Validation of a real-time monitoring method for aniline in freshwater by high-performance liquid chromatography on porous graphitic carbon/electrospray ionization tandem mass spectrometry

Aniline is an anthropogenic organic compound widely used in polymer, rubber, pharmaceutical and dye industries but also used in biodegradability assays of chemical compounds as a positive biodegradation standard. By the two approaches, the rapid determination of aniline is necessary because of the high toxicity of aniline on hemoglobin. A high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS) method for the determination of aniline in water is described here. This method, using benzylamine as internal standard, was validated. No time-consuming sample preparation was needed. A rapid separation (7 min between two chromatographic runs) of aniline and benzylamine was performed on a Hypercarb porous graphitic carbon column using a gradient of methanol and 100 mM formic acid. The obtained limits of detection and quantification were 10 and 1 ng/mL, respectively. The response for aniline was quadratic. We show that this problem could be circumvented by showing that the [calculated concentration = f(introduced concentration)] function was linear. The linearity range was 10-1000 ng/mL. An example of an application consisting of an aniline 42-day degradation kinetic in water was demonstrated.     

Molecular mechanics and dynamics study of DNA-furocoumarins complexes: Effect of methylation of the angular derivatives on the intercalation geometry

Summary Results of molecular mechanics calculations on intercalation complexes between DNA and angelicin derivatives: angelicin, 4-methylangelicin, 5-methylangllicin, 4,4-dimethylangelicin, 4,5-dimethylangelicin, 4,6,4-trimethylangelicin and 4,6,5-trimethylangelicin, are presented. The correlation between the presence of methyl groups and an increase in DNA photobinding affinity is discussed on the basis of the molecular structures. The influence of the orientation of the angelicins within the intercalation cavity is also discussed. Finally, the consequences of the dynamical behaviour of angelicin in the intercalation cite are studied.Abbreviations CNDO complete neglect of differential overlap - NMR nuclear magnetic resonance - rms root mean square - UV-A ultraviolet light of class A (320<<400 nm)     

First synthesis of 2-aminosubstituted-2-perfluoroalkyl-3,6-dihydro-2H-thiopyrans by hetero-Diels-Alder reactions of fluorinated thioamides under microwave heating

This Letter presents the first examples of hetero-Diels-Alder reactions of polyfluoroalkanethiocarboxylic acid amides and 2,3-dimethylbutadiene under microwave heating. Cycloaddition reactions proved to be dependent on the nature of perfluoroalkyl chain and on the substituents attached to the nitrogen atom. Formation of ammonium salts was also performed by simple treatment of the corresponding cycloadducts with trifluoromethanesulfonic acid. In the case of octafluorobutyl-substituted derivative, one spontaneous desamination reaction took place leading to new 2H-thiopyran.     

Development of a metabonomic approach based on LC-ESI-HRMS measurements for profiling of metabolic changes induced by recombinant equine growth hormone in horse urine

Despite the worldwide existing regulation banning the use of the recombinant equine growth hormone (reGH) as growth promoter, it is suspected to be used in horseracing to improve performances. Various analytical methods previously developed to screen for its misuse have encountered some limitations in terms of detection timeframes, in particular during the first days following reGH administration. A novel strategy involving the characterization of global metabolomic fingerprints in urine samples of non-treated and reGH-treated horses by liquid chromatography–electrospray–high-resolution mass spectrometry (LC-ESI-HRMS) is described and assessed in this paper in order to develop a new screening tool for growth hormone abuse in horseracing. The strategy involves a limited sample preparation of the urine samples and the use of appropriate software for data processing and analysis. As preliminary work, reproducibility of both sample preparation and mass spectrometry (MS) measurements was evaluated in order to demonstrate the reliability of the method. Application of the developed protocol on two horses demonstrated the suitability of the developed strategy and preliminary results showed significant modifications of the metabolome after treatment with reGH.       

Heck, direct arylation, and hydrogenation: two or three sequential reactions from a single catalyst

Palladium-catalyzed tandem multifunctional reactions leading to the synthesis of substituted biaryl molecules have been developed including tandem Heck-direct arylation and tandem-sequential Heck-direct arylation-hydrogenation. These reactions occur in good yield and have been employed in the synthesis of a cytotoxic biaryl compound.     

