A Novel,One‐Pot Four‐Component Route to 2′‐Thioxo‐2′,3′‐dihydrospiro[indole‐3,6′‐[1,3]thiazin]‐2‐one Derivatives

An efficient route to 2′,3′‐dihydro‐2′‐thioxospiro[indole‐3,6′‐[1,3]thiazin]‐2(1H)‐one derivatives is described. It involves the reaction of isatine, 1‐phenyl‐2‐(1,1,1‐triphenyl‐λ⁵‐phosphanylidene)ethan‐1‐one, and different amines in the presence of CS₂ in dry MeOH at reflux (Scheme 1). The alkyl carbamodithioate, which results from the addition of the amine to CS₂, is added to the α,β‐unsaturated ketone, resulting from the reaction between 1‐phenyl‐2‐(1,1,1‐triphenyl‐λ⁵‐phosphanylidene)ethan‐1‐one and isatine, to produce the 3′‐alkyl‐2′,3′‐dihydro‐4′‐phenyl‐2′‐thioxospiro[indole‐3,6′‐[1,3]thiazin]‐2(1H)‐one derivatives in excellent yields (Scheme 2). Their structures were corroborated spectroscopically (IR, ¹H‐ and ¹³C‐NMR, and EI‐MS) and by elemental analyses.     

Synthesis and characterization of Schiff-base-containing polyamides

A series of new Schiff base polyamides（PAs） were synthesized by polycondensation of benzilbisthiosemicarbazone diamine（LH₆） with different commercially available aliphatic and aromatic diacid chlorides. The monomer and all the PAs were characterized by FTIR,¹H-NMR,and elemental analysis.The prepared polyamides showed inherent viscosities in the range of 0.30-0.36 dL/g in DMF at 25℃,indicating their moderate molecular weight.The PAs were completely soluble in aprotic polar solvents such as dimethylformamide（DMF）,N-methylpyrolidone（NMP）, tetrachloroethane（TCE）,dimthylsulfoxide（DMSO） and also in H₂SO₄ and partially soluble in THF,acetone and chloroform at room temperature.Thermal analysis showed that these PAs were practically amorphous and exhibited 10%weight loss above 220℃.     

Synthesis of New LnxBi2–xSe3 (Ln: Sm3+, Eu3+, Gd3+, Tb3+) Nanomaterials and Investigation of Their Optical Properties

New Ln_xBi_2–xSe₃ (Ln: Sm³⁺, Eu³⁺, Gd³⁺, Tb³⁺) based nanomaterials were synthesized by a co‐reduction method. Powder XRD patterns indicate that the Ln_xBi_2–xSe₃ crystals (Ln = Sm³⁺, Eu³⁺, x = 0.00–0.44 and Ln = Gd³⁺, Tb³⁺, x = 0.00–0.50) are isostructural with Bi₂Se₃. The cell parameter c decreases for Ln = Eu³⁺, Gd³⁺, Tb³⁺ upon increasing the dopant content (x), while a slightly increases. Changes in lattice parameters could be related to the radii of cations. SEM images show that doping of the lanthanide ions in the lattice of Bi₂Se₃ generally results in nanoflowers. For the terbium compound two kinds of morphologies (nanoflowers and nanobelts) were observed. UV/Vis absorption and emission spectroscopy reveals mainly electronic transitions of the Ln³⁺ ions. Emission spectra show intense transitions from the excited to the ground state of Ln³⁺ and energy transfer from the Bi₂Se₃ lattice. Emission spectra of europium‐doped materials, in addition to the characteristic red emission peaks of Eu³⁺, show an intense blue emission band centered at 432 nm, originating from the 4f⁶5d¹ to 4f⁷ configuration in Eu²⁺. EPR measurements confirm the existence of Eu²⁺ in the materials. Interestingly, for all samples starting at low Ln³⁺ concentration, the emission intensity rises to a maximum at a Ln³⁺ concentration of x = 0.2 and falls again steadily to a minimum at x = 0.45.     

