High-performance thin-layer chromatography method for the quantification of quetiapine fumarate and its related genotoxic impurities using green solvents

A novel high-performance thin-layer chromatographic (HPTLC) analytical method has been developed and optimized for the quantification of quetiapine fumarate (QF) and its two genotoxic impurities in drug substance and drug product. The desired separation was achieved on 60F₂₅₄ pre-coated HPTLC plates using combination of green solvents, ethyl acetate‒ethanol‒n-heptane (5:1:4, V/V) as developing solvents. The detection wavelength used for quantification was 229 nm. QF and its two related genotoxic impurities, namely, 2-chloroaniline and 2-aminodiphenylsulfide, were well resolved from one another with retention factor values of 0.13 ± 0.02, 0.57 ± 0.02 and 0.76 ± 0.02, respectively. The optimized method was validated according to the guidelines laid down by the International Council for Harmonisation. The linearity was determined in the range of 100–600 ng/spot for QF and 10‒60 ng/spot for its two related genotoxic impurities; R² ≥ 0.993. The method exhibited precision along with good accuracy, where 0.51, 0.86 and 1.86. The percentage recoveries obtained for 2-chloroaniline and 2-aminodiphenylsulfide were 99.04‒101.04%. The developed method can be successfully used for the analysis of drug samples.

     

Polymer blend nanocomposites: effect of mercapto silane modified kaolin clay on the thermal properties of Polypropylene/Polystyrene blend

Nanocomposites based on polypropylene/polystyrene blends were prepared by melt mixing in a Thermo Haake Rheochord mixer. The effect of mercapto silane modified kaolin clay on the properties of nanocomposites has been studied. The characterization of polypropylene/polystyrene/clay nanocomposites was made by dynamic mechanical analysis, scanning electron microscope, and transmission electron microscopic, and the thermal stability was determined by using Thermogravimetric analysis. The activation energy of degradation was determined using three mathematical models, namely Horowitz–Metzger, Coats–Redfern and Broido's methods, and the results were compared. TGA results show an improved thermal stability for nanocomposite than the pure blend. The improvement in thermal stability of nanocomposites was confirmed by increasing the activation energy. Transmission electron microscopic observations showed that nanoclay layers were intercalated on the polymer matrix and were located at the interface between the two polymers Copyright © 2014 John Wiley & Sons, Ltd.     

Determination of stability and degradation in polysilanes by an electronic mechanism

Polysilanes are potential candidates for active materials in light emitting diodes because of possible emission in the near-ultraviolet to blue region. Unfortunately, they degrade rapidly upon exposure to light because of scission of sigma bonds. Relative stability of four polysilanes, for example, poly(di-n-butylsilane) (PDBS), poly(di-n-hexylsilane) (PDHS), poly(methylphenylsilane) (PMPS), and poly[bis(p-butylphenyl)silane] (PBPS), which have been reported as active materials in light emitting diodes, have been investigated theoretically through semiempirical (AM1) and ab initio (HF/6-31g) methods and density functional theory using B3LYP parametrization. The AM1 level of calculation predicts the absorption maxima reasonably, but it fails to explain the relative stabilities of the four polysilanes in the excited state. However, calculations based on configuration interaction with single excitation and time-dependent density functional theory suggest additional stabilization in the excited states through intersystem crossing to triplets for PMPS and PBPS, consistent with the experimental observation. In contrast, no such stabilization is predicted for PDBS and PDHS. Furthermore, the existence of a stable triplet state in PMPS may also explain the visible emission observed experimentally in PMPS.     

Random and AB diblock copolymers of tricyclodecanemethanol urethane methacrylate with styrene: Synthesis and morphology characterization

A monomer design having a bulky terminal tricyclodecane (TCD) unit linked via hydrogen bondable urethane to an ethyleneoxy methacrylate unit, and capable of generating three‐dimensional honeycomb patterns upon solvent casting has been investigated. Random copolymers as well as a diblock copolymer Poly(Sty₄₂‐b‐TCD₁₈) of this monomer with styrene were prepared by free‐radical polymerization route and atom transfer radical polymerization (ATRP) route. Morphology characterization was carried out using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis. Particle size was measured by dynamic light scattering measurements (DLS). Irrespective of the wide differences in molecular weight and polydispersity index values, the random copolymers having TCD content >30 mol % were found to form microporous films upon solvent casting from a THF/water 9:1 solvent combination. The amount of TCD in the copolymer was found to have an influence on the pore size formed. The diblock copolymer formed microspheres ～200 nm in diameter. The thermal properties of all the polymers were studied using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), and the copolymers were found to have good thermal stability. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1278–1288, 2008     

