Monoterpenoid glucoindole alkaloids and iridoids from Pterocephalus pinardii

A new secondary metabolite, pterocephaline, along with the known cantleyoside, 7α‐morroniside, 3β,5α‐tetrahydrodesoxycordifoline lactam, 5S‐5‐carboxyvincoside, sweroside, and loganin have been isolated from the aerial parts of P. pinardii (Dipsacaceae). Moreover, cantleyoside‐methyl‐hemiacetal and cantleyoside‐dimethyl‐acetal were obtained as seco‐iridoid artifacts. The structures were elucidated by extensive spectroscopic methods including 1D‐(¹H, ¹³C and TOCSY) and 2D‐NMR (DQF‐COSY, HSQC and HMBC). Monoterpenoid glucoindole alkaloids were encountered for the first time in Dipsacaceae family. Copyright © 2010 John Wiley & Sons, Ltd.     

Nucleophilic attack by bromide ions as a first step of conversion of Se(VI) to Se(IV)

Numerous commonly used analytical methods allow only determination of a total amount of selenium in a given sample. Electroanalytical methods as well as those based on hydride generation or on formation of piazselenol allow only determination of Se(IV). To determine Se(VI) by these procedures, present alone or in mixtures with Se(IV), it is first necessary to convert Se(VI) to Se(IV). Such conversion is effective in the presence of excess of halides in acidic media or by photoreduction. In the often used conversion of Se(VI) in the presence of chlorides or less frequently of that of bromides, it has been assumed that the halide ion acts as a reducing agent. Kinetic studies of conversion of Se(VI) in acidic solutions containing an excess of bromide ions indicated that the rate determining first step of the reaction with Se(VI) is a nucleophilic substitution of the OH₂⁺ group in the protonated form of H₂SeO₄ by bromide ions. For the overall reaction with rate −d[Se(VI)]/dt = k₁[H⁺][Br⁻]^1.15[Se(IV)] the rate constant 1 × 10⁻³ L² mol⁻² s⁻¹ was found. The following formation of Se(IV) from the bromo derivative is a fast reaction probably resulting in elimination of HBrO.     

Determination of antimony by using tungsten trap atomic absorption spectrometry

An electrically heated tungsten coil was used as a trap in the determination of antimony. The technique consists of three steps. Initially, SbH₃ is formed by hydride generation procedure; then the analyte species in vapor form are transported to W-coil trap heated at 370 °C. Following the preconcentration step, the trap is heated to 895 °C; analyte species are revolatilized and transported to the flame-heated quartz atom cell where atomization and the formation of signal take place. The experimental parameters were optimized both for trap and no-trap studies. The most important experimental parameters are concentrations of HCl and NaBH₄ solutions, H₂ and Ar gas flow rates, and collection and revolatilization temperatures of W-coil. Accuracy was tested using a certified reference material, waste water EU-L-1. Limit of detection for the system is 16 ng l^− 1 using a sample of 36 ml collected in 4.0 min. Enhancement factor in sensitivity was 17.     

Indium determination using slotted quartz tube-atom trap-flame atomic absorption spectrometry and interference studies

Sensitivity enhancement of indium determination by flame atomic absorption spectrometry (FAAS) was achieved; using a slotted quartz tube (SQT-FAAS) and slotted quartz tube atom trap (SQT-AT-FAAS). SQT was used as an atom trap (AT) where the analyte is accumulated in its inner wall prior to re-atomization. The signal is formed after re-atomization of analyte on the trap surface by introduction of 10 μL of isobutyl methyl ketone (IBMK). Sensitivity was improved 400 times using SQT-AT-FAAS system with respect to conventional FAAS and 279 times with respect to SQT-FAAS without any collection. Characteristic concentration (C₀) and limit of detection values were found to be 3.63 ng mL⁻¹ and 2.60 ng mL⁻¹, respectively, using a sample flow rate of 7.0 mL min⁻¹ and a collection period of 5.0 min. In addition, interference effects of some elements on indium signal were studied. In order to characterize indium species trapped, X-ray Photoelectron Spectrometry (XPS) was utilized and it was found that indium was collected on the inner surface of SQT as In₂O₃. The accuracy of the procedure was checked to determine indium in the standard reference material (Montana Soil, SRM 2710).     

Synergistic effect of boron containing substances on flame retardancy and thermal stability of clay containing intumescent polypropylene nanoclay composites

The functions of nanoclay and three different boron containing substances, zinc borate (ZnB), borophosphate (BPO₄), and boron silicon containing preceramic oligomer (BSi), were studied to improve the flame retardancy of polypropylene (PP)‐nanoclay‐intumescent system composed of ammonium polyphosphate (APP) and pentaerythritol (PER). The flame retardancy of PP composites was investigated using limiting oxygen index (LOI), UL‐94 standard, thermogravimetric analysis (TGA), and cone calorimeter. According to the results obtained, the addition of 20 wt% intumescent flame retardant (IFR) improved the flame retardancy by increasing the char formation. Addition of clay slightly increases the LOI value and reduces the maximum heat release rate (HRR). Addition of clay also increases the barrier effect due to intumescent char, especially in thin samples. Boron compounds show their highest synergistic effect at about 3 wt% loading. According to UL‐94 test and LOI test, 3 wt% ZnB containing composite shows the highest rating (V0) and BPO₄ containing sample shows the highest LOI value (26.5). Copyright © 2010 John Wiley & Sons, Ltd.     

