Synthesis of α,β‐ and β‐Unsaturated Acids and Hydroxy Acids by Tandem Oxidation,Epoxidation, and Hydrolysis/Hydrogenation of Bioethanol Derivatives

We report a reaction platform for the synthesis of three different high‐value specialty chemical building blocks starting from bio‐ethanol, which might have an important impact in the implementation of biorefineries. First, oxidative dehydrogenation of ethanol to acetaldehyde generates an aldehyde‐containing stream active for the production of C₄ aldehydes via base‐catalyzed aldol‐condensation. Then, the resulting C₄ adduct is selectively converted into crotonic acid via catalytic aerobic oxidation (62 % yield). Using a sequential epoxidation and hydrogenation of crotonic acid leads to 29 % yield of β‐hydroxy acid (3‐hydroxybutanoic acid). By controlling the pH of the reaction media, it is possible to hydrolyze the oxirane moiety leading to 21 % yield of α,β‐dihydroxy acid (2,3‐dihydroxybutanoic acid). Crotonic acid, 3‐hydroxybutanoic acid, and 2,3‐dihydroxybutanoic acid are archetypal specialty chemicals used in the synthesis of polyvinyl‐co‐unsaturated acids resins, pharmaceutics, and bio‐degradable/ ‐compatible polymers, respectively.     

Specific Non-Reducing Ends in Heparins from Different Animal Origins: Building Blocks Analysis Using Reductive Amination Tagging by Sulfanilic Acid

Heparins are linear sulfated polysaccharides widely used as anticoagulant drugs. Their nonreducing-end (NRE) has been little investigated due to challenges in their characterization, but is known to be partly generated by enzymatic cleavage with heparanases, resulting in N-sulfated glucosamines at the NRE. Uronic NRE (specifically glucuronic acids) have been isolated from porcine heparin, with GlcA-GlcNS,3S,6S identified as a porcine-specific NRE marker. To further characterize NRE in heparinoids, a building block analysis involving exhaustive heparinase digestion and subsequent reductive amination with sulfanilic acid was performed. This study describes a new method for identifying heparin classical building blocks and novel NRE building blocks using strong anion exchange chromatography on AS11 columns for the assay, and ion-pair liquid chromatography-mass spectrometry for building block identification. Porcine, ovine, and bovine intestine heparins were analyzed. Generally, NRE on these three heparins are highly sulfated moieties, particularly with 3-O sulfates, and the observed composition of the NRE is highly dependent on heparin origin. At the highest level of specificity, the isolated marker was only detected in porcine heparin. However, the proportion of glucosamines in the NRE and the proportion of glucuronic/iduronic configurations in the NRE uronic moieties greatly varied between heparin types.     

苹果酸——天然产物对映选择性全合成和合成方法学中多用途的手性合成砌块

合成砌块策略是天然产物生源合成的基本策略之一。对映纯天然手性合成砌块,由于价廉、易得,在天然产物的对映选择性全合成中获得广泛应用。这一策略,兴起于四十年前,至今仍是复杂分子对映选择性全合成的重要工具。L-苹果酸是一种价廉易得的天然手性源,D-苹果酸虽然价格稍贵,也是一种商品化试剂。苹果酸所包含的四个碳原子均可被转化或官能化,因而被广泛应用于各类天然产物的对映选择性全合成。本文综述了L-和D-苹果酸在有机合成中的应用进展:归纳总结了从苹果酸衍生的多种C₄手性合成砌块,重点评述了近年来这些合成砌块在复杂天然产物全合成中的应用,结合作者实验室的工作介绍基于苹果酸的新型合成方法学研究进展,并对基于苹果酸的合成方法学的发展进行了展望。     

Applications of versal deformations to Galois theory

In this paper we study which solutions to an embedding problem can be constructed using a versal deformation of a group representation over an algebraically closed field of positive characteristic. This question reduces (at least stably) to finding which representations of finite groups have faithful versal deformations. We determine exactly when a versal deformation of a representation of a finite group is faithful in case the representation belongs to a cyclic block and its endomorphisms are given by scalar multiplications. Received: January 30, 2001     

