Incoherent quasielastic neutron scattering study of molecular dynamics of 4-n-octyl-4'-cyanobiphenyl

We report incoherent quasielastic neutron scattering experiments on the thermotropic liquid crystal 4-n-octyl-4'-cyanobiphenyl. The combination of time-of-flight and backscattering data allows analysis of the intermediate scattering function over about three decades of relaxation times. Translational diffusion and uniaxial molecular rotations are clearly identified as the major relaxation processes in, respectively, the nanosecond and picosecond time scales.     

Electrokinetic supercharging for highly efficient peptide preconcentration in capillary zone electrophoresis

Electrokinetic supercharging has been integrated in CZE for the development of a highly sensitive methodology for protein tryptic digest analysis. A careful choice of the experimental conditions led to sensitivity enhancement factors between 1000 and 10,000 whilst maintaining a satisfactory resolution. Peptides in the low nanomolar concentration range have been detected despite the use of the poorly sensitive UV absorbance detection mode. The buffer system used in this study is fully suitable for coupling CE to MS.     

Inner membrane lipids of Escherichia coli form domains

In prokaryotic cells, the hypothesis of the existence of lipid domains was considered. In order to test this hypothesis and study the organization of lipids in the inner membrane of Escherichia coli, we elaborated Langmuir films mimicking the inner leaflet of this membrane by considering lipids extracted from the inner membrane of E coli by Folch protocol.

Lipid monolayers were elaborated by using these extracts (Langmuir technique); the organization of the resulting films was studied at the air–water interface by Brewster angle microscopy and after transfer onto muscovite by atomic force microscopy. The existence of domains was demonstrated for different interfacial pressures of biological interest, and their stability was studied.     

Extraction and purification procedures for simultaneous quantification of phenolic xenoestrogens and steroid estrogens in river sediment by gas chromatography/ion trap mass spectrometry

A sensitive and simple method based on ultrasonication extraction with a hexane/acetone (2:1, v/v) mixture, followed by clean up of the extract by solid-phase extraction (SPE) and gas chromatography/mass spectrometry (GC/MS) detection, has been developed and validated for the analysis of 20 estrogenic endocrine-disrupting chemicals (EEDCs) including phenolic xenoestrogens, synthetic and natural estrogens in river sediment. After extraction and purification, analytes are derivatised with a BSTFA/TMCS/pyridine (49:1:50, v/v/v) mixture and quantified by GC/MS. The GC/MS method involves switching between electron ionisation (EI) and chemical ionisation (CI); it also switches between selected ion storage and tandem mass spectrometry detection. The applicability of the method has been demonstrated by analysing extracts of French river sediments for which bioanalytical tests (in vitro) had already shown that they were impacted by estrogenic endocrine disrupters. The biological contribution of all the products detected in each sediment extract was compared to the estrogenic activity measured by bioassays.     

Elucidation of nitrate reduction pathways in anaerobic bioreactors using a stable isotope approach

Leachate recirculation allows an increase of moisture content and the enhancement of the anaerobic digestion of wastes in landfill. Since there is no ammonia elimination process in landfill when leachate is recirculated, NH(4) (+) may accumulate. One strategy for NH(4) (+) removal is to treat aerobically the leachate outside the landfill to convert NH(4) (+) into NO(3) (-). When nitrified leachate is recirculated, denitrification should occur in the waste. We have previously shown that wastes have a large capacity to convert nitrate into N(2). Nevertheless, in some cases we observed nitrate reduction without gaseous nitrogen production. Using a stepwise multiple regression models, H(2)S concentration was the unique parameter found to have a negative effect on N(2) production. We then suspected that dissimilatory nitrate reduction to ammonium (DNRA) occurred in the presence of H(2)S. In order to verify this hypothesis, (15)N nitrate injections were performed into microcosms containing different H(2)S concentrations. The ammonium (15)N enrichment was measured using an elemental analyser coupled to an isotope ratio mass spectrometer. In the two microcosms containing the highest H(2)S concentrations, the ammonium was (15)N enriched and at the end of the experiment all the added nitrate was converted into ammonium. For the two microcosms containing the lowest H(2)S concentrations, no (15)N enrichment of ammonium was observed. This isotopic approach has allowed us to demonstrate that, in the presence of significant concentrations of H(2)S, denitrification is replaced by DNRA.     

