Synthesis of Pyranopyrazoles Using Magnetically Recyclable Heterogeneous Iron Oxide‐silica Core‐shell Nanocatalyst

The Fe₃O₄@SiO₂ core‐shell nanocatalyst were prepared and efficiently used for four‐component coupling reaction of aromatic aldehydes, malononitrile, ethyl acetoacetate and hydrazine hydrate in water/ethanol mixture. Various aromatic aldehydes possessing electron‐withdrawing and electron‐donating groups in different positions on the ring were successfully transformed to substituted pyranopyrazoles in high yields in short time. The nanocatalyst was easily recovered, and reused five times without significant loss in cata‐ lytic activity and performance. The structure, size and morphology of the nanosized catalyst were studied by various techniques such as Fourier transform infrared spectroscopy, powder X‐ray diffraction, dynamic light scattering and transmission electron microscopy.     

Performance evaluation of fast Fourier-transform continuous cyclic-voltammetry pesticide biosensor

In this work, a method for the fast monitoring of OPs in flow-injection systems was evaluated. The fast Fourier transform continuous cyclic-voltammetry (FFTCCV) at the carbon-paste electrode in a flowing solution system was used for determination of OPs. In this method the S/N ratio is enhanced by using of fast Fourier transform of the analyte and signal integration. FFTCCV can be considered as a new sensitive, accurate and fast method for determination of drugs and some pesticides. However, in order to obtain better sensitivity for a specific target, experimental parameters should be optimized. Response surface methodology (RSM) was applied to optimize three effective parameters (enzyme activity, multiwall carbon nanotube quantity and acidic sol–gel quantity). The optimum values for the tested parameters were enzyme amount H0.169 U cm⁻², multiwall carbon nanotube (MWCNT) 0.607 mL and acidic sol–gel 1.012 mL. The optimum feed pH, feed flow rate, ATChCl concentration and sweeping-rate were found to be 7.4, 0.34 mL min⁻¹, 0.750 mM and 10 V s⁻¹, respectively. The long-term stability of this flow-through system was 80% of its initial response after 120 days. Based on an incubation time of 12 min, it was found that the detection limit for paraoxon was equal to 1.7 × 10⁻⁷ mg L⁻¹ (6.2 × 10⁻¹³ M). The developed biosensor exhibited good repeatability and reproducibility. This study provides a new, modern, sensitive tool for the analysis of organophosphate pesticides.     

Optimal synthesis of function generator of four-bar linkages based on distribution of precision points

This article describes a method for optimizing the synthesis of a four-bar linkage mechanism to generate a definite mathematic function. In this research, the objective function was defined based on the least squares of error between the generated function and the desired function. Because of non-linearity of the objective function and the constraint, SQP method has been used to find the optimal mechanism. This method of optimization is a gradient-based method and its result is more trustable than heuristic methods. In this study, five precision points have been used to synthesize four-bar linkages; therefore, by using this amount of precision points, a set of non-linear equations was obtained for mechanism synthesis. Unlike the previous researches that dimensional parameters are used as optimization variables, precision points distribution was used in current research. The main innovation of this paper is presentation of some directions to have estimative prediction for distribution of precision points in optimal mechanism which maybe useful for designers. These directions were obtained based on the method that presented in current work and regard to shape of desired function and its first and second derivative.     

Homogeneous geodesics and the critical points of the restricted Finsler function

In this paperwe study the set of homogeneous geodesics of a left-invariant Finsler metric on Lie groups. We first give a simple criterion that characterizes geodesic vectors. We extend J. Szenthe’s result on homogeneous geodesics to left-invariant Finsler metrics. This result gives a relation between geodesic vectors and restricted Minkowski norm in Finsler setting. We show that if a compact connected and semisimple Lie group has rank greater than 1, then for every left-invariant Finsler metric there are infinitely many homogeneous geodesics through the identity element.     

Selective and non-selective determination of heavy metal ions in flowing solutions by fast stripping cyclic voltammetry.

A simple and fast stripping voltammetric detection method has been designed for selective and non-selective measurements of heavy metal ions in a flow-injection system. A special computer numerical method is introduced for calculating the analyte signal and noise reduction, where the signal is calculated based on the partial and total charge exchange at electrode surface. For a selective determination, the currents are integrated in the range of the oxidation and reduction of the analyte. For non-selective measurements, the integration range is set for the whole potential scan range (including oxidation and reduction of the Au surface). The time for stripping has been shown to be less than 300 ms. The main advantages of the detection method are as follows: first, removal of oxygen from the measured solution is not required; second, it is sufficiently fast for the determination of heavy metal ions in various chromatographic analysis methods. The limit of detection for tested ions was between 3 x 10(-9) and 6 x 10(-10) M, and the relative standard deviation at 50 ppb Pb2+ was 4.7% for 10 runs.     

Biological Production of Gold Nanoparticles at Different Temperatures: Efficiency Assessment

The study aims to compare different approaches and efficacies during the biological production of nanoparticles (NPs). Gold nanoparticles (AuNPs) are produced by Fusarium oxysporum at two different temperatures. One flask is incubated at 37 °C (“Common”) and the other is directly heated for 5 min at 80 °C (“Heat-treated”). Obtained AuNPs are analyzed and compared by spectrophotometry, transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), dynamic light scattering (DLS), and Fourier transform infrared spectroscopy (FTIR). Graphite furnace atomic absorption spectroscopy (GF-AAS) is used to determine the particle concentration after the AuNPs production. The AuNPs prepared by both (the Common and the Heat-treated) methods exhibit maximum absorption peaks at 541 and 528 nm, respectively, and have round shapes and sizes of less than 50 nm. Their zeta potential is about −28 mV. GF-AAS shows that the efficiency of AuNP production in Common- and Heat-treated samples is equal, between 65% and 68%. Since the Heat-treated sample shows a better size distribution, the use of higher temperature and shorter time period is preferable for the bioproduction of AuNPs. It seems that shortening the time for the production of AuNPs prevents the formation of larger NPs.     

Quantum Dot-Based Biosensor for the Detection of Human T-Lymphotropic Virus-1

A method was developed to identify human T-lymphotropic virus-1 (HTLV-1) using cadmium–tellurium quantum dots. Two probes including the biotin-labeled acceptor and NH2-reporter probes with target DNA were hybridized. The resulted sandwich complex was immobilized on a well containing streptavidin. The quantum dot solution was added to the sandwich complex, conjugated with the amine group of reporter probe, and emission spectra of the quantum dots were recorded. The biosensor response was linear with HTLV-1 concentrations from 10 pg/µl to 0.24?ng/µl, with a detection limit of 19.5 pg/µl. The assay may be successfully used for detection of long nucleic acids.