Internal energy effects in collision induced dissociation spectra

The effect of the precursor ion internal energy on the branching ratios obtained from collision induced dissociation fragmentation patterns was examined for [NH₃]⁺ and [C₂H₄N]⁺. The ion internal energy was changed by varying both the chemical ionization reagent gas and the ion source pressure. Effects observed in the collision induced dissociation fragmentation patterns as a function of the ion source pressure are explained by the reaction exothermicities and by collisional deactivation of internally excited ions (at high pressure).     

Human biomonitoring of emerging pollutants through non-invasive matrices: state of the art and future potential

Human biomonitoring (HBM) is a scientific technique that allows us to assess whether and to what extent environmental pollutants enter humans. We review here the current HBM efforts for organophosphate esters, emerging flame retardants, perfluoroalkyl substances, and phthalate esters. Use of some of these chemicals has already been banned or restricted; they are regularly detected in the environment, wildlife, and human matrices. Traditionally, blood and urine collection have been widely used as sampling methods. New non-invasive approaches (e.g., saliva, hair, nails) are emerging as valid alternatives since they offer advantages with respect to sampling, handling, and ethical aspects, while ensuring similar reliability and sensitivity. Nevertheless, the identification of biomarkers of exposure is often difficult because chemicals may be metabolized in the human body. For many of the above-mentioned compounds, the mechanisms of the favorable metabolization pathways have not been unraveled, but research on important metabolites that could be used as biomarkers of exposure is growing. This review summarizes the state of the art regarding human exposure to, (non-invasive) HBM of, and metabolism of major organophosphate esters, emerging flame retardants, perfluoroalkyl substances, and phthalate esters currently detected in the environment.

Combined Chemical and Enzymatic Synthesis of a Disialylated Tetrasaccharide Analogous to M and N Bloodgroup Determinants of Glycophorin a

Abstract

Reaction of 2,3,4,6-tetra-O-acetyl-α-D-galactopyraaosyl bromide (1) with phenyl 2-acetamido-2-deoxy-4,6-O-(4-methoxy-benzylidene)-α-D-galactopyranoside (3) mediated by mercuric salts, followed by removal of the 4-methoxybenzylidene group and O-deacylation afforded phenyl 2-acetamido-2-deoxy-3-O-p-D-galactopyranosyl-α-D-galactopyranoside (6). Compound 6 was used as a substrate for the selective introduction of two neuraminic acid residues with partially purified sialyltrans-ferase preparations. First, disaccharide 6 was treated with CMP-[¹⁴c]-NeuAc as donor substrate and CMP-NeuAc: Gal-p(l-3)-GalNac-a(2-3)sialyltransferase from human placenta to afford trisaccharide 7 (yield 85X), sialylated at C-3 of the galactose residue. Treatment of 7 with CMP-[³H]-NeuAc and a micro-somal fraction from regenerating rat liver, containing the CMP-NeuAc: NeuAc-a(2-3)-Gal-p(l-3)GalNAc-α(2-6) sialyltrans-ferase activity, gave the disialylated tetrasaccharide 8 in 10X yield.     

On Isotypic Decompositions for Non-Semisimple Hopf Algebras

In this paper we study the isotypic decomposition of the regular module of a finite-dimensional Hopf algebra over an algebraically closed field of characteristic zero. For a semisimple Hopf algebra, the idempotents realizing the isotypic decomposition can be explicitly expressed in terms of characters and the Haar integral. In this paper we investigate Hopf algebras with the Chevalley property, which are not necessarily semisimple. We find explicit expressions for idempotents in terms of Hopf-algebraic data, where the Haar integral is replaced by the regular character of the dual Hopf algebra. For a large class of Hopf algebras, these are shown to form a complete set of orthogonal idempotents. We give an example which illustrates that the Chevalley property is crucial.

