Brominated poly(isobutylene‐co‐para‐methylstyrene) (BIMS)‐clay nanocomposites: Synthesis and characterization

In this work, preparation and properties of different nanoclays modified by organic amines (octadecyl amine, a primary amine, and hexadecyltrimethylammonium bromide, a tertiary amine) and brominated polyisobutylene‐co‐paramethylstyrene (BIMS)‐clay nanocomposites are reported. The clays and the rubber nanocomposites have been characterized with the help of Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and X‐ray diffraction (XRD). The X‐ray diffraction peaks observed in the range of 3 °–10 ° for the modified clays disappear in the rubber nanocomposites. TEM photographs show predominantly exfoliation of the clays in the range of 12 ± 4 nm in the BIMS. In the FTIR spectra of the nanocomposites, there are common peaks of virgin rubber as well as those of the clays. Excellent improvement in mechanical properties like tensile strength, elongation at break, and modulus is observed on incorporation of the nanoclays in the BIMS. Structure‐property correlation in the above nanocomposites is attempted. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4489–4502, 2004     

Conceptions of function translation: obstacles, intuitions, and rerouting

A horizontal translation of a function is the focus of this study. We examine the explanations provided by secondary school students and secondary school teachers to a translation of a function, focusing on the example of the parabola y=(x−3)² and its relationship to y=x². The participants’ explanations focused on attending to patterns, locating the zero of the function, and the point-wise calculation of function values. The results confirm that the horizontal shift of the parabola is, at least initially, inconsistent with expectations and counterintuitive to most participants. We articulate possible sources of this perceived inconsistency and describe a pedagogical approach aimed at resolving it.     

Highly stereoselective synthesis of peracylated α-aldopyranosyl chlorides from aldopyranose peracetates and thionyl chloride catalyzed by BiCl3 generated in situ from the procatalyst BiOCl

Aldopyranose peracetates react with thionyl chloride and BiCl₃, generated in situ from a substoichiometric amount of the procatalyst BiOCl, producing the corresponding peracylated aldopyranosyl chlorides in very good to excellent yields (82–97%) with exclusive α-anomeric selectivity.     

Synthesis and evaluation of iron chelators with masked hydrophilic moieties

Synthetic iron chelators based on the natural siderophore ferrichrome have previously been shown to bind Fe(III) with high affinity (pKf > 27) and have shown no toxicity to mammalian cell cultures in vitro. A new class of lipophilic ferrichrome analogues carrying acetoxymethyl ester moieties has been synthesized. We have shown that these molecules penetrate rapidly through cell membranes and turn highly hydrophilic while inside the cells, upon esterase mediated hydrolysis of the lipophilic termini. The intracellular retention was visualized by labeling these analogues with a fluorescent naphthalic diimide probe. The prohydrophilic iron chelators have been shown to inhibit the metal-catalyzed intracellular formation of reactive oxygen species with high effectivity, and preliminary results suggest these molecules to be potent antimalarial agents.     

A two-step conversion of alpha,beta-unsaturated ketones to their alpha-carbalkoxy or alpha-carbamoyl derivatives

Several enones are converted into their alpha-iodo derivatives in excellent yields and carbonylated with palladium catalysis in the presence of alcohol or amines to the alpha-carbonyl enones in satisfactory yields.     

Studies on crosslinking of EPDM-PE blends by thermoanalytical techniques

The effect of blend ratio and peroxide concentration on crosslinking characteristics of EPDM-PE blends were studied by Differential Scanning Calorimetry, Brabender plasticorder and Rheometer. Crosslinking of EPDM-PE blends follows first order reaction kinetics. The curing exotherm increases but activation energy decreases with increase in EPDM content in the blends. The same however increases with the increase in concentration of DCP upto a certain level, while the activation energy is almost independent of peroxide concentration. The cure rate increases whereas optimum cure time and energy consumption for curing decrease with increase in the EPDM-PE ratio. A method for determination of crosslinking efficiency in the case of blend systems was developed from high temperature modulus to predict the properties and the curing behaviour of the blends.

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Zusammenfassung Mittels DSC, Brabender Plasticorder und Rheometer wurde der Einfluß von Mischungsverhältnis und Peroxidkonzentration auf den Vernetzungsverlauf von EPDM-PE-Gemischen untersucht. Die Vernetzung von EPDM-PE-Gemischen verläuft nach einer Reaktion erster Ordnung. Je höher der Anteil von EPDM im Gemisch, um so exothermer ist die Vernetzung und um so kleiner ist die dazugehörige Aktivierungsenergie. Mit dem Anwachsen der DCP-Konzentration bis zu einem gewissen Niveau wächst der exotherme Charakter, während die Aktivierungsenergie fast unabhängig von der Peroxidkonzentration ist. Mit dem Anstieg des EPDM/PE-Verhältnisses wächst die vernetzungsgeschwindigkeit, während die optimale Vernetzungszeit und der Energieverbrauch für die Vernetzung sinken. Es wurde ein Verfahren zur Bestimmung der Vernetzungseffizienz bei Mischsystemen entwickelt, um Eigenschaften und Vernetzungsverhalten von Gemischen voraussagen zu können.

     

Silver (I)-promoted asymmetric halohydrin reaction of chiral N-enoyl-2-oxazolidinones: scope and limitations

The halohydrin reaction of chiral N-enoyl-2-oxazolidinones 1 by halogen (Br₂/I₂) and water were efficiently carried out in aqueous organic solvent promoted by silver(I) with high anti- and regioselectivity and moderate to good diastereoselectivities. The alkenoyl, cinnamoyl and electron-deficient cinnamoyl substrates smoothly underwent bromohydrin reaction in aqueous acetone but no iodohydrin reaction, where as electron-rich cinnamoyl substrates preferred to undergo iodohydrin reaction in aqueous acetone with moderate diastereoselectivity and enhanced diastereoselectivity was observed in aqueous THF.     

The solvation of iodine anions in water clusters: PES studies

We have measured the photoelectron-spectra of I^? (H₂O)_n clusters in the size range n=1–60. We have found that the first six water molecules form a solvation layer with an average 0.35 eV electrostatic stabilization of the anion. At larger cluster sizes the electrostatic stabilization of water does not fit a continuous dielectric solvent. The most stable structures of the clusters consist of internally solvated anions. In the size range n=34–40 we have found evidence for existence of cluster structures with surface solvated anions.     

Intein-mediated biotinylation of proteins and its application in a protein microarray

We report here the first example using an intein-mediated expression system to generate biotinylated proteins suitable for immobilization onto avidin-functionalized glass slides. With this novel array, proteins are site-specifically immobilized on the glass surface and are able to retain their native activity. The advantage of the avidin/biotin linkage over his-tag/Ni-NTA strategies for protein immobilization is highlighted by its ability to withstand a variety of chemical conditions, which makes this new protein array compatible with most biological assays.     

Facile catalyzed acylation of alcohols, phenols, amines and thiols based on ZrOCl2·8H2O and acetyl chloride in solution and in solvent-free conditions

Acylation of heteroatoms (O, N and S) with acetyl chloride based on the use of a catalytic amount of the moisture stable, inexpensive ZrOCl₂·8H₂O, proceeds efficiently producing the corresponding acylated products in excellent yields.