Study of asymmetric aldol and Mannich reactions catalyzed by proline–thiourea host–guest complexes in nonpolar solvents

A proline–thiourea host–guest complex has been described as a good catalyst for asymmetric reactions such as aldol and Mannich reactions. High stereoselectivities were obtained under optimal conditions. Thiourea was observed to have an important effect on the reactivity and selectivity, even in an unconventional nonpolar reaction medium and without the need to utilize low temperatures. This proline–thiourea host–guest system has the ability to participate in a hydrogen bonding network.     

Crystal structure of an unsymmetrical Schiff base, immobilization of its cobalt and manganese complexes on a silica support, and catalytic studies

An unsymmetrical tetradentate Schiff base (H₂L) was synthesized by the reaction of 3-methoxysalicylaldehyde, o-phenylenediamine, and salicylaldehyde in EtOH. H₂L was characterized by single-crystallographic X-ray analysis. Its Co(II) and Mn(III) complexes ([CoL] and [MnLCl]) were prepared and immobilized on 3-aminopropyltriethoxysilane functionalized silica gel. The immobilized materials were found to be efficient catalysts for epoxidation of styrene in the presence of tert-BuOOH in acetonitrile at 40 °C. The catalysts can be reused several times without significant loss of performance.     

Synthesis in water-free DMF, characterization, electrical, and gas sensing properties of bis[2-(2-aminoethylamino)ethanol]copper(II) dibromide

2-(2-Aminoethylamino)ethanol (L) reacts with cupric bromide in dimethylformamide to give a mononuclear complex of Cu(II) [L₂Cu]Br₂, with six-coordinate distorted octahedral geometry, in which two molecules of tridentate (N,N,O) ligand are involved. The structure was confirmed by spectroscopic methods, elemental and thermogravimetric analyses, and magnetic measurements. Optimization of possible configurations indicated the formation of the trans structure of the complex. Experimental results indicate that the investigated complex, bis[2-(2-aminoethylamino)ethanol] copper(II) bromide, behaves as a semiconductor in the studied temperature range of 298–388 K. Gas sensing properties of the film for the volatile organic compounds (VOCs): acetone, tetra-chloromethane, chloroform, ethanol, and methanol, were also investigated as a function of vapor concentration and temperature in dark. The film showed maximum sensitivity to tetrachloromethane and ethanol vapors at room temperature. Responses of the film to the tested gases are reversible.     

Three-Phase Partitioning as a Rapid and Easy Method for the Purification and Recovery of Catalase from Sweet Potato Tubers (Solanum tuberosum)

Three-phase partitioning (TPP) was used to purify and recover catalase from potato crude extract. The method consists of ammonium sulfate saturation, t-butanol addition, and adjustment of pH, respectively. The best catalase recovery (262 %) and 14.1-fold purification were seen in the interfacial phase in the presence of 40 % (w/v) ammonium sulfate saturation with 1.0:1.0 crude extract/t-butanol ratio (v/v) at pH 7 in a single step. The sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS-PAGE) analysis of the enzyme showed comparatively purification and protein molecular weight was nearly found to be 56 kDa. This study shows that TPP is a simple, economical, and quick method for the recovering of catalase and can be used for the purification process.     

Cross-section calculations of proton induced (p,n) and (p,2n) reactions for production of diagnostic 67Ga, 81Rb, 111In, 123,124I, 123Cs and 123Xe radioisotopes

Investigation of pre-equilibrium (PEQ) and equilibrium (EQ) effects on proton induced reactions for production of radioisotopes are very important. Therefore, in this study, we have calculated the PEQ and EQ cross-sections for ⁶⁷Zn(p,n)⁶⁷Ga, ⁶⁸Zn(p,2n)⁶⁷Ga, ⁸²Kr(p,2n)⁸¹Rb, ¹¹¹Cd(p,n)¹¹¹In, ¹¹²Cd(p,2n)¹¹¹In, ¹²³Te(p,n)¹²³I, ¹²⁴Te(p,2n)¹²³I, ¹²⁴Te(p,n)¹²⁴I and ¹²⁴Xe(p,2n)¹²³Cs reactions for production diagnostic radioisotopes. Calculations have been performed by using the hybrid model, geometry dependent hybrid model and full exciton model of PEQ reaction mechanism with 1–40 MeV proton incident energy. We have also investigated the EQ effects on these reactions using the Weisskopf–Ewing model in the same energy range. The excitation functions including the PEQ and EQ effects on these reactions are evaluated by using the ALICE/ASH (2006) and the TALYS 1.4 (2011) codes. Our results have shown that using these codes is suitable for production diagnostic isotopes mentioned above. To obtain excitation functions for producing the diagnostic radioisotopes the PEQ mechanism has been found more dominant than that of the EQ. The results are discussed and compared with the available experimental data.     

