Fabrication of monolithic frits and columns for chip-based multidimensional separation devices

In this work, devices for two-dimensional separations are considered. The device contains a flow distributor, a first-dimension channel, and 17 second-dimension outlets. In the design, all connections between the first-dimension channel, the flow distributor, and the second-dimension outlets were tapered, with a minimal diameter of 20 μm. The use of photo-masking is explored for the fabrication of monolithic frits in all tapered connections. Monolithic frits with optimized permeability and length were successfully fabricated in all 33 tapered channels through light-induced polymerization, photo-masking, and selective exposure. The efficacy of the monolithic frits was demonstrated by creating a packed bed of 15-μm particles, confined within the first-dimension channel. The outlet of the first-dimension channel was successfully connected to a mass spectrometer. Effective flow confinement was demonstrated with a reversed-phase separation of a mixture of five standard peptides.     

Time‐Dependent Surface Plasmon Resonance Spectroscopy of Silver Nanoprisms in the Presence of Halide Ions

Herein, we find that the surface plasmon resonance (SPR) spectra of silver nanoprisms in the presence of halide ions change gradually with reaction time. The changes in the spectra correspond to the shape transformation of silver nanoprisms. There are threshold concentrations of halide ions that initiate the shape‐transformation reaction. The threshold concentrations for Cl^?, Br^?, and I^? are about 3×10^?4 M , 1×10^?6 M , and 1.5×10^?6 M , respectively. Any concentrations of the added halide ions above these thresholds can eventually etch the silver nanoprisms into nanodisks if the reaction time is long enough. The higher the concentration of the halide ions, the higher the etching rate will be. The kinetics of the shape transformation of the silver nanoprisms can be studied by recording their time‐dependent surface plasmon resonance (SPR) spectra on a commercial UV/Vis–NIR spectrometer. The peak positions of in‐plane dipole SPR bands of silver colloids in the presence of chloride and bromide ions can be fitted very well with the biexponential functions. We propose that the fast components of the biexponential behaviors should correlate to the truncating effect on the corners of silver nanoprisms, and the slow component should correlate to the redeposition of the truncated residues onto the basal plane of the nanoplates.     

Some reducible Specht modules for Iwahori–Hecke algebras of type A with q=−1

The reducibility of the Specht modules for the Iwahori–Hecke algebras in type A is still open in the case where the defining parameter q equals ?1. We prove the reducibility of a large class of Specht modules for these algebras.     

An inverse vibration problem in estimating the spatial and temporal-dependent external forces for cutting tools

An inverse forced vibration problem, based on the conjugate gradient method (CGM), (or the iterative regularization method), is examined in this study to estimate the unknown spatial and temporal-dependent external forces for the cutting tools by utilizing the simulated beam displacement measurements. The tool is represented by an Euler–Bernoulli beam. The accuracy of the inverse analysis is examined by using the simulated exact and inexact displacement measurements. The numerical experiments are performed to test the validity of the present algorithm by using different types of external forces, sensor arrangements and measurement errors. Results show that excellent estimations on the external forces can be obtained with any arbitrary initial guesses.     

The Effects of Microenvironment Polarity and Dendritic Branching of Aliphatic Hydrocarbon Dendrons on the Self‐Assembly of 2‐Ureido‐4‐pyrimidinones

Two series of aliphatic hydrocarbon‐based G1–G3 dendritic 2‐ureido‐4‐pyrimidinones (UPy) ( S‐Gn )₂ and ( L‐Gn )₂, differing from one another by the distance between the branching juncture to the urea end, were prepared and characterized. These hydrocarbon dendrons were also appended to a p‐aminonitrobenzene solvatochromic chromophore in order to probe their microenvironment polarity. While positive solvatochromism was observed which indicated the chromophore was solvent accessible, there was no significant difference between the microenvironment polarities on going from the G1 to the G3 dendrons. The self‐assembling behavior and tautomeric preference of the dendritic UPy derviatives were examined by ¹H NMR spectroscopy. The dimerization constants (K_dim*) of the DDAA tautomers were unchanged at 10⁷ M ^?1 in CDCl₃ at both 25 and 50 °C, which were comparable to those of UPy compounds bearing other nonpolar substitutents. Furthermore, the lower limits on the K′_dim* of the DADA tautomeric forms of the ( S‐Gn )₂ and ( L‐Gn )₂ series were determined to be 10⁶ and 10⁵ M ^?1 in CDCl₃, respectively. It was found that a closer proximity of the dendron branching juncture to the UPy unit could lead to a destabilization effect on the dimeric states. Hence, the ( L‐Gn )₂ dimers are more stable than those of ( S‐Gn )₂ in the DDAA form, but the latter are more stable than the former in the tautomeric DADA state. This study showed that both the highly nonpolar microenvironment and the proximity of the dendritic branching juncture to the UPy motif could alter the strength and profile of the hydrogen bond‐mediated self‐assembling process.     

