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.     

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.     

Fluorescence Interaction and Determination of Sulfathiazole with Trypsin

The mechanism of interaction of trypsin with the sulfathiazole was studied through using fluorescence quenching and UV-visible absorption spectra at pH 7.4. The Stern-Volmer quenching constants, binding constants, number of binding sites and the corresponding thermodynamic parameters ΔH^o, ΔS^o and ΔG^o were calculated at different temperatures. The effect of common metal ions on the constants was also discussed. The results suggest that sulfathiazole can interact strongly trypsin and that there is the formation of trypsin-sulfathiazole complex and the interaction can be explained on the basis of hydrogen bonds and van der Waals forces. The binding distance (r) between the donor (trypsin) and acceptor (sulfathiazole) was 3.52 nm based on the Förster’s non-radiative energy transfer theory. The detection and quantification limits of sulfathiazole were calculated as 2.52 and 8.40 μM in the presence of trypsin, respectively. The relative standard deviation (RSD) was 4.086 % for determinations (n?=?7) of a sulfathiazole solution with the concentration of 7.54 μM.     

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.     

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.     

Some Aspects of Magnetic Filtration Theory for Removal of Fine Particles from Aqueous Suspensions

The magnetic filtration theory was evaluated to intensify the filtration of industrial fluids by magnetic filters. Effects of filtration velocity and external magnetic field intensity on filter performance were investigated and the dependence of the logarithmic efficiency coefficient on filtration velocity was questioned. It was concluded that change in the magnetic susceptibility of the dispersion particles, caused by external magnetic field, and change in the flow rate properties of the liquid alongside the filter pores are the most essential factors to be considered in the design, development, and modeling of magnetic filtration systems in various industrial areas.