Stereoselective total syntheses of (+)-exo- and (−)-exo-brevicomins, (+)-endo- and (−)-endo-brevicomins, (+)- and (−)-cardiobutanolides, (+)-goniofufurone

Stereoselective total syntheses of aggregation pheromones (+)-exo-brevicomin (9a), (−)-exo-brevicomin (9b), (+)-endo-brevicomin (9c), (−)-endo-brevicomin (9d) and styryllactones (+)-cardiobutanolide (14a), (−)-cardiobutanolide (14b), and (+)-goniofufurone (19a) were achieved in good yields from enantiomerically pure highly functionalized furanoid glycal building blocks (1a-d) involving similar synthetic strategies, thus making these furanoid glycals highly useful building blocks in diversity-oriented synthesis (DOS).     

Molecular Self‐Assembly of Multifunctional Nanoparticle Composites with Arbitrary Shapes and Functions: Challenges and Strategies

The assembly of nanoparticles into complicated, anisotropic shapes has much promise for advanced materials and devices. Developing effective and efficient anisotropic mono‐functionalization strategies is an imperative step in realizing this potential. By functionalizing DNA one at a time to the nanoparticle, a DNA‐nanoparticle building block could have distinct DNA sequences at different locations on the surface of the particle. Since this technology could incorporate nanoparticles of different composition, generating toolboxes of various nanoparticle building blocks (“nano‐toolboxes”) with DNA at defined locations and in defined 3D orientations on a nanoparticle, it promises not only complicated shapes, but also the ability to tune the function of the assembly. The challenges of programmable and scalable multifunctional nanostructure self‐assembly with DNA conjugated to nanoparticles are reviewed. The first difficulty is to control the assembly process so that designed products are formed, and unwanted products are minimized. The design problem for nanostructure construction is both physically and computationally complex. Thus, the other major challenge is to devise design methodologies that move nanostructure construction from trial and error to principled approaches. Strategies to overcome these challenges are also presented by realizing greater control over the final shapes and functions of the self‐assembled nanostructures. Finally, the future perspectives of nano‐toolboxes and their promise in applications such as multifunctional, multicolor, and multimodal contrast nanoagents for medical therapy and diagnostics (theranostics) are described.     

Etching technique study for POF coupler fabrication using circular blocks

A method for developing polymer optical fiber (POF) directional coupler is introduced where the initial procedure is explained. The procedure of fabrication includes using chemical solvent to remove the cladding and exposed the core in order to align the unclad center of the fiber with another similar fiber to develop the coupler. Several experiments using different radii of circular blocks attached with the etched fibers are demonstrated to investigate the output power and losses of the developed coupler in order to build an efficient yet low-cost device. Instead of relying only on silica or glass fiber, POF now can be used as an alternative to improve the network performance in short distance communication system. The measurement parameters laid out offer great outcomes, however, the couplers intended to develop is yet to be realized where deeper research and various experiments are needed in order to develop a simple but optimum performance coupler that can be used for various applications.     

局域网中网络拥塞的成因分析及改进策略

局域网中网络拥塞问题对于大规模的上机考试来说是十分严重的，发生的可能性也比较大，涉及的环节多，原因复杂，加上条件限制，分析处理有一定难度。针对上机考试中的网络拥塞现象进行了分析，并提出了改进策略。     

Transversal Heteroclinic Bifurcation in Hybrid Systems with Application to Linked Rocking Blocks

In this paper, we study heteroclinic bifurcation and the appearance of chaos in time-perturbed piecewise smooth hybrid systems with discontinuities on finitely many switching manifolds. The unperturbed system has a heteroclinic orbit connecting hyperbolic saddles of the unperturbed system that crosses every switching manifold transversally, possibly multiple times. By applying a functional analytical method, we obtain a set of Melnikov functions whose zeros correspond to the occurrence of chaos of the system. As an application, we present an example of quasiperiodically excited piecewise smooth system with impacts formed by two linked rocking blocks.