An integrated solid-phase extraction system for sub-picomolar detection

A microchip structure etched on a glass substrate for packed column solid-phase extraction (SPE) and capillary electrochromatography (CEC) is described. A 200 microm long, octadecylsilane (ODS) packed column was secured using two different approaches: solvent lock or polymer entrapment. The former method was utilized for SPE while the latter approach was applied for CEC. In SPE, the ODS packed chamber gave a detection limit of 70 fM for a nonpolar BODIPY (493/503) dye when concentrated for 3 min at an electroosmotic flow rate of 4.14 nL/min, compared to 30 pM for this detector without the SPE step. SPE beds showed reproducible, linear calibration curves (R(2) = 0.9989) between 1 and 100 pM BODIPY at fixed preconcentration times. Breakthrough curves for the 330 pL (ODS-packed) bed indicated a capacity for BODIPY dye of 8.1 x 10(-14) mmol, or 0.25 mmol dye per liter of bed. The ODS-chamber could also be used to analyze dilute amino acid and peptide solutions. In the CEC format, two neutral dyes (BODIPY and acridine orange) were baseline-separated in an isocratic run with a theoretical plate count of 84 (420 000 plates/m) and a reduced plate height of about 1. A labeled peptide was also analyzed by CEC, using the acidic eluent (84% acetonitrile, and 26% aqueous trifluoroacetic acid (0.05%)) preferred for peptide separations on ODS-coated silica particles.     

Investigations into the parallel kinetic resolution of 2-phenylpropanoyl chloride using quasi-enantiomeric oxazolidinones

The resolution of 2-phenylpropanoyl chloride using an equimolar combination of quasi-enantiomeric oxazolidinones is discussed. The levels of diastereoselectivity were found to be dependent upon the structural nature of the metallated oxazolidinone, temperature and metal counter-ion.     

Copper-mediated chelation-assisted ortho nitration of (hetero)arenes

A novel copper-mediated chelation-assisted ortho C-H nitration of (hetero)arenes has been developed for the first time, which used dioxygen as terminal oxidant and 1,2,3-TCP as solvent, leading to the synthesis of nitroaromatics with excellent regioselectivity and in good yields. Mechanistic investigations indicate a mechanism involving a four-centered transition state, with simultaneous cleavage of an ortho C-H bond and a N-O bond of the nitrate anion on the 2-arylpyridine-coordinated copper(II) complex.     

Determination of vanillin and related flavor compounds in natural vanilla extracts and vanilla-flavored foods by thin layer chromatography and automated multiple development

Summary Thin layer chromatography on silica gel high performance layers and automated multiple development was used to separate the polar aromatic flavor compounds vanillin, ethyl vanillin, 4-hydroxybenzaldehyde, 4-hydroxybenzoic acid, 4-hydroxybenzyl alcohol, vanillic acid, coumarin, piperonal, anisic acid, and anisaldehyde commonly found in extracts of natural and artificial vanilla flavors. The ratio of 4-hydroxybenzoic acid, 4-hydroxybenzaldehyde and vanillic acid to vanillin in natural vanilla extracts was used to confirm the authenticity of extracts purchased in the United States of America and the United Kingdom. Natural vanilla extracts purchased in Mexico and Puerto Rico were identified as counterfeit products based on changes in the above ratio and the presence of synthetic flavor compounds such as ethyl vanillin and coumarin. It is also demonstrated that the proposed method is suitable for the determination of natural and synthetic vanilla flavors in solvent extracts from food, beverage and confectionery products. The main advantage of thin layer chromatography for the analysis of vanilla extracts and food stuffs flavored with vanilla is its high sample throughput since sample preparation requirements are minimal and multiple samples can be separated simultaneously.     

