China Science

As master craftsmen, modern synthetic chemists are challenged to achieve remarkable feats of efficiency and elegance toward molecular targets. The nature of this pursuit necessitates the collection of synthetic repertoires that are tried and true. With methodologies and pathways increasingly scrutinized, the adept chemist must seek out propitious tools to incorporate into the arsenal. With this in mind, this Account highlights the versatility of alkoxyallenes as precursors to valuable heterocyclic building blocks for such efforts as natural product synthesis. Accessed by the etherification of either propargyl alcohols or propargylic halides, alkoxyallenes are obtained after base-catalyzed isomerizations of the propargylic ethers. A host of umpolung synthons are available through this scheme after metalation, generating C3 nucleophiles synthetically equivalent to vital anionic and zwitterionic synthons. Reactions with a diverse set of heteroatomic electrophiles yield carbohydrates, spiroketals, alkaloids, and heteroaromatics via [3 + 2] or [3 + 3] cyclizations. By employing lithiated alkoxyallenes into transformation routes, the natural product chemist can utilize this methodology as a viable resource in stereoselective synthesis. A survey of our own utilization of alkoxyallenes along synthetic pathways toward natural product targets reveals their suitability for generating advantageous precursors. A set of four stereoisomeric 2,6-dideoxyhexoses were stereoselectively obtained after an initial lithiated alkoxyallene and lactaldehyde cyclization, followed by the oxidative ring opening of the dihydrofurans. Through the addition of a lithiated alkoxyallene to a functionalized benzaldehyde, an essential spiroketal diastereomer was rapidly achieved in a few steps. We greatly benefitted from alkoxyallenes in the construction of complex nitrogen-containing synthetic targets, whether pyrrolidine alkaloids, substituted imidazole derivatives, or functionalized pyridines. A pinnacle example of their utility came from the coupling of alkoxyallenes to nitrones affording 1,2-oxazines, which served as a gateway to an array of novel polyfunctionalized compounds such as aminopolyols, hydroxylated pyrrolidines, or carbohydrate mimetics. Alkoxyallenes have proven themselves to be powerful C3 building blocks toward complex molecular targets, revealing novel pathways to a variety of desirable highly functionalized heterocycles. In our view, the full extent of their synthetic utility has yet to be truly realized.

Malte Brasholz?Hans-Ulrich Reissig?Reinhold Zimmer
Freie Universitt Berlin, Institut fr Chemie and Biochemie, Takustrasse 3, D-14195 Berlin, Germany

The article discusses the gendered respectability, which was built into a labour process of shop work in South Africa. It offers a brief history of the interactions between white women and black service workers in the late 1960s and early 1970s. It is said that the National Union of Distributive Workers (NUDW) had protected the rights and reputability of white women workers. It is cited that the NUDW had raised public claims to employers and to their white customers, to defend for the legitimacy of women’s status as workers.

Kenny, Bridget1
[1]University of the Witwatersrand,

The structural blue color of a Morpho butterfly originates from the diffraction of light and interference effects due to the presence of the microstructures on the wing of the butterfly. Structural color on the surface of a damselfish reversibly changes between green and blue. Inspired by these creatures, we have been trying to prepare high-quality and functional structural color films. We describe our efforts in this Account. A useful technique to prepare such structural color films in colloidal solution is a “lifting” method, which allows us to quickly fabricate brilliant colloidal crystal films. The thicknesses of the films can be controlled by precisely adjusting the particle concentration and the lifting speed. Moreover, in order to prepare a complicated structure, we have used template methods. Indeed, we have successfully prepared the inverse structure of the wing of a Morpho butterfly with this technique. Initially, however, our structural color films had a whitish appearance due to the scattering of light by defects in the colloidal crystal film. Later, we were able to prepare a non-whitish structural color film by doping an appropriate dye in the colloidal particles to absorb the scattering light. In addition to the structural blue color, the wing of the Morpho butterfly has superhydrophobic properties. According to Wenzel’s equation, the hydrophobic and hydrophilic properties are enhanced when the roughness of the hydrophobic and hydrophilic surface is increased, respectively. Based on this mechanism, we have successfully prepared structural color films with superhydrophobic properties, as well as with superhydrophilic properties. Another important property that can be seen in nature is tunable structural color, such as the color change that can be seen on the surface of a damselfish. In order to mimic such color change, we have developed several tunable structural color films. In particular, we have successfully prepared phototunable photonic crystals using photoresponsive azobenzene derivatives. In order to apply these structural color films, we developed a technique for patterning them by taking advantage of the wettability of the substrate surface. These materials can be used in the future for self-cleaning pigments and tunable photonic crystals.

Osamu Sato#8224?Shoichi Kubo#8225?Zhong-Ze Gu§

Conclusions The ionotropic gelation method for formation of crosslinked chitosan particles can be easily modified from ionic cross-linking to deprotonation by adjusting the pH of TPP. Chitosan was cross-linked ionically with TPP at lower pH; by deprotonation mechanism at higher pH. The swelling behavior of cross-linked chitosan appeared to depend on the pH of TPP. The ionically cross-linked chitosan showed higher swelling ability. Thus the nature of crosslinked chitosan can be tailor made to obtain the desired properties in terms of cross-linking density, crystallinity,; hydrophilicity.

