Conformational behavior of nylon 6 in mixed solvents

The intrinsic viscosity [η], Huggins constant (K_H), laser light scattering, UV and IR measurements of Nylon 6 are made in m‐cresol and its mixture with 1,4‐dioxane at 20–60 °C. The intrinsic viscosity, R_g, A₂, (<S>²)^1/2 (calculated from viscosity data), R_H, and UV absorbance initially increase and then decrease with the rise in 1,4‐dioxane contents. The K_H and the transmittance of ? OH group in IR spectra show an opposite trend to that of [η]. The dielectric constant calculated from the refractive index of the solvent (m‐cresol with 1,4‐dioxane) and polymer solution shows a continuous decrease with the amount of 1,4‐dioxane. Activation energy shows a minimum while linear expansion coefficient (α³) maximum with the addition of 1,4‐dioxane. Change in [η], K_H, and other characteristics of the polymer solutions with alterations in solvent composition and temperature are the result of variation in the thermodynamic quality of the solvent, its selective adsorption, hydrogen bonding, and conformational transitions. It has been concluded that the addition of 1,4‐dioxane first enhances the quality of the solvent, encourages hydrogen bonding, and specific adsorption, and then deteriorates, bringing conformational transitions in the polymer molecules. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 534–541, 2005     

Formation of layered titania and zirconia catalysed by surface-bound silicatein

Silicatein immobilised on self-assembled polymer layers using a histidine-tag chelating anchor group retains its hydrolytical activity for the formation of biosilica, and catalyses the formation of layered arrangements of biotitania and biozirconia.     

Haloxylines A and B, antifungal and cholinesterase inhibiting piperidine alkaloids from Haloxylon salicornicum

Haloxylines A (1) and B (2), new piperidine alkaloids, have been isolated from the chloroform soluble fraction of Haloxylon salicornicum and their structures elucidated by spectroscopic techniques including 2D-NMR. Both the compounds displayed antifungal and cholinesterase enzymes inhibitory potentials.     

Lipoxygenase inhibiting ethyl substituted glycoside from Symplocos racemosa

Phytochemical investigation of Symplocos racemosa resulted in the isolation of a new ethyl substituted glycoside, 1-ethyl brachiose-3'-acetate (1) along with four known compounds ketochaulmoogric acid (2), nonaeicosanol (3), triacontyl palmitate (4) and methyl triacontanoate (5). The substitution of ethyl group on 1 was natural because during the course of extraction and purification ethanol was not used. The structural elucidation of the isolated compounds was based primarily on 1D- and 2D-NMR analysis, including COSY, HMQC, and HMBC correlations. The glycoside 1 and triacontyl palmitate (4) displayed the inhibitory potential against lipoxygenase and urease enzyme, respectively.     

A novel beta-glucuronidase inhibiting triterpenoid from Paeonia emodi

A novel beta-glucuronidase inhibiting triterpene (1) has been isolated from the chloroform fraction of Paeonia emodi beta-glucuronidase inhibit established ase chloroform fraction of Pa 11,beta,5alpha,23,24-pentahydroxy-30-norolean-12,20(29)-d ien-28-oic acid on the basis of spectroscopic analysis, including high resolution mass spectroscopy, one and two-dimensional NMR techniques. Oleanolic acid, betulinic acid, ethyl gallate, methyl grevillate and 1,5-dihydroxy-3-methylanthraquinone are also reported for the first time from Paeonia emodi.     