Investigation of Water-Soluble Binders for LiNi0.5Mn1.5O4-Based Full Cells

Two water-soluble binders of carboxymethyl cellulose (CMC) and sodium alginate (SA) have been studied in comparison with N-methylpyrrolidone-soluble poly(vinylidene difluoride–co-hexafluoropropylene) (PVdF-HFP) to understand their effect on the electrochemical performance of a high-voltage lithium nickel manganese oxide (LNMO) cathode. The electrochemical performance has been investigated in full cells using a Li₄Ti₅O₁₂ (LTO) anode. At room temperature, LNMO cathodes prepared with aqueous binders provided a similar electrochemical performance as those prepared with PVdF-HFP. However, at 55 °C, the full cells containing LNMO with the aqueous binders showed higher cycling stability. The results are supported by intermittent current interruption resistance measurements, wherein the electrodes with SA showed lower resistance. The surface layer formed on the electrodes after cycling has been characterized by X-ray photoelectron spectroscopy. The amount of transition metal dissolutions was comparable for all three cells. However, the amount of hydrogen fluoride (HF) content in the electrolyte cycled at 55 °C is lower in the cell with the SA binder. These results suggest that use of water-soluble binders could provide a practical and more sustainable alternative to PVdF-based binders for the fabrication of LNMO electrodes.     

Non-quantum-confinement optics in (CdS)n clusters

Geometry optimizations and the calculation of properties of (CdS)_n clusters for n = 2–12 are performed using density functional theory (DFT) with generalized gradient approximation. The all-electron basis is used for sulfur atoms while cadmium atoms are treated using relativistic effective core potentials. It is confirmed that the lowest energy state of (CdS)_n has a ring structure for n = 3–5 and a cage geometry for n ? 6. Optical absorption spectra are simulated using the energies and oscillator strengths of the first 20 singlet–singlet transitions computed for each cluster by time-dependent DFT. It is found that the energies of the lowest optical transitions do oscillate around the bulk gap value, which contradicts the concept of quantum confinement. The congender (CdSe)₁₂ and (CdTe)₁₂ clusters are found to show similar optical properties as the (CdS)₁₂ cluster.     

Efficient parallel resolution of an active ester of 2-phenylpropionic acid using quasi-enantiomeric Evans’ oxazolidinones

The parallel kinetic resolution of pentafluorophenyl 2-phenylpropionate using an equimolar combination of quasi-enantiomeric oxazolidinones is discussed. The levels of diastereocontrol were excellent leading to separable quasi-enantiomeric syn-oxazolidinone adducts in good yield.     

Effect-Directed Profiling of Monofloral Honeys from Ethiopia by High-Performance Thin-Layer Chromatography and High-Resolution Mass Spectrometry

Ethiopian honey is used not only as food but also for treatment in traditional medicine. For its valorization, bioactive compounds were analyzed in nine types of monofloral Ethiopian honey. Therefore, a non-target effect-directed profiling was developed via high-performance thin-layer chromatography combined with multi-imaging and planar effect-directed assays. Characteristic bioactivity profiles of the different honeys were determined in terms of antibacterial, free-radical scavenging, and various enzyme inhibitory activities. Honeys from Hypoestes spp. and Leucas abyssinica showed low activity in all assays. In contrast, others from Acacia spp., Becium grandiflorum, Croton macrostachyus, Eucalyptus globulus, Schefflera abyssinica, Vernonia amygdalina, and Coffea arabica showed more intense activity profiles, but these differed depending on the assay. In particular, the radical scavenging activity of Croton macrostachyus and Coffea arabica honeys, the acetylcholinesterase-inhibiting activity of Eucalyptus globulus and Coffea arabica honeys, and the antibacterial activity of Schefflera abyssinica honey are highlighted. Bioactive compounds of interest were further characterized by high-resolution mass spectrometry. Identifying differences in bioactivity between mono-floral honey types affects quality designation and branding. Effect-directed profiling provides new insights that are valuable for food science and nutrition as well as for the market, and contributes to honey differentiation, categorization, and authentication.     

Diffusion and solubility of some interstitial impurities in deformed metals

Summary The problem of impurity diffusion accompanying segregation phase nucleation on dislocations has been studied using the approximation of the local equilibrium with respect to the impurity distribution between the volume solution and dislocation regions. It has been shown that the known experimental data on diffusion and solubility of some interstitial impurities in cold-worked b.c.c. and f.c.c. metals and alloys can be described in the framework of the dislocation trap model. The characteristics of the impurity segregation regions near dislocations have been obtained from the treatment of the diffusion and solubility data for the systems. On the basis of the crystallographic and thermodynamic considerations the possibility of the existence of such segregation phase regions along dislocations in the systems in question has been shown.