A Structure-Properties Relationship Study of Self-Healing Materials Based on Styrene and Furfuryl Methacrylate Cross-Linked via Diels–Alder Chemistry

A series of copolymers of styrene and furfuryl methacrylate characterized by various molecular structures (linear and star, block and random) is synthesized via atom transfer radical polymerization, and cross-linked with a bismaleimide by means of thermally reversible Diels–Alder (DA) reaction, to obtain self-healing materials. The prepared materials are studied in terms of gelation, swelling, thermal, and dynamic-mechanical analysis, with the aim of correlating relevant properties to their chemical structure. It is found that the furan/styrene ratio, as well as the molecular architecture, have a major influence on the properties. It is also found that the reversibility of the DA reaction is not complete in the solid state for materials with high cross-linking density. This study provides some important tools for the design of materials characterized by thermally reversible behavior, which find usually application as self-healing thermosets, coatings, or adhesives.     

Self-healing polymers: evaluation of self-healing process via non-destructive techniques

The scope of this study is the real-time monitoring and evaluation of the healing process using novel testing procedures and non-destructive evaluation techniques. In this work, the healing approach that has been followed is that of the intrinsic Diels–Alder (DA) and retro-DA mechanism. Two polymers were used as adhesives in single lap-joint specimens that were subjected to static tensile loading. The healed specimens were subjected to the same testing procedure as the one before the first failure and the healing efficiency was assessed by the correlation of the experimental results prior and after healing. Acoustic emission and infrared thermography were employed with the destructive tests so as to monitor changes in the acoustic and the thermal profile between the virgin and the ‘healed’ specimen.     

Metal‐Free Click Chemistry Reactions on Surfaces

In the last decade, interest in the functionalization of surfaces and materials has increased dramatically. In this regard, click chemistry deserves a central focus because of its mild reaction conditions, high efficiency, and easy post‐treatment. Among such novel click reactions, those that do not require any metal catalyst are of special interest, as metals may have undesirable effects in many fields. In this Review, the backgrounds and application of such metal‐free click reactions for the modification of surfaces are highlighted.     

荞麦七中黄酮类物质的抗氧化活性研究

以邻二氮菲法测定羟基自由基清除率、邻苯三酚法测定超氧阴离子自由基抑制率、铁氰化钾法测定还原力,研究了荞麦七不同溶剂提取物中的黄酮类物质的抗氧化活性。结果表明:荞麦七不同溶剂提取物的抗氧化活性因黄酮类物质的种类及含量不同而不同,其中60%乙醇-乙酸乙酯提取物中的黄酮类物质含量最多,抗氧化活性最强,提取物浓度与其抗氧化活性呈线性关系。该研究为荞麦七中抗氧化黄酮类物质的进一步分离奠定了基础。     

Synthetic Studies of Biomimetic Diels–Alder Processes toward the Helicterin Family of Natural Products

Although the [2.2.2]-bicyclooctene core of the helicterin, helisorin, and helisterculin class of neolignan natural products could conceivably arise in Nature via Diels–Alder reactions, synthetic explorations have revealed that only under very non-biomimetic conditions can such cycloadditions be performed. In this article, we provide a personal account of explorations towards this natural product family, sharing some additional unpublished synthetic work to test the viability of an alternate, Diels–Alder-based, biogenetic hypothesis for the generation of this unique collection of secondary metabolites.     

Studies on the Biosynthesis of the Stephacidin and Notoamide Natural Products: A Stereochemical and Genetic Conundrum

The stephacidin and notoamide natural products belong to a group of prenylated indole alkaloids containing a bicyclo[2.2.2]diazaoctane core. Biosynthetically, this bicyclic core is believed to be the product of an intermolecular Diels–Alder (IMDA) cycloaddition of an achiral azadiene. Since all of the natural products in this family have been isolated in enantiomerically pure form to date, it is believed that an elusive Diels–Alderase enzyme mediates the IMDA reaction. Adding further intrigue to this biosynthetic puzzle is the fact that several related Aspergillus fungi produce a number of metabolites with the opposite absolute configuration, implying that these fungi have evolved enantiomerically distinct Diels–Alderases. We have undertaken a program to identify every step in the biogenesis of the stephacidins and notoamides, and by combining the techniques of chemical synthesis and biochemical analysis we have been able to identify the two prenyltransferases involved in the early stages of the stephacidin and notoamide biosyntheses. This has allowed us to propose a modified biosynthesis for stephacidin A, and has brought us closer to our goal of finding evidence for, or against, the presence of a Diels–Alderase in this biosynthetic pathway.     

Essential oils of Zingiber officinale var. rubrum Theilade and their antibacterial activities

The essential oils obtained by hydrodistilation of the leaves and rhizomes of Zingiber officinale var. rubrum Theilade were analysed by capillary GC and GC–MS. Forty-six constituents were identified in the leaf oil, while 54 were identified in the oil from the rhizomes. The leaf oil was clearly dominated by β-caryophyllene (31.7%), while the oil from the rhizomes was predominantly monoterpenoid, with camphene (14.5%), geranial (14.3%), and geranyl acetate (13.7%) the three most abundant constituents. The evaluation of antibacterial activities using the micro-dilution technique revealed that both the leaf and rhizome oils were moderately active against the Gram-positive bacteria Bacilluslicheniformis, Bacillus spizizenii and Staphylococcus aureus, and the Gram-negative bacteria Escherichia coli, Klebsiella pneumoniae and Pseudomonas stutzeri.     

罗汉果生姜饮料的加工工艺研究

采用单因素试验、正交设计及感官评价等方法研究了罗汉果生姜饮料的关键工艺和配方。通过产品风味确定工艺流程、产品配方和最佳工艺参数。结果表明,罗汉果最佳水浸提条件为固液比1∶35(g∶mL),100 ℃水浴恒温浸提40 min;通过感官评定得到罗汉果生姜饮料的最佳配方为罗汉果浸提液中添加20%姜汁,8.5%木糖醇,0.25‰的柠檬酸;所得产品具有罗汉果特有的香气及甜味,姜味协调柔和,口感清爽;甜酸咸苦适中,无异味;色泽纯正透亮,呈均匀棕红色,澄清透明无杂质。     

翅果油超临界CO2流体萃取工艺优化及其不同提取方法的比较

对翅果油的超临界CO_2流体萃取工艺条件进行研究。在单因素试验的基础上,以萃取压力、萃取温度、萃取时间和原料粒度为影响因素,以翅果油得率为指标,采用正交试验优化工艺条件。比较了浸出法、超临界CO_2流体萃取法、冷榨法和热榨法4种不同提取方法对翅果油得率和微量活性成分的影响。结果表明:超临界CO_2流体萃取翅果油最优工艺条件为萃取压力30 MPa、萃取温度50℃、萃取时间150 min、原料粒度80目,此条件下翅果油得率为(28. 32±1. 15)%; 4种提取方法中,浸出法的翅果油得率、VE及甾醇含量最高,其次是超临界CO_2流体萃取法,除热榨法的翅果油角鲨烯含量最高外,压榨法的其他指标均最低。