A new approach to NMR chemical shift additivity parameters using simultaneous linear equation method

A new approach to NMR chemical shift additivity parameters using simultaneous linear equation method has been introduced. Three general nitrogen-15 NMR chemical shift additivity parameters with physical significance for aliphatic amines in methanol and cyclohexane and their hydrochlorides in methanol have been derived. A characteristic feature of these additivity parameters is the individual equation can be applied to both open-chain and rigid systems. The factors that influence the (15)N chemical shift of these substances have been determined. A new method for evaluating conformational equilibria at nitrogen in these compounds using the derived additivity parameters has been developed. Conformational analyses of these substances have been worked out. In general, the results indicate that there are four factors affecting the (15)N chemical shift of aliphatic amines; paramagnetic term (p-character), lone pair-proton interactions, proton-proton interactions, symmetry of alkyl substituents and molecular association.     

Structural and co-conformational effects of alkyne-derived subunits in charged donor-acceptor [2]catenanes

Four donor-acceptor [2]catenanes with cyclobis(paraquat-p-phenylene) (CBPQT4+) as the pi-electron-accepting cyclophane and 1,5-dioxynaphthalene (DNP)-containing macrocyclic polyethers as pi-electron donor rings have been synthesized under mild conditions, employing Cu+-catalyzed Huisgen 1,3-dipolar cycloaddition and Cu2+-mediated Eglinton coupling in the final steps of their syntheses. Oligoether chains carrying terminal alkynes or azides were used as the key structural features in template-directed cyclizations of [2]pseudorotaxanes to give the [2]catenanes. Both reactions proceed well with precursors of appropriate oligoether chain lengths but fail when there are only three oxygen atoms in the oligoether chains between the DNP units and the reactive functional groups. The solid-state structures of the donor-acceptor [2]catenanes confirm their mechanically interlocked nature, stabilized by [pi...pi], [C-H...pi], and [C-H...Omicron] interactions, and point to secondary noncovalent contacts between 1,3-butadiyne and 1,2,3-triazole subunits and one of the bipyridinum units of the CBPQT4+ ring. These contacts are characterized by the roughly parallel orientation of the inner bipyridinium ring system and the 1,2,3-triazole and 1,3-butadiyne units, as well as by the short [pi...pi] distances of 3.50 and 3.60 A, respectively. Variable-temperature 1H NMR spectroscopy has been used to identify and quantify the barriers to the conformationally and co-conformationally dynamic processes. The former include the rotations of the phenylene and the bipyridinium ring systems around their substituent axes, whereas the latter are confined to the circumrotation of the CBPQT4+ ring around the DNP binding site. The barriers for the three processes were found to be successively 14.4, 14.5-17.5, and 13.1-15.8 kcal mol-1. Within the limitations of the small dataset investigated, emergent trends in the barrier heights can be recognized: the values decrease with the increasing size of the pi-electron-donating macrocycle and tend to be lower in the sterically less encumbered series of [2]catenanes containing the 1,3-butadiyne moiety.     

An Improvement on Modeling of Forced Gravity Drainage in Dual Porosity Simulations Using a New Matrix-Fracture Transfer Function

In fractured oil reservoirs, the gravity drainage mechanism has great potentials to higher oil recovery in comparison with other mechanisms. Recently, the forced gravity drainage assisted by gas injection has also been considered; however, there are few comprehensive studies in the literature. Dual porosity model, the most common approach for simulation of fractured reservoirs, uses transfer function concept to represent the fluid exchange between matrix and its neighborhood fractures. This study compares the results of different available transfer functions with those of fine grid simulations when forced gravity drainage contributes to oil production from a single matrix block. These comparisons can lead to a more sophisticated formulation including the interplay of capillary, gravity and viscous forces. As a result, a new matrix-fracture transfer function can be developed and its results can be tested against the results of fine-grid simulations. Moreover, the reliability of this model for simulation of forced gravity drainage has been demonstrated by performing some sensitivity analysis.     

Fe3O4@MCM-48–SO3H:合成苯并[f]色烯并[2,3-d]嘧啶酮的高效、可磁性分离纳米催化剂（英文）

Sulfonic acid groups were grafted onto three different types of synthesized magnetic nanoparticles, namely Fe3O4, Fe3O4@SiO2, and Fe3O4@MCM‐48. The sulfonic acid‐functionalized nanoparticles were evaluated as catalysts for the synthesis of 5‐aryl‐1H‐benzo[f]chromeno[2,3‐d]pyrimidine‐2,4(3H,5H)‐dione derivatives in terms of activity and recyclability. Their catalytic activities were compared with that of the homogeneous acid catalyst 1‐methylimidazolium hydrogen sulfate ([HMIm][HSO4]). The activity of Fe3O4@MCM‐48–SO3H was comparable to those of the other heter‐ogeneous and homogeneous catalysts.     