A comparison of complexation of Li+ ion with macrocyclic ligands 15-crown-5 and 12-crown-4 in binary nitromethane-acetonitrile mixtures by using lithium-7 NMR technique and ab initio calculation

Lithium-7 NMR measurements were used to investigate the stoichiometry and stability of Li+ complexes with 15-crown-5 (15C5), benzo-15-crown-5 (B15C5), dibenzo-15-crown-5 (DB15C5) and 12-crown-4 (12C4) in a number of nitromethane (NM)-acetonitrile (AN) binary mixtures. In all cases, the exchange between the free and complexed lithium ion was fast on the NMR time scale and a single population average resonance was observed. While all crown ethers form 1:1 complexes with Li+ ion in the binary mixtures used, both 1:1 and 2:1 (sandwich) complexes were observed between lithium ion and 12C4 in pure nitromethane solution. Stepwise formation constants of the 1:1 and 2:1 (ligand/metal) complexes were evaluated from computer fitting of the NMR-mole ratio data to equations which relate the observed metal ion chemical shifts to formation constants. There is an inverse linear relationship between the logarithms of the stability constants and the mole fraction of acetonitrile in the solvent mixtures. The stability order of the 1:1 complexes was found to be 15C5·Li+>B15C5·Li+>DB15C5·Li+>12C4·Li+. The optimized structures of the free ligands and their 1:1 and 2:1 complexes with Li+ ion were predicted by ab initio theoretical calculations using the Gaussian 98 software, and the results are discussed.     

Stoichiometric and free radical-scavenging kinetic studies of extractable polyphenols from pomegranate husk and pistachio hull

In this work, the antiradical activity of fresh and aged skins of two Iranian varieties of pomegranate husk and pistachio hull was measured in order to assess their concentration in antioxidant potential usable in various fields. The radical scavenging capacity (RSC) of pomegranate husks and pistachio hulls samples were studied using the 2,2-diphenyl-1-picrylhydrazyl radical (DPPH^.) assay. To determine the RSC and stoichiometric factor of the samplers, the second-order rate constants (k ₂) and total H-atom-donating capacities (n) for the oxidation of polyphenol extracts by DPPH^. were evaluated. The resulting k ₂ values were also compared with those of the natural and synthetic antioxidants. The order of relative second-order rate constants in methanol at 25 °C found to be pomegranate husk > gallic acid > tannic acid > pistachio hull. Furthermore, the RSCs based on the calculation of area under kinetic curve (AUC), total stoichiometric factor of natural phenolics and commercial antioxidants were also compared.     

Synthesis and characterization of new LnxSb2−xSe3 (Ln: Yb, Er) nanoflowers and their physical properties

New Ln_xSb_2−xSe₃ (Ln: Yb³⁺, Er³) based nanomaterials were synthesized by a co-reduction method. Powder XRD patterns indicate that the Ln_xSb_2−xSe₃crystals (Ln=Yb³⁺, Er³⁺, x=0.00-0.12) are isostructural with Sb₂Se₃. The cell parameters b and c decrease for Ln=Er³⁺ and Yb³⁺ upon increasing the dopant content (x), while a increases. SEM images show that doping of the lanthanide ions in the lattice of Sb₂Se₃ generally results in nanoflowers. UV-vis absorption and emission spectroscopy reveals mainly electronic transitions of the Ln³⁺ ions in case of Yb³⁺ doped nanomaterials. Emission spectra of doped materials, in addition to the characteristic red emission peaks of Sb₂Se₃, show additional emission bands centered at 955 nm, originating from the ²F_7/2→²F_5/2 transition (f-f transitions) of the Yb³⁺ ions. DSC curves indicate that Sb₂Se₃ has the highest thermal stability. The temperature dependence of the electrical resistivity of doped-Sb₂Se₃ with Yb³⁺ and Er³⁺ was studied.     

Optimal sliding mode control of single degree-of-freedom hysteretic structural system

This paper addresses the controller design problem of a nonlinear single degree-of-freedom structural system excited by the earthquake. Bouc–Wen model, as an efficient hysteresis modeling method, is used to model the system nonlinearity. Sliding mode control (SMC), due to its robustness in dealing with uncertainty, is utilized as the main control strategy. An optimal sliding surface is presented which minimizes the displacement and control force in terms of a quadratic cost function. Two numerical examples are given to illustrate the effectiveness of the proposed strategy subject to three earthquakes of El-Centro, Rinaldi and Kobe. Simulation results show a significant and considerable reduction in structural response and indicate that the performance of suggested optimal SMC strategy is remarkable.     

