Novel nucleoside analogues via direct attack of carbon : Nucleophiles on nucleosides containing epoxy-sugars

Direct ring-opening of the epoxide ring in 1-(5′-$\text{O}$-trityl-2′,3′-anhydro-β-D-lyxo-furanosyl) uracil (1) by lithium acetylide or vinylmagnesium bromide/cuprous iodide affords the corresponding 5′-$\text{O}$-trity]-3′-$\text{C}$-substituted-3′-deoxy-$\text{ara}$-uridine species.     

Acyl/aroyl Meldrum’s acid as an enol surrogate for the direct organocatalytic synthesis of α,β-unsaturated ketones

The operationally simple, robust and straightforward organocatalytic protocol is developed for the synthesis of E-selective α,β-unsaturated ketones. The method utilizes simple and easily accessible starting materials such as Meldrum’s acid, carboxylic acid, aldehyde and simple bifunctional amine catalyst. The tandem organocatalytic process utilizes acyl/aroyl Meldrum’s acid as an enol surrogate for the effective Doebner-Knoevenagel type condensation reactions. A wide variety of aldehydes, carboxylic acids and base sensitive functional groups are well tolerated under the mild reaction conditions.     

Transition-metal-free synthesis of primary to tertiary carboxamides: A quick access to prodrug-pyrazinecarboxamide

One-pot expedient and direct carbamoylation of heterocyclics is described. The transformation is realized via direct dehydrogenative aminocarbonylation of heterocyclic compounds under transition-metal-free conditions. This method is regioselective and the protocol is proved to be scalable on a gram scale. Further, the therapeutically useful antitubercular agent pyrazinecarboxamide is successfully synthesized by employing this protocol.     

Composition-dependent crystallization behavior of copolyperoxides from methyl methacrylate and 4-vinylbenzyl stearate

To study the composition-dependent crystallization behavior of copolyperoxides, herein a series of copolymers were prepared by varying the ratios of methyl methacrylate (MMA) and 4-vinylbenzyl stearate (VBS) under 100 psi oxygen pressure using AIBN as an initiator at 50°C in toluene. Both ¹³C NMR and electron impact mass spectroscopy (EI-MS) approved an alternative placement of either of the monomer and peroxy (–O–O–) links throughout the polymer chain. Thermal stability of the resulting copolyperoxides was investigated by thermogravimetric analysis (TGA) and the degradation fragments have been recognized from EI-MS study. In addition, differential scanning calorimetry (DSC) displayed an endothermic peak as well as an exotherm associated with the melting of the side chain crystalline domains and degradation of –O–O– links in the polymer main chain, respectively. Furthermore, DSC thermograms unveiled a systematic decrease of the crystalline melting temperature (T_m) with the enhancement of MMA content in the copolymers. Small angle X-ray scattering (SAXS) revealed the existence of lamellar morphology (depends on VBS content in the copolyperoxide) in the synthesized polyperoxide materials, further supported by atomic force microscopy (AFM) analysis showing a layered fibrillar assembly with multiple heights of the lamella. The significant crystalline nature of the polyperoxides was further evidenced from the appearance of lattice fringes in the transmission electron microscope (TEM) micrographs. The crystalline morphology with birefringent texture was further evidenced from the polarized optical microscopy (POM) study. Thus, the present study reported the effective variation of crystalline behavior in copolyperoxide materials with the incorporation of MMA units in the copolyperoxide chains.     

Zero-Order Catalysis in TAML-Catalyzed Oxidation of Imidacloprid,a Neonicotinoid Pesticide

