Determination of Henry's law constants for low volatile mixed halogenated anisoles using solid-phase microextraction

Trihalogenated anisoles (THAs) that have been identified at low concentration levels (ng L⁻¹) in drinking water are suspected of causing odor episodes, which are a frequent source of complaint by consumers. Henry's law constant (K_H) is an important parameter in controlling the diffusion of organic compounds from the water to the vapor-phase, so its evaluation is of significance in the study of odor events. In this paper, the K_H of a wide range of trihalogenated anisoles - in its dimensionless form K^′H - were calculated at two temperatures, 45 and 22 °C using equilibration partitioning in a closed system and headspace microextraction (EPICS-SPME). Two methodological approaches, Ramachandran and Dewulf, were used for the assessment of the Henry's law constant. Nevertheless, to apply these methods to THAs, a relatively narrow headspace/water volume ratio range (80/1-8/1) is required. At these conditions, a linearity (r²) using Ramachandran's theoretical relationship from 0.9276 to 0.9989 was obtained and the variability (R.S.D.%) when Dewulf's theoretical relationship was employed was lower than 20% (n = 5).     

Synthesis, structural characterization and anion binding studies of palladium macrocycles with hydrogen-bonding ligands

The reactions between [Pd(P-P)(OTf)2] (where P-P=dppp or dppf) and two different bipyridyl ligands (=1,3-bis(4-pyridylmethyl)urea and=1,3- bis(pyridinylmethyl)benzenedicarboxamide) containing hydrogen-bonding units have been studied. The X-ray crystal structures of three of these assemblies have been solved showing them to be the [2+2] metallo-macrocycles [Pd(P-P)(n)]2(OTf)4 [P-P=dppp, n=1, (); P-P=dppp, n=2, (); P-P=dppf, n=1, ()]. To confirm whether the dimeric assembly of one of these species () is retained in solution, several investigations have been carried out. 1H NMR studies in DMSO and high resolution ESI mass spectrometry have shown that is in equilibrium with a larger [3+3] metallo-macrocycle. The equilibrium between these two species can be modified by changing the temperature, concentration or solvent. Also, addition of certain anions (e.g. [H2PO4]-) to the mixture shifts the equilibrium favoring the formation of the [2+2] metallo-macrocycle over the [3+3] (initially present in a larger proportion).     

Langmuir-Blodgett films formed by continuously varying surface pressure. Characterization by IR spectroscopy and epifluorescence microscopy

Monolayer films of phospholipids at the air-water interface have been transferred to solid substrates under conditions of continuously varying surface pressure, an approach termed COVASP. The molecular and supramolecular properties of the film constituents have been characterized with two complementary techniques. IR spectroscopy was used to monitor chain conformation as a function of transfer surface pressure. Results were compared to those from Langmuir films determined directly at the A/W interface by IR reflection-absorption spectroscopy (IRRAS). The methylene stretching frequencies for both proteated and acyl chain perdeuterated 1,2-dipalmitoylphosphatidylcholine (DPPC and DPPC-d62) in the transferred molecules indicate that the phospholipids retain at least, in part, their surface pressure-dependent chain-conformational order characteristics. The line widths of these modes are somewhat reduced, suggestive of slower rates of reorientational motion in the Langmuir-Blodgett (LB) films. Epifluorescence microscopy reveals a progressive condensation gradient, including nucleation and growth of probe-excluding condensed domains along the transfer line. DPPC condensation, observed along a single LB film, was qualitatively comparable to compression-driven condensation as observed in situ or in conventional LB films transferred at constant pressures. However, condensation along the compression isotherm in COVASP-LB films was reduced by 15-20% as compared to films equilibrated at different constant pressures, probably the result of kinetic differences in equilibration processes. As a preliminary demonstration of the utility of this new approach, the monolayer --> multilayer transition known to occur (Eur. Biophys. J. 2005, 34, 243) in a four-component model for pulmonary surfactant has been examined. IR parameters from both the lipid and the protein constituents of the film all indicate that the transition persists during the transfer process. This new approach for the study of transferred films will permit the efficient characterization of lipid-protein interactions and structural transitions occurring in pulmonary surfactant films subjected to dynamic compression.     

Coupled hydrogen-bonding interactions between beta-carboline derivatives and acetic acid

In this work, we have analysed the tendency of two beta-carboline derivatives, harmane and norharmane, in the formation of hydrogen bonds. We obtained the (1)H and (13)C NMR spectra of different mixtures of these derivatives with acetic acid (AcOH) in CDCl(3). A cyclic 1:3 complex is proposed between harmane and AcOH, while a 1:2 complex is proposed for norharmane. Chemical shifts at temperatures between 233 and 323 K were measured: lowering the temperature produces the same effect as increasing the amount of AcOH in solution. The (13)C data confirm a delocalisation of the pi electron density towards the pyridinic ring that occurs when AcOH is added.     

Mechanism of Cu deposition on the alpha-Al(2)O(3) (0001) surface

The growth mechanism of the Cu/alpha-Al(2)O(3) (0001) interface is studied by first-principles molecular-dynamics simulations as a function of the transition-metal coverage (theta) and the temperature of the system. On the anhydrous surface growth of Cu(0) 3D clusters is predicted. On the partially hydroxylated surface, a Cu(I) monolayer, relatively stable upon the temperature rising, is first observed (theta<1/3 ML). Increasing Cu loading leads to Cu(I)/Cu(0) mixed phases that when heated aggregate into 3D particles increasing the number of Cu(0) atoms, in agreement with the Auger spectra of Kelber et al.     

Polymerization by phase-transfer catalysis 3: Poly(1,4-oxylylene thioethers) synthesis

Poly(1,4-oxylylenethioethers) were synthesized from 2,5-disubstituted-1,4-bis(chloromethyl)-benzenes and sodium sulfide under phase-transfer conditions. The polythioethers were characterized by elemental analysis and infrared spectroscopy. The effect of the catalyst, solvent, and temperature were studied. Their glass transition temperature and thermal decomposition were determined.     

Picosecond pulse generation by intracavity nonlinear compression in self-injected Nd-YAG laser

A new type of laser which generates pulses with amplification band-limited picosecond duration is presented. 15 ps, 0.9 GW, 3 pps, λ = 1.06 μm in a single pulse are obtained with good stability. Accurate timing of the pulses can be achieved and no external pulse selection is required.     

A double-membrane nitrate ion-selective electrode based on aliquat-nitrate in paraffin

Summary A double-membrane nitrate-selective electrode [as a modified coated wire electrode (CWE)] was prepared with an internal conductor membrane made of tetrabutylammonium bromide (BrTBA) in naphthalene, and an external active membrane (Aliquat-NO ₃ ^– in paraffin), on an Agamalgamated electrode. The nitrate-electrode exhibits linear Nernstian response over the range 1 to 10^–4.5 mol/l of nitrate, with a slope of 56.01 ± 0.9 mV decade^–1. The selectivity coefficients for 17 ions were calculated. The effects of pH, membrane composition and thickness were also studied. The life-time of the electrode is 15 days and the stability of its potential is 0.6 mV/12 h. The electrode was preserved dry because of the better sensitivity, range of linear response and detection limit attained. The determination of nitrates in waters and fertilizers was also attemped with this electrode, using the interpolation and standard-addition methods.

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Nitrationenselektive Doppelmembranelektrode aufgrund von Aliquat-Nitrat in Paraffin