Comparison of analytical strategies for the chromatographic and mass spectrometric measurement of brominated flame retardants: 1. Polybrominated diphenylethers

The chromatographic and mass spectrometric (MS) behaviors of 49 polybrominated diphenylether (PBDE) homologues toward various techniques is investigated. Special attention is paid to chromatographic separation, ionization processes, and signal acquisition modes. Different liquid chromatographic (LC) separation systems and gas chromatographic (GC) temperature program parameters are studied. For LC-MS experiments, the ionization efficiencies of electrospray, atmospheric pressure chemical ionization, and atmospheric pressure photoionization (APPI) are evaluated. For GC-MS experiments, negative chemical ionization with ammonia as reagent gas as well as negative and positive electron impact (EI) ionization are studied. Thus, fragmentation pathways of PBDEs are investigated, with the main objective being to determine the sensitivity/specificity balance of each tested technique with respect to their potential respective application (parent compound focusing, metabolite identification, and screening of analogue compounds). Finally, performances of the different tested techniques are compared and evaluated in terms of detection limits on standard solutions for each homologue group. In terms of ionization, EI remains the best compromise between sensitivity and specificity with possible complementary applications in MS-MS and high-resolution MS. Nevertheless, APPI appears to be a promising alternative.     

Structures of the radical P[N(SiMe3)2](NPri2), its dimer, cation and chloro derivative

Treatment of PCl[N(SiMe3)2](NPri2) (1) with potassium-graphite in thf afforded the colourless, crystalline diphosphine [P[N(SiMe3)2](NPri2)]2 (2) in good yield. Sublimation of 2 in vacuo yielded the yellow phosphinyl radical P[N(SiMe3)2](NPri2) (3), which upon cooling reverted to 2; the latter in C6D6 at 298 K was a mixture of rac and meso diastereoisomers. The yellow, crystalline phosphenium salt [P[N(SiMe3)2](NPri2)][AlCl4] (4) was obtained from 1 and 1/2Al2Cl6 in CH2Cl2. By single-crystal X-ray diffraction (XRD) the structures of the known compound 1 and of 2 and 4 were determined. The structure of the radical 3, formed by the thermal homolytic dissociation of the diphosphine 2, was determined in the gas phase by electron diffraction (GED), utilising data from UMP2/6-31+G*ab initio calculations. The model of the molecule in the GED structure analysis was described by a set of internal coordinates and an initial set of Cartesian coordinates from ab initio calculations, facilitating the structure analysis. The experimental data were found to be consistent with the presence of a single conformer of the radical in the gas phase. The computed standard homolytic dissociation enthalpy of the P-P bond in the corresponding diphosphine 2, corrected for BSSE, 54 kJ mol(-1), is substantially reduced compared to the dissociation enthalpy of tetramethyldiphosphine by the reorganisation energies of the fragments that form upon dissociation. The intrinsic energy content of the P-P bond in the diphosphine 2 was estimated to be 286 kJ mol(-1), in agreement with the results of previous work on a series of crowded diphosphines.     

New ammunition for the proteomic reactor: strong anion exchange beads and multiple enzymes enhance protein identification and sequence coverage

The enrichment and processing of proteomic samples prior to multi-dimensional chromatography remain a challenge in ‘gel-free’ proteomics. We previously reported the development of a microfluidic device called the “proteomic reactor” that relied on enriching proteins by using strong cation exchange (SCX) followed by trypsin digestion in an interstitial volume as little as 50 nL. Here, we report a novel proteomic reactor that is based on polymeric strong anion exchange (SAX) material to analyse proteomic samples. We also compare the performance of the SAX proteomic reactor to our previously reported SCX proteomic reactor for analysing complex yeast proteomes. Our results indicate that the SAX protein reactor preferentially identifies more acidic peptides and proteins compared to the SCX reactor. We show that the SAX and SCX reactors are complementary and that their combination increases the number of unique peptides and proteins identified by 50%. Furthermore, we show that the number of protein identified can be increased further by up to 40% using different proteolytic enzymes on the proteomic reactor.     

On the Adam-Gibbs-Kirkpatrick-Thirumalai-Wolynes scenario for the viscosity increase in glasses

We reformulate the interpretation of the mean-field glass transition scenario for finite dimensional systems, proposed by Kirkpatrick, Thirumalai, and Wolynes (KTW). This allows us to establish clearly a temperature dependent length xi( *) above which the mean-field glass transition picture has to be modified. We argue in favor of the mosaic state introduced by KTW, which leads to the Adam-Gibbs relation between the viscosity and configurational entropy of glass forming liquids. Our argument is a mixture of thermodynamics and kinetics, partly inspired by the random energy model: small clusters of particles are thermodynamically frozen in low energy states, whereas large clusters are kinetically frozen by large activation energies. The relevant relaxation time is that of the smallest "liquid" clusters. Some physical consequences are discussed.