Cyclization of functionalized ketene-N,S-acetals to substituted pyrroles: applications in the synthesis of marine pyrrole alkaloids

α-Oxoketene-N,S-acetals, prepared by the reaction of alkyl glycinates with β-oxodithiocarboxylates followed by alkylation, underwent cyclization in the presence of the Vilsmeier reagent to afford alkyl 3-aryl-4-formyl-5-(alkylsulfanyl)-1H-pyrrole-2-carboxylates in excellent yields. When the reaction was extended to β-oxodithiocarboxylates derived from deoxyanisoin, 3,4-diarylpyrrole-2-carboxylates, the key intermediates in the synthesis of lukianol A and lamellarin Q were formed.     

Improvement of properties of silica‐filled styrene‐butadiene rubber composites through plasma surface modification of silica

The performance of plasma surface modified silica filler in styrene‐butadiene rubber (SBR) matrix has been analyzed. The conditions of plasma modification have been optimized by taking secant modulus as a standard parameter and the occurrence of the modification has been confirmed by surface area determination and Fourier transform infrared spectroscopy. The plasma‐modified surface of silica has been found to be composed of carbon–carbon double bonds and carbon–hydrogen bonds. Silane treatment also has been carried out on silica filler surface for a comparative assessment of its influence in the curing behavior and filler–rubber interaction. The cure reactions of all the rubber compounds have been found to be proceeded according to first‐order kinetics. A reduction in the cure reaction rate constant has been observed with the loading of unmodified and surface modified silica, emphasizing the cure deactivation of the matrix rubber by the silica filler. The filler dispersion, as revealed by scanning electron microscopy, has been found to be greatly improved by the plasma as well as silane treatment. The filler–rubber interaction has been found to be greatly improved by both surface treatments, but the best balance of mechanical properties has been observed with plasma surface modification only. Copyright © 2004 John Wiley & Sons, Ltd.     

Size-controlled assembly of gold nanoparticles induced by a tridentate thioether ligand

The ability to control the size and shape of nanoparticle assemblies is essential for the ultimate applications in sensors, catalysis, medical diagnostics, information storage, and quantum computation. This report demonstrates a novel mediator-template strategy toward this ability by exploring molecular driving forces exerted by a tridentate thioether as a mediator and tetraoctylammonium bromide as a templating agent. A combination of the ligand mediation, the surfactant templating, and their relative concentrations served as the driving forces. This combination leads to unprecedented spherical assemblies of gold nanoparticles in controllable sizes via manipulation of the relative concentrations of mediating and templating components.     

Raman scattering spectra of sodium n-butyl(n-hexyl) phosphate aggregates and conformation about the phosphodiester PO bonds in coagel phases

A new double-chain surfactant molecule, sodium n-butyl(n-hexyl)phosphate (BHP), having an asymmetric molecular structure, has been synthesized. For anhydrous BHP in the solid state and the BHP---H₂O system in the lyotropic liquid crystalline and coagel states, the Raman scattering spectra arising from the accordion vibrational mode were studied in the temperature range −170 to 25°C. For anhydrous BHP, the GG form about the phosphodiester P---O bonds was preferentially stabilized at lower temperature. In the coagel phase of the BHP---H₂O system, preferential stabilization of a specific conformation about the P---O bonds occurred and which molecular form was stabilized was dependent on the water content: for the 8:2 BHP---H₂O sample in the coagel the GT form was stabilized, while for the 7:3 BHP---H₂O coagel sample the TT form was preferentially stabilized. The stabilization of such a specific conformation was also reflected in the higher-frequency region.     

An Easy Spectrophotometric Method for the Determination of Hypochlorite Using Thionin

A simple, rapid, and sensitive spectrophotometric method has been developed for the determination of hypochlorite using thionin. The method is based on the reaction of hypochlorite with potassium iodide in acidic medium to liberate iodine. The liberated iodine bleaches the violet color of thionin, which is measured at 600 nm. The decrease in absorbance is directly proportional to the concentration of hypochlorite. Beer’s law is obeyed in the range 0.2– 1.2 µg/mL of hypochlorite. The molar absorptivity, Sandell’s sensitivity, detection limit, and quantitation limit are found to be 1.489 × 10⁴ L/(mol cm), 3.25 × 10⁻³ µg cm⁻², 0.1026 µg/mL, and 0.3112 µg/mL, respectively. The method has been successfully applied to the determination of hypochlorite in various samples of natural water, tap water, milk, etc.__________From Zhurnal Analiticheskoi Khimii, Vol. 60, No. 8, 2005, pp. 798–801.Original English Text Copyright © 2005 by Narayana, Mathew, Vipin, Sreekumar, Cherian.The text was submitted by the authors in English.     

Kinetics of emulsion polymerization of methyl methacrylate

The kinetics of the emulsion polymerization of methyl methacrylate at 50°C have been studied in seeded systems using both chemical initiation and γ-radiolysis initiation. Both steady-state rates and (for γ-radiolysis) the relaxation from the steady state were observed. The average number of free radicals per particle was quite high (e.g., ～0.7 for 10^?3 mol dm^?3 S₂O²₈ initiator). The data are quantitatively interpreted using a generalized Smith–Ewart–Harkins model, allowing for free radical entry, exit, biomolecular termination within the latex particles, and aqueous phase hetero-termination and re-entry. From this treatment, there results (i) the dependence of the termination rate coefficient (k_t) on the weight fraction of polymer (w_p), (ii) lower bounds for the dependence of the entry rate coefficient on initiator concentration, and (iii) the conclusion that most exited free radicals undergo subsequent re-entry into particles rather than hetero-termination. The results for k_t(w_p) are consistent with diffusion control at temperatures below the glass transition point. Comparisons are presented of the behavior of methyl methacrylate, butyl methacrylate, and styrene in emulsion polymerization systems.     

Suitability of commercial colloids for magnetic hyperthermia

Commercial nanoparticles supplied by Chemicell, Micromod and Bayer-Schering were characterised with regard to their nanocrystalline diameter, hydrodynamic diameter, total iron content and relative ferrous iron content. Additionally, calorimetric measurements were taken using a 900 kHz AC magnetic field of amplitude 5.66 kA/m. It was found that those samples containing relatively high (>18%) ferrous content generated a substantially smaller (12% on average) intrinsic loss power (ILP) than those samples with a lower ferrous content. Two nominally identical Chemicell samples that differed only in their production date showed significantly different ILPs, attributed to a variation in batch-to-batch crystallite sizes. The highest ILP values in the cohort, ca. 3.1 nHm²/kg, were achieved for particles with hydrodynamic diameters of ca. 70 nm and nanocrystalline diameters of ca. 12 nm. These compare favourably with most samples prepared in academic laboratories, although they are not as high as the ca. 23.4 nHm²/kg reported for naturally occurring bacterial magnetosomes.     

Mesoporous aluminosilicate promoted protection and deprotection of carbonyl compounds

Mesoporous aluminosilicates are efficient heterogeneous catalysts for both the formation and hydrolysis of a range of acetals under mild conditions and in short reaction times.