Macromolecule mediated bioinspired silica synthesis using a diol-modified silane precursor

Following recent investigations on the role of synthetic and biological macromolecules in silicification and biosilicification, we report here the bioinspired synthesis of silica structures under ambient conditions and neutral pH mediated by two synthetic macromolecules. In this research ethylene glycol modified silane (EGMS) was used as the silica precursor. The macromolecules used were either poly(allylamine hydrochloride) (PAH) or poly-l-lysine (PLL), both being cationically charged at neutral pH in an aqueous medium. Mild conditions that constitute the bioinspired or biomimetic synthesis were used to compare the behaviour of the EGMS to other silica precursors. The products were characterised by Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and Fourier Transform Infrared Spectroscopy (FTIR). The formation of well-defined spherical silica particles (for both PAH and PLL) and hexagons (for PLL only), was shown by electron microscopy. In addition, it was also found that these macromolecules were incorporated into the silica products, thus fulfilling the dual role of catalysts and structure directing agents in a similar fashion to that described in the literature for the formation of (bio)silica, as facilitated by (bio)macromolecules.This paper is dedicated to Mike Owen on occasion of his winning the DeBruyn medal, the first silicon chemist to do so.     

Determination of selected polycyclic aromatic hydrocarbons and oxygenated polycyclic aromatic hydrocarbons in aerosol samples by high-performance liquid chromatography and liquid chromatography–tandem mass spectrometry

Fine and ultrafine particles are probably responsible for numerous health effects, but it is still unclear whether and to what extent the particle itself or organic compounds adsorbed or condensed on the particle are responsible for the effects observed. One important class of particle-bound substances are the polycyclic aromatic hydrocarbons (PAH) and their oxygenated derivatives. To improve the tools used for chemical characterization of particulate matter analytical methods for the determination of PAH and oxygenated PAH in aerosol samples of different origin have been developed and optimized. PAH on high-volume filters and on soot aerosols were analyzed by using accelerated solvent extraction for extraction and high-performance liquid chromatography with fluorescence detection for separation and quantification. Total PAH concentrations were in the range 0.3–9.3 ng m^–3. For analysis of selected oxygenated PAH on high-volume filters a liquid chromatography–tandem mass spectrometric method was developed and optimized. Preliminary investigations showed that oxygenated PAH at pg m^–3 concentrations can be determined.     

An overview of lipid membrane supported by colloidal particles

In recent years, original hybrid assemblies composed of a particle core surrounded by a lipid shell emerged as promising entities for various biotechnological applications. Their broadened bio-potentialities, ranging from model membrane systems or biomolecule screening supports, to substance delivery reservoirs or therapeutic vectors, are furthered by their versatility of composition due to the possible wide variation in the particle nature and size, as well as in the lipid formulation. The synthesis, the characteristics, and the uses of these Lipid/Particle assemblies encountered in the literature so far are reviewed, and classified according to the spherical core size in order to highlight general trends. Moreover, several criteria are particularly discussed: i) the interactions involved between the particles and the lipids, and implicitly the assembly elaboration mechanism, ii) the most suited techniques for an accurate characterization of the entities from structural and physicochemical points of view, and iii) the remarkable properties of the solid-supported lipid membrane obtained.     

A solvent recirculation trapping device for supercritical fluid extraction of polyaromatic hydrocarbons

A new device has been developed for the trapping of volatile pollutants in trapping solvents. The device allows solvent recirculation and cryogenic trapping of evaporated volatiles to minimize the stripping effect and any losses of volatile analytes. Due to solvent recirculation, the trapping solvent column height remains constant during the extraction without any need for replenishment. Also mass transfer conditions are favorable due to the flattened shape of bubbles of CO2 and the longer extraction time. The bubbles have higher interfacial area and they have to pass a three times longer distance in the solvent column. The device produces more concentrated extracts, reduces solvent consumption, and reduces or eliminates its evaporation to the environment. The cryotrapping part reduces losses of volatile analytes and the stripping effect. It also enables single-phase extraction into much smaller solvent volumes. Due to constant and favorable extraction conditions, the precision of the method was also greatly improved (RSDs decreased from 2.2 to 0.8%). As proved by a set of rapid spiked-sample extractions of highly volatile compounds at very high flow rates, the relative standard deviation of the experiments performed in the new device is 3.5 times lower.     

An experimental study of the premixed benzene/oxygen/argon flame with tunable synchrotron photoionization

A comprehensive experimental study of the premixed benzene/oxygen/argon flame at 4.0 kPa with a fuel equivalence ratio (?) of 1.78 has been performed with the tunable synchrotron photoionization and molecular-beam sampling mass spectrometry. Isomers of most observed species in the flame have been unambiguously identified by measurements of the photoionization efficiency spectra. Mole fraction profiles of species up to C₁₆H₁₀ have been measured at the selective photon energies near ionization thresholds, and the flame temperature profile is obtained using Pt/Pt-13%Rh thermocouple. Compared with previous studies on benzene flames by Bittner and Howard, and by Defoeux et al., a number of new species are observed in the present work. These new combustion intermediates should be included in the kinetic models of the growth of polycyclic aromatic hydrocarbons (PAHs) and benzene oxidation. Free radicals detected in the flame include CH₃, C₂H, C₂H₃, C₂H₅, C₃H, C₃H₃, C₃H₅, C₄H, C₄H₃, C₄H₅, C₄H₇, C₅H₃, C₅H₅, C₅H₇, C₆H₅, C₆H₅O, C₇H₇, and C₉H₇. More significantly, isomers of some PAHs have been identified, which should be of importance in understanding the mechanism of soot formation.     

