-1-phenylethylammonium ion by the (2R,3R,11R,12R)-ionophor of 2.7 allows a reliable determination of ee even in the presence of known concentrations of the heavy interferent KCl.     

Molecular Receptors. Functionalized and chiral macrocyclic polyethers derived from tartaric acid

A number of functionalized and chiral macrocyclic polyethers have been synthesized by condensation of the dithallium alcoholate of (R,R)-(+)-tartaric acid derivatives with α, ω-dihalides. In this way for instance, the tetracarboxylic [18]-O₆ macrocycle 3c and its derivatives become readily available. They form complexes with various cationic substrates. NMR. and crystal-structure data provide information about the orientation of the side chains X in 3 with respect to the macrocycle. It is concluded that in the secondary amides like 3b and in their complexes the four X-groups are preferentially in an axial orientation on the average. This property is of much significance for the design of molecular receptors and catalysts based on this macrocyclic structure. The preparation of a number of other macrocycles is also described.     

Synthesis of BILN 2061, an HCV NS3 protease inhibitor with proven antiviral effect in humans

The synthesis of BILN 2061, an NS3 protease inhibitor with proven antiviral effect in humans, was accomplished in a convergent manner from four building blocks. The procedure described here was suitable for the preparation of multigram quantities of BILN 2061 for preclinical pharmacological evaluation.     

Universal behavior of linear alkanes in a confined medium: toward a calibrationless use of thermoporometry

A general law has been derived for predicting the transition temperature of linear alkanes confined in nanoporous materials from the simple knowledge of the free solvent transition temperature. This law is in very good agreement with the one previously determined for substituted benzenes, attesting a possible universal behavior of confined solvents.     

Comparison of H3PW12O40 and H4SiW12O40 heteropolyacids supported on silica by H MAS NMR

The H₃PW₁₂O₄₀ and H₄SiW₁₂O₄₀ heteropolyacids supported on silica were studied by ¹H MAS NMR as a function of both the coverage and the dehydroxylation temperature. The signal at ca. 8 ppm attributed to the highly acidic protons of the anhydrous form of the heteropolyacid was never observed in the case of the phosphotungstic polyanion supported on silica while it was clearly present in the case of the silicotungstic species. These results explain the different activities of the two supported heteropolyacids in acid reactions involving strong acid sites. To cite this article: A. Thomas et al., C. R. Chimie 8 (2005).     

Continuous process for singlet oxygenation of hydrophobic substrates in microemulsion using a pervaporation membrane

Chemically generated singlet oxygen (1O2, 1Deltag) is able to oxidize a great deal of hydrophobic substrates from molybdate-catalyzed hydrogen peroxide decomposition, provided a suitable reaction medium such as a microemulsion system is used. However, high substrate concentrations or poorly reactive organics require large amounts of H2O2 that generate high amounts of water and thus destabilize the system. We report results obtained on combining dark singlet oxygenation of hydrophobic substrates in microemulsions with a pervaporation membrane process. To avoid composition alterations after addition of H2O2 during the peroxidation, the reaction mixture circulates through a ceramic membrane module that enables a partial and selective dewatering of the microemulsion. Optimization phase diagrams of sodium molybdate/water/alcohol/anionic surfactant/organic solvent have been elaborated to maximize the catalyst concentration and therefore the reaction rate. The membrane selectivity towards the mixture constituents has been investigated showing that a high retention is observed for the catalyst, for organic solvents and hydrophobic substrates, but not for n-propanol (cosurfactant) and water. The efficiency of such a process is illustrated with the peroxidation of a poorly reactive substrate, viz., beta-pinene.     

Circular dichroism of olefins—IV: A semiquantitative prediction of the intensity of the cotton effect of allyl alcohols and ethers

A semi quantitative prediction of the intensity of the Cotton effect of a few allyl alcohols and ethers in the steroid and diterpene series has been derived. It relies on a calculation of the weight of the various conformations and on the allylic bond polarization model.     

Supramolecular spintronic devices: spin transitions and magnetostructural correlations in [Fe4IIL4]8+ [2x2]-grid-type complexes

The magnetism of a series of tetranuclear complexes of the [Fe4IIL4]8+ [2x2]-grid-type was investigated, revealing the occurrence of spin transition behavior within this class of compounds. The phenomenon depends directly on the nature of the substituent R(1) in the 2-position on the central pyrimidine group of the ligand L. All Fe(II) ions in compounds with R(1) substituents favoring strong ligand fields (R(1)=H; OH) remain completely in the diamagnetic low-spin state. Only complexes bearing R(1) substituents attenuating the ligand field by steric (and to a lesser extent electronic) effects (R(1)=Me; Ph) exhibit spin transition behavior triggered by temperature. In general, gradual and incomplete transitions without hysteresis were observed for magnetically active complexes. The systems described provide approaches to the development of (supra)molecular spintronics.     

Crystal Structures of the Lanthanum(III), Europium(III), and Terbium(III) Cryptates of Tris(bipyridine) Macrobicyclic Ligands

The crystal structures of the La^III, Eu^III, and Tb^III complexes of macrobicyclic [bpy.bpy.bpy] ligands, [La³⁺ ? 1 ]3 Cl^? ( = 3- La), [Tb³⁺ ? 1 ]3 Cl^? ( = 3- Tb), and [Eu³⁺ ? 2 ]3 C1^? ( = 3- Eu), have been determined. They confirm the cryptate nature of these species, the cations being bound to the eight N-sites of the ligand. The macrobicycle presents two open faces, thus allowing additional coordination of two species, Cl^? ions or H₂O molecules, to the bound cations. These data provide structural support for the photophysical studies of the luminescent properties of the Eu^III and Tb^III cryptates, which indicated residual coordination of H₂O molecules.