On-line analysis of volatile chlorinated hydrocarbons in air by gas chromatography–mass spectrometry: Improvements in preconcentration and injection steps

An analytical system composed of a cryofocusing trap injector device coupled to a gas chromatograph with mass spectrometric detection (CTI-GC–MS) specific for the on-line analysis in air of volatile chlorinated hydrocarbons (VCHCs) (dichloromethane; chloroform; 1,1,1-trichloroethane; tetrachloromethane; 1,1,2-trichloroethylene; tetrachloroethylene) was developed. The cryofocusing trap injector was the result of appropriate low cost modifications to an original purge-and-trap device to make it suitable for direct air analysis even in the case of only slightly contaminated air samples, such as those from remote zones. The CTI device can rapidly and easily be rearranged into the purge-and-trap allowing water and air analysis with the same apparatus. Air samples, collected in stainless steel canisters, were introduced directly into the CTI-GC–MS system to realize cryo-concentration (at −120 °C), thermal desorption (at 200 °C) and for the subsequent analysis of volatiles. The operating phases and conditions were customised and optimized. Recovery efficiency was optimized in terms of moisture removal, cold trap temperature and sampling mass flow. The injection of entrapped volatiles was realized through a direct transfer with high chromatographic reliability (capillary column–capillary column). These improvements allowed obtaining limits of detection (LODs) at least one order of magnitude lower than current LODs for the investigated substances. The method was successfully employed on real samples: air from urban and rural areas and air from remote zones such as Antarctica.     

Mechanistic studies of the isomerization of peroxynitrite to nitrate catalyzed by distal histidine metmyoglobin mutants

Hemoproteins are known to react with the strong nitrating and oxidizing agent peroxynitrite according to different mechanisms. In this article, we show that the iron(iii) forms of the sperm whale myoglobin (sw Mb) mutants H64A, H64D, H64L, F43W/H64L, and H64Y/H93G catalyze the isomerization of peroxynitrite to nitrate. The two most efficient catalysts are H64A (k(cat) = (5.8 +/- 0.1) x 10(6) M(-1) s(-1), at pH 7.5 and 20 degrees C) and H64D metMb (k(cat) = (4.8 +/- 0.1) x 10(6) M(-1) s(-1), at pH 7.5 and 20 degrees C). The pH dependence of the values of k(cat) shows that HOONO is the species which reacts with the heme. In the presence of physiologically relevant concentrations of CO(2) (1.2 mM), the decay of peroxynitrite is accelerated by these metMb mutants via the concurring reaction of HOONO with their iron(iii) centers. Studies in the presence of free added tyrosine show that the metMb mutants prevent peroxynitrite-mediated nitration. The efficiency of the different sw metMb mutants correlates with the value of k(cat). Finally, we show that sw WT-metMb is nitrated to a larger extent than horse heart metMb, a result that suggests that the additional Tyr151 is a site of preferential nitration. Again, the extent of nitration of the tyrosine residues of the metMb mutants correlates with the values of k(cat).     

Preparation of Some Substituted Terephthalic Acids

We report in detail the preparation of two substituted terephthalic acids: 2‐sulfomethylterephthalic acid (1) and 2‐phosphonoterephthalic acid (2). Efficient, short syntheses have been developed for both compounds. They are potentially useful monomers for construction of acid‐pendant polymer chains.     

Polyethylene Glycols as Solvents for Anionic Activation: Synthesis of Thioacetates by Means of Potassium Thioacetate in Polyethylene Glycol 400

Recently, polyethylene glycols (PEGS) of various molecular weights have been proposed as solvent promoters for various reactions ^{1, 2}. We wish to report on the use of PEG 400 as solvent for the anionic activation of potassium thioacetate, which could be used for the preparation of alkyl and benzyl thioacetates from the corresponding halides or alcohol derivatives. The method can be synthetically significant, since from thioacetates the corresponding thiols can be easily prepared under a variety of mild conditions ³.     

Fluorescence spectra of organic dyes in solution: a time dependent multilevel approach

Classical all-atom molecular dynamics (MD) simulations and quantum mechanical (QM) time-dependent density functional theory (TD-DFT) calculations are employed to study the conformational and photophysical properties of the first emitter excited state of tetramethyl-rhodamine iso-thiocyanate fluorophore in aqueous solution. For this purpose, a specific and accurate force field has been parameterised from QM data to model the fluorophore's first bright excited state. During the MD simulations, the consequences of the π→π* electronic transition on the structure and microsolvation sphere of the dye has been analysed in some detail and compared to the ground state behaviour. Thereafter, fluorescence has been calculated at the TD-DFT level on configurations sampled from the simulated MD trajectories, allowing us to include time dependent solvent effects in the computed emission spectrum. The latter, when compared with the absorption spectrum, reproduces well the experimental Stokes shift, further validating the proposed multilevel computational procedure.     

