Synthesis,characterization, DFT calculations and antimicrobial activity of pentagonal-bipyramidal Zn(II) and Cd(II) complexes with 2,6-diacetylpyridine-bis(trimethylammoniumacetohydrazone)

Isothiocyanate complexes of Zn(II) and Cd(II) with the condensation product of 2,6-diacetylpyridine and trimethylammoniumacetohydrazide (Girard’s T reagent) were synthesized, characterized, and their antimicrobial activities were evaluated. The structures of the complexes were determined by elemental analysis, IR, and NMR spectroscopy. The crystal structure of the Zn(II) complex was also determined. Quantum-chemical calculations of the geometry and total energy of isomers of 2,6-diacetylpyridine-bis(trimethylammoniumacetohydrazone) were performed in vacuum and methanol solution, with the aim to explain conformational behavior and E/Z isomerism of this compound. DFT calculations of the molecular structures and the relative stabilities of linkage isomers of the Cd(II) complex showed that the isomer with N–Cd–N coordination of SCN^? is the most stable. Complexes of Zn(II) and Cd(II) exhibited low to moderate activity against the tested microbial strains.     

Interactions of the “piano‐stool” [ruthenium(II)(η6‐arene)(quinolone)Cl]+ complexes with water; DFT computational study

Full optimizations of stationary points along the reaction coordinate for the hydration of several quinolone Ru(II) half‐sandwich complexes were performed in water environment using the B3PW91/6‐31+G(d)/PCM/UAKS method. The role of diffuse functions (especially on oxygen) was found crucial for correct geometries along the reaction coordinate. Single‐point (SP) calculations were performed at the B3LYP/6‐311++G(2df,2pd)/DPCM/saled‐UAKS level. In the first part, two possible reaction mechanisms—associative and dissociative were compared. It was found that the dissociative mechanism of the hydration process is kinetically slightly preferred. Another important conclusion concerns the reaction channels. It was found that substitution of chloride ligand (abbreviated in the text as dechlorination reaction) represents energetically and kinetically the most feasible pathway. In the second part the same hydration reaction was explored for reactivity comparison of the Ru(II)‐complexes with several derivatives of nalidixic acid: cinoxacin, ofloxacin, and (thio)nalidixic acid. The hydration process is about four orders of magnitude faster in a basic solution compared to neutral/acidic environment with cinoxacin and nalidixic acid as the most reactive complexes in the former and latter environments, respectively. The explored hydration reaction is in all cases endergonic; nevertheless the endergonicity is substantially lower (by ～6 kcal/mol) in basic environment. © 2016 Wiley Periodicals, Inc.     

The Kinetic Modeling of Strong Diffusion‐Limited Reaction with Cyclization for Three Isomers – Diallyl Ortho‐, Iso‐ and Tere‐Phthalate in a Bulk

Free radical polymerization kinetic in a bulk for three diallyl phthalate isomers – diallyl orthophthalate, diallyl isophthalate and diallyl terephthalate was investigated in a temperature range from 50 to 70 °C initiated with dicyclohexan peroxydicarbonate as initiator at three different initiator concentrations. Conversion points were measured using Fourier Transform Raman measurements. A new kinetic model for polymerization of three diallyl phthalate isomers was developed. It demands the inclusion of only two new kinetic parameters k_DegC and k_pc which were obtained as a ratio k_DegC/k_pc from an additional set of experiments conducted. Computed conversions from the proposed kinetic model show good agreement with the conversion and molecular weight measured data for all three investigated diallyl phthalate isomers.

     

Rapid high-performance liquid chromatography method for determination of pregabalin in a pharmaceutical dosage form following derivatization with fluorescamine

A simple, fast, and sensitive HPLC method was developed and validated for the evaluation of pregabalin in a pharmaceutical dosage form using fluorescamine as a derivatization agent for the first time. After a precolumn derivatization (5 min, room temperature), the reaction mixture was chromatographed on a C18 column with isocratic elution using 0.2% of triethylamine in a mixture of methanol and water (10 + 90, v/v). 3-Aminopentanoic acid was used as the internal standard. Using fluorescent detection (lamdaex 395 nm, lamdaem 476 nm), a low detection limit of 0.02 microg/mL was reached. The method was linear (r > 0.999) over the lower (0.125-25 microg/mL) and higher (1.25-250 microg/mL) concentration range. The intraday and interday precision of the QC samples was < 4.3%, and the accuracy was 94.2-102.5%. The samples were stable for 24 h at 4 degrees C. The robustness study showed that the derivatization is more robust than the chromatography method. The method was applied for the analysis of pregabalin content in 25, 75, and 300 mg capsules, and a good agreement was found with the declared amount of pregabalin (the relative error did not exceed 3.2%). Finally, the method was successfully used for dissolution studies of pregabalin capsules.     

