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

Abstract

We report about the first Raman spectroscopy study of a vesicle-assisted enzyme-catalyzed oligomerization reaction. The aniline dimer N-phenyl-1,4-phenylenediamine (= p-aminodiphenylamine, PADPA) was oxidized and oligomerized with Trametes versicolor laccase and dissolved O2 in the presence of sodium bis(2-ethylhexyl)sulfosuccinate (AOT) vesicles (80–100 nm diameter) as templates. The conversion of PADPA into oligomeric products, poly(PADPA), was monitored during the reaction by in situ Raman spectroscopy. The results obtained are compared with UV/vis/NIR and EPR measurements. All three complementary methods indicate that at least some of the poly(PADPA) products, formed in the presence of AOT vesicles, resemble the conductive emeraldine salt form of polyaniline (PANI-ES). The Raman measurements also show that structural units different from those of “ordinary” PANI-ES are present too. Without vesicles PANI-ES-like products are not obtained. For the first time, the as-prepared stable poly(PADPA)-AOT vesicle suspension was used directly to coat electrodes (without product isolation) for investigating redox activities of poly(PADPA) by cyclic voltammetry (CV). CV showed that poly(PADPA) produced with vesicles is redox active not only at pH 1.1–as expected for PANI-ES–but also at pH 6.0, unlike PANI-ES and poly(PADPA) synthesized without vesicles. This extended pH range of the redox activity of poly(PADPA) is important for applications.

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

“…ESI–MS measurements indicated that the extent of formation of unwanted oxygen-containing species during the early stages of PADPA polymerization is decreased in the presence of AOT vesicles (Junker et al 2014b). The conversion of PADPA into poly(PADPA) in the TvL/O 2 /AOT reaction system was also recently monitored during the reaction by in situ Raman spectroscopy which indicated, in accordance with complementary UV/Vis/NIR and EPR measurements, that at least some of the poly(PADPA) products resemble the conductive PANI emeraldine salt form (Janošević-Ležaić et al 2016). The Raman measurements showed that structural units different from those of “ordinary” PANI emeraldine salt are also present in poly(PADPA) (Janošević-Ležaić et al 2016).…”

“…The conversion of PADPA into poly(PADPA) in the TvL/O 2 /AOT reaction system was also recently monitored during the reaction by in situ Raman spectroscopy which indicated, in accordance with complementary UV/Vis/NIR and EPR measurements, that at least some of the poly(PADPA) products resemble the conductive PANI emeraldine salt form (Janošević-Ležaić et al 2016). The Raman measurements showed that structural units different from those of “ordinary” PANI emeraldine salt are also present in poly(PADPA) (Janošević-Ležaić et al 2016). It is important to note that PANI emeraldine salt-like poly(PADPA) products were not obtained in the PADPA/TvL/O 2 system without AOT vesicles.…”

“…The obtained PADPA oligomers prevalently have the molecular structure of emeraldine salt. Poly(PADPA) was also synthesized with TvL and O 2 at pH 3.5 in an aqueous solution in the presence of AOT vesicles as templates (Junker et al 2014b; Carić et al 2015; Janošević-Ležaić et al 2016) (Fig. 17).…”

“…It is important to note that PANI emeraldine salt-like poly(PADPA) products were not obtained in the PADPA/TvL/O 2 system without AOT vesicles. Cyclic voltammetry measurements indicated an extended pH range of the redox activity of poly(PADPA) products obtained in the presence of AOT vesicles, i.e., poly(PADPA) produced in the PADPA/TvL/O 2 /AOT system is redox active not only at pH 1.1 (characteristic for PANI emeraldine salt) but also at pH 6.0, unlike PANI emeraldine salt and poly(PADPA) synthesized without AOT vesicles (Janošević-Ležaić et al 2016).

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The influence of anionic vesicles on the oligomerization of p-aminodiphenylamine catalyzed by horseradish peroxidase and hydrogen peroxide

“…From a number of previous studies it has become clear that aqueous suspensions of anionic vesicles with a diameter of about 80-100 nm are suitable reaction media for the enzymatic oligo-or polymerization of aniline [1][2][3][4][5][6], the aniline dimer N-phenyl-1,4phenylenediamine (= p-aminodiphenylamine = PADPA; the trivial name is p-semidine) [7,8], or pyrrole [9]. With "suitable" we mean (i) that the presence of the vesicles as templates has a positive and desired influence on the outcome of the reaction with respect to the chemical structure of the products formed [10], (ii) that the reaction occurs with a high monomer conversion, and (iii) that no significant product precipitation is observed.…”