Devika R. Bhumkar1?Varsha B. Pokharkar1Email:vbpokharkar@yahoo.co.in
[1] Department of Pharmaceutics, Poona College of Pharmacy, Bharati Vidyapeeth Deemed University, Erandwane, 411038 Pune, Maharashtra State, India

Conclusions Spherical agglomeration techniques were developed for improving the flow; compressibility characteristics of microcrystalline mefenamic acid; nabumetone. The process involved agglomerating microcrystals using agglomerating solvents. Temperature; speed of agitation were optimized to obtain spherical agglomerates in a desired range, which was found to be essential to enhance compressibility. Incorporation of polymer HPMC during agglomeration significantly enhanced the dissolution rate of mefenamic acid while incorporation of solubilizing agent lecithin improved the solubility of nabumetone. Thus, spherical agglomeration is an important technique for improving direct compressibility of pharmaceutical powders; is especially useful when the drug dosage is high.

Chelakara L. Viswanathan1Email:chelakara_viswanathan@yahoo.com?Sushrut K. Kulkarni1?Dhanashri R. Kolwankar1
[1] Bombay College of Pharmacy, Kalina, Santacruz ;[East], 400 098 Mumbai, India

Bulk ceramic materials based on TiC–TiB2–MexOy systems have been produced by means of pressure-assisted self-propagating high-temperature synthesis (SHS). The selection of the SHS systems was based on thermodynamic analyses in order to obtain regimes of synthesis with formation of liquid phase allowing a proper densification. The liquid phase formed in the products consisted of either melted oxides or TiC–TiB2 eutectic depending on the combustion temperature. The mechanisms of structure formation and the effect of grain growth inhibition due to the metal oxide particles have been evaluated. The microstructural investigations have confirmed the role of the metal oxides as promoter of the final products densification and of the grain refinement in the SHS ceramic materials. A core–shell model is proposed to explain the structure formation of the SHS composites through a chemical interaction involving two stages. The good agreement between calculated and experimental results confirmed the validity of the core–shell mechanism.

D. VallauriaEmail:dario.vallauri@polito.it?V.A. Shcherbakovb?A.V. Khitevb?F.A. Deorsolaa
[a]Department of Material Science; Chemical Engineering, Politecnico di Torino, Torino, Italy;[b]Institute of Structural Macrokinetics; Materials Science, Russian Academy of Science, Chernogolovka, Russia

The morphology evolution of binary blends subjected to a two-step quench in the presence of external surfaces, such as a static substrate or immobile fillers, was studied using the cell dynamical system (CDS) simulation method. When the binary blends were first annealed at a shallow quench for a long time followed by a second further deep quench into a two-phase region, transient lamellar structures were formed in the blends with both critical and off-critical compositions. The occurrence of the lamellar structure was found to be correlative with the compositional difference between the separated phases formed during the first shallow quench as well as the quench depth of the second quench. For blends contacted with a selective substrate or fillers, well-defined layer structures or target-like compositional waves which were paralleled to the external surfaces were formed during the two-step quench. In these systems, the bulk lamellar structure was affected by the concentration of components and fillers in the blend. The simulation by CDS demonstrated that the combination of various quench conditions and external surfaces play an important role in the pattern formation of binary blend, and provide a new approach in tailoring the morphologies of binary blends in addition to the other available methods.

Yajiang Huanga?Rui Wanga?Yajie Suna?Guangxian LiaEmail:nic8601@scu.edu.cn?Guangling Chena?Qi Yanga
[a]College of Polymer Science; Engineering, Sichuan University, Chengdu 610065, PR China;[b]State Key Laboratory of Polymer Material; Engineering, Sichuan University, Chengdu 610065, PR China

A hierarchal scale transition technique is introduced to model the effect of imperfect interfaces on the elastoviscoplastic response of composite materials. This novel framework is based on a two-step procedure. In the first step, an inclusion is embedded in a matrix phase and the interface between the two phases is imperfect. The embedded inclusion is homogenized via the use of a Mori–Tanaka scheme. In a second step the homogenized inclusion is introduced in a matrix phase representing the homogeneous equivalent material, and the macroscopic response of the material is obtained via the self-consistent approximation. The model is applied to the case of pure nanocrystalline copper and allows the activity of grain boundary sliding to be quantified.

L. CapolungoaEmail:laurentc@lanl.gov?S. Benkassemc?M. Cherkaouia?J. Qua
[a]UMI 2958 GT-CNRS, Metz 57000, France;[b]George W. Woodruff School of Mechanical Engineering, Atlanta, GA 30332-0405, USA;[c]LPMM-CNRS Université Paul Verlaine, Ile du Saulcy, 57045 Metz Cedex 1, France