Mercury speciation analysis in human hair by species-specific isotope-dilution using GC–ICP–MS

We optimized a mercury (Hg) speciation extraction method for human hair in combination with species-specific isotope-dilution analysis by gas chromatography–inductively coupled plasma–mass spectrometry (GC–ICP–MS). The method was validated on human hair reference material RM (IAEA-086), which is recommended for analysis of monomethylmercury (MMHg) and inorganic mercury (IHg). Three reagents, hydrochloric acid (HCl), nitric acid (HNO₃), and tetramethylammonium hydroxide (TMAH), and three extraction procedures, at ambient temperature for 12 h, microwave-assisted at 75 °C for 6 min, and oven heated at 80 °C for 2 h were tested. Extraction efficiency, recovery, and potential species transformations were evaluated for each method. The most efficient procedures, with recovery of ~90 % for each species with limited demethylation (<5 %) and methylation (0 %), were HNO₃ digestion, irrespective of temperature, and microwave-assisted TMAH extraction. Acidic extraction with HCl induces significant demethylation, with production of artifacts. To correct for potential demethylation artifacts we recommend spiking with isotopically enriched standards before the extraction step.     

Ene-reaction between a dienolic compound and 2-methyl-2-nitrosopropane: an EPR-MS study

The combination of electron paramagnetic resonance (EPR) and mass spectrometry (MS) was used as an efficient tool to elucidate the mechanism of an ene-reaction between a dienol compound and 2-methyl-2-nitrosopropane.     

Crystalline Amyloid Structures at Interfaces

Laying the groundwork : The interfacial self‐assembly properties of an amyloid peptide were used to develop crystalline nanostructures at air–water interfaces, which were studied by both AFM microscopy and X‐ray diffraction (see image). These structures generate regular arrays of functional groups and pave the way to controlled deposition of inorganic materials like that observed in biomineralization.

     

Überm-Bromphenole

Ohne ZusammenfassungM. Kohn und J. Wiesen, V. Mitteilung über Bromphenole.     

Influence of mixing conditions on rheological behavior and electrical conductivity of polyamides filled with carbon black

The introduction of carbon black in a polyamide matrix allows one to obtain conductive materials because of the formation of a filler network. Resulting electrical properties depend, among others, on the processing conditions. In a first part, we investigate the influence of mixing conditions (rotor speed, temperature, mixing time) on electrical conductivity. Then, in a second part, we try to characterize the conducting network by rheological measurements and to establish relationships between rheological parameters and electrical properties. For that purpose, we propose to perform successive strain sweep experiments at constant frequency, from 0.5 to 100%, then from 100 to 0.5%, and finally, again, from 0.5 to 100%. Between two successive strain sweeps, we observe a drop in the moduli values that can be attributed to the breakdown of the carbon black network. A clear relationship is established between rheological and electrical properties of the compounds. Moreover, we propose a presentation of the rheological data that permits to rank the samples according to the strength of the carbon black network.     

Hemoglobin as a major binding protein for methylmercury in white-sided dolphin liver

As methylmercury (MeHg) can be bioaccumulated and biomagnified in the trophic web, its toxicity for marine mammals is of major concern. Mercury speciation in marine biota has been widely studied, mainly focused on the discrimination and quantification of inorganic Hg and MeHg. Less attention has been paid to the interactions of Hg with biomolecules and the characterization of its specific binding, which play a key role in metabolic pathways controlling its uptake, transformation, and toxicity. In the studied white-sided dolphin (Lagenorhynchus acutus) liver homogenate (QC04LH4) sample, approximately 60 % of the total MeHg was found in the water soluble fraction, specifically associated with high molecular weight biomolecules. The identity of the involved proteins was investigated (after tryptic digestion of the fraction) by μRPLC with parallel detection by ICP-MS and ESI-MS/MS. Molecular mass spectrometry experiments were carried out at high resolution (100000) to ensure accurate protein identification and determination of the MeHg binding sites. Cysteine residue on the dolphin hemoglobin β chain was found to be the main MeHg binding site, suggesting that hemoglobin is a major MeHg binding protein in this marine mammal and could be a potential carrier of this MeHg from blood to liver prior to its degradation in this organ. In parallel, a significant proportion of selenium was found to be present as selenoneine and a potential role for this compound in Hg detoxification is discussed.     

The synthetic challenge of diazonamide A, a macrocyclic indole bis-oxazole marine natural product

The complex structure of the marine metabolic diazonamide A comprises a dichlorinated indole bis-oxazole heteroaromatic fragment, and a [b]-fused dihydrobenzofuran-dihydroindole unit containing an animal carbon, all incorporated within a strained double macrocyclic array. This review details the synthetic studies on this fascinating natural product starting from early studies on the original structure (1991-2001), through the synthesis of the originally proposed structure and the subsequent structural revision, to the eventual successful syntheses of the natural product itself. Throughout we focus on the innovative ways in which synthetic chemists have approached the challenges posed by this natural product.