Analysis of organomercury compounds in sediments by capillary GC with atomic fluorescence detection

Analysis of methyl- and ethylmercury (MM and EM) halides in biological and environmental samples is generally performed by gas chromatography with electron capture detection. Tedious sample work-up protocols and poor chromatographic response (using packed columns) have, however, shown the need for the development of new methods in this field. This paper reports a sensitive method, free from these deficiencies, for the determination of methyl- and ethylmercury. The organomercury compounds (MM and EM) are first released from the sample matrix, by the combined action of acidic potassium bromide and cupric ions, and then extracted into dichloromethane. The initial extracts are subjected to thiosulfate clean-up and the organomercury species are isolated as their chloride derivatives by addition of cupric chloride, and subsequent extraction into a small volume of organic solvent. Capillary GC coupled with atomic fluorescence detection provided excellent separation efficiencies for methyl- and ethylmercury and proved to be a very selective and sensitive technique. The absolute detection limit for both MM and EM was found to be 0.2 pg.     

Applications of mass spectrometry to food proteins and peptides

The application of mass spectrometry (MS) to large biomolecules has been revolutionized in the past decade with the development of electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI) techniques. ESI and MALDI permit solvent evaporation and sublimation of large biomolecules into the gaseous phase, respectively. The coupling of ESI or MALDI to an appropriate mass spectrometer has allowed the determination of accurate molecular mass and the detection of chemical modification at high sensitivity (picomole to femtomole). The interface of mass spectrometry hardware with computers and new extended mass spectrometric methods has resulted in the use of MS for protein sequencing, post-translational modifications, protein conformations (native, denatured, folding intermediates), protein folding/unfolding, and protein-protein or protein-ligand interactions. In this review, applications of MS, particularly ESI-MS and MALDI time-of-flight MS, to food proteins and peptides are described.     

Étude expérimentale de l'influence de l'angle d'incidence des électrons primaires sur le rendement de l'émission Auger

We have studied the variation of several components of the secondary emission from a (001) surface of aluminum as a function of the polar and azimuthal angles of incidence, the current being measured on the whole half-space of re-emission. We have observed an important modulation of the L₂₃VV Auger peak, that may amount to 30%, when the crystal is rotated in its own plane.     

UV‐Vis Spectroscopy Reveals a Correlation Between Y263 and BV Protonation States in Bacteriophytochromes

Red‐light photosensory proteins, phytochromes, link light activation to biological functions by interconverting between two conformational states. For this, they undergo large‐scale secondary and tertiary changes which follow small‐scale Z to E bond photoisomerization of the covalently bound bilin chromophore. The complex network of amino acid interactions in the chromophore‐binding pocket plays a central role in this process. Highly conserved Y263 and H290 have been found to be important for the photoconversion yield, while H260 has been identified as important for bilin protonation and proton transfer steps. Here, we focus on the roles these amino acids are playing in preserving the chemical properties of bilin in the resting Pr state of the photosensory unit of a bacteriophytochrome from Deinococcus radiodurans. By using pH‐dependent UV‐Vis spectroscopy and spectral decomposition modeling, we confirm the importance of H260 for biliverdin protonation. Further, we demonstrate that in the canonical bacteriophytochromes, the pK_a value of the phenol group of the Y263 is uncommonly low. This directly influences the protonation of the bilin molecule and likely the functional properties of the protein. Our study expands the understanding of the tight interplay between the nearby amino acids and bilin in the phytochrome family.     

Optimisation and characterisation of various extraction conditions of phenolic compounds and antioxidant activity in olive seeds

This study was conducted to optimise the extraction conditions of phenolic compounds to evaluate antioxidant extraction parameters and to identify the major free and bound phenolic compounds in olive seeds. The results obtained using methanol as an extraction solvent for olive seeds indicated that the optimised total phenolic content and antioxidant activity were obtained at an extraction time of 12 h, an extraction temperature of 70°C and an extraction cycle of three stages. The correlation coefficient between total phenolic compounds and antioxidant activities was positive (R2 = 0.83). The major finding is that the predominant phenolic compounds in olive seeds were present in free form. However, a small percentage of the bound phenolic compounds was found in olive seeds compared to that of the free phenolic compounds. This study recommends that olive seeds with optimised extraction conditions (i.e. optimised correlation between phenolic compound contents and antioxidant activities) can be used as potential food additive candidates in functional, nutraceutical and pharmaceutical industries.     

