Thermotropic polyesters. 1: Synthesis, characterization and thermal transition of poly[4,4-bis(ω-alkoxy)biphenyl isophthalate]

A new homologous series of thermotropic polyesters has been synthesized by polycondensation reaction between isophthaloyl chloride and mesogenic diols 4,4^′-bis(ω-hydroxyalkoxy)biphenyl in which the spacer length is varied from 3 to 6 methylene units. The thermal behavior of the polymers has been characterized using polarized light microscopy and differential scanning calorimetry (DSC). The odd members exhibit a smectic C (S_C) phase in a narrow temperature interval, while the even members form a smectic A (S_A) phase in a broader temperature range. All of the obtained compounds were characterized by conventional spectroscopic methods.     

Polyol‐enhanced dispersive liquid–liquid microextraction coupled with gas chromatography and nitrogen phosphorous detection for the determination of organophosphorus pesticides from aqueous samples,fruit juices,and vegetables

Polyol‐enhanced dispersive liquid–liquid microextraction has been proposed for the extraction and preconcentration of some organophosphorus pesticides from different samples. In the present study, a high volume of an aqueous phase containing a polyol (sorbitol) is prepared and then a disperser solvent along with an extraction solvent is rapidly injected into it. Sorbitol showed the best results and it was more effective on the extraction recoveries of the analytes than inorganic salts such as sodium chloride, potassium chloride, and sodium sulfate. Under the optimum extraction conditions, the method showed low limits of detection and quantification within the ranges of 12–56 and 44–162 pg/mL, respectively. Enrichment factors and extraction recoveries were in the ranges of 2799–3033 and 84–92%, respectively. The method precision was evaluated at a concentration of 10 ng/mL of each analyte, and relative standard deviations were found to be less than 5.9% for intraday (n = 6) and less than 7.8% for interday (n = 4). Finally, some aqueous samples were successfully analyzed using the proposed method and four analytes (diazinon, dimethoate, chlorpyrifos, and phosalone) were determined, some of them at ng/mL level.     

Estimation of thermal conductivity of ethylene glycol-based nanofluid with hybrid suspensions of SWCNT–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles by correlation and ANN methods using experimental data

In the present paper, the effects of temperature and volume fraction on thermal conductivity of SWCNT–Al₂O₃/EG hybrid nanofluid are investigated. Single-walled carbon nanotube with outer diameter of 1–2 nm and aluminum oxide nanoparticles with mean diameter of 20 nm with the ratio of 30 and 70%, respectively, were dispersed in the base fluid. The measurements were conducted on samples with volume fractions of 0.04, 0.08, 0.15, 0.3, 0.5, 0.8, 1.5 and 2.5. In order to investigate the effects of temperature on thermal conductivity of the nanofluid, this characteristic was measured in five different temperatures of 30, 35, 40, 45 and 50 °C. The results indicate that enhancement of nanoparticles’ thickness in low volume fractions and at any temperature causes a considerable increment in thermal conductivity of the nanofluid. In this study, the highest enhancement of thermal conductivity was 41.2% which was achieved at the temperature of 50 °C and volume fraction of 2.5%. Based on the experimental data, an experimental correlation and a neural network are presented and for thermal conductivity of the nanofluid in terms of volume fraction and temperature. Comparing outputs of the experimental correlation and the designed artificial neural network with experimental data, the maximum error values for the experimental correlation and the artificial neural network were, respectively, 2.6 and 1.94% which indicate the excellent accuracy of both methods in prediction of thermal conductivity.     

Determination of migrated phthalic acid residues into edible oils using a green mode of air-assisted liquid–liquid microextraction followed by high-performance liquid chromatography–diode array detector

In this study, for the first time, an organic solvent-free air-assisted liquid–liquid microextraction method has been reported for the extraction and preconcentration of phthalic acids (o-phthalic acid, m-phthalic acid, and p-phthalic acid) from edible oil samples. The method is based on the repeated aspirating/injection of an alkaline aqueous solution and the oil sample mixture in a conical bottom centrifuge tube to form a cloudy solution. After phase separation by centrifuging, the sedimented phase is directly analyzed by high-performance liquid chromatography–diode array detection. Under the optimum extraction conditions, the method showed low limits of detection and quantification between 0.11–0.29 and 0.28–0.91 ng mL^?1, respectively. Extraction recoveries and enrichment factors were from 81 to 97% and 406 to 489, respectively. The relative standard deviations for the analysis of 5 ng mL^?1 of each analyte were less than 5.9% for intraday (n = 6) and interday (n = 5) precisions. Finally, different oil samples were successfully analyzed using the proposed method and m-phthalic acid, and p-phthalic acid were determined in some of them at ng mL^?1 level.     

Inhibitory effect of safranal and crocin,two principle compounds of <Emphasis Type="Italic">Crocus sativus</Emphasis>, on fibrillation of lysozyme

A key feature in more than twenty amyloid-related diseases is the aggregation of intra-and/or extracellular misfolded proteins as amyloid fibrils. Therefore, preventing or reversing amyloid aggregation by using of small molecules is considered as useful approaches to the treatment of these diseases. We have evaluated the ability of safranal and crocin, to inhibit amyloid self-assembly of hen egg white lysozyme (HEWL), as an in vitro model system. Structural properties of HEWL in the presence of these compounds were investigated individually using thioflavin T, anilinonaphthalene-8-sulfonic acid fluorescence assays, far-UV circular dichroism and scanning electron microscopy as well as docking method. Our results showed that incubation of HEWL with either crocin or safranal at various concentrations leads a significant inhibition in the rate of amyloid formation. Docking analysis revealed crocin and safranal interact with the central hydrophobic region of lysozyme through van der Waals interaction. Hydroxyl group in crocin through hydrogen bonds connected to the several hydrophilic amino acids of lysozyme, while in safranal there are just one aldehyde group that through hydrogen bonds connected to aspartic acid in lysozyme. It can be concluded that both hydrophobic and hydrophilic groups contribute to lower lysozyme fibril accumulation.     

An adaptive nonmonotone global Barzilai–Borwein gradient method for unconstrained optimization

The Barzilai–Borwein (BB) gradient method has received many studies due to its simplicity and numerical efficiency. By incorporating a nonmonotone line search, Raydan (SIAM J Optim. 1997;7:26–33) has successfully extended the BB gradient method for solving general unconstrained optimization problems so that it is competitive with conjugate gradient methods. However, the numerical results reported by Raydan are poor for very ill-conditioned problems because the effect of the degree of nonmonotonicity may be noticeable. In this paper, we focus more on the nonmonotone line search technique used in the global Barzilai–Borwein (GBB) gradient method. We improve the performance of the GBB gradient method by proposing an adaptive nonmonotone line search based on the morphology of the objective function. We also prove the global convergence and the R-linear convergence rate of the proposed method under reasonable assumptions. Finally, we give some numerical experiments made on a set of unconstrained optimization test problems of the CUTEr collection. The results show the efficiency of the proposed method in the sense of the performance profile introduced (Math Program. 2002;91:201–213) by Dolan and Moré.