Low flow rate modifier addition in packed capillary column supercritical fluid chromatography

A new method to accurately deliver small amounts (0.5 to 20 mol%) of modifier into CO₂ was used to study the effects of three different modifiers (methanol, water, and formic acid) in packed capillary column SFC. The method allows the use of different modifiers, with minimal instrument modification. The effects of the different modifiers at different concentrations on retention and peak shape are shown by analyzing a polarity test mixture and a sample of free fatty acids.     

Evaluation of physico-chemical properties of electron beam-irradiated polycarbonate film

In this work, polycarbonate (PC) film samples were irradiated with 10 MeV electrons at different doses ranging from 25 to 250 kGy. Characterization techniques viz. thermogravimetric analysis (TGA), Fourier transform infra-red spectroscopy (FTIR), X-ray diffraction analysis (XRD) and electron paramagnetic resonance (EPR) were exploited to understand the induced changes in the physico-chemical properties of the polymer. An increase in the decomposition temperature with increasing dose was observed, while the crystallinity remained unchanged as a result of the formation of cross-link bond. EPR technique characterized the stability of the free radicals in the irradiated PC. The result showed that cross-linking process occurs at low absorbed doses, whereas polymer degradation happens at higher doses.     

Thermoanalytical behavior of cadmium(II) oxide—alkali persulfate binary systems

The non-isothermal behavior of two binary CdO—persulfate systems has been investigated. The molar ratios and T_i—T_f are established. The temperatures for the α- to β-Na₂SO₄ phase transition, as well as for α- to β- to γ-CdSO₄ of the CdONa₂S₂O₈ system have been fixed. No evidence for the occurrence of the β- to γ-CdSO₄ polymorphic trans-formation has been obtained from the reaction of the CdOK₂S₂O₈ system. This is because of the formation of a CdSO₄/K₂SO₄ eutectic mixture which melts at 653°C, i.e., before the β- to γ-phase change transition, which usually occurs later. No basic cadmium sulfate has been identified. The excess cadmium oxide acts as a p-type semiconductor which accelerates the thermal decomposition of pyrosulfates.     

The effect of pH and ionic strength on the transport of alumina nanofluids in water-saturated porous media

Alumina nanofluids are one of the most useful nanofluids, especially for increasing the thermal conductivity. Due to importance of porous media in the improvement of heat transfer, this study investigates the transport and retention of gamma alumina/water nanofluid in the water-saturated porous media. For this purpose, alumina nanofluids were introduced to the porous media consisting of water-saturated glass beads possessing various pH values (4, 7 and 10) and different ionic strengths (0.001 M of KCl, CaCl₂, AlCl₃, K₂SO₄, CaSO₄, Al₂(SO₄)₃, K₂CO₃ and CaCO₃). Then the break through curve of each experiment was drawn and modeled by combining classical filtration theory with advection–dispersion equation. Single collector efficiency (η₀) and attachment efficiency (α) were calculated by classical filtration theory. Also curve fitting of experiments and modeling was achieved by minimizing the sum of squared residuals, to calculate retardation factor (R) and hydrodynamic dispersion coefficient (D) of each experiment. According to the results, in general, increase in pH and ionic strength will enhance the removal rate coefficient, retardation factor and retention while decreasing the steady-state break through concentration and the hydrodynamic dispersion coefficient. The opposite of this rule was observed and analyzed for aluminum salts. The lowest retention of nanoparticles at 31.04% can be related to their transport in background solution with pH = 4 [α = \(3.87 \times 10^{ - 2}\), K_att = \(3.33 \times 10^{ - 3}\) (min⁻¹), R = 3.93, D = 0.91 (cm² min⁻¹)], and the highest retention in nanoparticle content of 94.29% was observed in background solution containing CaCO₃ [α = \(14.33 \times 10^{ - 2}\), K_att = \(137.82 \times 10^{ - 3}\) (min⁻¹), R = 12.02, D = 0.62 (cm² min⁻¹)]. Therefore, chemistry of water plays an important role in transport and retention parameters. The classical filtration theory and the advection–dispersion model are able to perfectly model and quantify the parameters of the alumina nanofluid transport in saturated porous media.

     

11‐Methyl‐12a‐phenyl‐9a,12a‐di­hydro­phenanthro­[9′,10:5,6][1,4]­dioxino­[2,3‐d]­thia­zole

In the title compound, C₂₄H₁₇NO₂S, the dioxine and thia­zoline rings are distorted from planarity towards a half‐chair and an envelope conformation, respectively. The configurations of the dioxine ring, the thiazoline ring and the attached phenyl ring are conditioned by the sp³ state of the two bridgehead C atoms. The phenanthrene system is nearly coplanar with the dioxine ring, while the attached phenyl ring is orthogonal to the thia­zoline ring.     

