Determination of phenolic compounds in environmental water samples after solid-phase extraction with β-cyclodextrin-bonded silica particles coupled with a novel liquid-phase microextraction followed by gas chromatography-mass spectrometry

A novel approach for the sample pre-treatment and determination of eight phenolic compounds in environmental water samples has been developed by hyphenating solid-phase extraction (SPE) and liquid-phase microextraction (LPME) techniques based on solid organic drop combined with gas chromatography-mass spectrometry detection (GC-MS). After pre-concentration and purification of the sample through column containing 60 mg of β-cyclodextrin-bonded silica particles as stationary phase, under the optimum conditions, LPME technique has been performed on the eluent solution. Under the selected conditions, limit of detection (LOD) of 0.002-0.04 μg/L (S/N=3), limit of quantification (LOQ) of 0.007-0.15 μg/L (S/N=10), pre-concentration factor of 752-3135 and linearity range of 0.01-25 μg/L have been obtained. A reasonable repeatability (RSD≤9.5%, n=5) with satisfactory coefficient of determination has been obtained between 0.9981 and 0.9997. The relative recoveries of the waste, sea, river and well water samples were higher than 79%.     

Inclusion complexes of EMPO derivatives with 2,6-di-O-methyl-beta-cyclodextrin: synthesis, NMR and EPR investigations for enhanced superoxide detection

The free radical trapping properties of eight 5-alkoxycarbonyl-5-methyl-1-pyrroline N-oxide (EMPO) type nitrones and those of 5,5-dimethyl-1-pyrroline N-oxide (DMPO) were evaluated for trapping of superoxide anion radicals in the presence of 2,6-di-O-methyl-beta-cyclodextrin (DM-beta-CD). (1)H-NMR titrations were performed to determine both stoichiometries and binding constants for the diamagnetic nitrone-DM-beta-CD equilibria. EPR titrations were then performed and analyzed using a two-dimensional EPR simulation program affording 1 : 1 and 1 : 2 stoichiometries for the nitroxide spin adducts with DM-beta-CD and the associated binding constants after spin trapping. The nitroxide spin adducts associate more strongly with DM-beta-CD than the nitrones. The ability of the nitrones to trap superoxide, the enhancement of the EPR signal intensity and the supramolecular protection by DM-beta-CD against sodium L-ascorbate reduction were evaluated.     

Novel neon-hydrate of cubic ice structure

The stability of ice I cubic (ice I_c) whose voids are occupied by neon particles is investigated using a hybrid type of isobaric grand-canonical Monte Carlo simulation. We show that the resulting neon hydrate is stable under high pressure and temperature where ice I_c alone is unstable, suggesting the existence of a novel neon hydrate of ice I_c. We also show through chemical potential calculation that the neon hydrate of the ice I_c structure is more favorable than the neon hydrate of the ice II structure, whose existence was proven from experiment under high pressure condition.     

ESR-spin trapping in the presence of cyclodextrins. Detection of PBN-superoxide spin adduct

In phosphate buffer solution the half-life of the PBN-superoxide spin adduct is very short. However, as a result of the formation of inclusion complexes, its ESR signal was easily detected for up to 25 min when the trapping of superoxide anion with PBN was carried out in the presence of different cyclodextrins. Furthermore, the formation of these inclusion complexes results in a significant protection of the PBN-superoxide adduct against l-ascorbate monoanion reduction.     

Non‐smooth atomic decomposition for generalized Orlicz‐Morrey spaces

In the present paper, we consider the non‐smooth atomic decomposition of generalized Orlicz‐Morrey spaces. The result will be sharper than the existing results. As an application, we consider the boundedness of the bilinear operator, which is called the Olsen inequality nowadays. To obtain a sharp norm estimate, we first investigate their predual space, which is even new, and we make full advantage of the vector‐valued inequality for the Hardy‐Littlewood maximal operator.     

