Characterizing the impact of thermal gels on isotachophoresis in microfluidic devices

Thermally reversible Pluronic gels have been employed as separation matrices in microfluidic devices in the analysis of biological macromolecules. The phase of these gels can be tuned between liquid and solid states using temperature to vary fluidic resistance and alter peak resolution. Although separations in thermal gels have been characterized, their effect on isotachophoresis has not. This study used fluorescein as a model analyte to evaluate isotachophoretic preconcentration as a function of thermal polymer concentration and temperature. Results demonstrated that increasing polymer concentration in microfluidic channels increased the apparent analyte concentration. A critical minimum of 10% (w/v) Pluronic was required to achieve efficient preconcentration with maximum focusing occurring in 20 and 25% polymer gels. Temperature of the thermal gel also impacted analyte focusing. Most efficient focusing was achieved at 25°C with diminishing analyte accumulation at higher and lower temperatures. Under optimal conditions, isotachophoretic preconcentration increased an additional threefold simply by including thermal gels in the system. This approach can be readily implemented in other applications to increase detection sensitivity and measure low-concentration analytes within simple microfluidic devices.     

CHR‐Insertion (RH,CH3) into Cyclohexyl‐Substituted Silsesquioxanes: Reactivity and Decomposition Studies

Amorphous silica plays an important role in heterogeneous catalysis as a support and is frequently presumed to be “inert”. The structure of the supported catalyst is key to understanding the stability and reactivity of catalytic systems. To provide vital insights into the surface reactivity of silica, Polyhedral oligomeric silsesquioxanes (POSSs) can act as realistic homogeneous molecular models for silica surfaces. Here, we report novel reactivities associated with the silica surface, derived from our insights obtained by means of such model systems with potentially significant implications in catalysis when employing silica‐supported catalysts. In this work, the gas‐phase reactivities of two cyclohexyl‐substituted POSSs, namely the completely condensed triganol prism [Si₆cy₆O₉] (a6b0), and the incompletely‐condensed partial cube [Si₇cy₇O₉(OH)₃] (a7b3), with cy=c‐C₆H₁₁, were studied by using atmospheric pressure chemical ionisation (APCI) and collision‐induced decomposition (CID) spectroscopies. Silsesquioxane a6b0, containing three‐membered rings, was found to be much more reactive, undergoing novel CH₂‐insertion on reaction with gas phase molecules—a reaction not observed for a7b3, containing only four‐membered rings. Both silsesquioxanes displayed the ability to trap ammonia formed in situ within the mass spectrometer from N₂ in the instrument. This work also demonstrates the applicability of APCI and the role of CID in elucidating reactive POSS structures, highlighting novel gas‐phase reactivities of POSS.     

Pulse-Splitting for Some Reaction-Diffusion Systems in One-Space Dimension

Pulse-splitting, or self-replication, behavior is studied for some two-component singularly perturbed reaction-diffusion systems on a one-dimensional spatial domain. For the Gierer-Meinhardt model in the weak interaction regime, characterized by asymptotically small activator and inhibitor diffusivities, a numerical approach is used to verify the key bifurcation and spectral conditions of Ei et al. [Japan. J. Indust. Appl. Math., 18, (2001)] that are believed to be essential for the occurrence of pulse-splitting in a reaction-diffusion system. The pulse-splitting that is observed here is edge-splitting, where only the spikes that are closest to the boundary are able to replicate. For the Gray–Scott model, it is shown numerically that there are two types of pulse-splitting behavior depending on the parameter regime: edge-splitting in the weak interaction regime, and a simultaneous splitting in the semi-strong interaction regime. For the semi-strong spike interaction regime, where only one of the solution components is localized, we construct several model reaction-diffusion systems where all of the pulse-splitting conditions of Ei et al. can be verified analytically, yet no pulse-splitting is observed. These examples suggest that an extra condition, referred to here as the multi-bump transition condition , is also required for pulse-splitting behavior. This condition is in fact satisfied by the Gierer–Meinhardt and Gray–Scott systems in their pulse-splitting parameter regimes.     

Untersuchung von Tintenschriftspuren

Ohne Zusammenfassung     

The Nonexistence of a [207,4,165] Code over GF(5)

A divisibility theorem for codes meetingthe Griesmer bound is used to establish that there is no [207, 4, 165]code over GF(5).     

Synthesis of chiral chelating N-heterocyclic carbene complexes of ruthenium

The first 9-membered chiral chelating bidentate imidazol-2-ylidene ruthenium (II) benzylidene complexes based on a cyclopentane backbone were synthesised and characterised via NMR and HRMS.     

Accelerated imidization reactions using microwave radiation

Microwave radiation has been clearly shown to result in enhancement of the rate of reaction for an imidization reaction. Analysis of the kinetic parameters showed that the apparent activation energy for the reaction was reduced from 105 to 55 kJ/mol, under the conditions of this experiment. The mechanism which has been proposed to explain this enhancement is based on the concept of a nonuniform temperature on a molecular scale, rather than a true reduction in the activation energy. © 1992 John Wiley & Sons, Inc.