Weak chemiluminescence emission during base induced rearrangement of G-factors

A rearrangement in basic medium of the natural endoperoxide G3-factor extracted from Eucalyptus grandis is described. Evidence to support a 1,2-dioxetane intermediate that decomposes with weak luminescence emission (quantum yield) is presented.     

A selective synthesis of hydroxyborate anions as novel anchors for zirconocene catalysts

A new family of hydroxytris(pentafluorophenyl)borate anions [B(C6F5)3OH](-) associated with organic and aprotic cations c+ (imidazolium, pyrrolidinium and phosphonium) has been prepared by a general one-pot synthesis that implies the chloride borate analogues [B(C6F5)3Cl](-)[c]+. The [c]+[B(C6F5)3OH](-) salts have been isolated and fully characterized. The borate anion [B(C6F5)3OH](-) has been shown to protonate the Zr-Me bond in the Cp2ZrMe2 complex forming CH4 and the first published example of anionic [Cp2Zr(Me)OB(C6F5)3](-) species. Standard spectroscopic methods demonstrate the covalent character of the Zr metal center and the anionic character of the boron atom. This protonolysis methodology using [B(C6F5)3OH](-) anion affords a new route for the incorporation of a covalently bonded anionic functionality on organometallic complexes. This provides a new way to immobilize transition metal complexes in ionic liquids.     

Square versus tetrahedral iron clusters with polyoxometalate ligands

Two new insoluble transition metal substituted phosphotungstates, (C2N2H10)11[{(B-alpha-PW9O34)Fe3(OH)3}4(PO4)4Fe].38H2O(1) and K4(C2N2H10)12[(alpha-PW10Fe2O39)4].30H2O(2), have been isolated by the hydrothermal reaction of [A-alpha-PW9O34]9-, Fe(III) ions and ethylenediamine. Compound 1 has a tetrahedral symmetry and contains a Fe13 core built from the assembly of four Fe(III) trisubstituted [B-alpha-PW9O34]9- anions around a central disordered iron ion via four phosphato ligands. The anion in 2 can be described as a square of disubstituted [PW10O37]9- anions linked by Fe(III)-O-Fe(III) bridges. Magnetic measurements performed on 1 and 2 have shown the occurrence of antiferromagnetic interactions between the iron ions and have allowed the coupling constants between the magnetic centers to be determined.     

One-electron reduction of superoxide radical-anions by 3-alkylpolyhydroxyflavones in micelles. Effect of antioxidant alkyl chain length on micellar structure and reactivity

In micellar solutions, one-electron reduction of (*)O 2 (-) radical-anions by 3-alkylpolyhydroxyflavones (FnH) with alkyl chains of n = 1, 4, 6, 10 carbons produces phenoxyl radicals ( (*)Fn) identical to those obtained by one-electron oxidation by (*)Br 2 (-) radical-anions or by repair of tryptophan radicals. In cetyltrimethylammonium bromide (CTAB), F1H localizes in the Stern layer, and alkyl chains of other FnH solubilize in the hydrophobic interior, interacting with cetyl tails. This interaction produces more compact micelles with lower intramicellar fluidity, as suggested by the increase in the pseudo-first-order rate constant of (*)Fn formation ( k 1) from approximately 390 s (-1) for n = 1 to 610 s (-1) for n = 10, leading to an intramicellar bimolecular rate constant of 1 x 10 (5) M (-1) s (-1). Additionally, (*)F1 and (*)F4 decay by intermicellar bimolecular reaction (2 k = 20 and 2 x 10 (5) M (-1) s (-1), respectively) whereas other (*)Fn radicals are stable over seconds due to increased localization with regards to the Stern layer. In contrast, the thick uncharged hydrophilic palisade layer and the compact hydrophobic core of Triton X100 micelles are responsible for a much higher microviscosity resulting in a decrease in k 1 from approximately 15.6 s (-1) for n = 1 to 9.6 s (-1) for n = 10.     

A stereodivergent synthesis of beta-hydroxy-alpha-methylene lactones via vinyl epoxides

A catalytic diastereoselective sulfonium ylide epoxidation of aldehydes furnished original vinyl epoxides, having an MBH backbone. These highly functionalized building blocks were used for a formal synthesis of the antibiotic conocandin, and opened up a stereodivergent route towards beta-hydroxy-alpha-methylene lactones, core units of naturally occurring compounds. Under acidic conditions, the oxiranes were mainly transformed, with moderate to good yields, into trans beta-hydroxy-alpha-methylene lactones. On the other hand, a user-friendly palladium-catalysed CO2 insertion and cyclisation sequence gave the cis beta-hydroxy-alpha-methylene lactone counterparts along with an interesting cis-trans equilibration of the pi-allyl intermediates.     