     

Improved liquid chromatography-Online radioactivity detection for metabolite profiling

If very-high-pressure liquid chromatography (VHPLC) is to replace conventional HPLC as the ultimate separation tool for metabolism studies in development, coupling it efficiently with online radioactivity detection (RAD) is needed. We describe the successful combination of VHPLC/RAD, facilitated by improvements in online radioactivity detection, as well as in column loading and peak capacity. The sensitivity of (14)C detection was improved by the use of a variable scintillation flow achieved via a simple modification to the classical online radiochemical detection set-up. A modification of the flow-through cell design in which internal diameter of the tubing was reduced further increased the sensitivity and resolution by decreasing peak tailing. The injection of relatively large injection volumes was made possible by the use of columns packed at ultra-high pressure with 2.2 microm particles. Because of the reduced back pressure generated using these larger particle sizes, two 150 mm x 3 mm columns could be coupled, allowing 4-fold larger injection volumes and a 50% increase in theoretical plate number at a similar back pressure compared to a standard 150 mm x 2.1mm Waters UPLC column. The value of the methodology described was demonstrated by the analysis of in vitro and in vivo metabolism samples of (3)H- and (14)C-labeled compounds and compared with conventional radio-HPLC. We have shown that metabolite separation can be achieved with increased efficiency while maintaining a sensitivity comparable to that of conventional HPLC/RAD.     

Clustering and activation in reactions of CoCp with hydrogen and methane

Gas-phase clustering reactions of CoCp⁺ with H₂ and with CH₄ were investigated using temperature-dependent equilibrium experiments. In both systems, the CoCp⁺ ion was found to form strong interactions with two ligands. The first and second H₂ groups cluster to CoCp⁺ with bond energies of 16.2 and 16.8 kcal/mol, respectively, while the first and second CH₄ groups cluster to CoCp⁺ with bond energies of 24.1 and 12.1 kcal/mol, respectively. These bond energies are in good agreement with those determined by density functional theory (DFT). Molecular geometries for the four clusters determined with DFT are also presented. Weak experimental bond energies of 0.9 kcal/mol for the third H₂ and 2.2 kcal/mol for the third CH₄ clustering to CoCp⁺ suggest these ligands occupy the second solvation shell of the ion. In addition to clustering in the methane system, H₂-elimination from CoCp(CH₄)₂⁺ was observed. The mechanism for this reaction was investigated by collision-induced dissociation experiments and DFT, which suggest the predominate H₂-elimination product is (c-C₅H₆)Co⁺---C₂H₅. Theory indicates that dehydrogenation requires the active participation of the Cp ring in the mechanism. Transfer of H and CH₃ groups to the C₅-ring ligand allows the metal center to avoid the high-energy Co(IV) oxidation state required when it forms two covalent bonds in addition to its interaction with a C₅-ring ligand.     

Quantification of PCDD/Fs and dioxin-like PCBs in small amounts of human serum using the sensitive H1L7.5c1 mouse hepatoma cell line: optimization and analysis of human serum samples from adolescents of the Flemish human biomonitoring program FLEHS II

Since the CALUX (Chemically Activated LUciferase gene eXpression) bioassay is a fast and inexpensive tool for the throughput analysis of dioxin-like compounds in a large number of samples and requires only small sample volumes, the use of this technique in human biomonitoring programs provides a good alternative to GC-HRMS. In this study, a method for the separate analysis of PCDD/Fs and dioxin-like PCBs (dl-PCBs) in human serum with the new sensitive H1L7.5c1 mouse hepatoma cell line was optimized.Sample dilution factors of 5 and 2.4 were selected for routine analysis of respectively the PCDD/Fs and dl-PCBs. The validation studies showed that repeatability and within-lab reproducibility for the quality control (QC) standard were within the in-house criteria. A long-term within-lab reproducibility of 25% for the PCDD/F fraction and 41% for the dl-PCB fraction for the analysis of pooled serum samples, expressed as pg BEQ/g fat, was determined. CALUX recoveries of the spiked procedural blanks were within the acceptable in-house limits of 80-120% for both fractions and the LOQ was 30.3 pg BEQ/g fat for the PCDD/Fs and 14.5 pg BEQ/g fat for the dl-PCBs. The GC-HRMS recovery of a C13-spiked pooled serum sample was between 60 and 90% for all PCDD/F congeners and between 67 and 82% for the non-ortho PCBs. An adequate separation between both fractions was found. The CALUX/GC-HRMS ratio for a pooled serum sample was respectively 2.0 and 1.4 for the PCDD/Fs and the dl-PCBs, indicating the presence of additional AhR active compounds. As expected, a correlation was found between human serum samples analyzed with both the new H1L7.5c1 cell line and the more established H1L6.1c3 cell line. The geometric mean CALUX-BEQ values, reported for the adolescents of the second Flemish Environment and Health Study (FLEHS II) recruited in 2009-2010, were 108 (95% CI: 101-114) pg CALUX-BEQ/g fat for the PCDD/Fs and 32.1 (30.1-34.2) pg CALUX-BEQ/g fat for the dioxin-like PCBs.