PIV space-time resolution of flow behind blast waves

An ultra-high speed, time-resolved particle image velocimetry (PIV) system is developed to measure velocity fields created by explosive detonators. When initiated into a gas, the detonators generate blast waves that propagate outwards from the origin of initiation at supersonic speeds. The PIV system consists of a custom eight-pulse Nd:YAG laser system and an ultra-high speed camera system comprising four dual-frame CCD cameras optically combined to share a single optic axis. The system is capable of sampling the flow field four times at up to 333 MHz or eight times at up to 8 MHz. System development is discussed, and preliminary application to the complex flow behind the blast wave from an exploding bridge wire detonator is demonstrated.     

Ring conformations and intermolecular interactions in two fused dibenzoazocines

5‐Acetyl‐2‐chloro‐8,11‐dimethyl‐5,6,11,12‐tetrahydrodibenzo[b,f]azocine, C₁₉H₂₀ClNO, (I), crystallizes as a single fully ordered isomer, but 14‐acetyl‐8,11‐dimethyl‐7,8,13,14‐tetrahydrobenzo[f]naphtho[1,2‐b]azocine–14‐acetyl‐8,9‐dimethyl‐7,8,13,14‐tetrahydrobenzo[f]naphtho[1,2‐b]azocine (74/26), C₂₃H₂₃NO, (II), exhibits threefold whole‐molecule disorder involving both configurational and structural isomers. In (I) and in the predominant form of (II), the azocine rings adopt very similar conformations, forming boat‐shaped rings having approximate twofold rotational symmetry. There are no direction‐specific intermolecular interactions in the crystal structure of (I), but the molecules of (II) are weakly linked into chains by an aromatic π–π stacking interaction. The compounds were made under green conditions using an acid‐catalysed cyclization process having very high atom utilization.     

Characterization of dielectric barrier electrospray ionization for mass spectrometric detection

A novel electrospray interface is presented which induces an electric field by dielectric polarization through a non-conductive barrier. Therefore, a square-wave high-voltage signal is applied. This technique allows mass spectrometric measurements in the positive as well as in the negative mass spectrometry mode without changing the polarity of the potential applied, and it decreases the risk of undesired discharges, induced by high electric currents. The applicability of this technique is demonstrated by mass spectrometric determination of reserpine.     

Microfluidic multi-analyte gradient generator

A microfluidic device was developed to produce temporal concentration gradients of multiple analytes. Four on-chip pumps delivered pulses of three analytes and buffer to a 14-cm channel where the pulses were mixed to homogeneity. The final concentration of each analyte was dependent on the temporal density of the pulses from each pump. The concentration of each analyte was varied by changing the number of pump cycles from each reservoir while maintaining the total number of pump cycles per unit time to ensure a constant total flow rate in the device. To gauge the independent nature of each pump, sinusoidal waves of fluorescein concentration were produced from each pump with independent frequencies and amplitudes. The resulting fluorescence intensity was compared with a theoretical summation of the waves and the experimental data matched the theoretical waves within 1%, indicating that the pumps were operating independently and outputting the correct frequency and amplitude. The device was used to demonstrate the role of adenosine triphosphate-sensitive K⁺ channels in glucose-stimulated increases in intracellular [Ca²⁺] in islets of Langerhans. Perfusion of single islets of Langerhans with combinations of glucose, diazoxide, and K⁺ resulted in intracellular Ca²⁺ patterns similar to what has been observed using conventional perfusion devices. The system will be useful in other studies with islets of Langerhans, as well as other assays that require the modulation of multiple analytes in time.     

Development and validation of an LC–MS/MS method for the quantification of artificial sweeteners in human matrices

Artificial sweeteners are widely used as substitutes for sugar. The sweeteners are generally considered safe, however their whereabouts during pregnancy and lactation and the effect on child development are poorly explored. There is a need for new tools to measure these substances during pregnancy and lactation. Here, we describe the development and validation of a sensitive liquid chromatography–tandem mass spectrometry method for the simultaneous quantification of acesulfame, cyclamate, saccharin and sucralose in human plasma, umbilical cord blood, amniotic fluid and breast milk. The samples were prepared by protein precipitation and separated on a Luna Omega Polar C₁₈ column (2.1 × 50 mm, 1.6 μm). Electrospray ionization in negative mode and multiple reaction monitoring were used to monitor the ion transitions. The validated concentration ranges were from 1 to 500 ng/ml (10–500 ng/ml for sucralose). Interassay precisions were all ≤15% and the accuracies were within ±15%. Stability, linearity, dilution integrity, carryover and recovery were also examined and satisfied the validation criteria. Finally, this analytical method was successfully applied on spiked samples of plasma, umbilical cord blood, amniotic fluid and breast milk, proving its suitability for use in clinical studies on artificial sweeteners, including during pregnancy and lactation.     