Production of vibrationally excited hydrogen molecules by atom recombination on Cu and W materials

We have measured vibrational population of H(2) and D(2) molecules produced by atom (H or D) recombination on tungsten and copper material. The vibrational spectroscopy, based on the properties of dissociative electron attachment to hydrogen molecule, was used. The vibrationally excited molecules were produced by atom recombination in a cell where the studied sample is exposed to hydrogen atoms, from hot tungsten filament. Vibrational populations were obtained for the studied materials, which can be well described by the Boltzmann distribution, with specific vibrational temperatures for each material. The experimentally obtained vibrational populations for copper approximately agree with the theoretical predictions, whereas the experimentally obtained vibrational temperature for tungsten is higher and thus showing a considerable overpopulation of highly excited vibrational states than predicted. We propose that the origin of this higher excitation is related to the existence of high hydrogen surface coverage on tungsten, where hydrogen is occupying binding sites with different desorption energies. In order to obtain an insight into the recombination mechanism with more than one binding site per unit cell, a Monte Carlo simulation was performed, where it was assumed that the main production of molecules proceeds through the hot-atom recombination with an adsorbed atom. The results show that the recombination proceeds mainly through the weak binding sites, once they are occupied.     

Intervals and Convex Sets in Strong Product of Graphs

In this note we consider intervals and convex sets of strong product. Vertices of an arbitrary interval of ${G\boxtimes H}$ are classified with shortest path properties of one factor and a walk properties of a slightly modified second factor. The convex sets of the strong product are characterized by convexity of projections to both factors and three other local properties, one of them being 2-convexity.     

Convex Sets in Lexicographic Products of Graphs

Geodesic convex sets, Steiner convex sets, and J-convex (alias induced path convex) sets of lexicographic products of graphs are characterized. The geodesic case in particular rectifies Theorem 3.1 in Canoy and Garces (Graphs Combin 18(4):787–793, 2002).     

Limits of inverse limits

We study the following problem: if a sequence of graphs of upper semi-continuous set valued functions fn converges to the graph of a function f, is it true that the sequence of corresponding inverse limits obtained from fn converges to the inverse limit obtained from f?     

A PLIC–VOF method suited for adaptive moving grids

This paper presents a new variant of the volume-of-fluid (VOF) color function C advection algorithm based on the piecewise linear interface construction (PLIC) method suitable for use on general moving grids. From several existing methods for reconstructing the linear interface we adopted the least squares volume-of-fluid interface reconstruction algorithm (LVIRA) which can be easily implemented on general grids. The distinguishing step in the advection algorithm that takes into account the grid movement is the construction of the donating region containing the fluid passing through corresponding cell-faces in a single time-step. The donating regions are constructed utilizing fluid velocity in cell corners relative to grid (corner) velocities. The method is conservative as it complies with the space conservation law (SCL) and requires a proper definition of the grid velocities and fluxes due to the grid movement. The accuracy of the presented advection algorithm is assessed with standard test cases. It is comparable with other PLIC based algorithms on fixed grids, while the applicability on adaptive moving grids enables a considerable reduction in the number of grid cells.     

The structure of compositionally constrained zinc-ferrite spinel nanoparticles

ZnFe₂O₄ bulk material shows a normal-spinel structure and a closely defined composition at Zn²⁺/Fe³⁺ ≅ 0.5. However, the composition of zinc ferrite, prepared as nanoparticles, can be varied in a broad range without losing the single-phase spinel structure. In this article, structural mechanisms enabling this non-stoichiometry were studied using the X-ray absorption fine structure (EXAFS) in combination with X-ray diffractometry (XRD), transmission electron microscopy (TEM), and magnetic measurements. Nanoparticles with a narrow size distribution were synthesized using co-precipitation in water-in-oil microemulsions. First, the structure of the stoichiometric zinc-ferrite nanoparticles was studied in dependence of their size and the annealing temperature. EXAFS analysis showed that the degree of inversion x (as defined in the compound formula (Zn_1 − x Fe _x )[Fe_2 − x Zn _x ]O₄, with round and square brackets representing the tetrahedral and octahedral sites, respectively) increased with decreasing nanoparticles size. The structure of the stoichiometric nanoparticles and the nanoparticles of comparable size displaying Zn/Fe ratio of 0.2 (Fe-rich) and 0.7 (Zn-rich) were then compared. Analysis showed that the non-stoichiometry is structurally compensated predominantly in the core of the nanoparticle by the adjusted distribution of Zn and Fe ions over the two sublattices of the spinel structure.