Preparation and properties of the biodegradable graded blend of poly(L‐lactic acid) and poly(ethylene oxide)

We prepared biodegradable poly(ethylene oxide) (PEO)/poly(L ‐lactic acid) (PLLA) graded blends by the dissolution–diffusion process, and discussed the biodegradability and tensile strength of the graded blends by comparing isotropic blend and PLLA only. All the graded blends were degraded more largely than the PLLA only and isotropic blend (PEO: 37.5 wt %), which had the same content as the total content of those graded blends. The graded blend having most excellent wide compositional gradient was degraded most largely with the enzyme. Thus, graded structure of the blends promoted their biodegradabilities large. It was considered that the dissolution of PEO with water increased the surface area attacked by the enzyme, while PEO caught PLLA oligomers to promote the biodegradation of PLLA. Then, the biodegradabilities of the graded blends were suppressed by the increasing crystallinity of PLLA. Furthermore, the strengths of all the graded blends were larger than those of the isotropic blend. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2972–2981, 2007     

Chiral discrimination of a helically organized crown ether array parallel to the helix axis of polyisocyanate

The asymmetric polymerization of 4′‐isocyanatobenzo‐18‐crown‐6 with the lithium amide of (S)‐(2‐methoxymethyl)pyrrolidine successfully proceeded to afford end‐functionalized poly(4′‐isocyanatobenzo‐18‐crown‐6) with (S)‐(2‐methoxymethyl)pyrrolidine (polymer 2 ). In the circular dichroism (CD) spectrum of 2 , a clear positive Cotton effect was observed in the range of 240–350 nm corresponding to the absorption of the polymer backbone, indicating that 2 partially formed a one‐handed helical structure, which was preserved by the chirality of (S)‐(2‐methoxymethyl)pyrrolidine bonding to the terminal end in 2 . In the titration experiments for the CD intensity of 2 in the presence of D ‐ and L ‐Phe·HClO₄ (where Phe is phenylalanine), a small but remarkable difference was observed in the amount of the chiral guest needed for saturation of the CD intensity and in the saturated CD intensity, indicating that the extremely stable, one‐handed helical part should exist in the main chain of 2 , which was not inverted even when the unfavorable chiral guest for the predominant helical sense, L ‐Phe·HClO₄, was added. In addition, helical polymer 2 exhibited a chiral discrimination ability toward racemic guests; that is, the guests were extracted from the aqueous phase into the organic phase with enantiomeric excess. The driving force of the chiral discrimination ability of 2 should certainly be attributed to the one‐handed helical structure in 2 . © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 325–334, 2006     

Transformation of indole alkaloids—I : Conversion of oxindole alkaloids into indole alkaloids

Chemical conversion of some natural oxindoles (pteropodine, isopteropodine and isorhynchophylline) into the corresponding indole alkaloids has been made by way of a sequence of reactions which include formation of iminoethers of the natural oxindoles with Meerwein's reagent, reduction of the iminoethers to 2,3-seco-indoles and cyclization of 2,3-seco-indoles to the desired natural indole alkaloids. Sodium borohydride in acetic acid was found to be a specific reagent for the reduction of oxindole-iminoethers to 2,3-seco-indoles which were the key intermediates in these transformations. Yohimbine-oxindole iminoether was similarly converted to yohimbine and pseudoyohimbine. A number of by-products were obtained and their structures were elucidated.     

Ruthenium-catalyzed arylation of 2-alkenylpyridines with aryl bromides: alternative E,Z-selectivity to Mizoroki-Heck reaction

Regio- and stereoselective arylation of 2-alkenylpyridines with aryl bromides is catalyzed by specific Ru(II)-phosphine complexes affording beta-arylated (Z)-2-alkenylpyridines, in which the aryl moiety is introduced cis to the pyridyl group. This geometrical selectivity is in sharp contrast to the Mizoroki-Heck reaction. [reaction: see text]     

Chemical structure of iodine-doped polyisoprene

A nonconjugated conducting polymer (1,4-rans-polyisoprene) at different iodine doping levels has been studied with the 27.7-keV Mössbauer resonance of¹²⁹I. At the light doping level, almost all iodines are covalently bonding to the carbon atoms, breaking the double bonds of the main chain. At the medium doping level, other iodine species are found, which are idendified as anion species, l^?, l ₃ ^? and l ₃ ^? .At the heavy doping level, polyiodide anions, l ₃ ^? and l ₅ ^? , increase as compared to the covalently bonding iodine atoms and addtionally molecular iodine l₂ exists.     

Hyperspaces of Normed Linear Spaces with the Attouch–Wets Topology

Let Cld _AW (X) be the hyperspace of nonempty closed subsets of a normed linear space X with the Attouch–Wets topology. It is shown that the space Cld _AW (X) and its various subspaces are AR's. Moreover, if X is an infinite-dimensional Banach space with weight w(X) then Cld _AW (X) is homeomorphic to a Hilbert space with weight 2 ^w(X).