Homoleptic Platinum(II) and Palladium(II) Organothiolates and Phenylselenolates: Solvothermal Synthesis,Structural Determination,Optical Properties,and Single‐Source Precursors for PdSe and PdS Nanocrystals

Homoleptic d⁸‐metal organothiolates and phenylselenolates [M(EC₆H₅)₂]_∞ (E=S, M=Pt 1 , M=Pd 2 , M=Ni 5 ; E=Se, M=Pt 3 , M=Pd 4 ) were prepared as crystalline solids under solvothermal conditions. Their structures were solved using powder X‐ray diffraction data. In each case, the EC₆H₅ (E=S, Se) ligand binds to two metal ions (M=Pt, Pd, and Ni) to form chain‐like structures with planar (in 1 ) or zig‐zag (in 2 , 3 , 4 , 5 ) conformations. The [M(SR)₂]_∞ complexes (M=Pt, R=4‐tert‐butylphenyl 6 ; R=2‐naphthyl 8 ; R=4‐nitrophenyl 10 and M=Pd, R=4‐tert‐butylphenyl 7 ; R=2‐naphthyl 9 ; R=4‐nitrophenyl 11 ) were prepared under similar solvothermal conditions. Based on the XPS binding energies and elemental analyses, complexes 6 , 7 , 8 , 9 , 10 , 11 have the same [M(SR)₂]_∞ formulation as 1 and 2 . The cyclic complex [Pd₆(SCH₃)₁₂] 12 was prepared as a crystalline solid by solvothermal annealing treatment of the amorphous precipitate. A chain‐like polymer structure is proposed for both [Pd(SC₁₂H₂₅)₂]_∞ 13 and [Pd(SC₁₆H₃₃)₂]_∞ 14 ; these polymeric chains self‐assemble to give layer‐like structures. Solid‐state diffuse reflectance spectra reveal that the optical band gap E_g (eV) of complexes 1 , 6 , 8 , 10 and of 2 , 7 , 9 , 11 are in the range of 2.10–3.00 eV and 2.10–2.63 eV, respectively, and 5 has the lowest E_g value (1.72 eV). Heating solid samples of 4 and 13 under solvothermal conditions afforded phase‐pure Pd₁₇Se₁₅ and PdS nanocrystals, respectively. Field‐effect transistors fabricated with a drop‐cast thin film made from Pd₁₇Se₁₅ nanocrystals prior treated with an ethanolic solution of 1‐hexadecanethiol displayed ambipolar charge transporting properties with hole and electron mobility being 7×10^?2 cm² V^?1 s^?1 and 6×10^?2 cm² V^?1 s^?1, respectively.     

Determination and on-line clean-up of (fluoro)quinolones in bovine milk using column-switching liquid chromatography fluorescence detection

A simple, cost-effective, and high throughput method using on-line column-switching liquid chromatography fluorescence detection was developed and validated for analysing five (fluoro)quinolones (FQs)--enrofloxacin (ENRO), ciprofloxacin (CIPR), sarafloxacin (SARA), oxolinic acid (OXOL), and flumequine (FLUM) in bovine milk. Norfloxacin (NORF) and nalixidic acid (NALI) were used as internal standards. After simple deproteination of milk sample with 5% (w/v) metaphosphoric acid, the supernatant was subject to on-line column clean-up and direct analysis by LC-FLD. The extraction cartridge was prepared in-house by slurry packing with hydrophilic-lipophilic polymer sorbent. The accuracy of measurement for each (fluoro)quinolone at different maximum residue limits (MRL) was 101-103% (ENRO), 92.8-97.4% (CIPR), 89.8-92.8% (SARA), 116-121% (OXOL), and 81.3-85.5% (FLUM), whilst the precision was 2.9-6.1% (ENRO), 2.5-5.1% (CIPR), 2.3-5.0% (SARA), 3.1-5.9% (OXOL), and 5.6-6.5% (FLUM). The decision limits, detection capabilities, specificity and analytes stability during storage were also investigated.