Nucleophilic Aromatic Substitution Between Halogenated Benzene Dopants and Nucleophiles in Atmospheric Pressure Photoionization

In a preceding work with dopant assisted-atmospheric pressure photoionization (DA-APPI), an abundant ion at [M + 77]⁺ was observed in the spectra of pyridine and quinoline with chlorobenzene dopant. This contribution aims to reveal the identity and route of formation of this species, and to systematically investigate structurally related analytes and dopants. Compounds containing N-, O-, and S-lone pairs were investigated with APPI in the presence of fluoro-, chloro-, bromo-, and iodobenzene dopants. Computational calculations on a density functional theory (DFT) level were carried out to study the reaction mechanism for pyridine and the different halobenzenes. The experimental and computational results indicated that the [M + 77]⁺ ion was formed by nucleophilic aromatic ipso-substitution between the halobenzene radical cation and nucleophilic analytes. The reaction was most efficient for N-heteroaromatic compounds, and it was weakened by sterical effects and enhanced by resonance stabilization. The reaction was most efficient with chloro-, bromo-, and iodobenzenes, whereas with fluorobenzene the reaction was scarcely observed. The calculated Gibbs free energies for the reaction between pyridine and the halobenzenes were shown to increase in the order I < Br < Cl < F. The reaction was found endergonic for fluorobenzene due to the strong C–F bonding, and exergonic for the other halobenzenes. For fluoro- and chlorobenzenes the reaction was shown to proceed through an intermediate state corresponding to [M + dopant]⁺, which was highly stable for fluorobenzene. For the bulkier bromine and iodine, this intermediate did not exist, but the halogens were shown to detach already during the approach by the nucleophile.

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In Situ Synchrotron X-ray Diffraction Studies of the Mechanochemical Synthesis of ZnS from its Elements

Mechanochemistry, as a synthesis tool for inorganic materials, became an ever-growing field in material chemistry. The direct energy transfer by collision of the educts with the milling media gives the possibility to design environmental-friendly reactions. Nevertheless, the underlying process of energy transfer and hence the kinetics of mechanosynthesis remain unclear. Herein, we present in situ synchrotron X-ray diffraction studies coupled with pressure measurements performed during the formation of ZnS and the subsequent phase transition (PT) from the hexagonal to the cubic modification. Milling Zn and S₈ results in the sublimation of S₈, observed by a sudden pressure increase. Simultaneously, the hexagonal metastable ZnS-modification (wurtzite) forms. Via detection of the pressure maximum, the exact start of the wurtzite formation can be determined. Immediately after the formation of wurtzite, the structural PT to the thermodynamic stable cubic modification sphalerite takes place. This PT can be described by the Prout-Tompkins equation for autocatalytic reactions, similar to thermally induced PT in sulfur vapor at high temperatures (T>1133 K). The increase in the reactivity of the wurtzite formation is explained by the reaction in sulfur vapor and the induction of defect structures by the collisions with the milling media.     

The CALUX bio-assay: analytical comparison between mouse hepatoma cell lines with a low (H1L6.1c3) and high (H1L7.5c1) number of dioxin response elements

Dioxins, furans and polychlorinated biphenyls are contaminants of high concern and as such, sensitive tools are needed to detect these persistent organic compounds in a variety of matrices. Due to the large amount of samples that need to be investigated for example for food and feed control, the CALUX bioassay (H1L6.1 clone) was developed allowing rapid and cost-efficient analysis of biological and environmental samples. Recently, a new and more sensitive clone (H1L7.5) was constructed as the third generation CALUX bioassay. This new cell line was subject of an amplification of dioxin response elements (DREs), allowing lower concentrations of target compound to be analyzed. A comparison is made between the previous, well-defined H1L6.1c3 cell line and the new H1L7.5c1 cell line: it appears that the bioassay making use of the higher number of DREs is more stable and robust, shows better repeatability and reproducibility and is; on average, 3 times more sensitive.     

Possibilities and pitfalls in analyzing (upgraded) pyrolysis oil by size exclusion chromatography (SEC)

The applicability of size exclusion chromatography (SEC) to analyze (upgraded) pyrolysis oil samples has been studied using model compounds, pyrolysis oils and hydrodeoxygenated pyrolysis oils. The assumptions needed for the conversion of the chromatogram to the M_w-distribution were validated. It was shown that the conversion of elution volume to molecular weight (based on polystyrene calibration curves) can introduce substantial errors in the prediction of the molecular weight. The conversion of RID response to W(log M) (as plotted on the y-axis of the M_w-distribution) is based on the assumption of a compound independent RID response factor and linear response to concentration. While the latter was shown to be true within the concentration range studied, the former was not true: the RID response factor depends on the type of (upgraded) pyrolysis oil. It was shown that within a single pyrolysis oil sample, the RID response for the low molecular weight fraction was a factor 3 lower than the high molecular weight fraction. Furthermore long term column fouling can influence SEC results that cannot be corrected with regular polystyrene recalibrations.Based on the results we recommend SEC not to be used as a quantitative method for characterization (upgraded) pyrolysis oil samples, but as a tool to compare (upgraded) pyrolysis oil samples, preferably prepared using incremental operating conditions and expected to have similar molecular composition. This work has further shown that (i) the ∫UVDdv/∫RIDdv ratio can be used as an indication of the sum of the relative aromaticity and conjugated double bond content for (upgraded) pyrolysis oil, and (ii) the negative peak area appearing in the low molecular weight part of the chromatogram can be used to estimate the water content of (upgraded) oil samples.     

