XANES speciation of mercury in three mining districts – Almadén,Asturias (Spain), Idria (Slovenia)

The mobility, bioavailability and toxicity of mercury in the environment strongly depend on the chemical species in which it is present in soil, sediments, water or air. In mining districts, differences in mobility and bioavailability of mercury mainly arise from the different type of mineralization and ore processing. In this work, synchrotron‐based X‐ray absorption near‐edge spectroscopy (XANES) has been taken advantage of to study the speciation of mercury in geological samples from three of the largest European mercury mining districts: Almadén (Spain), Idria (Slovenia) and Asturias (Spain). XANES has been complemented with a single extraction protocol for the determination of Hg mobility. Ore, calcines, dump material, soil, sediment and suspended particles from the three sites have been considered in the study. In the three sites, rather insoluble sulfide compounds (cinnabar and metacinnabar) were found to predominate. Minor amounts of more soluble mercury compounds (chlorides and sulfates) were also identified in some samples. Single extraction procedures have put forward a strong dependence of the mobility with the concentration of chlorides and sulfates. Differences in efficiency of roasting furnaces from the three sites have been found.     

Modeling of rod-structures in nonlinear elasticity

This Note deals with the modeling of a structure made of straight elastic rods whose thickness tends to 0. We show that, upon an adequate scaling, the infimum of the total elastic energy tends to the minimum of a functional which depends on fields defined on the centerlines of the rods.     

Trityl Salt-Initiated Cationic Polymerization of 1,2-Cyclohexene Oxide: Structural Analyses of the Products

The polymerization of 1,2-cyclohexene oxide was carried out at 0°C in dichloroethane with triphenylmethyl hexafluoroarsenate as the initiator. A typical reaction product (PCHO-1) was analyzed by infrared and nuclear magnetic resonance spectroscopy as well as by gel-permeation chromatography, x-ray diffraction, and differential scanning calorimetry (DSC). The x-ray and DSC data show that PCHO-1 is an amorphous substance. The results of the NMR analyses show that the propagation step in the trityl salt-initiated polymerization obeys Bernoullian statistics with a P_m value of 0.38.     

Collision cell pressure effect on CID spectra pattern using triple quadrupole instruments: a RRKM modeling

Control of the ion internal energy in mass spectrometry is needed to establish a workable mass spectral library. The purpose of this study is to understand and to compare the pressure effects on the collision‐induced dissociation (CID) spectrum pattern recorded using triple quadrupole instruments. The monoprotonated Leucine enkephalin [YGGFL, H⁺] was used as a thermometer molecule to calibrate the electrospray ionization (ESI) and the CID internal energies deposited on the molecular species and the time scale of ion decompositions. The survival yield and the ratio of a₄/b₄ fragment ions were mainly monitored. The energy uptake for the ESI source geometry used in our study has no impact on the CID spectrum fingerprint. The collision cell pressure for the [YGGFL, H⁺] has a major influence on the SY curves slope and on the experimental time scale. To demonstrate the pressure effect on internal energy distribution, three models (threshold, thermal and collisional) based on RRKM theory were built using the Masskinetics software. As a result, the limit of each model is discussed, and the investigation demonstrates that the thermal model, using truncated Maxwell‐Boltzmann internal energy distribution, is well‐suited for simulating the experimental data at high pressure widely used in the analytical conditions. Copyright © 2013 John Wiley & Sons, Ltd.     

N-Glycosidase treatment with 18O labeling and de novo sequencing argues for flagellin FliC glycopolymorphism in Pseudomonas aeruginosa

In prokaryote organisms, N-glycosylation of proteins is often correlated to cell–cell recognition and extracellular events. Those glycoproteins are potential targets for infection control. To date, many surface-glycosylated proteins from bacterial pathogens have been described. However, N-linked Pseudomonas surface-associated glycoproteins remain underexplored. We report a combined enrichment and labeling strategy to identify major glycoproteins on the outside of microorganisms. More precisely, bacteria were exposed to a mix of biotinylated lectins able to bind with glycoproteins. The latter were then recovered by avidin beads, digested with trypsin, and submitted to mass spectrometry. The targeted mixture of glycoproteins was additionally deglycosylated in the presence of H₂ ¹⁸O to incorporate ¹⁸O during PNGase F treatment and were also analyzed using mass spectrometry. This approach allowed us to identify a few tens of potential N-glycoproteins, among which flagellin FliC was the most abundant. To detect the possible sites of FliC modifications, a de novo sequencing step was also performed to discriminate between spontaneous deamidation and N-glycan loss. This approach led to the proposal of three potential N-glycosylated sites on the primary sequence of FliC: N26, N69, and N439, with two of these three asparagines belonging to an N-X-(S/T) consensus sequence. These observations suggest that flagellin FliC is a heterogeneous protein mixture containing both O- and N-glycoforms.

QMX: A versatile environment for hybrid calculations applied to the grafting of Al2Cl3Me3 on a silica surface

We present a new software to easily perform QM:MM and QM:QM' calculations called QMX. It follows the subtraction scheme and it is implemented in the Atomic Simulation Environment (ASE). Special attention is paid to couple molecular calculations with periodic boundaries approaches. QMX inherits the flexibility and versatility of the ASE package: any combination of methods namely force field, semiempirical, first principle, and ab initio, can be used as hybrid potential energy surface (PES). Its ease of use is demonstrated by considering the adsorption of Al₂Cl₃Me₃ on silica surface and by combining different levels of theory (from standard DFT to MP2 calculations) for the so‐called High Level cluster with standard PW91 density functional theory calculations for the Low Level environment. It is shown that the High Level cluster must contain the silanol group close to the aluminum atoms. The bridging adsorption is favored by 58 kJ mol^?1 at the MP2:PW91 level with respect to the terminal position. Using large clusters at the MP2:PW91 level, it is shown that PW91 calculations are sufficient for structure optimization but that embedded methods are required for accurate energy profiles. © 2013 Wiley Periodicals, Inc.     

Small D–π–A Systems with o‐Phenylene‐Bridged Accepting Units as Active Materials for Organic Photovoltaics

Donor–acceptor (D–π–A) systems that combine triarylamine donor blocks and dicyanovinyl (DCV) acceptor groups have been synthesized. Starting from the triphenylamine (TPA)? thiophene? DCV compound ( 1 ) as a reference system, various synthetic approaches have been developed for controlling the light‐harvesting properties and energy levels of the frontier orbitals in this molecule. Thus, the introduction of methoxy groups onto TPA, the replacement of one phenyl ring of TPA by a thiophene ring, or the extension of the π‐conjugating spacer group lead to the modulation of the HOMO level. On the other hand, the fusion of the DCV group onto the vicinal thiophene ring by an ortho‐phenylene bridge allows for a specific fine‐tuning of the LUMO level. The electronic properties of the molecules were analyzed by using UV/Vis spectroscopy and cyclic voltammetry and the compounds were evaluated as donor materials in basic bilayer planar heterojunction solar cells by using C₆₀ as acceptor material. The relationships between the electronic properties of the donors and the performance of the corresponding photovoltaic devices are discussed. Bilayer planar heterojunction solar cells that used reference compound 1 and C₇₀ afforded power‐conversion efficiencies of up to 3.7 %.