In situ TEM study of reversible and irreversible electroforming in Pt/Ti:NiO/Pt heterostructures

Experimental verification of the microscopic origin of resistance switching in metal/oxide/metal heterostructures is needed for applications in non‐volatile memory and neuromorphic computing. Numerous reports suggest that resistance switching in NiO is caused by local reduction of the oxide layer into nanoscale conducting filaments, but few reports have shown experimental evidence correlating electroforming with site‐specific changes in composition. We have investigated the mechanisms of reversible and irreversible electroforming in 250–500 nm wide pillars patterned from a single Ta/Ti/Pt/Ti‐doped NiO/Pt/Ta heterostructure and have shown that these can coexist within a single sample. We performed in situ transmission electron microscopy (TEM) electroform‐ ing and switching on each pillar to correlate the local electron transport behavior with microstructure and composition in each pillar. DFT calculations fitted to electron energy loss spectroscopy data showed that the Ti‐doped NiO layer is partially reduced after reversible electroforming, with the formation of oxygen vacancies ordered into lines in the 〈110〉 direction. However, under the same probing conditions, adjacent pillars show irreversible electroforming caused by electromigration of metallic Ta to form a single bridge across the oxide layer. We propose that the different electroforming behaviors are related to microstructural variations across the sample and may lead to switching variability. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Synthesis and Spin‐Trapping Properties of a Trifluoromethyl Analogue of DMPO: 5‐Methyl‐5‐trifluoromethyl‐1‐pyrroline N‐Oxide (5‐TFDMPO)

The 5‐diethoxyphosphonyl‐5‐methyl‐1‐pyrroline N‐oxide superoxide spin adduct (DEPMPO?OOH) is much more persistent (about 15 times) than the 5,5‐dimethyl‐1‐pyrroline N‐oxide superoxide spin adduct (DMPO?OOH). The diethoxyphosphonyl group is bulkier than the methyl group and its electron‐withdrawing effect is much stronger. These two factors could play a role in explaining the different half‐lifetimes of DMPO?OOH and DEPMPO?OOH. The trifluoromethyl and the diethoxyphosphonyl groups show similar electron‐withdrawing effects but have different sizes. We have thus synthesized and studied 5‐methyl‐5‐trifluoromethyl‐1‐pyrroline N‐oxide (5‐TFDMPO), a new trifluoromethyl analogue of DMPO, to compare its spin‐trapping performance with those of DMPO and DEPMPO. 5‐TFDMPO was prepared in a five‐step sequence by means of the Zn/AcOH reductive cyclization of 5,5,5‐trifluoro‐4‐methyl‐4‐nitropentanal, and the geometry of the molecule was estimated by using DFT calculations. The spin‐trapping properties were investigated both in toluene and in aqueous buffer solutions for oxygen‐, sulfur‐, and carbon‐centered radicals. All the spin adducts exhibit slightly different fluorine hyperfine coupling constants, thereby suggesting a hindered rotation of the trifluoromethyl group, which was confirmed by variable‐temperature EPR studies and DFT calculations. In phosphate buffer at pH 7.4, the half‐life of 5‐TFDMPO?OOH is about three times shorter than for DEPMPO?OOH and five times longer than for DMPO?OOH. Our results suggest that the stabilization of the superoxide adducts comes from a delicate balance between steric, electronic, and hydrogen‐bonding effects that involve the β group, the hydroperoxyl moiety, and the nitroxide.     

The Moduli Space of n+1 Points in Complex Hyperbolic n-Space

The structure of the space of orbits of PU(n, 1) acting on (n+1)-tuples of points in complex hyperbolic space is characterized in terms of side lengths and angular invariants. The more general situation in which some of the points lie on the boundary of complex hyperbolic space is described in terms of other basic invariants.     

DEPMPO: an efficient tool for the coupled ESR-spin trapping of alkylperoxyl radicals in water

Peroxidation is an important process both in chemistry and biology, and peroxyl radicals play a crucial role in various pathological situations involving lipid and protein peroxidation. A few secondary and tertiary peroxyl radicals can be detected directly by Electron Spin Resonance (ESR). However, primary and secondary alkylperoxyl radicals have extremely short lifetimes and their direct observation is impossible in biological samples. DMPO has been used to trap alkylperoxyl radicals generated in biological systems and the characterization of DMPO-alkylperoxyl spin adducts has been claimed by different authors. However, it was then clearly shown that all the assignments made previously to DMPO-OOR adducts were actually due to DMPO-OR adducts. We have investigated the potential of DEPMPO to characterize the formation of alkylperoxyl radicals in biological milieu. Various DEPMPO-OOR (R = Me, primary or secondary alkyl group) spin adducts were unambiguously characterized and the formation of DEPMPO-OOCH(3) was clearly established during the reaction of tert-butylhydroperoxide with chloroperoxidase and cytochrome c.