Determination of electron density and energy influx in a hollow cathode glow discharge used for powder modification

The electron density and energy influx in an argon hollow cathode glow discharge were determined to obtain adequate parameters for subsequent surface modification of low density polyethylene (LDPE) powder to change the wettability. The electron density was studied by Langmuir probe measurement in dependence on process gas pressure and hollow cathode material. Besides the determination of the rate of increasing electron density with input power an optimal experimental pressure was determined. The energy influx was studied by thermal probe measurements in dependence on process gas pressure, bias voltage, axial position and hollow cathode material. Inside the hollow cathode the energy influx is nearly constant along the whole cathode length. With increasing pressure the energy influx decreased. At biased thermal probe the energy influx was observed to decrease up to the floating potential and beyond it increases with increasing voltage. Using different hollow cathode materials the electron density as well as the energy influx reach higher values for aluminum than for copper and stainless steel.     

Bottom‐Up Assembly of DNA–Silica Nanocomposites into Micrometer‐Sized Hollow Spheres

Although DNA nanotechnology has developed into a highly innovative and lively field of research at the interface between chemistry, materials science, and biotechnology, there is still a great need for methodological approaches for bridging the size regime of DNA nanostructures with that of micrometer‐ and millimeter‐sized units for practical applications. We report on novel hierarchically structured composite materials from silica nanoparticles and DNA polymers that can be obtained by self‐assembly through the clamped hybridization chain reaction. The nanocomposite materials can be assembled into thin layers within microfluidically generated water‐in‐oil droplets to produce mechanically stabilized hollow spheres with uniform size distributions at high throughput rates. The fact that cells can be encapsulated in these microcontainers suggests that our concept not only contributes to the further development of supramolecular bottom‐up manufacturing, but can also be exploited for applications in the life sciences.     

Micro‐Disperse Particles in Plasmas: From Disturbing Side Effects to New Applications

The research effort in the area of dusty plasmas initially aimed at avoiding particle formation and controlling the contamination level in industrial reactors. Nowadays, dusty plasmas have grown into a vast field and new applications of plasma‐processed dust particles are emerging. There is demand for particles with special properties, and for particle‐seeded composite materials. Low‐pressure plasmas offer a unique possibility of confinement, control and fine tailoring of particle properties. The role of plasma technology in treatment and surface modification of powder grains is reviewed and illustrated with examples. The interaction between plasma and injected micro‐disperse powder particles can also be used as a diagnostic tool for the study of plasma surface processes.     

180° -turns in integrated optics

Integrated optic devices, such as directional couplers, typically have a length to width ratio of 1:1000. Therefore economical use of quadratic substrate areas requires 180° wave guide turns to cover the whole substrate with a complex circuit in a zick-zack manner. For 180° -turns only curved guides have been considered. Radii of > 1 cm are necessary to avoid loss, and therefore are useless. A new concept for 180° -turns is proposed consisting of a halved 3 stage Δβ-reversal coupler with mirrors at one end. It is demonstrated that these 180° -turns may be fabricated providing high efficiency.     

Correlation of solute retention in gas chromatography with properties of the anion for tetra-n-butylammonium salts

Variations in the molar retention volume of organic solutes on thirteen tetra-n-butyl-ammonium salts with a common liquid temperature range are correlated with the properties of the anion. The anions studied include the chloride, bromide, nitrate, nitrite, methanesulfonate, trifluoromethanesulfonate, ethanesulfonate, 4-toluenesulfonate, sulfamate, thiocyanate, picrate, pentacyanopropenide, and tetra-n-butylborate. The high melting points and poor thermal stabilities of camphorsulfonate, dihydrogenphosphate, hydrogensulfate, and perrhenate precluded their use. The properties of the anions have only smallinfluences on the magnitudes of dispersive, orientative, and proton-donor interactions with the test solutes. Orientative interactions are strong for polar solutes but vary little with anion structure. There was no correlation between the dipole moment of the tetra-n-butylammonium salts and the retention of polar solutes. The structures of the anion do, however, have large influences on the retention of proton-donor solutes. for these solutes, a good correlation was found between molar retention volume and the basicity of the anions, represented by their pK_a values in aqueous solution.     

Engineering and assaying of cytochrome P450 biocatalysts

Cytochrome P450s constitute a highly fascinating superfamily of enzymes which catalyze a broad range of reactions. They are essential for drug metabolism and promise industrial applications in biotechnology and biosensing. The constant search for cytochrome P450 enzymes with enhanced catalytic performances has generated a large body of research. This review will concentrate on two key aspects related to the identification and improvement of cytochrome P450 biocatalysts, namely the engineering and assaying of these enzymes. To this end, recent advances in cytochrome P450 development are reported and commonly used screening methods are surveyed.