Water‐Assisted Nitrile Oxide Cycloadditions: Synthesis of Isoxazoles and Stereoselective Syntheses of Isoxazolines and 1,2,4‐Oxadiazoles

Conventional methods generate nitrile oxides from oxime halides in organic solvents under basic conditions. However, the present work revealed that water‐assisted generation of nitrile oxides proceeds under mild acidic conditions (pH 4–5). Cycloadditions of nitrile oxides with alkynes and alkenes easily occurred in water without using catalysts, thus yielding isoxazoles and isoxazolines, respectively, with excellent stereoselectivity toward five‐ and six‐membered cyclic alkenes. A double stereoselective cycloaddition of two units of a nitrile oxide with cyclohexene was also achieved, thus yielding 1,2,4‐oxadiazole derivatives having a unique hybrid isoxazoline‐oxadiazole skeleton. Enantiomerically pure isoxazolines were prepared from monoterpenes with a ring strain. In one case, the isoxazoline with a butterfly‐like structure was simply prepared, and it might be used as a ligand in asymmetric catalysis.     

A comprehensive chromatographic comparison of amphetamine and methylamphetamine extracted from river water using molecular imprinted polymers and without the need for sample derivatization

This work explores the differences between two GCMS instruments for the determination of amphetamine and methylamphetamine extracted from water samples (ultra pure water and river water) without the necessity for derivatization. The instruments contained different generations of gas chromatograph and mass selective detector components and revealed significantly different results when presented with the same samples. The extraction methodology also compared two SPE systems. The extraction efficiency of commercially available molecular imprinted polymers as a sorbent in SPE was compared with commonly used hydrophilic balance sorbent. Molecular imprinted polymers provided excellent recoveries (81 ± 2% and 108 ± 3% at 30 μg L^?1, and 94 ± 2% and 94 ± 2% at 200 μg L^?1 for amphetamine and methylamphetamine, respectively). The best LOD obtained was sufficient for the determination of both drugs extracted from river water (0.029 ± 0.003 and 0.015 ± 0.004 μg L^?1 for amphetamine and methylamphetamine, respectively). These were comparable to literature values obtained through conventional extraction and analysis using LC‐MS/MS but had the advantage of being achieved using an underivatized GCMS method.     

Crystal Structures of β-Cyclodextrin Complexes with Formic Acid and Acetic Acid

β-Cyclodextrin (β–CD)-formic acid (1) andβ-CD–acetic acid (2) inclusion complexes crystallizeas β-CD...0.3HCOOH...7.7H₂O andβ-CD...0.4CH₃COOH...7.7H₂O in themonoclinic space group P2₁ with comparable unit cell constants.Anisotropic refinement of atomic parameters against X-ray diffractiondata with F_o ² > 2σ (F_o ²) (986/8563 and 991/8358)converged at R-factors of 0.051 and 0.054 for 1 and 2,respectively. In both complexes, the β-CD molecularconformation, hydration pattern and crystal packing are similar,but the inclusion geometries of the guest molecules are different.The β-CD macrocycles adopt a ``round'' conformationstabilized by intramolecular, interglucose O3(n)...O2(n + 1)hydrogen bonds and their O6–H groups are systematically hydratedby water molecules. In the asymmetric unit, each complex contains oneβ-CD, 0.3 formic acid (or 0.4 acetic acid), and 7.7 water moleculesthat are distributed over 9 positions. Water sites located in theβ-CD cavity hydrogen bond to the guest molecule. In thecrystal lattice, β-CD molecules are packed in a typical ``herringbone'' fashion. In 1, the formic acid (occupancy 0.3) is entirely included in the β-CD cavity such that its C atom is shifted from the O4-plane center to the β-CD O6-side by 2.90 Å and C=O, C–-O bonds point to this side. In 2, the acetic acid (occupancy 0.4) is completely embedded in the β-CD cavity, in which the carboxylic C atom is displaced from the O4-plane centerto the β-CD O6-side by 0.87 Å; the C=O bond directsto the β-CD O6-side and makes an angle of 15°to the β-CD molecular axis. Furthermore, bothdimethyl-β-CD-acetic acid and β-CD-acetic acidcomplexes form a cage structure, showing that the small guestsenclosed entirely in the cavity either in β-CD or indimethyl-β-CD do not affect the packing of the host macrocycles.     

Effect of the ring size and asymmetry of cyclodextrins on their inclusion ability: a theoretical study

Effect of the ring size and asymmetry upon methylation of cyclodextrins (CDs) on their inclusion ability has been demonstrated for the inclusion complexes of native α-, β-, γ-CDs, dimethylated β-CD (DIMEB) and trimethylated β-CD (TRIMEB) with piperazine (PIZ) by PM3 and ONIOM calculations. In all complexes, PIZ prefers residing mostly in the central CD cavity. The complex stability in the order TRIMEB–PIZ > DIMEB–PIZ > α-CD–PIZ > γ-CD–PIZ > β-CD–PIZ indicates that the CD-ring asymmetry promotes the macrocycle deformation and inclusion ability. Our calculation results suggest that the inclusion complexes of both native and methylated CDs with PIZ in the gas phase are energetically stable, in addition to the β-CD–PIZ inclusion complex that has been evidenced thus far by X-ray crystallographic and spectroscopic analyses. Further calculations in the presence of water and adjacent CD molecules show that the increased intermolecular hydrogen bond interactions enhance the stability of β-CD–PIZ complex.     

