Multiwavelength spectrophotometric determination of acidity constants of 1-（2-thiazolylazo）-2-naphthol in methanol-water mixtures

The acid-base properties of 1-(2-thiazolylazo)-2-naphthol (TAN) in mixtures of methanol-water at 25℃and an ionic strength of 0.1 mol/L are studied by a multi-wavelength spectrophotometric method.The acidity constants of all related equilibria are estimated using the whole spectral fitting of the collected data to an established factor analysis model DATAN program was used for determination of acidity constants.The corresponding pK_a values in methanol-water mixtures were determined.There is a linear relationship between acidity constants and the mole fraction of methanol in the solvent mixtures.     

Simultaneous spectrophotometric determination of mercury and palladium with Thio-Michler's Ketone using partial least squares regression and orthogonal signal correction

A simple, novel and sensitive spectrophotometric method was described for simultaneous determination of mercury and palladium. The method is based on the complex formation of mercury and palladium with Thio-Michler's Ketone (TMK) at pH 3.5. All factors affecting on the sensitivity were optimized and the linear dynamic range for determination of mercury and palladium found. The simultaneous determination of mercury and palladium mixtures by using spectrophotometric method is a difficult problem, due to spectral interferences. By multivariate calibration methods such as partial least squares (PLS), it is possible to obtain a model adjusted to the concentration values of the mixtures used in the calibration range. Orthogonal signal correction (OSC) is a preprocessing technique used for removing the information unrelated to the target variables based on constrained principal component analysis. OSC is a suitable preprocessing method for PLS calibration of mixtures without loss of prediction capacity using spectrophotometric method. In this study, the calibration model is based on absorption spectra in the 360-660 nm range for 25 different mixtures of mercury and palladium. Calibration matrices were containing 0.025-1.60 and 0.05-0.50 microg mL(-1) of mercury and palladium, respectively. The RMSEP for mercury and palladium with OSC and without OSC were 0.013, 0.006 and 0.048, 0.030, respectively. This procedure allows the simultaneous determination of mercury and palladium in synthetic and real matrix samples good reliability of the determination.     

A Novel Electrochemical Method for the Sensitive Determination of Aflatoxin B1 Using a Bivalent Binding Aptamer-cDNA Structure

In this study, a simple electrochemical sensing platform with the employment of a bivalent binding aptamer-cDNA probe (BBA-cDNA) structure is constructed for the detection of aflatoxin B₁ (AFB₁) as a mycotoxin. The BBA-cDNA structure is composed of two strands of aptamer (Apts) and their complementary strand (CS). Using a simple but accurate design, the presented measurement approach showed enhanced sensitivity and selectivity for AFB₁ detection with a LOD of 0.1 ng/mL. The approach presented in this study can be applied to the development of biosensors for the measurement of various toxins by substituting the proper aptamers and complementary strands.     

The Meir–Keeler fixed point theorem in incomplete modular spaces with application

In this paper, we present a new generalized modular version of the Meir–Keeler fixed point theorem endowed with an orthogonal relation. Our results improve the results of (Eshaghi Gordji et al., On orthogonal sets and Banach fixed point theorem, Fixed Point Theory, 2017). Finally, this result is applied to the existence and uniqueness of solutions to perturbed integral equations in modular function spaces.     

Electrochemical aptamer based assay for the neonicotinoid insecticide acetamiprid based on the use of an unmodified gold electrode

The authors report on an aptamer-based electrochemical assay for the insecticide acetamiprid. It is based on the target-induced release of the redox probe Methylene Blue (MB) from the dsDNA formed between aptamer and complementary strand (Apt/CS), exonuclease I (Exo I) and silica nanoparticles coated with streptavidin (SiNP-Streptavidin). MB is detected electrochemically using an unmodified gold electrode. In the presence of acetamiprid, MB is released from the Apt/CS dsDNA and accumulated in the close environment of the gold electrode. This results in a strong electrochemical signal for MB at fairly low working voltage of typically ?0.27 V. In the absence of target, however, the SiNP-streptavidin conjugate modified MB-dsDNA remains intact. Hence, the electrochemical signal remains weak. The method displays high selectivity for acetamiprid and a limit of detection as low as 153 pM. The assay was successfully applied to the determination of acetamiprid in (spiked) water and serum samples, with LODs of 161 and 209 pM, respectively.

Open image in new window

Graphical abstract Schematic illustration of acetamiprid detection based on electrochemical assay. In the absence of acetamiprid, MB-dsDNA-modified SiNP-Streptavidin complex is intact and redox probe (MB) does not exist in the environment of electrode, resulting in a weak electrochemical signal (a). In the presence of target, Apt binds to acetamiprid and CS and MB leave the SiNP-Streptavidin. Exo I digests CS. So, a huge amount of MB is present in the environment of electrode and a strong electrochemical signal is observed (b).