Backstepping-based Lyapunov redesign control of hysteretic single degree-of-freedom structural systems

This paper considers the problem of active control design for a hysteretic single-degree-of-freedom (SDOF) structural system which is exposed to an earthquake excitation. First, backstepping-based control is used to design a controller for the structural system neglecting the effect of the earthquake disturbance. Then, Lyapunov redesign is utilized to design a robust controller for the system in the presence of the earthquake excitation. The hysteretic part of the structural system is modeled by the well-known Bouc–Wen equation, and this equation is directly utilized in the controller design. The controller is proposed for two cases: (a) when the parameters of the structure and the Bouc–Wen model are known, and (b) when these parameters are uncertain. A Lyapunov function is introduced for the closed-loop system, which guarantees the stability of the system equilibrium point. Since the controllers use the nominal and/or minimum and maximum values of the system parameters, the proposed methods are model based. Numerical evaluations are conducted to show the effectiveness of the proposed method. Seven different earthquakes are considered as the external excitations. Simulation results show that the displacement, velocity, and acceleration responses of the controlled structure are reduced significantly compared to the uncontrolled structure.     

Conductometric study of complex formations between some substituted pyrimidines and some metal ions in acetonitrile and the determination of thermodynamic parameters

The complexation reactions between Cr³⁺, Cd²⁺, Co²⁺, Ni²⁺, Hg²⁺, Zn²⁺, Pb²⁺,and Ag⁺ metal ions with diethyl-3-(4-hydroxy-6-methylpyrimidin-2-yl) guanidine (L1), 2-amino,4-hydroxy,6-methylpyrimidine (L2), and 2-(diethylamin),4-hydroxy,6-methylpyrimidine (L3) in acetonitrile (AN) were studied using a conductometric method. The formation constants of the resulting complexes were determined from computer fitting conductance-mole ratio data. The results revealed that the formation constants of L1 with metal ions are varying in order of Cr³⁺ > Pb²⁺ > Zn²⁺ > Co²⁺ > Hg²⁺ > Ag⁺ ~ Cd²⁺ > Ni²⁺. For L2 and L3 the sequence of complex formation constants are follow as Cr³⁺ > Pb²⁺ > Zn²⁺ > Co²⁺ > Cd²⁺ > Hg²⁺ > Ag⁺ > Ni²⁺ and Cr³⁺ > Pb²⁺ > Zn²⁺ > Co²⁺ > Ni²⁺ ~ Hg²⁺ ~ Cd²⁺ ~ Ag⁺, respectively. The values of the thermodynamic parameters (ΔH, ΔS and ΔG) for complexation reactions were obtained from the temperature dependence of the stability constants. In all cases, the complexes were found to be enthalpy stabilized but entropy destabilized. In addition, some ab-initio quantum-mechanical calculations were carried out, in order to obtain a clue about the degree tendency of ligands to metal ions.     

Developing electrodeposition techniques for preconcentration of ultra-traces of Ni, Cr and Pb prior to arc-atomic emission spectrometry determination

Electrodeposition is known to be proper for separation and preconcentration of extremely low concentrations of analytes from the bulk sample which is instrumentally very simple. In the present research, a combination of electrodeposition with arc atomic emission spectrometry (ED-AAES) method has been developed in order to improve the analytical performance of this spectrometry technique. The results show that sensitivity and detection limits by using ED-AAES were improved 1000–2000 folds over those of normal arc atomic emission spectrometry in determination of the selected elements. The detection limits for measurement of Ni, Cr and Pb were 2.56, 3.05 and 2.11 µg L^{− 1} for monodeposition and 3.31, 3.72 and 3.25 µg L^{− 1} for simultaneously deposition, respectively. The precision of determination was in the range of 2–4% RSD. Typical calibration graphs for these elements were linear up to 100 µg L^{− 1}, depending on the element and matrix.Application of this technique was also tested on determination of the studied elements in an electroplating plant's waste water. The accuracy of technique was verified by comparing the results of the waste water analysis with those of electrothermal atomic absorption spectroscopy as a reference standard method.The obtained results show that the combined technique (ED-AAES) has been progressed substantially toward the ultimate goal of direct interference-free determination of trace analysis in complex samples by AAES.