Oxythallation of norbornene derivatives with thallium(III) acetate in methanol

Treatment of norbornene, norbornadiene, benzonorbornadiene, and chloro- and methoxy-benzonorbornadiene with thallium(III) acetate in methanol affords only the corresponding cis-exo-acetoxythallation adducts in a sharp contrast to oxymercuration of such strained olefins where methoxymercuration prevails. In the cases of substituted benzonorbornadienes the products are obtained as the regioisomeric mixtures, the isomer ratio being determined by ¹³C NMR. In the cases of 5-norbornene-2,3-dicarboxylic anhydride, 5-norbornene-2-methyl-2,3-dicarboxylic anhydride, and 5-norbornen-2-endo-carboxylic acid, lactonization occurs to give a trans-oxythallation adduct having a lactone ring, no introduction of either methoxy or acetoxy groups being observed. ¹H and/or ¹³C NMR data for several new oxythallation adducts are provided. The alkaline sodium borohydride reduction of adducts in methanol affords mainly the parent olefin together with 10–16% yields of the corresponding exo-alcohol.     

Vinyl polymerization. 413. Polymerization of vinyl monomer initiated by poly(vinylbenzyltrimethyl)-ammonium chloride

The polymerization of vinyl monomer initiated by an aqueous solution of poly(vinylbenzyltrimethyl)ammonium chloride (Q-PVBACI) was carried out at 85°C. Styrene, p-chlorostyrene, methyl methacrylate, and i-butyl methacrylate were polymerized, whereas acrylonitrile and vinyl acetate were not. The effects of the amounts of vinyl monomer, Q-PVBACI, and water on the conversion of vinyl monomer were studied. The overall activation energy in the polymerization of styrene was estimated as 79.1 kJ mol^?1. The polymerization proceeded through a radical mechanism. The selectivity of vinyl monomer was discussed by “a concept of hard and soft hydrophobic areas and monomers.”     

Multilayer vesicles and vesicle clusters formed by the fullerene-based surfactant C60(CH3)5K

The self-assembly behavior of a fullerene-based surfactant, C60(CH3)5K, in water was studied using a combination of static and dynamic light scattering, as well as transmission electron microscopy, and compared to that of the compound C60(C6H5)5K. Both fullerene surfactant systems spontaneously assemble into large vesicles consisting of closed spherical shells formed by bilayers, with critical aggregation concentrations (CAC) lower than 10(-6) g ml(-1). At low concentrations, the aggregate sizes of C60(CH3)5K (radius R approximately 26.8 nm) and C60(C6H5)5K (R approximately 17.0 nm) were found to be substantially different from each other, showing that the change of the substituents surrounding the polar cyclopentadienide head group makes it possible to control the size of the resulting aggregates. Furthermore, the C60(CH3)5K vesicles were found to exist in two qualitatively different types of aggregation with a critical reaggregation concentration (CRC) located at 3.30 x 10(-6) g ml(-1). Above the CRC, larger aggregates were observed (R approximately 37.6 nm), showing a more complex form of supramolecular aggregation, e.g., in terms of multi-bilayer vesicles and/or of clusters of bilayer vesicles.     

Diacetoxylation of conjugated dienes with thallium(III) acetate in acetic acid

The reaction of conjugated dienes such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2,5-dimethyl-2,4-hexadiene, 1,3-cyclopentadiene, and 1,3-cyclohexadiene, with thallium(III)acetate in acetic acid at 10–65° for 0.5–15 hr affords an isomeric mixture of the corresponding diacetoxyalkenes (1,2- and 1,4-addition products) in 10–92% yields. The 1,2-addition products are predominantly formed in all cases examined except the case of 1,3-cyclopentadiene. The reaction is assumed to proceed through acetoxythallation and dethallation steps, the latter step being accompanied and/or followed by an attack of acetoxyl group. An initial attack of thallium moiety is proposed to occur mainly at C-1 and C-2 carbons in the cases of linear terminal dienes and cyclic dienes, respectively.     

Concentrated reverse micelles in a random graft block copolymer system: structure and in-situ synthesis of silver nanoparticles

The structure and rheological properties of a poly(dimethylsiloxane)-graft-poly(oxyethylene) copolymer at high concentrations in block-selective solvents were studied by small-angle X-ray scattering (SAXS) and rheometry. Analysis of SAXS data indicates that quasispherical, reverse micellar aggregates (with no ordered packing) are present in concentrated solutions of the copolymer in nonpolar solvents, and that upon addition of water, the size of such aggregates increases due to the solubilization inside the micellar cores. The viscosity of concentrated polymer solutions increases exponentially as water is added, and finally, viscoelastic, gel-like behavior is found in the vicinity of the phase separation limit. It was found that small silver nanoparticles with an average diameter of ≈3 nm can be synthesized inside the copolymer aggregates without the need of a reducing agent; namely, particles embedded in a viscoelastic matrix are obtained. The synthesis seems to follow first-order kinetics. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