Modelling NiFe hydrogenases: nickel-based electrocatalysts for hydrogen production

NiFe hydrogenases are unique enzymes that catalyze the H+/H2 interconversion with remarkable efficiency. The determination of the tridimensional structure of their active site (a sulfur-rich dinuclear nickel-iron cluster with diatomic cyanide and carbonyl ligands) has stimulated the synthesis of a variety of nickel-based complexes as potential electrocatalysts for hydrogen production. These catalysts may provide an adequate alternative to platinum. This paper gives an historical perspective of this biomimetic structural approach and then focusses on recently reported bio-inspired functional mimics displaying electrocatalytic activity for hydrogen production.     

Alkylammonium-based protic ionic liquids. II. Ionic transport and heat-transfer properties: fragility and ionicity rule

The physicochemical characterization of six alkylammonium-based protic ionic liquids (PILs) is presented. These compounds were prepared through a simple and atom-economic neutralization reaction between a tertiary amine and a Br?nsted acid, HX, where X- is HCOO-, CH3COO-, HF2-. The temperature dependency and the effect of added water on properties such as density, viscosity, ionic conductivity, and the thermal comportment of these PILs were measured and investigated. The results allowed us to classify them according to a classical Walden diagram and to appreciate their great "fragility". PILs have applicable perspectives in replacements of conventional inorganic acids for fuel cell devices and thermal transfer fluids.     

Advantages of hydride generation interface for selenium speciation in waters by high performance liquid chromatography-inductively coupled plasma mass spectrometry coupling

This paper focuses on the analytical performance improvement of the coupled technique HPLC-ICPMS using on-line collision/reaction cell technology for selenium elemental and speciation analyses at the ng (Se) l(-1) level in aquatic environment. Collision/reaction cell operating parameters were optimised, resulting in selected conditions of 5.5 ml min(-1) H(2) and 0.5 ml min(-1) He mixture. The detection limits obtained were around 5 ng (Se) l(-1) for total analysis, and between 7 and 15 ng (Se) l(-1) depending on the species for speciation analysis. The capability of UV irradiation-hydride generation interfacing to increase detector sensitivity was also evaluated for speciation analysis. The detection limits obtained were in the range 2-8 ng (Se) l(-1) depending on the species. Moreover, such interface allowed to prevent bromine introduction to the ICPMS which is particularly convenient for selenium trace analysis in natural waters as (80)Se is preserved free from BrH interferences. The developed method was validated using certified water with low selenium content (TM Rain 95, NWRI, Canada) and applied to the analysis of different waters.     

Analysis of high molecular mass proteins larger than 150 kDa using cyanogen bromide cleavage and conventional 2-DE

Proteomic approaches including high-resolution 2-DE are providing the tools needed to discover disease-associated biomarkers in complex biological samples. Although 2-DE is an extremely powerful approach to analyze the proteome, the separation of proteins with extreme molecular masses still remains an issue requiring improvement. Because high molecular mass (HMM) proteins larger than 150 kDa have already been observed to be differentially expressed in several pathologies such as cancer, we developed an original strategy to analyze this part of the proteome that is not easily separated by 2-DE in polyacrylamide gels. This strategy is based on the 2-DE separation of cyanogen bromide (CNBr) fragments of purified HMM protein fractions, and combines techniques including SEC fractionation, TCA precipitation, CNBr cleavage, 2-DE and MS analysis. The method was first tested on a model protein, the BSA. Preliminary results obtained using colonic tissues led to the identification of six HMM proteins with M(r) comprised between 163 and 533 kDa in their reduced state. These results demonstrated that our CNBr/2-DE approach should provide a powerful tool for identification of new biomarkers larger than 150 kDa.     

Multi-screening approach to monitor and quantify 42 antibiotic residues in honey by liquid chromatography-tandem mass spectrometry

A multi-screening approach for monitoring potential chemical contaminants in honey by liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) has been developed. A total of 42 veterinary drugs (5 tetracyclines, 7 macrolides, 3 aminoglycosides, 8 beta-lactams, 2 amphenicols and 17 sulfonamides) were surveyed with the ultimate goal of unambiguously confirmed and quantified these analytes at a concentration level of 20 microg/kg. A basic sample preparation including four subsequent liquid/liquid extraction steps was necessary to adequately extract the compounds of interest from the honey. The four extracts were injected into the LC-ESI-MS/MS using a stacking injection procedure. Validation of the entire procedure was carried out according to the European Union directive 2002/657/EC at three concentration levels, i.e., 10, 20 and 30 microg/kg. Good performance data were obtained for 37 analytes, out of the 42 studied. Limit of compliance and detection limit were calculated based on an internal limit set at 20 microg/kg for all the compounds and ranged between 24-30 and 27-80 microg/kg, respectively. A limited survey on honeys of different geographical origins has demonstrated that positive honey samples were often contaminated by more than one class of drugs, thus highlighting the usefulness of such multi-screening approach to ensure and warrants the quality of honey.