MORPHOLOGY EVOLUTION IN PTFE AS A FUNCTION OF MELT TIME AND TEMPERATURE Ⅰ. HIGH MOLECULAR WEIGHT SINGLE- AND MULTI-MOLECULE FOLDED CHAIN SINGLE CRYSTALS AND BAND STRUCTURES

The effect of sintering dispersed dispersion and nano-emulsion particles of high molecular weight polytetrafluoroethylene (PTFE) on a substrate as a function of "melt" time and temperature is described. Folded chain single crystals parallel to the substrate and as ribbons on-edge (with double striations), as well as bands, are produced for longer sintering times; particle merger and diffusion of individual molecules, crystallizing as folded chain, single (or few) molecule,single crystals when "trapped" on the substrate by cooling occur for shorter sintering times. It is suggested the observed structures develop with sintering time, in a mesomorphic melt. The structure of the nascent particles is also discussed.     

A tetrathiafulvalene–perylene diimide conjugate prepared via click chemistry

A new tetrathiafulvalene (TTF)–perylene diimide (PDI) conjugate is prepared from an azide-functionalized TTF and an acetylenic PDI employing a Cu(I)-catalyzed Huisgen-Meldal-Sharpless reaction (‘click chemistry’). Thus, the TTF donor and PDI acceptor units are linked together by a 1,2,3-triazole unit. The molecules are found to assemble on a mica surface, forming fibrilar structures.     

Laboratory intercomparison study on the analysis of short-chain chlorinated paraffins in an extract of industrial soil

Short-chain chlorinated paraffins (SCCPs) comprise a class of organic pollutants used in many industrial applications and released into the environment. The analytical determination of SCCPs is very challenging. Although there is at present no fully validated measurement procedure that might be applied in routine monitoring, the European Union Water Framework Directive (WFD) has required regular monitoring of this class of compounds at river-basin scale since 2007.To assess the status quo of the analysis of SCCPs in relation to the requirements of the WFD, we organized an interlaboratory comparison on the quantification of SCCPs in an extract of an industrial soil. Six laboratories participated in the exercise using three different techniques [i.e. gas chromatography (GC) coupled to mass spectrometry (MS) in electron-capture negative ionization mode, GC with atomic emission detection, and carbon-skeleton GC-MS]. The results reported were in the range 8.5–3200 mg/L. This confirms that reliable quantification of SCCPs is still very difficult to achieve and that the comparability of SCCP data reported to the European Commission is at least questionable.     

Absorption Spectra of 4‐Nitrophenolate Ions Measured in Vacuo and in Solution

From blue to red: While four π‐conjugated nitrophenolates absorb within a relatively narrow region in solution, they cover the entire visible spectrum when isolated in vacuo (see picture). The work combines gas‐ and solution‐phase spectroscopy and provides the first benchmark of theoretical excitation energies for nitrophenolates.

     

Phototriggered S --> O isomerization of a ruthenium-bound chelating sulfoxide

We have prepared and characterized [Ru(bpy)2(OS)]+ (bpy = 2,2'-bipyridine; OS = 2-methylthiobenzoate) and the chelating sulfoxide S-[Ru(bpy)2(OSO)]+ (OSO = methylsulfonylbenzoate) by 1H NMR (1-D and 2-D COSY), IR, UV-visible spectroscopy, electrochemistry, and X-ray crystallography. Many of the metrical and crystal parameters are nearly identical between the two structures. The sulfoxide is produced from m-cpba oxidation of the thioether. Photolysis of S-[Ru(bpy)2(OSO)]+ results in a dramatic shift in the metal-to-ligand charge-transfer (3MLCT) transition from 396 to 496 nm, with a new higher-energy 3MLCT transition appearing at 355 nm. Concomitant with this change, the Ru3+/2+ reduction potential shifts from 1.25 V vs Ag/AgCl to 0.9 V vs Ag/AgCl. These changes are ascribed to phototriggered excited-state isomerization of the sulfoxide from S- to O-bonded. Examination of the 1H NMR spectra in a CD3OD solvent before, during, and after irradiation shows the presence of two O-bonded complexes that revert to the structurally characterized S-bonded ground state. This represents the first report of isomerization of a chelating sulfoxide in a photochromic Ru complex.     

