Mechanistic aspects of the horseradish peroxidase-catalysed polymerisation of aniline in the presence of AOT vesicles as templates

Abstract

The mechanism of the horseradish peroxidase (HRP)-H 2 O 2 -catalysed polymerisation of aniline in the presence of AOT vesicles was investigated. AOT (= bis-(2-ethylhexyl)sulfosuccinate) served as vesicleforming 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 H 2 O 2 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. H 2 O 2 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.

Insight into the template effect of vesicles on the laccase-catalyzed oligomerization of N-phenyl-1,4-phenylenediamine from Raman spectroscopy and cyclic voltammetry measurements

“…More from an application point of view, the suitability of the direct use of the “as obtained” poly(PADPA)/AOT vesicle suspension for bioelectrode fabrication needs to be investigated. At least with respect to the first CV results obtained in this work, it seems appropriate to continue research in this field, and to compare the advantages and disadvantages of the PANI-ES-like poly(PADPA)–as obtained from PADPA in the present work with TvL/O 2 and AOT vesicles–with, for example, PANI-ES as obtained from aniline with horseradish peroxidase isoenzyme C/H 2 O 2 and the same type of vesicles55, even though we know that in this latter case much more enzyme is required for the synthesis than in the case of TvL/O 2 and PADPA1.…”

Enzymatic oligomerization and polymerization of arylamines: state of the art and perspectives

“…The importance of templates was shown using SDBS micelles vs. non-aggregating sodium benzenesulfonate (Liu et al 1999b), or AOT vesicles vs. non-aggregating sodium di- n -butylsulfosuccinate (Junker et al 2012). The non-aggregating sulfonates did not yield a PANI product in the emeraldine salt form although in both cases, the sulfonate concentration was kept constant.…”

Photochlorination of aniline in Fe3+-containing saline water under simulated solar light irradiation

“…[14,26] The colour of the reaction solutions deepened with more dark precipitates generated at higher Fe 3þ concentrations. Fig.…”

“…Anilino radical cations rather than the neutral forms of radicals dominated under our experimental conditions because pH 2.4 is below its pK a (7.05). [13,14] It was reported that anilino radical cations showed absorptions at 407 and 423 nm, and chloroanilino radical cations showed absorption at 447 nm in the transient absorption spectra of LFP. [15,16] The absorptions observed at ,406, ,424 and ,448 nm were most likely from the anilino radical cations and the CA radical cations as shown in Fig.…”