Effect of Mg doping on the superconducting properties of Cu/sub 1-x/Tl/sub x/Ba/sub 2/Ca/sub 3-y/Mg/sub y/Cu/sub 4/O/sub 12-/spl delta//

Superconducting properties of Cu/sub 1-x/Tl/sub x/Ba/sub 2/Ca/sub 3-y/Mg/sub y/Cu/sub 4/O/sub 12-/spl delta// (Cu/sub 1-x/Tl/sub x/Mg/sub y/-1234) material have been studied in the composition range y=0,1.5,2.25. The zero resistivity critical temperature [T/sub c/(R=0)] was found to increase with the increased concentration of Mg in the unit cell; for y=1.5 [T/sub c/(R=0)]=131 K was achieved which is hitherto highest in Cu/sub 1-x/Tl/sub x/-based superconductors. The X-ray diffraction analyses have shown the formation of a predominant single phase of Cu/sub 0.5/Tl/sub 0.5/Ba/sub 2/Ca/sub 3-y/Mg/sub y/Cu/sub 4/O/sub 12-/spl delta// superconductor with an inclusion of impurity phase. It is observed from the convex shape of the resistivity versus temperature measurements that our as-prepared material was in the region of carrier over-doping, and the number of carriers was optimized by postannealing experiments in air at 400/spl deg/C, 500/spl deg/C, and 600/spl deg/C. The T/sub c/(R=0) was found to increase with postannealing and the best postannealing temperature was found to be 600/spl deg/C. The mechanism of increased T/sub c/(R=0) is understood by carrying out infrared absorption measurements. It was observed through softening of Cu(2)-O/sub A/-Tl apical oxygen mode that improved interplane coupling was a possible source of enhancement of T/sub c/(R=0) to 131 K.     

Axisymmetric magnetohydrodynamic flow of Jeffrey fluid over a rotating disk

This paper examines the magnetohydrodynamic boundary layer flow of Jeffrey fluid due to a rotating disk. The governing partial differential equations are first transformed into the coupled system of ordinary differential equations and then solved by using the homotopy analysis method. The influence of various involved physical parameters on the dimensionless radial and azimuthal velocities is sketched and analyzed. The variation of skin friction coefficients in radial and azimuthal directions is studied for various values of pertinent parameters. Copyright © 2011 John Wiley & Sons, Ltd.     

Hydroxypropylcellulose-aceclofenac conjugates: high covalent loading design, structure characterization, nano-assemblies and thermal kinetics

This article presents synthesis of novel macromolecular prodrugs of aceclofenac (an anti-inflammatory drug) onto hydroxypropylcellulose (HPC). The HPC-aceclofenac conjugates were prepared using an acylating agent 1,1′-carbonyldiimidazole (CDI) under homogenous reaction conditions. Aceclofenac was first activated by using CDI to form its N-acylimidazole. The N-acylimidazole of aceclofenac was then reacted with HPC polymer at 80 °C for 24 h. Highly pure prodrugs of aceclofenac were synthesized with a wide range of moderate to high degree of substitution (DS 0.41–2.12) as calculated by ¹H NMR spectroscopy. The UV spectroscopic analysis has also revealed that the active drug aceclofenac was found in different conjugates from 28 to 67 mg/100 mg of HPC-aceclofenac conjugates which are in good agreement with DS calculated by ¹H NMR spectroscopy. The gel permeation chromatography showed unimodal absorption that indicates no significant degradation in polymer chains during the reaction. The macromolecular prodrugs of aceclofenac were characterized using different spectroscopic and chromatographic techniques. The thermal analysis has revealed that HPC-aceclofenac conjugates (prodrugs) are 92 and 96 °C more stable than pure aceclofenac regarding their initial (Tdi) and maximum degradation temperatures (Tdm), respectively. The activation energy (Ea) and frequency factor (Z) of the degradation reactions were evaluated using Friedman, Broido and Chang methods. Degradation followed first order (n) kinetics. Transmission electron microscopy has revealed the formation of sponge like nano aggregates with population size distribution of around 80–150 nm.     

Synthesis of 8,9-disubstituted fluoranthenes by domino two-fold Heck/electrocyclization/dehydrogenation of 1,2-dibromoacenaphthylene

Fluoranthenes were prepared by domino two-fold Heck/electrocyclization/dehydrogenation reactions of 1,2-dibromoacenaphthylene.