Detection of PAH of molecular weight between 300 and 402 in airborne particulate matter by fused silica capillary GC and GC/MS

Gas chromatography (GC), low-voltage mass spectrometry (LV MS), and gas chromatography/mass spectrometry (GC/MS) have been used for detecting polycyclic aromatic hydrocarbons (PAH) of molecular weight between 300 and 402 in airborne particulate matter. Nearly 200 high molecular PAH separated by fused silica capillary columns could be characterized by their El mass spectra. The lack of reference substances precluded further structure elucidation.     

Factors affecting the reversed-phase liquid chromatographic separation of polycyclic aromatic hydrocarbon isomers

Reversed-phase liquid chromatography (LC) on C₁₈ stationary phases provides excellent selectivity for the separation of polycyclic aromatic hydrocarbons (PAH). Recent studies have shown that several factors affect selectivity for the LC separation of PAH including phase type (monomeric or polymeric), pore diameter and surface area of the silica substrate, and surface density of the C₁₈ ligands. In this paper the separation of eleven PAH isomers of molecular weight 278 is used to further illustrate the effect of stationary phase characteristics and shape of the solute (length-to-breadth ratio, L/B) on retention and selectivity. Only polymeric C₁₈ phases with a high C₁₈ surface coverage provided separation of all eleven isomers and the elution order of these isomers generally followed increasing L/B values. The effect of solute nonplanarity on reversed-phase LC retention was investigated on both monomeric and polymeric phases using a series of planar and nonplanar PAH pairs. For each solute pair, the nonplanar solute eluted earlier than the planar solute, the largest selectivity factors being observed on the C₁₈ phase with the highest percent carbon load. Based on these studies, a model is proposed to describe the retention of PAH on polymeric C₁₈ phases.     

Potential reaction initiation points of polycyclic aromatic hydrocarbons

Reaction initiation points of the 16 priority polycyclic aromatic hydrocarbons (PAHs) have been determined by calculating all the different C-H bond dissociation enthalpy (BDE) values. Six density functional theory methods (B3LYP, B3LYP-D3, B97D3, M06-LD3, M06-2X-D3, and ωB97X-D) in combination with 4 basis sets (6-31G(d), 6-31+G(d,p), 6-311++G(d,p), def2-TZVP) have been applied and the most feasible combination has been selected. The BDE values and the corresponding bond lengths have been used to determine potential attack points on the structures. The studied molecules have been categorized structurally as well, within which the position of the hydrogen atoms is considered. Results show that most of the hydrogens are in zig-zag positions, and the BDE and bond length values for the 16 priority PAHs are in a range between 342.0 and 485.6 kJ/mol and 1.0817–1.952 Å, respectively. Most of the initiation points are represented by armchair and peak hydrogens. The lowest and highest BDE and shortest and longest bond length values belong to fluorene and acenaphthylene where the hydrogens were aliphatic and in peak position, respectively.     

On-site determination of polynuclear aromatic hydrocarbons in seawater by stir bar sorptive extraction (SBSE) and thermal desorption GC-MS

The identification and quantification of semi-volatile contaminants dissolved in water is currently done in laboratory after a sampling step. This procedure is not satisfactory first because risks of samples contamination and analytes losses remain, in particular when these are present in ultra-trace concentrations, and secondly because procedures are time-consuming. The coupling of the stir bar sorptive extraction (SBSE), a new device of extraction technique, and a new generation of gas chromatography mass spectrometry (GC-MS), the field apparatus EM 640 S from Bruker, could be an answer to the challenge of on-site analysis. This analytical system was used to analyze 24 PAHs, among them 15 EPA priority pollutants. It was shown that this coupling led to encouraging results with LODs around the sub-ppt level for most of the compounds and R.S.D. included between 1 and 48%. The existence of competition phenomena between the various analytes inside the absorbent phase was demonstrated with the release (up to 80%) of light compounds. This result shows the necessity to work on the kinetic domain rather than on the thermodynamic equilibrium that is influenced by nature and concentration of other compounds. The matrix effects were also studied through the comparative analysis of ultrapure water, artificial and natural seawaters spiked with PAHs and the influence of ionic strength and particulate organic matter was investigated.     

Biomonitoring of traffic originated PAHs in the air

This article sets out the results of air quality biomonitoring along a transect bordering on the A32 Turin–Bardonecchia motorway (Italy). The results were obtained using aeroponic sampling units, an innovation insofar as the plants acting as monitor live and grow in these units above ground, assuring that atmospheric pollutants are absorbed only through the leaves. The accumulation of 15 polynuclear aromatic hydrocarbons (PAHs) on the leaves of Brassica oleracea var. Acephala, used as biosampler, was determined on samples taken in the months of February, July and October 2002, in each case after two months' exposure. The results highlight: (i) the influence of the seasons on the accumulation of pollutants, (ii) that phenanthrene, fluoranthene, pyrene and chrysene generally account for more than 80% of total PAHs, (iii) that the data may be considered representative of both volatile and non-volatile compounds. Comparison with other sampling methods are supplied and discussed.