Broad-Band Polarizing Light Beam Splitter Based on a Multilayer Thin-Film Coating

Journal of Applied Spectroscopy - A polarizing light beam splitter is created in the form of two Dove prisms of BK7 glass with a multilayer thin-fi lm coating made of two periodic substructures...     

Separation of short and medium-chain fatty acids using capillary electrophoresis with indirect photometric detection: Part I: Identification of fatty acids in rat feces

Short and medium-chain fatty acids (SMCFAs) are known as essential metabolites found in gut microbiota that function as modulators in the development and progression of many inflammatory conditions as well as in the regulation of cell metabolism. Currently, there are few simple and low-cost analytical methods available for the determination of SMCFA. This report focuses on SMCFA analysis utilizing CE with indirect photometric detection (CE-IPD). A ribonucleotide electrolyte, 5’-adenosine mono-phosphate (5’-AMP), is investigated as an IPD reagent due to its high molar absorptivity and dynamic reserve compatible with separation and detection of SMCFA. The operating parameters like the composition of organic solvent, millimolar concentrations of the complexing agent (alpha-cyclodextrin), 5’-AMP and non-absorbing electrolyte (boric acid), as well as the applied voltage, are optimized for resolution, efficiency, and signal-to-noise ratio. A baseline resolution of all nine SMCFAs is achieved in less than 15 min. Additionally, the developed CE-IPD method shows promising potential to identifying SMCFA in rat fecal supernatant. The presented analytical assay is simple, economical, and has considerably good repeatability. The intraday and interday RSD of less than 1 and 2% for relative migration time, as well as less than 14 and 15% for peak area, respectively, were obtained for SMCFA in fecal solution.     

Numerical simulation of nanofluid turbulent flow in a double-pipe heat exchanger equipped with circular fins

Journal of Thermal Analysis and Calorimetry - In this study, the thermal and flow characteristics of a nanofluid were evaluated numerically in a circular finned double-pipe heat exchanger. A 3D CFD...     

Spectral,morphological, and antibacterial studies of conducting copolymers,Ppy‐MA,and their nanocomposites,Ag@Ppy‐MA

Pyrrole and methyl anthranilate were copolymerized in different molar ratios in the presence of, H₂O₂, and FeSO₄ at ambient temperature and pressure to obtain efficient conducting copolymers, Ppy‐MA. These conducting copolymers, Ppy‐MA, were in situ reacted with silver nanoparticles to generate nanocomposites, Ag@Ppy‐MA, which exhibit enhanced electrical conductivity. The spectra and morphology of different copolymers, Ppy‐MA, and their nanocomposites, Ag@Ppy‐MA, were analyzed using Fourier transform infrared, SEM, tunneling electron microscopy, X‐ray diffraction, thermogravimetric analysis, and differential thermal analysis. These studies have shown that the nanocomposites, Ag@Ppy‐MA, are thermally more stable and good electrical conductors as compared with their copolymers, Ppy‐MA. The antibacterial activity of the copolymers, Ppy‐MA, prepared from different monomer ratios and their nanocomposites, Ag@Ppy‐MA, has been carried out using disk diffusion method. The copolymers, Ppy‐MA, and its nanocomposites, Ag@Ppy‐MA, were screened against the standard drug Ciprofloxacin. The results clearly suggest that the nanocomposites, Ag@Ppy‐MA, are better antibacterial agent as compared with their copolymers, Ppy‐MA. Copyright © 2016 John Wiley & Sons, Ltd.     

A new approach to extraction and preconcentration of Ce(III) from aqueous solutions using magnetic reduced graphene oxide decorated with thioglycolic-acid-capped CdTe QDs

In the present study, a nanocomposite consisting of magnetic reduced graphene oxide decorated with thioglycolic-acid-capped CdTe quantum dots (TGA/CdTe QDs/Fe₃O₄/rGO) was synthesised using simple ‘hydrothermal method’ and applied as a nanosorbent for extraction and preconcentration of cerium (Ce)(III) from aqueous solutions prior to inductively coupled plasma-optical emission spectroscopy detection. Under the optimised extraction conditions, the calibration graph for Ce(III) was linear in a concentration range of 0.1–511.0 μg L^?1 with a correlation coefficient of 0.9986. A detection limit of 0.1 μg L^?1 Ce(III) with an enrichment factor of 125 was obtained. Precisions, expressed as relative standard deviation for single-sorbent repeatability and sorbent-to-sorbent reproducibility, were 3.6% and 9.1% (n = 5), respectively. Finally, spiked sea, mineral and tap waters were analysed to evaluate the performance of the proposed method. The high recoveries indicated that the suggested protocol was acceptable for determination of Ce(III) ions in the water samples. The use of QDs and study of their ability for preconcentration of metal ions is an important achievement towards designing novel adsorbents with high efficiency.