Electrospun superhydrophobic polystyrene hollow fiber as a probe for liquid–liquid microextraction with gas chromatography‐mass spectrometry

A superhydrophobic polystyrene hollow fiber was electrospun around a copper spring collector. This approach led to the construction of a hollow fiber membrane, and the copper spring acted as a scaffold. The characteristic properties of the hollow fiber were studied by scanning electron microscopy. The membrane was used as a probe to transfer the extracting solvent from aquatic media to a gas chromatograph. After performing the liquid–liquid microextraction procedure on 10 mL of water sample by octanol, the whole solution was passed through the prepared polystyrene hollow fiber. Propanol, containing 2 mg/L lindane as the internal standard, was used for desorption and an aliquot of 2 μL of the desorbing solvent was subsequently injected into gas chromatography with mass spectrometry. Effects of different parameters influencing the extraction efficiency were optimized. The limits of detection and quantification were 2 and 6 ng/L, respectively. The relative standard deviations at a concentration level of 100 ng/L were between 2 and 6% (n = 3) while the method linearity ranged from 6 to 200 ng/L. Some real water samples were analyzed by the developed method and relative recoveries were in the range of 76–107%.     

Refinement of the primary hydration shell model for molecular dynamics simulations of large proteins

A realistic representation of water molecules is important in molecular dynamics simulation of proteins. However, the standard method of solvating biomolecules, that is, immersing them in a box of water with periodic boundary conditions, is computationally expensive. The primary hydration shell (PHS) method, developed more than a decade ago and implemented in CHARMM, uses only a thin shell of water around the system of interest, and so greatly reduces the computational cost of simulations. Applying the PHS method, especially to larger proteins, revealed that further optimization and a partial reworking was required and here we present several improvements to its performance. The model is applied to systems with different sizes, and both water and protein behaviors are compared with those observed in standard simulations with periodic boundary conditions and, in some cases, with experimental data. The advantages of the modified PHS method over its original implementation are clearly apparent when it is applied to simulating the 82 kDa protein Malate Synthase G. © 2009 Wiley Periodicals, Inc. J Comput Chem 2009     

Artificial neural network for quantitative determination of total protein in yogurt by infrared spectrometry

A method has been introduced for quantitative determination of protein content in yogurt samples based on the characteristic absorbance of protein in 1800-1500 cm^− 1 spectral region by mid-FTIR spectroscopy and chemometrics. Successive Projection Algorithm (SPA) wavelength selection procedure, coupled with feed forward Back-Propagation Artificial Neural Network (BP-ANN) model was the benefited chemometric technique. Relative Error of Prediction (REP) in BP-ANN and SPA-BP-ANN methods for training set was 7.25 and 3.70 respectively. Considering the complexity of the sample, the ANN model was found to be reliable, while the proposed method is rapid and simple, without any sample preparation step.     

Solid‐state synthesis of a new core–shell nanocomposite of polyaniline and silica via oxidation of aniline hydrochloride by FeCl3.6H2O

Among the different oxidants used for the preparation of polyaniline in the solid‐state, iron (III) chloride (FeCl₃.6H₂O) can act as both oxidant and dopant. This work reports the synthesis and characterization of novel composite of polyaniline/silica. The polymerization was performed by oxidative polymerization of aniline hydrochloride in the presence of silica and FeCl₃.6H₂O under solid‐state (solvent‐free) condition. The FeCl₃.6H₂O has been chemically supported on silica and generated silica‐supported FeCl₃ ( SSFe ), which plays three important roles simultaneously (a) oxidant, (b) primary dopant, and (c) secondary dopant (Lewis acid). Furthermore, the existence of silica is important for proceeding of polymerization in solid state. In the other words, the surface polymerization and green chemistry in solid state have been coupled. The characterization and doping process are verified by ultraviolet‐visible, Fourier transform infrared, atomic absorption spectroscopy, thermogravimetric analysis, differential scanning calorimetry, and elemental analysis (CHNS). From atomic absorption spectroscopy the ratio of Fe/N in the composite obtained about 1, which confirms the formation of delocalized polarons by SSFe in the composites. The conductivity is in the range of semi‐conductive. Furthermore, contact resistance was determined by circular‐transmission line measurement. According to scanning electron microscopy images silica particles have been thoroughly coated by polyaniline within the range of 0.2 to 1 µm. However, transition electron microscopy images depict the uniform solid nanospheres (no hollow spheres or fibers), and their mean diameters are under of 50 nm. It confirms nanocomposite of core–shell PANI‐SSFe. Copyright © 2016 John Wiley & Sons, Ltd.     

