The quantum chemical calculation of NMR two-bond spin–spin coupling constants in the N?···H–OH?→?N–H···OH? switching

A quantum chemical study has been carried out to investigate the effects of the size of H₂O cluster and substituents (X = H, Me, OMe, CHO, NO, and NO₂) in the para position of the anilide ion on the two-bond spin–spin coupling constants (SSCCs) ^2h J _N···O across in the N–H–O switching at B3LYP/6-311 ++G(2d,2p) level of theory. The changes in ^2h J _N···O SSCCs due to variation of substituent and H₂O cluster size were well monitored by changes in binding energy, structural parameter, electron density topography, natural charge, charge transfer, and percentage of p-character of N atom in the C–N bond. Linear correlations were found between ^2h J _N···O and above-mentioned properties.     

Oxidation and determination of Gabapentin on nanotubes of nickel oxide-modified carbon paste electrode

The electrooxidation of Gabapentin was studied on nanotubes of nickel oxide-modified carbon paste electrode for the first time. Cyclic voltammetry was employed to investigate the electrooxidation process. A simple, sensitive, and efficient amperometric method was developed for the analysis of the drug, and the corresponding analytical parameters were reported. For Gabapentin, a detection limit of 0.3 μM was obtained in a linear range of 2.4–50 μM. The proposed amperometric method was also applied to the analysis of commercial capsules, and the results were in good agreement with the declared values. Also, the applicability of the method to the direct assay of the drug in human serum and urine was described.     

Composition of the essential oils and antibacterial activities of Hymenocrater yazdianus, Stachys obtusicrena and Nepeta asterotricha three Labiatae herbs growing wild in Iran

Water-distilled essential oils from leaves of Hymenocrater yazdianus Rech.f., flowers of Stachys obtusicrena Boiss., and stems and flowers of Nepeta asterotricha Rech.f., which are endemic to Iran, were analyzed by GC and GC/MS. Fifty-five components of the leaf oil of H. yazdianus were characterized, representing 95.1% of the total components detected. The major constituents were identified as 1,8-cineole (17.6%), beta-caryophyllene (13.9%), alpha-pinene (10.6%) and caryophyllene oxide (10.4%). Germacrene-D (37.5%) and alpha-bisabolol (23.5%) were the main components among the twenty constituents characterized in the flower oil of S. obtusicrena, representing 90.8% of the total components detected. Thirty-five compounds representing 93.0% of the stem oil of N. asterotrica were identified among which terpinen-4-ol (22.8%) and gamma-terpinene (14.1%) were the major ones. The flower oil of the species was characterized by higher amounts of terpinen-4-ol (24.8%), 4a alpha, 7a beta-nepetalactone (18.2%) and 1,8-cineole (11.6%) among the thirty-three components comprising 98.5% of the total oil detected. The antibacterial activity of the stem, leaf and flower oils of Hymenocrater yazdianus, Stachys obtusicrena and Nepeta asterotricha against seven Gram-positive and Gram-negative bacteria were determined using the MIC method. The growth inhibitory zone (mm) was also measured.     

The electrochemical behaviors of methylene blue on the surface of nanostructured NiWO4 prepared by coprecipitation method

A simple coprecipitation method was used for preparation of monoclinic nanostructured NiWO₄ from an aqueous solution at a fixed pH and temperature of 7.0 and 80 °C, respectively. The prepared material was characterized by X-ray diffraction, scanning electron microscopy, photoluminescence spectroscopy, and electrochemical measurements. Nano-NiWO₄ was incorporated into a carbon paste electrode and by means of cyclic voltammetry; the electrochemical behavior of methylene blue on the surface of nano-NiWO₄ was investigated. A mechanism on terms of obtained cyclic voltammograms showing one reduction peak and two sequential oxidation peaks was suggested by emphasizing on the stabilizing role of nano-NiWO₄ for semi-methylene blue. A diffusion coefficient of 5.30?×?10^?6 cm²/s was gained for methylene blue.     

Heat-resistant pyridine-based poly(ether-ester)s: Synthesis, characterization and properties

A pyridine-based diacid was synthesized via nucleophilic substitution reaction of 4-hydroxy benzoic acid with 2,6-dichloropyridine in the presence of potassium carbonate. The diacid was characterized using FT-IR and 1H-NMR spectroscopic methods and also with elemental analysis. Polycondensation reaction of the diacid with different diols including 1,4-dihydroxy benzene, 1,5-dihydroxy naphthalene, bis-phenol A and bis-phenol-P resulted in preparation of pyridine-based poly(ether-ester)s. The polymers were characterized and their physical and thermal properties including inherent viscosity, molecular weight, solubility, thermal stability, thermal behavior and crystallinity were studied. They revealed high heat-resistance and improved solubility in polar solvents. Structure-property relations for the prepared polyester were also studied.     

A mild and green chemistry approach for the synthesis of symmetrical spirooxindole derivatives

A simple and eco-friendly synthesis of the biologically important spirooxindole scaffold was done by the reaction of isatin with activated pyrazolones in the presence of a catalytic amount of p-toluenesulfonic acid in water at room temperature. A variety of symmetrical spirooxindole derivatives were obtained with excellent yields within short reaction time. This method is of great value because of its environmentally benign character, high yield, and easy handling.     

A simple accurate model for prediction of deflagration temperature of energetic compounds

A novel general method is introduced to predict deflagration temperature of organic energetic compounds containing at least –NNO₂, –ONO₂, or –CNO₂ groups. Deflagration temperature is an important safety parameter in working with dangerous energetic compounds and their environmental problems. It is shown that the contribution of some molecular structure parameters can be used to interpret thermal decomposition of an energetic compound. For 86 energetic materials (corresponding to 102 measured values) with different molecular structures, the new correlation has the root mean square (rms) and the average deviations of 23.8 and 19.0 K, respectively. The new method is also tested for some energetic compounds with complex molecular structures, e.g., two new organic energetic molecules N,N′-bis(1,2,4-triazol-3yl)-4,4′-diamino-2,2′,3,3′,5,5′,6,6′-octanitroazobenzene (BTDAONAB) and 2,4,6-trinitrophloroglucinol.