Bis-sulfonamide bis-amide TAML activator [Fe{4-NO₂C₆H₃-1,2-(NCOCMe₂NSO₂)₂CHMe}]⁻ ( 2 ) catalyzes oxidative degradation of the oxidation-resistant neonicotinoid insecticide, imidacloprid (IMI), by H₂O₂ at pH 7 and 25 °C, whereas the tetrakis-amide TAML [Fe{4-NO₂C₆H₃-1,2-(NCOCMe₂NCO)₂CF₂}]⁻ ( 1 ), previously regarded as the most catalytically active TAML, is inactive under the same conditions. At ultra-low concentrations of both imidacloprid and 2 , 62 % of the insecticide was oxidized in 2 h, at which time the catalyst is inactivated; oxidation resumes on addition of a succeeding aliquot of 2 . Acetate and oxamate were detected by ion chromatography, suggesting deep oxidation of imidacloprid. Explored at concentrations [ 2 ]≥[IMI], the reaction kinetics revealed unusually low kinetic order in 2 (0.164±0.006), which is observed alongside the first order in imidacloprid and an ascending hyperbolic dependence in [H₂O₂]. Actual independence of the reaction rate on the catalyst concentration is accounted for in terms of a reversible noncovalent binding between a substrate and a catalyst, which usually results in substrate inhibition when [catalyst]≪[substrate] but explains the zero order in the catalyst when [ 2 ]>[IMI]. A plausible mechanism of the TAML-catalyzed oxidations of imidacloprid is briefly discussed. Similar zero-order catalysis is presented for the oxidation of 3-methyl-4-nitrophenol by H₂O₂, catalyzed by the TAML analogue of 1 without a NO₂-group in the aromatic ring.     

Microstructural and Radioluminescence Characteristics of Nd<Superscript>3+</Superscript> Doped Columbite-Type SrNb<Subscript>2</Subscript>O<Subscript>6</Subscript> Phosphor

Undoped and different concentration Nd³⁺ doped SrNb₂O₆ powders with columbite structure were synthesized by molten salt process using a mixture of strontium nitrate and niobium (V) oxide and NaCl-KCl salt mixture as a flux under relatively low calcining temperature. X-ray diffraction analysis results indicated that SrNb₂O₆ phases found to be orthorhombic columbite single phase for undoped, 0.5 and 3 mol% Nd³⁺ doping concentrations. Phase composition of the powders was examined by SEM-EDS analyses. Radioluminescence properties of Nd³⁺ doped samples from UV to near-IR spectral region were studied. The emissions increased with the doping concentration of up to 3 mol%, and then decreased due to concentration quenching effect. There is a sharp emission peak around 880 nm associated with ⁴F_5/2 → ⁴I_9/2 transition in the Nd³⁺ ion between 300 and 1100 nm. The broad emission band intensity was observed from 400 to 650 nm where the peak intensities increased by increasing Nd³⁺ doping concentration. All the measurements were taken under the room temperature.     

Mathematical modelling and dynamic response of a multi-straight-line path tracing flexible robot manipulator with rotating-prismatic joint

In this study, mathematical modelling and dynamic response of a flexible robot manipulator with rotating-prismatic joint are investigated. The tip end of the flexible robot manipulator traces a multi-straight-line path under the action of an external driving torque and an axial force. Considered robot manipulator consists of a rotating prismatic joint and a sliding flexible arm with a tip mass. Flexible arm is assumed to be an Euler–Bernoulli beam carrying an end-mass. Equations of motion of the flexible manipulator are obtained by using Lagrange’s equation of motion. Effect of rotary inertia, axial shortening and gravitation is considered in the analysis. Equations of motion are solved by using fourth order Runge–Kutta method. Numerical simulations obtained by using a developed computer program are presented and physical trend of the results are discussed.     

Characterization and Miscibility Dynamics of Dextran-Poly(vinylpyrrolidone)-Water System

Summary: The miscibility behavior and intermolecular interactions among Dextran (Dx) with different molecular weight and Polyvinylpyrrolidone (PVP) blends were studied as dilute aqueous solutions at 25 °C by viscosity method. The intrinsic viscosity and the interaction coefficient were experimentally measured for each polymer-water as well as for Dx-PVP-water systems. These results served for the prediction of miscibility of the Dx/PVP blends with various blend compositions by using , , , , and parameters. Except Dx4/PVP with its all compositions (Dx4 with nominal molecular weight of 110 000), other blend systems are found to be almost miscible. The density measurements of these polymer solutions and their blends were conducted in order to compare with the viscosity findings. Lastly, all Dx with different molecular weight, PVP and their blends were characterized by infrared spectroscopy (FT-IR), and differential scanning calorimetry (DSC).