Formation and stabilization model of the 42-mer Abeta radical: implications for the long-lasting oxidative stress in Alzheimer's disease

Amyloid fibrils mainly consist of 40-mer and 42-mer peptides (Abeta40, Abeta42). Abeta42 is believed to play a crucial role in the pathogenesis of Alzheimer's disease because its aggregative ability and neurotoxicity are considerably greater than those of Abeta40. The neurotoxicity of Abeta peptides involving the generation of free radicals is closely related to the S-oxidized radical cation of Met-35. However, the cation's origin and mechanism of stabilization remain unclear. Recently, structural models of fibrillar Abeta42 and Abeta40 based on systematic proline replacement have been proposed by our group [Morimoto, A.; et al. J. Biol. Chem. 2004, 279, 52781] and Wetzel's group [Williams, A. D.; et al. J. Mol. Biol. 2004, 335, 833], respectively. A major difference between these models is that our model of Abeta42 has a C-terminal beta-sheet region. Our biophysical study on Abeta42 using electron spin resonance (ESR) suggests that the S-oxidized radical cation of Met-35 could be generated by the reduction of the tyrosyl radical at Tyr-10 through a turn structure at positions 22 and 23, and stabilized by a C-terminal carboxylate anion through an intramolecular beta-sheet at positions 35-37 and 40-42 to form a C-terminal core that would lead to aggregation. A time-course analysis of the generation of radicals using ESR suggests that stabilization of the radicals by aggregation might be a main reason for the long-lasting oxidative stress of Abeta42. In contrast, the S-oxidized radical cation of Abeta40 is too short-lived to induce potent neurotoxicity because no such stabilization of radicals occurs in Abeta40.     

Dibenzoarsepins: Planarization of 8π‐Electron System in the Lowest Singlet Excited State

Dibenzo[b,f]arsepins possessing severely distorted cores compared to those of other heteropins were synthesized. These derivatives exhibited dual photoluminescence in the green‐to‐red region (500–700 nm) and the near‐ultraviolet region (<380 nm), which could be attributed to the planarization of the arsepin core in the lowest singlet excited (S₁) state. The computational approach for the assessment of the aromatic indices revealed that the dibenzoarsepins studied show aromaticity (8π system) in the S₁ states in line with Baird's rule. The lone pair electrons of the arsenic atoms play a crucial role in the aromaticity in the S₁ states.     

Enantioselective Morita–Baylis–Hillman reaction catalyzed by a chiral phosphine oxide

An application of a hypervalent silicon complex, generated from a chiral phosphine oxide catalyst and silicon tetrachloride, to the enantioselective organocatalytic Morita–Baylis–Hillman reaction is described. A chloride anion liberated from the hypervalent silicon complex smoothly generated a γ-chloro silyl enol ether that subsequently reacted with an aldehyde to afford the Baylis–Hillman adducts in good yields and with good enantioselectivities.     

The discovery of polymer‐clay hybrids

The first successful example of a polymer‐clay hybrid was nylon‐clay hybrid (NCH), which is a nano‐meter‐sized composite of nylon‐6 and 1‐nm‐thick exfoliated aluminosilicate layers of the clay mineral. NCH was found and developed at Toyota Central Research and Development Laboratories over 17 years ago. The NCH containing a few weight percentages of clay exhibits superior properties such as high modulus, high strength, and good gas‐barrier properties. The key for the discovery of NCH was the polymerization of a nylon monomer in the interlayer space of the clay. This highlight presents the development of NCH from its discovery to its commercialization. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 819–824, 2004     

Determination of a polymeric hindered amine light stabilizer in polypropylene formulated with magnesium hydroxide flame retardant by reactive thermal desorption-gas chromatography.

A polymeric hindered amine light stabilizer (HALS), Tinuvin 622 (MW [symbol: see text] 4000), in PP materials formulated with a magnesium hydroxide flame retardant was determined by reactive thermal desorption (RTD) gas chromatography (GC). Two kinds of the HALS components that were formed through the RTD in the presence of tetramethylammonium hydroxide [(CH3)4NOH, TMAH] were clearly observed in the chromatograms of the PP samples, with negligible interference from the other additives and the PP substrate. Here, the coexisting flame retardant was proved to affect significantly the RTD process of the occluded HALS. As a result, the recovery of the HALS components in the RTD-GC chromatograms of the PP samples increased with increase in the content of the flame retardant. This enhancement of the HALS recovery is attributed mainly to the preferential exposure of the HALS on the surface of the ground PP sample through the interaction between the polymeric HALS and the flame retardant in the molten PP during kneading. In spite of such a considerable action of the flame retardant, the observed intensities of the characteristic peaks of HALS by RTD-GC showed a good linear relationship with the HALS content in the PP samples with constant content of the flame retardant (50 phr); this relationship could be used as the calibration line for the determination of the polymeric HALS in the PP materials containing the flame retardant.