The uranium recovery from aqueous solutions using amidoxime modified cellulose derivatives. IV. Recovery of uranium by amidoximated hydroxypropyl methylcellulose

Amidoxime modified hydroxypropyl methylcellulose (HPMC) films (HPMC-g-AO) were used for the recovery of uranium from aqueous solutions by a complexation process. The adsorption experiments were carried out by immersion of a certain amount of films in UO₂ ²⁺ solutions (resultant pH 4.1) ranging in concentration from 100 to 1,000 ppm. The effect of temperature (25–50 °C) on the adsorption capacity of HPMC-g-AO was investigated at the optimized time. The adsorption kinetics and the thermodynamics as well as the adsorption capacity of HPMC-g-AO films were investigated. The adsorption capacity was found as 765 mg UO₂ ²⁺/g dry film. The kinetic and the thermodynamic parameters (i.e. activation energy, enthalpy, entropy and Gibbs free energy) for the interaction of UO₂ ²⁺ with HPMC-g-AO were calculated based on known basic relations. The results showed that adsorption occurred through strong electrostatic interactions with an enthalpy of ?36.5 kJ/mol. The desorption of UO₂ ²⁺ were investigated using different desorption agents such as EDTA, HCl, NaHCO₃, and NaOH. After the 2 weeks treatment period, the highest desorption yield were found as 23 % with NaHCO₃.     

Investigation of radiocesium biokinetics in Manila clam (Ruditapes philippinarum)

This study was carried out to better understand the biokinetics of radiocesium in clams living in sediment. The accumulation and depuration kinetics of ¹³⁴Cs were investigated in the Manila clam (Ruditapes philippinarum) under controlled laboratory conditions. The concentration factor was found to be 3.0 for ¹³⁴Cs in the whole body; however, the concentration factor in the soft part of the clams (12) was significantly higher than those in the whole body and shell (0.80). The depuration kinetics of the radionuclide were described by a two-component exponential model for the whole body. The biological half-lives in the fast and slow components were found to be 0.63 and 22.1 days, respectively. The depuration kinetics for ¹³⁴Cs in the soft parts were described by a single-component exponential model with a resultant the biological half-life of 18.0 days.     

Determination of Bismuth in Bottled and Mineral Water Samples at Trace Levels by T-Shaped Slotted Quartz tube-Atom Trap-Flame Atomic Absorption Spectrometry

An accurate and reliable analytical method for the determination of bismuth at trace levels in bottled and mineral water samples has been developed based on hydrogen assisted T-shape slotted quartz tube-atom trap-flame atomic absorption spectrometry (T-SQT-AT-FAAS). Conventional FAAS is not sufficiently sensitive to measure trace and ultra-trace levels of metals due to the low nebulization efficiency and short residence time of atoms in the light path. To overcome this problem, atom trapping with a T-shaped slotted quartz tube was coupled to the FAAS system. Bismuth atoms were trapped on the surface of T-SQT and released by hydrogen gas, which provided a reducing environment. All of the system parameters such as flame type, hydrogen flow rate, the height of T-SQT from the burner head, and trapping period were optimized to enhance the analytical signal to attain low detection limits. After obtaining the optimum conditions, the limit of detection and limit of quantitation of the developed method were found to be 0.95 and 3.2?µg L^?1, respectively. Recovery values were obtained between 90% and 104% that showed good accuracy and applicability of the proposed method to the analysis of bottled and mineral water samples.     

Synthesis of a bipyridine-derived achiral thiourea trifluoromethanesulfonic acid salt and its application as an additive in organocatalytic asymmetric reactions

The host–guest complex of a proline–thiourea bipyridine trifluoromethanesulfonic acid salt can catalyze organocatalytic asymmetric reactions such as aldol, Michael, and Mannich in polar protic medium with high stereoselectivities. The privileged bipyridine backbone and the thiourea motif are essential to the activity and enantioselectivity through hydrogen bonding interactions.     

Reversible Immobilization of Urease by Using Bacterial Cellulose Nanofibers

In this work, bacterial cellulose nanofibers were produced by using the Gluconacetobacter hansenii HE1 strain. These nanofibers were derivatized with dye affinity ligand Reactive Green 5, and these newly synthesized dye-attached nanofibers were used for affinity adsorption of urease. Reactive Green 5-attached nanofibers were characterized by Fourier transform infrared spectroscopy, SEM, and energy-dispersive x-ray spectroscopy analysis. Some adsorption conditions which significantly affect the adsorption efficiency were investigated. The maximum urease adsorption capacity was found to be 240 mg/g nanofiber in pH 6.0 and at room temperature. Dye-free plain nanofibers also used for studying nonspecific urease adsorption onto plain nanofibers and nonspecific adsorption were found to be negligible (3.5 mg/g nanofiber). Prepared dye-attached nanofibers can be used in five successive adsorption/desorption steps without any decrease in their urease adsorption capacity. The desorption rate of the adsorbed urease was found to be 98.9 %. The activity of the urease was also investigated, and it was found that free and desorbed urease from the dye-attached nanofibers showed similar specific activity.