Analysis of sorption and bioavailability of different species of mercury on model soil components using XAS techniques and sensor bacteria

The present work studies the adsorption behaviour of mercury species on different soil components (montmorillonite, kaolinite and humic acid) spiked with CH₃HgCl and CH₃HgOH at different pH values, by using XAS techniques and bacterial mercury sensors in order to evaluate the availability of methyl mercury on soil components. The study details and discusses different aspects of the adsorption process, including sample preparation (with analysis of adsorbed methyl mercury by ICP-OES), the various adsorption conditions, and the characterization of spiked samples by XAS techniques performed at two synchrotron facilities (ESRF in Grenoble, France and HASYLAB in Hamburg, Germany), as well as bioavailability studies using mercury-specific sensor bacteria. Results show that XAS is a valuable qualitative technique that can be used to identify the bonding character of the Hg in mercury environment. The amount of methyl in mercury adsorbed to montmorillonite was pH-dependent while for all soil components studied, the bond character was not affected by pH. On the other hand, clays exhibited more ionic bonding character than humic acids did with methyl mercury. This interaction has a higher covalent character and so it is more stable for CH₃HgOH than for CH₃HgCl, due to the higher reactivity of the hydroxyl group arising from the possible formation of hydrogen bonds.The bioavailability of methyl mercury adsorbed to montmorillonite, kaolinite and humic acids was measured using recombinant luminescent sensor bacterium Escherichia coli MC1061 (pmerBR_BSluc). In case of contact exposure (suspension assays), the results showed that the bioavailability was higher than it was for exposure to particle-free extracts prepared from these suspensions. The highest bioavailability of methyl mercury was found in suspensions of montmorillonite (about 50% of the total amount), while the bioavailabilities of kaolinite and humic acids were five times lower (about 10%). The behaviour of methyl mercury in the presence of montmorillonite could be explained by the more ionic bonding character of this system, in contrast to the more covalent bonding character observed for humic acids. Thus, XAS techniques seem to provide promising tools for investigating the mechanisms behind the observed bioavailabilities of metals in various environmental matrices, an important topic in environmental toxicology.     

PNPP Hydrolysis Catalyzed by Manganese(III) Complexes with Crowned Salicylaldimine Schiff Base Ligand

Four manganese(III) complexes (MnL¹Cl, MnL²Cl, MnL⁴₂Cl, MnL⁵₂Cl) with a crowned salicylaldimine Schiff base ligand have been synthesized and employed as models to mimic hydrolase in the hydrolysis of p-nitrophenyl picolinate (PNPP). The kinetics and mechanism of catalytic PNPP hydrolysis have been investigated. The kinetic mathematical model of PNPP cleavage catalyzed by these complexes has been proposed. The effects of the ligand structure and crown ether ring in complexes, and the reactive temperature on the rate of catalytic PNPP hydrolysis have been also examined. The results show that compared with the crown-free analogous MnL³Cl and MnL⁶₂Cl, the crowned Schiff base manganese(III) complexes, MnL¹Cl, MnL²Cl, MnL⁴₂Cl and MnL⁵₂Cl, exhibit more high catalytic activity, which follow the order: MnL¹Cl >MnL²Cl >MnL⁴₂Cl >MnL⁵₂Cl >MnL³Cl >MnL⁶₂Cl; the pseudo-first-order-rate (k_obs) for the PNPP hydrolysis catalyzed by the complex MnL¹Cl containing three crown ether rings is highest among six complexes and is 1.81 times that of MnL³Cl, 1.49 × 10³ times that of spontaneous hydrolysis of PNPP, respectively, at pH = 7.00, [S] = 2.0 × 10⁻⁴ mol dm⁻³.     

An automated method for the analysis of stable isotope labeling data in proteomics

An algorithm is presented for the generation of a reliable peptide component peak table from liquid chromatography-mass spectrometry (LC-MS) and subsequent quantitative analysis of stable isotope coded peptide samples. The method uses chemical noise filtering, charge state fitting, and deisotoping toward improved analysis of complex peptide samples. Overlapping peptide signals in mass spectra were deconvoluted by correlation with modeled peptide isotopic peak profiles. Isotopic peak profiles for peptides were generated in silico from a protein database producing reference model distributions. Doublets of heavy and light labeled peak clusters were identified and compared to provide differential quantification of pairs of stable isotope coded peptides. Algorithms were evaluated using peptides from digests of a single protein and a seven-protein mixture that had been differentially coded with stable isotope labeling agents and mixed in known ratios. The experimental results correlated well with known mixing ratios.     

Influence of nanoporous carbon electrode thickness on the electrochemical characteristics of a nanoporous carbon|tetraethylammonium tetrafluoroborate in acetonitrile solution interface

Electrochemical characteristics for the nanoporous carbon|Et₄NBF₄+acetonitrile interface have been studied by cyclic voltammetry and impedance spectroscopy methods. The influence of the electrolyte concentration and thickness of the nanoporous electrode material on the shape of the cyclic voltammetry and impedance curves has been established and the reasons for these phenomena are discussed. A value of zero charge potential, depending slightly on the structure and concentration of the electrolyte, the region of ideal polarizability and other characteristics have been established. The nanoporous nature of the carbon electrodes introduces a distribution of resistive and capacitive elements, giving rise to complicated electrochemical behaviour. Analysis of the complex plane plots shows that the nanoporous carbon|Et₄NBF₄+acetonitrile electrolyte interface can be simulated by an equivalent circuit, in which two parallel conduction paths in the solid and liquid phases are interconnected by the double-layer capacitance in parallel with the complex admittance of the hindered reaction of the charge transfer or of the partial charge transfer (i.e. adsorption stage limited) process. The values of the characteristic frequency depend on the electrolyte concentration and electrode potential, i.e. on the nature of the ions adsorbed at the surface of the nanoporous carbon electrode. The value of the solid state phase resistance established is independent of the thickness of the electrode material.     

