Synthesis of 1,3-Bis[(3-aryl)-S-triazolo[3,4-b]-[1,3,4]thiadiazole-6-yl]benzenes

1,3-bis[(3-aryl)-s-triazolo[3,4-b]-[1,3,4]thiadiazole-6-yl]benzenes 2 were synthesized in high yields by the reaction of 3-aryl 4-amino-5-mercapto-1,2,4-triazole 1 with m-phthalic acid.     

A Study of the Probe Effect on the Apparent Image of Biological Atomic Force Microscopy

The atomic force microscopy (AFM) possesses high spatial resolution and it is compatible with liquid environments. AFM can provide possibility to study a wide range of biological problems at the molecular level and acquire topological information at nanometre resolution under physiological conditions1,2. However, a major problem for image reconstruction of biological specimens is that structures of most biological molecules are very soft and delicate, which could be easily deformed and dama…     

Homogenous synthesis of 3-allyloxy-2-hydroxypropyl-cellulose in NaOH/urea aqueous system

3-Allyloxy-2-hydroxypropylcelluloses (AHP-celluloses), reactive unsaturated cellulose derivatives, were homogeneously synthesized by the reaction of cellulose with allyl glycidyl ether (AGE) in NaOH/urea aqueous solution. Water-soluble AHP-celluloses with DS_NMR = 0.32–0.67 were prepared from microcrystalline cellulose. The degree of substitution (DS) of AHP-celluloses could be controlled by varying the molar ratio of AGE and NaOH to AGU and the reaction conditions. The structure of AHP-cellulose samples were characterized by means of FT-IR, NMR spectroscopy and size exclusion chromatography. The cellulose ether shows thermoreversible flocculation. Bromination reactions were carried out as subsequent functionalization both to illustrate the reactivity of the allyl function and to determine the DS values.     

Speciation analysis of chromium in natural water samples by electrothermal atomic absorbance spectrometry after separation/preconcentration with nanometer zirconium phosphate

A sensitive and simple method for the electrothermal atomic absorption spectrometry (ETAAS) determination of Cr(III) after separation/preconcentration on a micro-column packed with nanometer sized zirconium phosphate has been developed. Total chromium was determined after the reduction of Cr(VI) to Cr(III) by 10% (m/v) of aqueous ascorbic acid. The limit of detection for Cr(III) was 1.5 ng/L with an enrichment factor of 300. The static adsorption capacity of the sorbent for Cr(III) was 9.34 mg/g. The relative standard deviation was 3.2% (n = 7, c = 10 ng/mL). The method was applied successfully to the determination of Cr(III) and Cr(VI) in natural water samples.     

Secondary ion mass spectrometry and alpha-spectrometry of electrodeposited thorium films

The main aim of this work was the preparation of samples with thorium content on the steel discs by electrodeposition for determination of natural thorium isotope by alpha spectrometry and secondary ion mass spectrometry and finding out their possible linear correlation between these methods. The analysis of the composition of surface was other aim of study. Discs were measured by alpha spectrometer. After that, alpha spectrometry discs were analyzed by TOF-SIMS IV, which is installed in the International Laser Centre in Bratislava. The integral and normalized intensities of isotope of ²³²Th and intensities of ions of ThO⁺, ThOH⁺, ThO₂H⁺, Th₂O₄H⁺, ThO₂ ^?, ThO₃H^?, ThH₃O₃ ^? a ThN₂O₅H^? were measured. The linear correlation is between surface’s weights of Th and intensities of ions of Th⁺ from identified in SIMS spectra. We found out the chemical binding between thorium and oxygen and hydrogen on the surface of samples by SIMS method. Obtained intensities of ions ²³²ThO⁺, ²³²ThOH⁺, ²³²ThO₂H⁺ prove the presence of oxidized forms of thorium in the upper layers of surface. The oxidized ions predominate in univalent form of thorium up to deep about 3,000 nm.     

The changes of crystalline structure of cellulose during dissolution in 1-butyl-3-methylimidazolium chloride

The morphology and crystalline structure changes of cellulose during dissolution in 1-butyl-3-methylimidazolium chloride [(BMIM)Cl] were investigated by optical microscopy and synchrotron radiation wide-angle X-ray diffraction (WAXD). Neither swelling nor dissolution of cellulose was observed under the melting point of [BMIM]Cl. While the temperature was elevated to 70 °C, the swelling phenomenon of cellulose happened with the interplanar spacing of ( _boxclose_boxclose_boxclose0 1\bar{1}0 ) and (020) planes increased slightly. With the temperature further going up to 80 °C, cellulose was dissolved gradually with the crystallinity (W _c,x) and crystalline index (CrI) of cellulose decreased rapidly, which indicated the crystalline structure of cellulose was destroyed completely and transformed into amorphous structure.     

Synthesis and characterization of a novel polymeric hydrogel based on hydroxypropyl methyl cellulose grafted with polyacrylamide

A novel hydrogel has synthesized by grafting polyacrylamide chains onto hydroxypropyl methylcellulose in presence of potassium persulphate as initiator using solution polymerization technique. The reaction was carried out in homogeneous aqueous medium. The effect of reaction parameters on percentage of grafting (% G) and grafting efficiency (% GE) were discussed. The parameters were varied systematically to achieve the best hydrogel. Developed hydrogels were characterized by various materials characterization techniques. The dynamic and equilibrium swelling properties of hydrogels were investigated as a function of pH and time in various buffer solutions similar to that of gastric and intestinal fluid. Results showed that with increase in % G and % GE, the rate of swelling decreases, which can opens the door for further study of their utilization as matrices for controlled/sustained/targeted drug delivery.     

Catalytic Desymmetrizing Dehydrogenation of 4‐Substituted Cyclohexanones through Enamine Oxidation

A desymmetrizing dehydrogenation process catalyzed by a chiral primary amine is described herein. The reaction proceeds through the oxidation of a ketone enamine by IBX and enables the highly enantioselective desymmetrization of 4‐substituted cyclohexanones with the generation of chiral 4‐substituted cyclohexenones containing a remote γ‐stereocenter.     

Thermally Rearranged Polymer Membranes Containing Tröger's Base Units Have Exceptional Performance for Air Separations

The influence of segmental chain motion on the gas separation performance of thermally rearranged (TR) polymer membranes is established for TR polybenzoxazoles featuring Tröger's base (TB) monomer subunits as exceptionally rigid sites of contortion along the polymer backbone. These polymers are accessed from solution‐processable ortho‐acetate functionalized polyimides, which are readily synthesized as high‐molecular‐weight polymers for membrane casting. We find that thermal rearrangement leads to a small increase in d‐spacing between polymer chains and a dramatic pore‐network reconfiguration that increases both membrane permeability and O₂/N₂ selectivity, putting its performance above the 2015 upper bound.     

Palladium-catalyzed 2-pyridylmethyl-directed β-C(sp~3)—H activation and cyclization of aliphatic amides with gem-dibromoolefins:A rapid access to γ-lactams

The direct Pd-catalyzed β-C(sp³) H activation and cyclization of aliphatic amides bearing a removable 2-pyridylmethyl directing group with gem-dibromoolefins is described for the first time to construct a variety of γ-lactams.