Synergistic enantioseparation systems with either cyclodextrins or cyclofructans and L‐alanine Tert butyl ester lactate

The combined use of chiral ionic liquids (CILs) and conventional chiral selectors (CSs) in CE, to establish a synergistic system, has proven to be an effective approach for the separation of enantiomeric pairs. In this study, a new CE method was developed, employing a binary system of a CS, either a cyclodextrin (CD) or a cyclofructan (CF), and a chiral amino acid ester‐based ionic liquid (AAIL), for the chiral separation of four basic, acidic and zwitterionic drug compounds. In particular, the enantioseparation of two anticoagulants, warfarin (WAR) and coumachlor (COU), a non‐opioid analgesic, nefopam (NEF) and a third‐generation antihistamine, fexofenadine (FXD), was examined, by supporting the BGE with a CS and the chiral AAIL L‐alanine tert butyl ester lactate (L‐AlaC₄Lac). Parameters, such as the type of the CS, the concentration of both the CS and L‐AlaC₄Lac, and the BGE pH, were methodically examined in order to optimize the chiral separation of each analyte. It was observed that, in some cases, the addition of the AAIL into the BGE improved both resolution (R_s) and efficiency (N) significantly. In other cases, the synergistic effect enabled baseline separation of analyte enantiomers, at a much lower concentration of the CS. Finally, after optimization of separation conditions, baseline separations (R_s>1.5) of all four analytes were achieved in less than 5 min.     

Double-networks based on interconnected amphiphilic “in–out” star first polymer conetworks prepared by RAFT polymerization

Double-network hydrogels were prepared using well-defined first networks comprising interconnected amphiphilic “in-out” star copolymers synthesized via sequential reversible addition-fragmentation chain transfer (RAFT) polymerization, and second networks based on a photopolymerized mixture of acrylamide and N,N′-methlyenebisacrylamide. All first and double-network hydrogels were characterized in terms of their aqueous degrees of swelling and mechanical properties in compression. The most hydrophobic first and double-network hydrogels exhibited the best mechanical properties, which may be attributed to their low aqueous swelling degrees and good mesoscale organization in water as revealed using small-angle neutron scattering (SANS) which showed that the size of the formed hydrophobic domains could be controlled by the polymer conetwork structure. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2161–2174     

Ion chromatographic method for the simultaneous determination of nitrite and nitrate by post-column indirect fluorescence detection

This short paper highlights the suitability of ion chromatography with post-column indirect fluorescence detection to determine simultaneously nitrite and nitrate based on the quenching of tryptophan native fluorescence. The method uses an enhanced fluorescence mobile phase containing tryptophan and detects the suppression of fluorescence of the mobile phase due to the elution of the target ions. The phenomenon of fluorescence quenching of tryptophan is highly induced by the presence of phosphate ions. The quenched fluorescence intensity exhibits concentration dependence in the range 1-25 mg/l and 3-65 mg/l for nitrite and nitrate, respectively. The relative standard deviation for five replicates of a standard solution containing a mixture of 5 mg/l of nitrite and 10 mg/l of nitrate lies around 2.8%. This simple coupling technique results in a relatively sensitive, fast, and accurate method, allowing for both qualitative and quantitative analysis of nitrite and nitrate. The method can easily be implemented to real samples such as foodstuffs, fertilizers and soils and is proven to be precise and accurate when compared with reference methods.     

Analytical separations in open-tubular capillary electrochromatography

This review represents a summary of recent progress in open-tubular capillary electrochromatography (OT-CEC) for chiral and achiral separations. The OT-CEC approach is an alternative to packed-CEC that could eliminate the problems associated with retaining frits and silica particles. In OT-CEC, the stationary phase is immobilized on the inner walls of the capillary. Preparation of the stationary phase is critical for OT-CEC. The preparation methods for capillary columns include (i) adsorption, (ii) covalent bonding and/or cross-linking, (iii) porous layers, (iv) chemical bonding after etching, (v) sol-gel, and (vi) molecular imprinting. Major developments, potential applications, technical difficulties and advantages associated with these wall coatings in OT-CEC are presented. In addition, the coupling of OT-CEC with mass spectrometry (MS) is briefly reviewed. Several applications of this hyphenated technique for analytical separations are also summarized.     