Structure and dielectric relaxations of antibacterial sulfonated polystyrene and silver nanocomposites

Structure and dielectric relaxations of antibacterial sulfonated polystyrene (SPS) and silver nanocomposites (SPS/Ag) were investigated via broadband dielectric spectroscopy, Fourier transform infrared spectroscopy, ultraviolet–visible spectroscopy, differential scanning calorimetry, scanning electron microscopy, and wide‐angle X‐ray diffraction. SPS/Ag nanocomposites were prepared from SPS containing 2, 4, and 7 mol% of acid contents, followed by ion exchange and a reduction process. Silver nanoparticles were formed in the structural cavities of SPS films. The single glass transition temperature of the SPS copolymers was observed and increased with increasing acid contents and more enhanced with embedded silver nanoparticles because of the restriction of the polymer chain movement. The particle size of embedded silver nanoparticles was about 10 nm and well dispersed in SPS matrices. Four dielectric relaxations were observed above the glass transition temperature, and they were attributed to the fast segmental relaxation, the slow‐hindered segmental relaxation, relaxations associated with Maxwell–Wagner–Sillars interfacial polarization and electrode polarization. Weak local relaxations were observed due to the motion of sulfonated phenyl groups. Copyright © 2014 John Wiley & Sons, Ltd.     

Dynamically adaptive tree grid modeling for simulation and visualization of rainwater overland flow

Modeling and visualization of a rainwater overland flow is an important tool for a risk assessment, preparation, evacuation planning, and real‐time forecasting of flood warning. The objective of this research is to develop a numerical software to visualize the rainwater overland flow based on a finite volume method for shallow water equations and in combination with the dynamically adaptive tree grid technique and the dynamic domain‐defining method. The obtained simulations for several experiments were tested and compared with results in literature, both theoretical and experimental results. The comparisons with non‐adaptive grids show that the developed algorithm for simulation is very efficient and has a potential for practical usages, in terms of computational times and accuracy. Copyright © 2015 John Wiley & Sons, Ltd.     

Fritless Xterra Particles Encapsulated Within a Poly(butylmethacrylate) Based Monolith for Use in CEC

Fritless columns were fabricated by encapsulating packing material within monolith for capillary electrochromatography. They were applied for separation of 3,4-methylenedioxymethamphetamine and metabolites. The packing material was suspended in polymerisation mixture and then forced into a pre-treated capillary following by polymerisation. This made the preparation much easier, saved time, cost and showed less tendency towards bubble formation with better resolution than with packed column. Using this fritless column, migration time of all analytes increased with buffer concentration and amount of organic component in mobile phase, but decreased on increasing the pH from 3.0 to 4.5 and then increased above pH 4.5.     

Modeling volatility and dependency of agricultural price and production indices of Thailand: Static versus time-varying copulas

Volatility and dependence structure are two main sources of uncertainty in many economic issues, such as exchange rates, future prices and agricultural product prices etc. who fully embody uncertainty among relationship and variation. This paper aims at estimating the dependency between the percentage changes of the agricultural price and agricultural production indices of Thailand and also their conditional volatilities using copula-based GARCH models. The motivation of this paper is twofold. First, the strategic department of agriculture of Thailand would like to have reliable empirical models for the dependency and volatilities for use in policy strategy. Second, this paper provides less restrictive models for dependency and the conditional volatility GARCH. The copula-based multivariate analysis used in this paper nested the traditional multivariate as a special case (Tae-Hwy and Xiangdong, 2009) [13]. Appropriate marginal distributions for both, the percentage changes of the agricultural price and agricultural production indices were selected for their estimation. Static as well as time varying copulas were estimated. The empirical results were found that the suitable margins were skew t distribution and the time varying copula i.e., the time varying rotate Joe copula (270°) was the choice for the policy makers to follow. The one-period ahead forecasted-growth rate of agricultural price index conditional on growth rate of agricultural production index was also provided as an example of forecasting it using the resulted margins and time-varying copula based GARCH model.     

Inclusion complexes of β-cyclodextrin with pyrazinamide and piperazine: Crystallographic and theoretical studies

The inclusion complexes of β-cyclodextrin (β-CD) with pyrazinamide (PYA) and piperazine (PIZ) have been investigated both in the solid phase by single-crystal X-ray diffraction analysis and in the gas phase by semi-empirical PM3 calculation. In the crystalline phase, the disordered PYA and PIZ molecules are entirely embedded in the β-CD cavity. The PYA pyrazine-centre displaces upwards by 1.15(1) Å from the β-CD plane, whereas the PIZ centre shifts downwards by 0.76(1) Å from the β-CD plane. The inclusion scenario changed in the gas phase. Two inclusion geometries of the PYA molecule are comparatively stable with binding energies of ? 22.28 and ? 25.29 kJ mol^? 1: the pyrazine centre shifts upwards by 0.5 Å and downwards by 2.0 Å from the β-CD plane. The PIZ molecule positioning at 2.0 Å below the β-CD plane gives a more stable inclusion complex than does the PYA molecule by 22–25 kJ mol^? 1.

Structural distinction of the β-CD–PYA and β-CD–PIZ inclusion complexes in the solid phase (by X-ray crystallography) and gas phase (by PM3 calculation) is a paradigm of the CD conformational flexibility, the induced-fit mechanism and the dynamics of the inclusion process.