Poly(ester urethane) guides for peripheral nerve regeneration

A biocompatible and elastomeric PU was synthesized from low-molecular-weight PCL as macrodiol, CMD as chain extender and HDI as chain linker for applications in the field of peripheral nerve repair. PU cast films supported in vitro attachment and proliferation of NOBEC. The in vitro adhesion and proliferation of S5Y5 neuroblastoma cells on the inner surface of uncoated, gelatin- and PL-coated PU guides were compared. Due to their superior in vitro performance, PL-coated PU guides were tested in vivo for the repair of 1.8 cm-long defects in rat sciatic nerves. The progressive regeneration was confirmed by EMG and histological analysis showing the presence of regenerating fibers in the distal stumps.     

Isolation and Characterization of Cellulosic Pulp Fines and Their Interactions with Cationic Polyacrylamides

Four different types of cellulosic fines were isolated from refiner mechanical and kraft pulp samples to characterize their chemical and physical properties. The pulp fines were flocculated using four different types of cationically modified polyacrylamides. The extent of flocculation was observed with multiple light scattering apparatus. The maximum adsorption of the polyelectrolytes on the pulp fines was determined by polyelectrolyte titration. It was concluded that it is the combination of the molar mass and the charge density of a polyelectrolyte, as well as the origins and characteristics of the fines which define the adsorption and flocculation behavior. None of these properties alone could fully describe these phenomena, but the molar mass of the polyelectrolyte was the predominant factor. The most important fines characteristics were the charge properties and the microstructure.     

Influence of structural features on the self‐assembly of short ionic oligopeptides

We investigated the self‐aggregation of 12 short ionic oligopeptides constituted by 4–7 amino acid residues to establish useful structure–property relationships that might be exploited in the biomedical field by using the concept of molecular Lego. We show that the critical aggregation concentration (CAC) of tetrapeptides decreases with increasing hydrophobicity of neutral residues. Additionally, the dependence of the CAC of isomeric oligopeptides on the distribution of amino acid residues confirms the high tendency to self‐organization of molecules with alternating ionic and neutral residues. Indeed, atomic force microscopy (AFM) images recorded on oligopeptide solutions above the CAC show the presence of either fibrillar or spherical aggregates depending on oligopeptide structure and concentration, steric hindrance, solution pH, and time. The potential of the investigated oligopeptides in tissue engineering applications is supported by their in vitro cytocompatibility. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 889–897, 2010     

Determination of phosphate/arsenate by a modified molybdenum blue method and reduction of arsenate by S2O4

A modified molybdenum blue method for fast and accurate measurement of arsenate and phosphate in aqueous solution at concentrations below 10 μmol l⁻¹ is reported. The modification consists of optimizing the composition of the molybdenum-containing solution (potassium antimony tartrate, ammonium molybdate, sulfuric acid).Selective reduction of arsenate by sodium dithionite is used to determine phosphate concentrations, and for the speciation of arsenate and arsenite, in an aqueous mixture according to the scheme developed by Johnston and Pilson. Sodium dithionite is used for the first time to achieve complete, fast (<10 min), and selective reduction of arsenate in neutral solution.These two significant improvements afforded a colorimetric limit for As detection near 1 ppb, which easily meets the requirements imposed by the revised EPA threshold levels for As in drinking water.     

Structure and dynamics of the hydrogen-bond network around (R,R)-pterocarpans with biological activity in aqueous solution

Molecular dynamics simulations were carried out in the presence of 2380 water molecules (TIP3P) to explore the conformational preferences of 3,9-dimethoxy-4-prenylpterocarpan (bitucarpin A) and 3,9-dihydroxy-4,8-diprenylpterocarpan (erybraedin C) and the H-bond network around them, using the empirical general AMBER force field (GAFF). Specific angle and torsional parameters have been improved in order to match the geometries of the minimum energy structures obtained from an earlier DFT/ab initio study in vacuo, taking into account a few configurations [Alagona, G.; Ghio, C.; Monti, S. Phys. Chem. Chem. Phys. 2004, 6, 2849-2857]. RESP partial charges were assigned to reproduce the electrostatic potential determined at the HF/6-31G level of theory. The analysis of trajectories allowed the conformations of bitucarpin and erybraedin as well as the distribution of water molecules around them to be elucidated. During one of the simulations only, the scaffold of erybraedin undergoes interconversion from its most stable Ht conformation to the Ot one and vice versa. Radial distribution functions, coordination numbers, and angular distributions put forward the extent of solvent structure and the hydrogen bonding behavior of their various (methoxy, hydroxyl, or ethereal) oxygen atoms. The distribution of solvent molecules in the first and second solvation shells as well as the residence times for the different solute-solvent interacting sites have been considered.