Synthesis and characterization of soluble,fluorescent poly(arylene ether)s,poly(arylene thioether)s,and poly(arylene sulfone)s containing 1,3,5‐triphenylbenzene segments

The bisphenol 4,4″‐dihydroxy‐5′‐phenyl‐m‐terphenyl ( 4 ), containing a 1,3,5‐triphenylbenzene moiety, was synthesized from a pyrylium salt obtained by the reaction of benzaldehyde with p‐methoxyacetophenone with boron trifluoride etherate as a condensing agent. Polymers were obtained from 4 by a nucleophilic displacement reaction with various activated difluoro monomers and with K₂CO₃ as a base. A series of new poly(arylene ether)s ( 8a – 8f ) were obtained that contained phenyl‐substituted m‐terphenyl segments in the polymer chain. Polymers with inherent viscosities of 0.41–0.99 dL/g were obtained in yields greater than 96%. The polymers were soluble in a variety of organic solvents, including nonpolar solvents such as toluene. Clear, transparent, and flexible films cast from CHCl₃ showed high glass‐transition temperatures (T_g = 198–270 °C) and had excellent thermal stability, as shown by temperatures of 5% weight loss greater than 500 °C. 4 was converted via N,N‐dimethyl‐O‐thiocarbamate into the masked dithiol 4,4″‐bis(N,N′‐dimethyl‐S‐thiocarbamate)‐5′‐phenyl‐m‐terphenyl and was polymerized with activated difluoro compounds in the presence of a mixture of Cs₂CO₃ and CaCO₃ as a base in diphenyl sulfone as a solvent. A series of new poly(arylene thioether)s ( 9a – 9e ) were obtained with T_g values similar to those of 8a – 8e . 9a – 9e were further oxidized into poly(arylene sulfone)s with T_g values 40–80 °C higher than those for 8a – 8e and 9a – 9e . These polymers also had good solubility in organic solvents. A sulfonic acid group was selectively introduced onto the pendent phenyl group of polymers 8a and 8f by reaction with chlorosulfonic acid. The polymers were soluble in dipolar aprotic solvents and formed films via casting from dimethylformamide. Polymers 8a – 8f , 11a , and 11f showed blue and red fluorescence under ultraviolet–visible light with emission maxima at 380–440 nm. © 2002 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 496–510, 2002; DOI 10.1002/pola.10136     

Étude expérimentale des électrons rétrodiffusés par les faces (001) de l'aluminium et (111) du silicium

We study the energy dependence of elastically reflected low energy electrons, as well as volume and surface plasmon excitations. The variations versus primary electron angle of incidence and surface “cleanliness” have been correlated with the electron mean free path. We show also that the collector solid angle is an important geometric factor.     

Effect of surface plasmon oscillations on Auger electron emission

The integrated areas of the Al L₂₃VV and O KL₂₃L₂₃ Auger peaks and the Al surface plasmon energy ?ω_S are reported for the Al(001) surface as a function of exposure to O in the exposure range 0–114 L(1 L=1langmuir=10^?6Torr sec). It is shown that for exposures below a critical value of 15 L, ?ω_S is constant within experimental error while the O Auger peak area increases linearly. For exposures above 15 L, ?ω_S decreases linearly from 10.5 eV to 8.5 eV and the O Auger peak area undergoes relatively slow linear increases correspondingly. The Al Auger peak area decreases by 30% per 1 eV decrease of ?ω_S. The results are discussed with reference to theory relating Auger transition intensities to the spectral density function.     

Experimental study of surface and bulk plasmon losses induced in Al(001) by low energy electrons

We have measured the relative intensity of the elastic peak, and of the surface and bulk plasmon loss peaks, for electrons backscattered from an Al(001) single crystal surface. The exciting beam has an energy between 100 and 2000 eV, and impiges on the surface in an high symmetry plane of incidence with a colatitude angle of incidence varying between 0° and 80°. In a first series of experiments called “angle integrated experiment”, all the backscattered electrons are collected in a 2π solid angle retarding field analyser as a function of the primary beam energy and colatitude angle of incidence. In a second series called “angle resolved experiment”, the acceptance angle of the detector is set at 10° or $\text{1}\text{2}\text{°}$ and the variable parameters are colatitude angles of incidence and emission. We observe mainly that very clean aluminum exhibits large plasmon loss peaks with a negligible background. The results cannot be accounted for without sophisticated models, but “angular resolved experiments” are more suitable for a simple discussion than the “angle integrated experiment” and show mainly the phonon-plasmon coupling plus a θ dependent creation probability.     

A selective and efficient chemosensor for the rapid detection of arsenic ions in aqueous medium

Research on Chemical Intermediates - The development of selective, efficient, and economical sensors for the rapid determination of arsenic in an aqueous medium is of paramount importance, due to...