Mechanistic aspects of the horseradish peroxidase-catalysed polymerisation of aniline in the presence of AOT vesicles as templates
Mechanistic aspects of the horseradish peroxidase-catalysed polymerisation of aniline in the presence of AOT vesicles as templates
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DOI：
10.1039/c2ra20566a
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发表时间：
2012-01-01
期刊：
影响因子：
3.9
通讯作者：
Walde, Peter
中科院分区：
文献类型：
--
作者：
Junker, Katja;Zandomeneghi, Giorgia;Walde, Peter
研究了辣根过氧化物酶（HRP）-H_2O_2催化苯胺在AOT囊泡存在下聚合的机理。AOT（二-（2-乙基己基）磺基琥珀酸酯）用作囊泡形成表面活性剂和掺杂剂，在pH = 4.3和室温下在最佳反应条件下在24小时内以90-95%的产率获得聚苯胺的绿色翠绿亚胺盐形式。基于聚合反应过程中进行的UV/维斯/NIR和EPR测量，并基于苯胺和H2 O2浓度和HRP活性的变化，提出了一种机制。根据这种“自由基阳离子机理”，通过将苯胺自由基阳离子添加到生长的聚合物链上，在囊泡表面上发生链生长。H2 O2起着两个重要的作用，氧化HRP的血红素基团，并氧化生长的聚合物链，以允许逐步添加新的苯胺自由基阳离子。整个反应可分为三个动力学上不同的阶段。在第一快速阶段（5-10分钟），发生实际的聚合物形成以产生处于其双极化子状态的聚苯胺的翠绿亚胺盐形式。在第二和第三个较慢的阶段（1-2天），双极化子转化为带有未成对电子的极化子。在反应过程中，HRP活性降低，直到聚合物形成后酶变得无活性。与部分氘代苯胺进行的反应进行了分析，通过2 H魔角旋转（MAS）NMR光谱，以证明链生长的区域选择性：苯胺单元的对位耦合明显占主导地位。从cryo-TEM和SANS测量中可以明显看出所形成的聚苯胺与囊泡膜的结合。
The mechanism of the horseradish peroxidase (HRP)-H2O2-catalysed polymerisation of aniline in the presence of AOT vesicles was investigated. AOT (= bis-(2-ethylhexyl)sulfosuccinate) served as vesicle-forming surfactant and dopant for obtaining at pH = 4.3 and room temperature within 24 h under optimal reaction conditions the green emeraldine salt form of polyaniline in 90-95% yield. Based on UV/VIS/NIR and EPR measurements carried out during the polymerisation reaction, and based on changes in aniline and H2O2 concentrations and HRP activity, a mechanism is proposed. According to this "radical cation mechanism" chain growth occurs on the vesicle surface through addition of aniline radical cations to the growing polymer chain. H2O2 plays two essential roles, to oxidise the heme group of HRP, and to oxidise the growing polymer chain for allowing the stepwise addition of new aniline radical cations. The entire reaction can be divided into three kinetically distinct phases. In the first rapid phase (5-10 min), the actual polymer formation takes place to yield the emeraldine salt form of polyaniline in its bipolaron state. In the second and third slower phases (1-2 days) the bipolarons transform into polarons with unpaired electrons. During the reaction, the HRP activity is decreasing until the enzyme becomes inactive after polymer formation. Reactions carried out with partially deuterated anilines were analysed by 2 H magic-angle spinning (MAS) NMR spectroscopy to demonstrate the regioselectivity of the chain growth: para-coupling of the aniline units clearly dominates. Association of the formed polyaniline with the vesicle membrane is evident from cryo-TEM and SANS measurements.