Combined use of β-cyclodextrin and ionic liquid as electrolyte additives in EKC for separation and determination of carob's phenolics—A study of the synergistic effect

In this work, a simple, reliable, and fast capillary electrophoretic method was developed and validated for the simultaneous determination of 12 polyphenolic compounds, the most frequently found in carob's pulp and seeds. The present work deals with the development of a novel dual electrophoretic system based on the combined use of β-CD and ionic liquid (IL) as buffer additives. A baseline separation of the target analytes was achieved in less than 10 min by using a BGE consisting of 35 mM borate along with 15 mM β-CD and 3 mM l -alanine tert butyl ester lactate (l -AlaC₄Lac) IL as buffer additives at pH 9.5, a temperature of 25°C, and an applied voltage of 30 kV. The application of the developed electrophoretic method to real samples enabled the identification and quantification of the main phenolic constituents of both ripe and unripe carob pulp extracts. The results revealed the predominance of gallic acid in both ripe (183.92 μg/g carob pulp) and unripe (205.10 μg/g carob pulp) carob pulp and highlighted the great influence of the ripening stage on carobs polyphenolic composition, with unripe pods being more enriched in polyphenols (total phenolics detected: 912.58 and 283.13 μg/g unripe and ripe carob pulp).     

The search for cobalt single-molecule magnets: A disk-like CoCo6 cluster with a ligand derived from a novel transformation of 2-acetylpyridine

The initial employment of 2-acetylpyridine, (py)(Me)CO, in Co cluster chemistry is reported, and the synthesis, crystal structure, and full magnetic study of [Co₇(OH)₆(L)₆](ClO₄)₃·1.6H₂O (1·1.6H₂O) are described; L⁻ is the anion of 2-(pyridine-2-yl)pentane-2-ol-4-one, (py)(Me)C(CH₂COCH₃)(O)⁻, formed in situ through a crossed-aldol reaction in acetone under strongly basic conditions. The reaction of Co(ClO₄)₂·6H₂O, (py)(Me)CO and NBuⁿ₄OMe (1:1:1.2) in acetone at room temperature under aerobic conditions affords 1·1.6H₂O in 35% yield. The mixed-valent cation possesses a wheel-shaped (or disk-like) structural motif comprising a central octahedral Co^III atom linked to six peripheral distorted octahedral Co^II atoms by six μ₃-ΟΗ⁻ groups; the six Co^II atoms on the rim are held together by six η¹:η¹:η¹:μ₂·L⁻ ligands and the oxygen atoms of the hydroxo groups. Variable-temperature, solid-state dc and ac magnetic susceptibility studies were carried out on 1. The dc magnetic study of 1 shows a decline in the product χ_ΜT with decreasing T. The observation of out-of phase (χ″_Μ) ac susceptibility signals below ∼4 K suggests that the Co^IIICo^II₆ complex may be a single molecule magnet, and this was confirmed by single-crystal magnetization vs. dc field sweeps down to 0.04 K that exhibited hysteresis. The study reveals that each complex cation is a weak single-molecule magnet, but that there are also intermolecular interactions (also confirmed crystallographically) to create a 3D ordered lattice; this still gives some hysteresis at 5 K.     

A new family of nonanuclear lanthanide clusters displaying magnetic and optical properties

The initial employment of 2-(hydroxymethyl)pyridine in 4f metal chemistry has afforded a new family of Ln(III)(9) clusters with a sandglass-like topology and dual physical properties; the Dy(III) member shows single-molecule magnetism behavior, while the Eu(III) analogue exhibits intense red photoluminescence.     

Performance of a Faradaic impedimetric immunosensor for blood group antigen A

The performance is described of a label-free Faradaic impedimetric immunosensor based on immobilized monoclonal IgM antibodies to blood group antigen A (anti–A) for blood typing. Anti–A was directly immobilized onto gold electrodes modified with an amine-reactive self assembled monolayer of dithiobis(succinimidylundecanoate). The alteration of the interfacial features of the electrodes due to different modification or recognition steps was probed by Faradaic impedance spectroscopy and cyclic voltammetry in the presence of a hexacyanoferrate(II)/(III) redox couple. Various optimization studies were undertaken with respect to the construction and potential use of the immunosensors as a diagnostic tool for blood typing.