One-pot Three-component Condensation Reactions in Water. An Efficient and Improved Procedure for the Synthesis of Furan Annulated Heterocycles

The environment-friendly one-pot three-component condensation reactions of 4-hydroxycoumarin or 4-hydroxy-6-methylpyrone, p-substituted benzaldehyde, and alkyl or aryl isocyanides to afford furocoumarines or furopyranones in water in good yields after about one hour at 75°C are reported.     

Electrocatalytic Reduction of Dioxygen on the Surface of Glassy Carbon Electrodes Modified with Cobalt Porphyrin Complexes

The preparation and electrocatalytic behavior of glassy carbon electrodes modified with three different cobalt porphyrin complexes were investigated. The electrocatalytic ability of the modified electrodes for the reduction of dioxygen to hydrogen peroxide and water in air‐saturated aqueous solutions was examined by cyclic voltammetry and chronoamperometry techniques. The porphyrin‐adsorbed glassy carbon electrodes possess excellent electrocatalytic abilities for dioxygen reduction with overpotential about 0.5 V lower than that at a plain glassy carbon electrode. The experimental parameters were optimized and the mechanism of the catalytic process was discussed. The possible effects of the electron‐donating properties of groups in the meso‐position of the porphyrin ring were investigated.     

Synthesis, characterization and ion transportation studies of some novel cyclophane amides

Various novel cyclophane amides with a large cavity have been synthesized. The structures of cyclophane amides 14 and 15 were resolved using XRD studies. Cyclophane amide 28 shows a shift in λ_max in the UV/Vis. spectra when treated with Cu (II) ion as well as with Pb (II) ion. Ion transportation studies were carried out with cyclophane amide 14 which proved that the Na⁺ ion passes through the cavity while K⁺ ions are retained.     

Lipase immobilized on poly(VP-co-HEMA) hydrogel for esterification reaction

Lipase from Candida rugosa was immobilized by entrapment on poly(N-vinyl-2-pyrrolidone-co-2-hydroxyethyl methacrylate)(poly[VP-co-HEMA]) hydrogel, and divinylbenzene was the crosslinking agent. The immobilized enzymes were used in the esterification reaction of oleic acid and butanol in hexane. The activities of the immobilized enzymes and the leaching ability of the enzyme from the support with respect to the different compositions of the hydrogels were investigated. The thermal, solvent, and storage stability of the immobilized lipases was also determined. Increasing the percentage of composition of VP from 0 to 90, which corresponds to the increase in the hydrophilicity of the hydrogels, increased the activity of the immobilized enzyme. Lipase immobilized on VP(%):HEMA(%) 90∶10 exhibited the highest activity. Lipase immobilized on VP(%):HEMA(%) 50∶50 showed the highest thermal, solvent, storage, and operational stability compared to lipase immobilized on other compositions of hydrogels as well as the native lipase.     

High-resolution iterative frequency identification for NMR as a general strategy for multidimensional data collection

We describe a novel approach to the rapid collection and processing of multidimensional NMR data: "high-resolution iterative frequency identification for NMR" (HIFI-NMR). As with other reduced dimensionality approaches, HIFI-NMR collects n-dimensional data as a set of two-dimensional (2D) planes. The HIFI-NMR algorithm incorporates several innovative features. (1) Following the initial collection of two orthogonal 2D planes, tilted planes are selected adaptively, one-by-one. (2) Spectral space is analyzed in a rigorous statistical manner. (3) An online algorithm maintains a model that provides a probabilistic representation of the three-dimensional (3D) peak positions, derives the optimal angle for the next plane to be collected, and stops data collection when the addition of another plane would not improve the data model. (4) A robust statistical algorithm extracts information from the plane projections and is used to drive data collection. (5) Peak lists with associated probabilities are generated directly, without total reconstruction of the 3D spectrum; these are ready for use in subsequent assignment or structure determination steps. As a proof of principle, we have tested the approach with 3D triple-resonance experiments of the kind used to assign protein backbone and side-chain resonances. Peaks extracted automatically by HIFI-NMR, for both small and larger proteins, included approximately 98% of real peaks obtained from control experiments in which data were collected by conventional 3D methods. HIFI-NMR required about one-tenth the time for data collection and avoided subsequent data processing and peak-picking. The approach can be implemented on commercial NMR spectrometers and is extensible to higher-dimensional NMR.