Chloride‐Anion‐Templated Synthesis of a Strapped‐Porphyrin‐Containing Catenane Host System

The synthesis, structure and anion‐recognition properties of a new strapped‐porphyrin‐containing [2]catenane anion host system are described. The assembly of the catenane is directed by discrete chloride anion templation acting in synergy with secondary aromatic donor–acceptor and coordinative pyridine–zinc interactions. The [2]catenane incorporates a three‐dimensional, hydrogen‐bond‐donating anion‐binding pocket; solid‐state structural analysis of the catenane?chloride complex reveals that the chloride anion is encapsulated within the catenane’s interlocked binding cavity through six convergent CH????Cl and NH???Cl hydrogen‐bonding interactions and solution‐phase ¹H NMR titration experiments demonstrate that this complementary hydrogen‐bonding arrangement facilitates the selective recognition of chloride over larger halide anions in DMSO solution.     

A note on minimal topological spaces

Let (X,τ) be a completely Hausdorff space. LetP be any topological property which is implied by complete regularity. Let (X,τ), be minimal-P. Then it has been shown that (X,τ), is completely regular and hence compact.     

Reliability modelling incorporating load share and frailty

The stochastic behaviour of lifetimes of a two component system is often primarily influenced by the system structure and by the covariates shared by the components. Any meaningful attempt to model the lifetimes must take into consideration the factors affecting their stochastic behaviour. In particular, for a load share system, we describe a reliability model incorporating both the load share dependence and the effect of observed and unobserved covariates. The model includes a bivariate Weibull to characterize load share, a positive stable distribution to describe frailty, and also incorporates effects of observed covariates. We investigate various interesting reliability properties of this model using cross ratio functions and conditional survivor functions. We implement maximum likelihood estimation of the model parameters and discuss model adequacy and selection. We illustrate our approach using a simulation study. For a real data situation, we demonstrate the superiority of the proposed model that incorporates both load share and frailty effects over competing models that incorporate just one of these effects. An attractive and computationally simple cross‐validation technique is introduced to reconfirm the claim. We conclude with a summary and discussion.     

Electronic structural studies of pyrrolidinium-based ionic liquids for electrochemical application

Electrochemical stability and noncovalent interactions escorting the cyclic ammonium-based ionic liquids composed of N-alkyl-substituted N-methyl pyrrolidinium (P_yr1R) (R = methyl, ethyl, propyl, butyl, pentyl, hexyl) cations and four anions hexafluorophosphate (PF₆), tetrafluoroborate (BF₄), bis(trifluoromethylsulfonyl-imide (TFSI), and trifluoromethane sulfonate (TFO) have been analyzed using the density functional theory. Electronic structures, electrochemical window, frontier orbital energy difference (HOMO-LUMO gap), binding energies, vibrational spectra of these ion pairs were characterized. It has been established that ion pair formation is largely reigned by C H⋯F interactions between anionic fluorine for BF₄⁻ and PF₆⁻ anions and C H⋯O interactions between anionic oxygen for TFSI and TFO anions and pyrrolidinic proton, methyl, or alkyl group protons of the cations. The effect of alkyl chain length and pairing anions of the alkyl substituted N-methyl pyrrolidinium-based ionic liquids on the electrochemical window was investigated. The results revealed that the HOMO energy of pairing anions is the key factor to decide the electrochemical window. Further quantification of noncovalent interactions in terms of electrostatic and hydrogen bonding interactions has been brought out employing a novel method with the aid of Mulliken and Merz-Singh-Kollman charges, prevailed in pyrrolidinium-based ionic liquids.     

A convenient route to 1,3-diynes using ligand-free Cadiot–Chodkiewicz coupling reaction at room temperature under aerobic conditions

In this study, we report a copper-catalyzed ligand-free Cadiot–Chodkiewicz coupling reaction. No additives or ligands are required for this Cu-catalyzed C(sp)–C(sp) coupling reaction of terminal alkynes with alkynyl halides. The low cost of copper catalyst, excellent yield of the products, suppression of side-products and mild reaction conditions are the major advantages of this protocol.