Trans‐3,5‐dihydroperoxy‐3,5‐dimethyl‐1,2‐dioxalane/HBr System as New,Effective, Mild and Non‐toxic Reagent for Synthesis of 2‐Aryl‐1H‐benzothiazoles and 2‐Aryl‐1‐arylmethyl‐1H‐benzimidazoles

Ttrans‐3,5‐dihydroperoxy‐3,5‐dimethyl‐1,2‐dioxalane has been used as new, effective, solid, inexpensive and nontoxic oxidant for in situ generation of Br⁺ from HBr. This system has been applied as catalyst for synthesis of 2‐aryl‐1H‐benzothiazoles and 2‐aryl‐1‐arylmethyl‐1H‐benzimidazoles at room temperature in excellent yields and high purity.     

Two new silver(I) complexes with 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz): Preparation,characterization, crystal structure and alcohol oxidation activity in the presence of oxone

Two new silver(I) complexes ((tptz)Ag₂(NO₃)₂ and [Ag₅(tptz)₄](NO₃)₅) with 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz) have been synthesized and characterized by X-ray diffraction, elemental analysis, ¹H NMR, IR, fluorescence, UV–Vis spectroscopy and electrochemistry. Oxidation of alcohols to their corresponding aldehydes and ketones was conducted with one of the Ag complexes as a catalyst, soluble enough in organic solvent, using oxone (2KHSO₅·KHSO₄·K₂SO₄) as an oxidant under biphasic reaction conditions (CH₂Cl₂/H₂O) and tetra-n-butylammonium bromide as phase transfer agent under air at room temperature.     

Effect of solvent on the stability constant of complex formation and the thermodynamic parameters between dicyclohexyl-18-crown-6 with Eu3+, La3+, Er3+ and Y3+ cations

The complexation reaction between Eu³⁺, La³⁺, Er³⁺ and Y³⁺ cations with the dicyclohexyl-18-crown-6 (DCH18C6) in acetonitrile (AN)–dimethylformamide (DMF) and AN–methanol (MeOH) binary systems have been studied at different temperatures using conductometric method. The conductometric data show that the stoichiometry of the complexes is 1:1 [ML]. The results show that the stability constant of complexes in various solvents is: AN > MeOH > DMF. In the some cases, the minimum of logK_f for (DCH18C6–Eu³⁺), (DCH18C6–La³⁺), (DCH18C6–Er³⁺) and (DCH18C6–Y³⁺) complexes in AN–MeOH binary systems obtain at χ_MeOH ~ 0.75, and also, the logK_f of (DCH18C6–Er³⁺) complex in AN–DMF binary systems show a minimum at χ_AN ~ 0.75. Non-linear behavior was observed for the stability constant of complexes versus the composition of the solvent systems. The experimental data show that the selectivity order of DCH18C6 for these cations in AN–MeOH binary systems (mol% AN = 50, 75) at 25 °C is: Y³⁺ > Er³⁺ > Eu³⁺ > La³⁺. The values of thermodynamic parameters (?H?_C) for formation of complexes were obtained from temperature dependence of stability constants of complexes using the van′t Hoff plots and the standard entropy (?S?_C) were calculated from the relationship: ?G?_C, 298.15 = ?H?_C ?298.15?S?_C. The results show that the values of these thermodynamic parameters are influenced by the nature and the composition of the binary systems.     

A MILD METHOD FOR CONVERSION OF ALCOHOLS TO DIALKYL SULFITES BY USE OF Na2SO3/SOCl2

Alcohols are easily converted to their corresponding dialkyl sulfite under mild reaction conditions using Na₂SO₃/SOCl₂ in moderate to good isolated yields.     

Kinetics study of selective removal of lead(II) in an aqueous solution containing lead(II), copper(II) and cadmium(II) across bulk liquid membrane

Transport of Pb(II) ion from equimolar aqueous solutions of Pb(II), Cu(II) and Cd(II) as well as from aqueous solutions containing only Pb(II) source phase (C_metal = 1.0 × 10^?4 mol L^?1) through bulk liquid membranes containing crown ether and oleic acid as carrier has been investigated. The initial fluxes of transported metal ions depend on the hydrophile–lipophile balance (HLB) and molar volumes (Vx) of crown ethers. The initial fluxes of Pb(II), Cu(II), and Cd(II) decrease with increase of HLB value for azacrown ether, i.e., tetraaza-14-crown-4 (A₄14C4), L1 > benzo-15-crown-5 (B15C5), L2 > 4′-Aminobenzo-15C5, L3 > nitrobenzo-15-crown-5 (NB15C5), L4. The selectivity of the metal ions showed the following separation factors (SF): SF_Pb–Cu = 2.15, SF_Cu–Cd = 2.10, SF_Pb–Cd = 4.52. The highest transport recovery for Pb(II) was observed for L1 (99.3 %).     

Spectroscopic study on the interaction of Bacillus subtilis α-amylase with cetyltrimethylammonium bromide

The interaction between α‐amylase from Bacillus subtilis and cetyltrimethylammonium bromide (CTAB) has been investigated at various temperature conditions using fluorescence and circular dichroism (CD) spectroscopic methods. Fluorescence data revealed that the fluorescence quenching of α‐amylase by CTAB is the result of complex formation between CTAB and α‐amylase. The thermodynamic analysis on the binding interaction data shows that the interactions are strongly exothermic (ΔH°=−17.92 kJ mol⁻¹) accompanied with increase in entropy (ΔS° between 109 to 135 J mol⁻¹ K⁻¹). Thus the binding of CTAB to α-amylase is both enthalpic and entropic driven, which represent the predominate role of both electrostatic and hydrophobic interactions in complex formation process. The values of 2.17×10⁻³ M⁻¹ and 1.30 have been obtained from associative binding constant (K_a) and stoichiometry of binding number (n), from analysis of fluorescence data, respectively. Circular dichroism spectra showed the substantial conformational changes in secondary structure of α‐amylase due to binding of CTAB, which represents the complete destruction of both secondary and tertiary structure of α-amylase by CTAB.     

Dependence of the amplifying parameters on buffer gases in copper-vapor lasers

We use a pair of copper-vapor lasers in the oscillator–amplifier configuration for investigating the small-signal gain and the intensity saturation as the amplifying parameters, versus the pressure of various types of buffer gases. We show that the small-signal gain increases and the intensity saturation decreases with increase in the air pressure. Moreover, the values of these parameters are different for various gases used in the amplifier media. We show that both parameters are greater at the atmosphere of neon as a buffer gas than that of a mixture of helium and neon or air.     

Depth in bucket recursive trees with variable capacities of buckets

We consider bucket recursive trees of sizen consisting of all buckets with variable capacities1,2,...,b and with a specifc stochastic growth rule.This model can be considered as a generalization of random recursive trees like bucket recursive trees introduced by Mahmoud and Smythe where all buckets have the same capacities.In this work,we provide a combinatorial analysis of these trees where the generating function of the total weights satisfes an autonomous frst order diferential equation.We study the depth of the largest label（i.e.,the number of edges from the root node to the node containing label n）and give a closed formula for the probability distribution.Also we prove a limit law for this quantity which is a direct application of quasi power theorem and compute its mean and variance.Our results for b=1 reduce to the previous results for random recursive trees.