     

Effect of conductive particles on the mechanical,electrical, and thermal properties of maleated polyethylene

Inclusion of conductive particles is a convenient way for the enhancement of electrical and thermal conductivities of polymers. However, improvement of the mechanical properties of such composites has remained a challenge. In this work, maleated polyethylene is proposed as a novel matrix for the production of conductive metal–thermoplastic composites with enhanced mechanical properties. The effects of two conductive particles (iron and aluminum) on the morphological, mechanical, electrical, and thermal properties of maleated polyethylene were investigated. Morphological observations revealed that the matrix had excellent adhesion with both metal particles. Increase in particle concentration was shown to improve the tensile strength and modulus of the matrix significantly with iron being slightly more effective. Through‐plane electrical conductivity of maleated polyethylene was also substantially improved after adding iron particles, while percolation was observed at particle contents of around 20–30% vol. In the case of aluminum, no percolation was observed for particle contents of up to 50% vol., which was linked to the orientation of the particles in the in‐plane direction due to the squeezing flow. Inclusion of particles led to substantial increase (over 700%) in the thermal conductivities of both composites. The addition of high concentrations of metal particles to matrix led to the creation of two groups of materials: (i) composites with high electrical and thermal conductivities and (ii) composites with low electrical and high thermal conductivities. Such characteristics of the composites are expected to provide a unique opportunity for applications where a thermally conductive/electrically insulating material is desired. Copyright © 2015 John Wiley & Sons, Ltd.     

Novel Photonic Bio-Chip Sensor Based on Strained Graphene Sheets for Blood Cell Sorting

A photonic biochip with a tunable response in the visible range is suggested for blood cell sorting applications. Multi-layers of ZnS and Ge slabs (as the main building blocks), hosting a cell in which bio-sample could be injected, are considered as the core of the sensor. In order to increase the sensitivity of the chip, the bio-cell is capsulated inside air slabs, and its walls are coated with graphene sheets. Paying special attention to white and red blood components, the optimum values for structural parameters are extracted first. Tunability of the sensor detectivity is then explored by finding the role of the probe light incident angle, as well as its polarization. The strain of the graphene layer and angle in which it is applied are also suggested to further improve the performance tunability. Results reflect that the biochip can effectively identify selected components through their induced different optical features, besides of the different figure of merit and sensitivity amounts that are recorded for them by the sensor.     

Impact of coupling geometry on thermoelectric properties of oligophenyl-base transistor

Thermal and electron transport through organic molecules attached to three-dimensional gold electrodes in two different configurations, namely para and meta with thiol-terminated junctions is studied theoretically in the linear response regime using Green's function formalism. We used thiol-terminated(–SH bond) benzene units and found a positive thermopower because the highest occupied molecular orbital(HOMO) is near the Fermi energy level. We investigated the influence of molecular length and molecular junction geometry on the thermoelectric properties. Our results show that the thermoelectric properties are highly sensitive to the coupling geometry and the molecular length. In addition, we observed that the interference effects and increasing molecular length can increase the thermoelectric efficiency of device in a specific configuration.     

Penicillamine functionalized B12N12 and B12CaN12 nanocages act as potential inhibitors of proinflammatory cytokines: A combined DFT analysis,ADMET and molecular docking study

The adsorption of penicillamine (PCA) on pure B₁₂N₁₂ and B₁₂CaN₁₂ nanocages in aqueous and chloroform solvents has been evaluated using density functional theory (DFT) calculations. The interaction of PCA on B₁₂N₁₂ nanocages is chemisorption through its four nucleophilic sites: amine, carbonyl, hydroxyl and thiol. The most stable adsorption configuration was achieved when zwitterionic PCA adsorbs via its carbonyl group in water with value of ?1.723 eV, in contrast, when neutral PCA adsorbs via its amine group in chloroform with value of ?1.68 eV. Intercalated calcium ion within B₁₂N₁₂ nanocage (B₁₂CaN₁₂) was shown to attract PCA onto nanocage surface, resulting in higher solubility and adsorption energy after their complexation in water and chloroform. The adsorption of multiple PCA molecules from their amine and carbonyl groups on pure and B₁₂CaN₁₂ nanocages were also evaluated where two and three molecules can be chemisorbed on boron atoms of the nanocage surfaces with the adsorption energy per PCA reduces slightly with the increasing the amount of drugs due to the curvature effects. Molecular docking study indicates that PCA from its NH₂ group on B₁₂CaN₁₂ nanocage has the best binding affinity and inhibition potential of tumor necrosis factor-alpha (TNF-α) and Interleukin-1 (IL-1) receptors as compared with the other adsorption systems. Molecular docking and ADMET analysis displayed that the chosen compounds pass Lipinski Rule and have appropriate pharmacokinetic features suitable as models for developing anti-inflammatory agents.