A novel fluorescent sensor for metal cations and protons based of bis-1,8-naphthalimide

A newly synthesized bis-1,8-naphthalimide aimed to increase its fluorescence intensity in the presence of protons or metal cations has been investigated. Its spectral photophysical characteristics in acetonitrile and chloroform solutions are described. The influence of metal cations (Zn(2+), Ni(2+), Ce(3+), Co(2+), Cu(2+) and Ag(+)) and protons on the fluorescence intensity has been investigate with regard to obtain fluorescence sensors for this ions in the environment.     

Intramolecular cyclopropanation of unsaturated terminal epoxides and chlorohydrins

Lithium 2,2,6,6-tetramethylpiperidide (LTMP)-induced intramolecular cyclopropanation of unsaturated terminal epoxides provides an efficient and completely stereoselective entry to bicyclo[3.1.0]hexan-2-ols and bicyclo[4.1.0]heptan-2-ols. Further elaboration of C-5 and C-6 stannyl-substituted bicyclo[3.1.0]hexan-2-ols via Sn-Li exchange/electrophile trapping or Stille coupling generates a range of substituted bicyclic cyclopropanes. An alternative straightforward cyclopropanation protocol using a catalytic amount of 2,2,6,6-tetramethylpiperidine (TMP) allows for a convenient (1 g-7.5 kg) synthesis of bicyclo[3.1.0]hexan-2-ol and other bicyclic adducts. The synthetic utility of this chemistry has been demonstrated in a concise asymmetric synthesis of (+)-beta-cuparenone. The related unsaturated chlorohydrins also undergo intramolecular cyclopropanation via in situ epoxide formation.     

PCB-based integration of electrochemiluminescence detection for microfluidic systems

This communication presents an instrumental development based on the printed circuit board (PCB) technology to integrate electrochemiluminescence (ECL) analysis in microfluidic systems. PCB gold macro- (10 mm2) and micro- (0.09 mm2) electrodes and two ECL microfluidic devices are designed, fabricated and tested via luminol ECL detection. Potential modulation is performed between 0.7 and 0 V vs. Ag/AgCl for luminol oxidation, thus giving rise to on/off ECL responses in the presence of hydrogen peroxide. Synchronous detection is adopted to allow weak ECL signal recovery at a very low signal-to-noise ratio (SNR). The detection limit obtained with the two ECL microfluidic devices is 50 nM and 100 nM H2O2 for macroelectrodes and microelectrodes, respectively.     

Strong ion-exchange centrifugal partition chromatography as an efficient method for the large-scale purification of glucosinolates

The glucosinolates sinalbin and glucoraphanin were purified by strong ion-exchange displacement centrifugal partition chromatography (SIXCPC). The optimized conditions involved the biphasic solvent system ethyl acetate/n-butanol/water (3:2:5, v/v), the lipophilic anion-exchanger Aliquat 336 (trioctylmethylammonium chloride, 160 and 408 mM) and a sodium iodide solution (80 and 272 mM) as displacer. Amounts as high as 2.4 g of sinalbin and 2.6g of glucoraphanin were obtained in one step in 2.5 and 3.5h respectively, starting from 12 and 25 g of mustard and broccoli seed aqueous extracts, using a laboratory scale CPC column (200 mL inner volume).     

Convertible and Constrained Nucleotides: The 2’-Deoxyribose 5’-C-Functionalization Approach,a French Touch

Many strategies have been developed to modulate the biological or biotechnical properties of oligonucleotides by introducing new chemical functionalities or by enhancing their affinity and specificity while restricting their conformational space. Among them, we review our approach consisting of modifications of the 5’-C-position of the nucleoside sugar. This allows the introduction of an additional chemical handle at any position on the nucleotide chain without disturbing the Watson–Crick base-pairing. We show that 5’-C bromo or propargyl convertible nucleotides (CvN) are accessible in pure diastereoisomeric form, either for nucleophilic displacement or for CuAAC conjugation. Alternatively, the 5’-carbon can be connected in a stereo-controlled manner to the phosphate moiety of the nucleotide chain to generate conformationally constrained nucleotides (CNA). These allow the precise control of the sugar/phosphate backbone torsional angles. The consequent modulation of the nucleic acid shape induces outstanding stabilization properties of duplex or hairpin structures in accordance with the preorganization concept. Some biological applications of these distorted oligonucleotides are also described. Effectively, the convertible and the constrained approaches have been merged to create constrained and convertible nucleotides (C₂NA) providing unique tools to functionalize and stabilize nucleic acids.