Ferrozine colorimetry and reverse flow injection analysis (rFIA) based method for the determination of total iron in aqueous solutions at nanomolar concentrations

Iron is one of the most microbiologically and chemically important metals in natural waters. The biogeochemical cycling of iron is significantly influenced by the redox cycling of Fe(II) and Fe(III). Because of the unique chemistry of iron, it is often needed to analyze iron at nano-molar concentrations. This article describes a reverse flow injection analysis (rFIA) based method with ferrozine spectrophotometric detection to quantify total iron concentration in stream water at nanomolar concentrations. The rFIA system has a 0.65 nM detection limit and a linear dynamic range up to 1.40 μM for the total iron analysis. The detection limit was achieved using a 1.0 m long liquid waveguide capillary flow cell, 1.50 m long knotted reaction coil, 87.50 μL injection loop and a miniature fiber optics spectrophotometer. The optimized colorimetric reagent has 1.0 mM ferrozine, 0.1 M ascorbic acid, 1.0 mM citric acid and 0.10 M acetate buffer adjusted to pH 4.0. The best sample flow rate is 2.1 mL min^?1 providing a sample throughput of more than 15 samples h^?1. The linear dynamic range of the method can be adjusted by changing the volume of the injection loop. The rFIA manifold was assembled exclusively from commercially available components.     

Diamond electrode facilitated electrosynthesis of water and wastewater treatment oxidants

While diamond electrodes have been commonly used to generate ^?OH to treat a variety of persistent water and wastewater micropollutants, mass transfer limitations and the non-selective, short-lived nature of the ^?OH restrict the degradation to the solution at, or near, the electrode surface. However, diamond electrodes can generate oxidizing species that facilitate micropollutant degradation in the bulk water solution. These include persulfate, sulfate radicals, peroxodiphosphate, ferrate, permanganate, reactive chlorine species, hydrogen peroxide, and ozone, which have been reported during electrochemical treatment of water with diamond electrodes. Although still restricted to specialized applications, recent studies, summarized in this review, have proven the electrogeneration of these additional oxidant species to be effective. They have shown the adaptability and potential of diamond electrode-based water treatment to mitigate the presence of micropollutants in water.     

From Light to Structure: Photo Initiators for Radical Two-Photon Polymerization

Two-photon polymerization (2PP) represents a powerful technique for the fabrication of precise three-dimensional structures on a micro- and nanometer scale for various applications. While many review articles are focusing on the used polymeric materials and their application in 2PP, in this review the class of two-photon photo initiators (2PI) used for radical polymerization is discussed in detail. Because the demand for highly efficient 2PI has increased in the last decades, different approaches in designing new efficient 2PIs occurred. This review summarizes the 2PIs known in literature and discusses their absorption behavior under one- and two-photon absorption (2PA) conditions, their two-photon cross sections (σ_TPA) as well as their efficiency under 2PP conditions. Here, the photo initiators are grouped depending on their chromophore system (D-π-A-π-D, D-π-D, etc.). Their polymerization efficiencies are evaluated by fabrication windows (FW) depending on different laser intensities and writing speeds.     

Advances towards Cell-Specific Gene Transfection: A Small-Molecule Approach Allows Order-of-Magnitude Selectivity

A transfection vector that can home in on tumors is reported. Whereas previous vectors that allow moderately cell selective gene transfection used larger systems, this small-molecule approach paved the way for precise structure-activity relationship optimization. For this, biotin, which mediates cell selectivity, was combined with the potent DNA-binding motif tetralysine-guanidinocarbonypyrrol via a hydrophilic linker, thus enabling SAR-based optimization. The new vector mediated biotin receptor (BR)-selective transfection of cell lines with different BR expression levels. Computer-based analyses of microscopy images revealed a preference of one order of magnitude for the BR-positive cell lines over the BR-negative controls.