An optimized kinetics model for OH chemiluminescence at high temperatures and atmospheric pressures

Chemiluminescence from the OH(A → X) transition near 307 nm is a commonly used diagnostic in combustion applications such as flame chemistry, shock‐tube experiments, and reacting‐flow visualization. Although absolute measurements of OH(X) concentrations are well defined, there is no elementary relation between emission from the electronically excited state (OH*) and its absolute concentration. Thus, to enable quantitative emission measurements, a kinetics model has been assembled and optimized to predict OH* formation and quenching at combustion conditions. Shock‐tube experiments were conducted in mixtures of H₂/O₂/Ar, CH₄/O₂/Ar, and CH₄/H₂/O₂/Ar with high levels of argon dilution (>98%). Elementary reactions to model OH*, along with initial estimates of their rate coefficients, were taken from the literature. The important formation steps follow: (R0) (R1) Sensitivity analyses were performed to identify experimental conditions under which the shape of the measured OH* profiles and the magnitude of the OH* emission would be sensitive to the formation reactions. A fitting routine was developed to express the formation rate parameters as a function of a single rate, k₁ at the reference temperature (1490 K). With all rates so expressed, H₂/CH₄ mixtures were designed to uniquely determine the value of k₁ at the reference temperature, from which the remaining rate parameters were calculated. Quenching rates were fixed at their literature values. The new model predicts the experimental data over the range of conditions studied and can be used to calibrate the emission diagnostic for other applications, such as measurements in real combustion environments, containing higher order hydrocarbon fuels and lower levels of dilution in air. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 714–724, 2006     

The properties of ion-water clusters. II. Solvation structures of Na+, Cl-, and H+ clusters as a function of temperature

Ion-water-cluster properties are investigated both through the multistate empirical valence bond potential and a polarizable model. Equilibrium properties of the ion-water clusters H+(H2O)100, Na+(H2O)100, Na+(H2O)20, and Cl-(H2O)17 in the temperature region 100-450 K are explored using a hybrid parallel basin-hopping and tempering algorithm. The effect of the solid-liquid phase transition in both caloric curves and structural distribution functions is investigated. It is found that sodium and chloride ions largely reside on the surface of water clusters below the cluster melting temperature but are solvated into the interior of the cluster above the melting temperature, while the solvated proton was found to have significant propensity to reside on or near the surface in both the liquid- and solid-state clusters.     

Determination of shikimate in crude plant extracts by micellar electrokinetic capillary chromatography

A method based on micellar electrokinetic capillary chromatography (MECC) has been developed for the determination of shikimate in water and crude plant extracts. The analytes are separated in a cholate-taurine buffer by MECC at pH 7.3 and measured by direct UV detection at 206 nm. Shikimate showed linearity up to 12.5 mM, with a squared correlation coefficient (r(2)) of 0.9997. The method has concentration limit of detection (cLOD) and concentration limit of quantification (cLOQ) at 24.4 and 67.8 microM, respectively, corresponding to detection in the femtomol range. The number of theoretical plates (N) was estimated to 245,000 for the optimized system using a capillary with an effective length of 560 mm. The method was tested on plant samples by measuring the shikimate content in leaves of rapeseed plants grown in hydroponic solutions containing the herbicide glyphosate, a well-known inhibitor of the shikimate pathway. In crude extracts of these plants, shikimate was found to accumulate in the leaves, confirming earlier reports of shikimate as a potential biomarker for glyphosate treatment. The method now developed was also able to detect shikimate-3-phosphate, but this compound was not accumulated in glyphosate inhibited plants as found for shikimate.     

Investigation of the primary photodynamics of the aqueous formate anion

We have investigated the primary photodynamics of the aqueous formate anion using femtosecond transient absorption spectroscopy. The formate anions are excited at 200 nm, and the resulting products are probed in the region 200-650 nm. The ultraviolet part of the transient spectrum compares favorably with that of O-(aq). However, its counter radical, HCO(aq), is not observed. In the visible region hydrated electrons are observed. The electrons are produced from photodetachment of the formate anions and from two-photon ionization of water.     

Analogues of a locked nucleic acid with three-carbon 2',4'-linkages: synthesis by ring-closing metathesis and influence on nucleic acid duplex stability and structure

Two bicyclic 2'-deoxynucleoside analogues containing a saturated and an unsaturated three-carbon 2',4'-linkage, respectively, have been synthesized using a ring-closing metathesis-based linear strategy starting from uridine. Both analogues have been incorporated into oligodeoxynucleotide sequences and increased the stability of DNA:RNA hybrid duplexes (DeltaT(m) approximately 2.5-5.0 degrees C per modification) and decreased the stability of dsDNA duplexes (DeltaT(m) approximately 2.5-1.0 degrees C per modification). CD spectroscopy revealed that the bicyclic nucleosides induced formation of A-type-like duplexes albeit to a lesser degree than found for locked nucleic acid (LNA) monomers. From the CD data and UV melting analysis, we propose that the 2'-oxygen atom of the bicyclic moiety is essential for the formation of stabilized A-type-like dsDNA but not for the formation of a stabilized A-type DNA:RNA hybrid.