离子液体/季铵盐辅助氯过氧化物酶促氧化合成聚酚

基于氯过氧化物酶(CPO)催化氧化苯酚衍生物单体,建立了一个聚酚的绿色合成体系.以对苯基苯酚、对甲基苯酚、4-乙基苯酚、对羟基肉桂酸、对异丙基苯酚和邻甲基苯酚等6种底物为考察对象,以聚合物的产率、聚合度及热稳定性为评价指标,研究了体系中引入离子液体(ILs)或季铵盐(QAS)以及底物结构和反应微环境等对聚合反应和聚合物性质的影响.结果表明,引入少量咪唑类ILs或QAS可有效提高产物收率,其中ILs/QAS的阳离子基团越大和疏水链越短,越有利于酶催化聚合反应的进行;而ILs/QAS添加量的影响则呈现"钟罩"型规律.同时,苯酚对位取代远比邻位取代有利于聚合反应进行;而对位取代基中烷基类给电子基团比芳香基取代更有优势,所得聚合物的聚合度和热稳定性相对增大,但随着取代基团的增大,其空间位阻不利于聚合物产率的提高;反应体系的p H应控制在弱酸性至近中性,以避免竞争性的副反应的发生;而氧化剂H_2O_2则需要采用间歇式加入以抑制瞬时过浓导致CPO活性中心卟啉环的氧化损伤.基于CPO的活性中心结构分析了聚合机理.

Enzymatic Polymerization of Phenols Catalyzed by Chloroperoxidase in the Presence of Ionic Liquids/Quaternary Ammonium Salts

A green enzymatic approach for the synthesis of phenol polymersfrom substituted phenols monomer by chloroperoxidase( CPO)-catalyzed H2 O2-oxidation was proposed in this paper. The yield and thermal stabi-lity of polymers of p-methyl phenol, p-ethyl phenol, p-propyl phenol, p-phenyl phenol and p-hydroxy-cinnamic acid were studied based on the presence of imidazolium-based ionic liquids ( ILs ) or quaternary ammonium salts( QAS) , the effect of structure of the substrates and the reaction microenvironment. The results showed that the introduction of little amount of ILs/QAS can improve the production of polymerization of phenols effi-ciently, in which ILs/QAS with bigger cation group and shorter hydrophobic chain was much more effective, while the influence of ILs/QAS amount on polymerization of phenols showed a“ball type” pattern. Moreover, it was found that p-substituted phenol and electron-donating group were more beneficial to the increase of yield and thermal stability of phenol polymers compared to o-substituted phenol and electron-withdrawing group. However, the steric hindrance was increased with the increasing size of substituent group, which was not bene-ficial to the polymerization of phenols. The pH value should be controlled as weak acid or even near-neutral to avoid competitive side reaction, while the adding of H2 O2 should be in a batch type to suppress the oxidative damage of heme caused by the instantaneous concentrated H2 O2 . The mechanism of polymerization was also analyzed and proposed based on the characteristics of structure of CPO active site.