Parallel factor analysis and trilinear partial least squares applied to the UPLC-PDA data array for the quantification of brimonidine tartrate and timolol maleate in an eye drop formulation

Simultaneous quantification of brimonidine tartrate (BRI) and timolol maleate (TIM) in an eye drop formulation was performed by applying parallel factor analysis (PARAFAC) and trilinear (three way) partial least squares to the ultra performance liquid chromatography-photodiode array (UPLC-PDA) data array. In PARAFAC and 3 W-PLS1 applications, the co-elution of the related compounds in their chromatograms obtained in the presence of ornidazole as an internal standard (IS) was resolved, and then analyses were performed. On the other hand, a new conventional ultra performance liquid chromatography (UPLC) method was developed after long and tedious studies to get desirable elution of BRI and TIM in a chromatogram using different column and mobile phase system than that of chromatographic conditions of PARAFAC and 3 W-PLS1 applications. The performance and validity of all the proposed methods were confirmed by analyzing independent validation samples consisting of synthetic mixture, intraday and interday samples, and standard addition samples. Analysis results of BRI and TIM in eye drop samples by chemometric PARAFAC and 3 W-PLS1, and conventional UPLC were statistically compared to each other. It was concluded that PARAFAC and 3 W-PLS1 have shortest analysis time and lower cost than the developed conventional UPLC method for the analysis of the related compounds in commercial eye drop preparation with adequate selectivity and sensitivity.     

An application of derivative and continuous wavelet transforms to the overlapping ratio spectra for the quantitative multiresolution of a ternary mixture of paracetamol, acetylsalicylic acid and caffeine in tablets

Quantitative multiresolution of tablets and ternary mixtures of paracetamol (PAR), acetylsalicylic acid (ASP) and caffeine (CAF) having strongly overlapping spectra was accomplished by two graphical transform methods as ratio spectra first derivative-zero crossing and ratio spectra-continuous wavelet transform-zero crossing (ratio spectra CWT-zero crossing) methods. In this study, ratio spectra derivative-zero crossing and ratio spectra CWT-zero crossing methods are based on the use of transformed signals of the ratio spectra and their calibration graphs were obtained by measuring the dA/dλ and CWT amplitudes of the ratio spectra corresponding to zero crossing points. For the comparison purpose, PLS calibration method was applied to predict the content of the same mixtures containing the subject active compounds. The obtained calibrations were tested by using the synthetic mixtures and standard addition technique and they applied to the simultaneous determination of PAR, ASP and CAF in commercial pharmaceutical preparation. The obtained results were statistically compared with each other as well as those obtained by HPLC method and they showed good agreement.     

MEIR-KEELER TYPE CONTRACTIONS FOR TRIPLED FIXED POINTS

In 2011,Berinde and Borcut [6] introduced the notion of tripled fixed point in partially ordered metric spaces.In our paper,we give some new tripled fixed point theorems by using a generalization of Meir-Keeler contraction.     

Morphology and thermal characterization of montmorillonite/polybenzimidazole nanocomposite

In this study, thermal and morphological properties of organically modified montmorillonite (mMMT)/poly(2,5-benzimidazole) (ABPBI) composite were investigated. The morphology and structure of mMMT/ABPBI composites were characterized by infrared, X-ray diffraction, scanning electron microscopy, and thermogravimetric analysis techniques. At low mMMT loading levels, exfoliation was the predominant mechanism of mMMT dispersion. At high mMMT loading levels, nonintercalated microcomposite morphology is partially favored in expense of the intercalated nanocomposite. Thermal degradation of nanocomposite occured in three stages. In the second stage of thermal degradation, the onset temperature of degradation for the mMMT/ABPBI nanocomposites was lower than that of ABPBI polymer. In the last stage, the improvement in thermal stability by the introduction of mMMT into the ABPBI was different from the second stage. The activation energy for degradation of ABPBI increased from 62.6 to 77.7 kJ mol^?1 after loading of 5 mass% of mMMT into ABPBI matrix under air atmosphere.     

5,6‐Di­phenyl­[1,3]­di­thiolo­[4,5‐b]di­thiine‐2‐thione

In the title compound, C₁₇H₁₀S₅, the dithiine ring adopts a boat conformation while the di­thiole ring has an envelope conformation. The phenyl groups are planar and make dihedral angles of 40.7 (2) and 59.8 (2)° with the best plane of the thiine ring. The shortest intermolecular S?S contact is 3.305 (2) Å.