Phonon-dependent transport through a serially coupled double quantum dot system

Using Keldysh nonequilibrium Green function formalism and mapping a many-body electron–phonon interaction onto a one body problem, the electron transport through a serially coupled double quantum dot system is analyzed. The influence of the electron–phonon interaction, temperature, detuning, and interdot tunneling on the transmission coefficient and current is studied. Our results show that the electron–phonon interaction results in the appearance of the side peaks in the transmission coefficient, whose height is strongly dependent on the phonon temperature. We have also found that the inequality of the electron–phonon interaction strength in two dots gives rise to an asymmetry in the current–voltage characteristic. In addition, the temperature difference between the phonon and electron subsystems results in the reduction of the saturated current and the destruction of the step-like behavior of the current. It is also observed that the detuning can improve the magnitude of the current by compensating the mismatch of the quantum dots energy levels induced by the electron–phonon interaction.     

Dislocation technique to obtain the dynamic stress intensity factors for multiple cracks in a half-plane under impact load

In this study, the transient response of multiple cracks subjected to shear impact load in a half-plane is investigated. At first, exact analytical solution for the transient response of Volterra-type dislocation in a half-plane is obtained by using the Cagniard-de Hoop method of Laplace inversion and is expressed in explicit forms. The distributed dislocation technique is used to construct integral equations for a half-plane weakened by multiple arbitrary cracks. These equations are of Cauchy singular type at the location of dislocation solved numerically to obtain the dislocation density on the cracks faces. The dislocation densities are employed to determine dynamic stress intensity factors history for multiple smooth cracks. Finally, several examples are presented to demonstrate the applicability of the proposed solution.     

Preparation of new supramolecular liquid-crystalline polyesters containing 3-chloro-4-(alkoxy)benzoic acids

Supramolecular liquid-crystalline polyester complexes based on intermolecular hydrogen bonds between the carboxylic group and the pyridyl moieties was prepared by using non-liquid-crystalline H-donors, [3-chloro-4-(butyloxy)benzoic acid (2a), 3-chloro-4-(octyloxy)benzoic acid (2b), 3-chloro-4-(dodecyloxy)benzoic acid (2c) and 3-chloro-4-(tetradecyloxy)benzoic acid (2d)] and H-acceptor-polyester containing pyridyl units. Intermolecular hydrogen bond formation was confirmed by Fourier transform infrared spectroscopy. The liquid-crystalline behavior of the complex formed was established by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). The polyester complexes containing 2c and 2d donor components exhibit liquid crystalline mesophase and behave as side-chain liquid-crystalline polymers. Compared with unsubstituted parent acid, the presence of chloro group as a lateral substituent has a little negative effect on the induction of liquid crystallinity on the polyester complexes systems. The results show that the more stability of the obtained H-bonded complexes in comparison with analogues without 3-Cl substituents is due to the increased acidity of benzoic acid moiety.     

A mechanistic insight into caspase-7 inhibition by BIR1-2 domains of XIAP and cIAP1

Previous studies failed to demonstrate any role for the BIR1 domain of the inhibitor of apoptosis proteins (IAPs) in inhibition of executioner caspases. In this study, XIAP-BIR1-2 and c-IAP1-BIR1-2 domains have been used to investigate the role of BIR1 in the inhibition of caspase-7. Kinetic analysis confirmed that caspase-7 was inhibited in an uncompetitive manner at lower concentrations of XIAP-BIR1-2, whereas the inhibition was switched to the mixed type mode at higher concentrations of the inhibitor. In contrast, cIAP1-BIR1-2 inhibited caspase-7 in a mixed type mode at all examined concentrations. These data suggest that the presence of BIR1 is essential for inhibition of caspase-7 by cIAP1. Far-UV CD and fluorescence spectroscopy experiments showed that despite similar secondary structures, XIAP-BIR1-2 and cIAP1-BIR1-2 have different biophysical properties. BIR1-2 domain of XIAP was found to be more flexible than cIAP1, which may be the reason behind differences in their kinetic properties.     

pharmaceutical and biological samples using modified multiwall carbon nanotubes paste electrode

A carbon paste electrode(CPE) chemically modified with multiwall carbon nanotubes and ferrocene(FC) was used as a selective electrochemical sensor for the simultaneous determination of trace amounts of cysteamine(CA) and folic acid(FA).This modified electrode showed very efficient electrocatalytic activity for the anodic oxidation of CA.The peak current of differential pulse voltammograms of CA and FA increased linearly with their concentration in the ranges of 0.7-200μmol/L CA and 5.0- 700μmol/L FA.The detection limits for CA and FA were 0.3μmol/L and 2.0μmoI/L,respectively.The diffusion coefficient(D) and transfer coefficient(α) of CA were also determined.These conditions are sufficient to allow determination of CA and FA both individually and simultaneously.