Thionyl chloride-mediated synthesis of 2-azaindolizine sulfur-bridged dimers by C?H bond direct chalcogenation of imidazo[1,5-a]pyridines

Thionyl chloride-mediated chalcogenation of imidazo[1,5-a]pyridine serves as a new protocol for the synthesis of rare bisimidazopyridyl sulfides. This method provides the new route to synthesis of 2-azaindolizine sulfur-bridged dimers called chalcogenide under metal-free, elemental sulfur-free conditions without the use of polar solvents in regio-selective manner, at room temperature with the simple operational procedure.     

A Switchable Catalyst Duo for Acyl Transfer Proximity Catalysis and Regulation of Substrate Selectivity

Enzymes are encoded with a gamut of information to catalyze a highly selective transformation by selecting the proper reactants from an intricate mixture of constituents. Mimicking biological machinery, two switchable catalysts with differently sized cavities and allosteric control are conceived that allow complementary size-selective acyl transfer in an on/off manner by modulating the effective local concentration of the substrates. Selective activation of one of two catalysts in a mixture of reactants of similar reactivity enabled upregulation of the desired product.     

Antioxidant activities of phenols in different solvents using DPPH assay

Studies on the antioxidant activity of two model phenols containing either an electron withdrawing (p-nitrophenol) or electron donating (p-aminophenol) group and p-hydroxyacetophenone in different solvents are reported using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical assay by spectrophotometry and stopped-flow techniques. The second-order rate constants measured with p-nitrophenol were found to be (1.2–5.5) × 10⁻² dm³ mol⁻¹ s⁻¹ but the DPPH radical reacts much faster with p-aminophenol (k = 0.5–1.1 × 10⁴ dm³ mol⁻¹ s⁻¹). The normal kinetic solvent effect in H atom transfer was seen in the case of p-nitrophenol with the solvent independent rate constant k _o = 0.1 dm³ mol⁻¹ s⁻¹. The IC₅₀ values in p-nitrophenol are similar to those measured in p-hydroxyacetophenone. On the other hand, much lower IC₅₀ values of more than four orders of magnitude with p-aminophenol were observed. This work demonstrates that the phenol with the electron donating –NH₂ substituent is a better antioxidant.     

Conformational and Functional Transitions in Class II α-mannosidase from <Emphasis Type="Italic">Aspergillus fischeri</Emphasis>

The conformational transitions in an oligomeric and high molecular weight class II α-mannosidase from Aspergillus fischeri were examined using fluorescence and CD spectroscopy under chemical, thermal and acid denaturing conditions. The enzyme lost the activity first and then the overall folded conformation and secondary structure. The midpoint values of GdnHCl mediated changes measured by inactivation; fluorescence and negative ellipticity were 0.48 M, 1.5 M and 1.9 M, respectively. The protein almost completely unfolded in 4.0 M GdnHCl but not at 90 °C. The inactivation and unfolding were irreversible. At pH 2.0, the protein exhibited molten-globule like intermediate with rearranged secondary and tertiary structures and exposed hydrophobic amino acids on the surface. This species showed increased accessibility of Trp to the quenchers and got denatured with GdnHCl in a different manner. The insoluble aggregates of a thermally denatured protein could be detected only in the presence of 0.25–0.75 M GdnHCl.     

Synthesis of (+)-isofagomine

The synthesis of (+)-isofagomine 1 using 4-pentenol 3 as a chiral precursor is described herein.     

Facile Synthesis of Nitriles from Aromatic Aldehydes Using DMSO‐I2

Nitriles have been prepared from different aromatic aldehydes by a one‐pot process using hydroxylamine hydrocloride and molecular iodine in the presence of dimethylsulphoxide.     

Elastic properties of the Ta–V system: bcc Ta0.33V0.67 and C15 TaV2

Resonant ultrasound spectroscopy was used to measure the elastic constants of bcc Ta_0.33V_0.67 over the temperature range 3.5–300?K; the results were compared to earlier measurements on C15 TaV₂. The temperature dependence of the polycrystalline shear modulus is completely different in the two phases; that of the bcc phase decreases with temperature whereas that of the C15 phases increases in an anomalous fashion. This difference is consistent with a model involving doubly-degenerate levels at the X point of the Brillouin zone in the C15 phase with the Fermi level lying near the doubly degenerate level. This model accounted for the unusual behaviour of the C15 phase. Debye temperatures were determined from the ultrasonic measurements: 295?K for the C15 phase and 315?K for the bcc phase.