Dynamic electrochemical impedance spectroscopy measurements of passive layer cracking under static tensile stresses

Electrochemical impedance spectroscopy allows the examination of corrosion susceptibility and resistance for different construction materials, in particular the determination of the properties of their passive films. This technique makes possible the analysis of electrochemical processes in time domain, including rapid phenomena such as changes in the properties of passive films, but it has never been used for passive layer cracking examination. In many cases, fracture of the passive film under tensile stresses leads to stress corrosion cracking. Therefore, investigations of passive layer cracking on austenitic stainless steels under tensile stresses facilitate the understanding of the mechanism of stress corrosion cracking in these common engineering materials. The effect of static tensile stresses on the passive film cracking behaviour of type 304L stainless steel immersed in 0.5 M NaCl solution at room temperature has been investigated. This paper presents the impedance spectra obtained for 304L stainless steel samples at different potential values.Contribution to the 3rd Baltic Conference on Electrochemistry, Gdansk-Sobieszewo, Poland, 23–26 April 2003Dedicated to the memory of Harry B. Mark, Jr. (28 February 1934–3 March 2003)     

A study of the chemiluminescence behavior of myoglobin with luminol and its analytical applications

A chemiluminescence signal at 425 nm was observed when ferric state myoglobin was mixed with luminol in alkaline medium. Because the signal was remarkably enhanced in the presence of Fe(CN)₆ ^4–, analytical applications were investigated in a flow-injection system. The increase in chemiluminescence was linearly dependent on myoglobin concentration in the range 0.1 to 100 nmol L^–1, and the limit of detection was 0.04 nmol L^–1 with relative standard deviation 3.2% (3). It was also found that binding of Mb with the ligands CN^–, SCN^–, and F^– significantly inhibited the chemiluminescence reaction. The linear dynamic ranges for the ligands were 1.0–300.0, 0.1–3.0, and 0.5–100.0 nmol L^–1, and the limits of detection (S/N=3) 0.4, 0.04, and 0.2 nmol L^–1, for F^–, CN^–, and SCN^–, respectively. The relative standard deviations were 5.32%, 6.13%, and 3.38% for 0.1 nmol L^–1 CN^–, 0.5 nmol L^–1 SCN^–, and 1.0 nmol L^–1 F^–, respectively. At a flow rate of 2.0 mL min^–1 the assay could be accomplished in 1 min, including sampling and washing. The method has been successfully applied to the determination of myoglobin in human urine and F^– in water samples. A possible mechanism of chemiluminescence production by myoglobin and luminol is presented.     

One-pot Three-component Condensation Reactions in Water. An Efficient and Improved Procedure for the Synthesis of Furan Annulated Heterocycles

Summary. The environment-friendly one-pot three-component condensation reactions of 4-hydroxycoumarin or 4-hydroxy-6-methylpyrone, p-substituted benzaldehyde, and alkyl or aryl isocyanides to afford furocoumarines or furopyranones in water in good yields after about one hour at 75°C are reported.     

The first example of Diels-Alder cycloaddition of ortho-xylylenes to meso-tetraarylporphyrins containing electron-deficient β,β-double bonds

β-Nitro-5,10,15,20-tetraphenylporphyrin and its zinc complex, or 2,7-dinitro-5,10,15,20-tetraphenylporphyrin, react with 1,3-dihydrobenzo[c]thiophene 2,2-dioxide in refluxing 1,2,4-trichlorobenzene, giving rise to chlorins, bacteriochlorins or isobacteriochlorins. The products obtained are attractive intermediates for further functionalization of porphyrins and may be of potential use as sensitizers in photodynamic therapy.     

Hydrothermal Synthesis,Conversion Reaction,and Crystal Structure of 2-D 2-bromo-1,4-benzenedicarboxylate Copper(II) Complex with 2,2′-bipyridine

A fully deprotonated 2-bromo-1,4-benzenedicarboxylate copper(II) complex, [Cu(bbdc)(2,2′-bipy)](H₂O) (bbdc= 2-bromo-1,4-benzenedicarboxylate dianion, 2,2′-bipy=2,2′-bipyridine), was synthesized under hydrothermal conditions. This compound also can be prepared from the partly deprotonated [Cu(Hbbdc)₂(2,2′-bipy)] under basic and hydrothermal conditions. The crystal structure consists of infinite chains of [Cu₂(μ₄-bbdc)]²⁺ building blocks connected by bis-monodentate bbdc ligands and exhibits an extended 2-D architecture. Electronic supplementary material Electronic supplementary material is available for this article at and accessible for authorised users.     

Determination of affinity constants and response factors of the noncovalent dimer of gramicidin by electrospray ionization mass spectrometry and mathematical modeling

The dimerization of gramicidin, a 15-residue membrane peptide, in solution can be viewed as a model for protein-protein interactions. We reported previously that the dimer can be observed when electrosprayed from organic solvents and that the abundances of the dimer depends on the dielectric constant of the solvent. Here, we report an effort to determine an affinity constant for the dimerization of gramicidin by using gas-phase abundance. Two issues affecting the determination are the electrospray-induced dissociation of the dimer and discrimination in the electrospray of the dimer compared with the monomer. Other methods developed for the purpose of determining affinity from mass spectral abundance do not address the dissociation of the complex in the gas phase or can not be applied for cases of low affinity constant, K(a). We present a mathematical model that uses the ratio of the signal intensities of the dimer and the monomer during a titration. The model also incorporates the dissociation and an electrospray ionization-response factor of the dimer for extracting the affinity constant for the dimerization of gramicidin. The dimerization constants from the new method agree within a factor of two with values reported in the literature.