Horseradish peroxidase-catalyzed oxidative polymerization of aniline in bicontinuous microemulsion stabilized by AOT/SDS

https://doi.org/10.1016/j.molliq.2020.112529Get rights and content

Highlights

  • The phase inversion temperature of AOT/SDS stabilized microemulsions closes to room temperature.

  • The PANI conductivity varies with the composition of bicontinuous microemulsions.

  • The microstructure of microemulsion has a template role in the HRP-catalyzed polymerization.

  • The microstructure of microemulsion affects the activity and stability of HRP.

  • The change of the PANI conductivity with temperature is ascribed to the thermal stability of HRP.

Abstract

A bicontinuous microemulsion system consisting of sodium bis(2-ethylhexyl) sulfosuccinate (AOT), sodium dodecylsulfate (SDS), an aqueous solution (a 0.1 M disodium hydrogenphosphate/citric acid buffer solution of pH = 4.3), and decane was investigated in detail for applications as reaction medium for the horseradish peroxidase (HRP)/hydrogen peroxide-mediated synthesis of the conductive form of polyaniline (PANI). To formulate the optimal single-phase microemulsion with the phase inversion temperature being close to room temperature, the T-γ fishlike phase diagram of the AOT/SDS-buffer-decane pseudoternary system was determined. The effects of the surfactant concentration (γ), the oil-to-water ratio (α) and the temperature (T) on the conductivity of the resulting PANI and the underlying mechanism were investigated using UV–vis-NIR, ESR and small-angle X-ray scattering (SAXS) techniques. Results show that the bicontinuous microemulsion plays a template role in the PANI biosynthesis, and the PANI conductivity also depends on the activity and stability of the solubilized HRP, which are determined by the microdomain size of the microemulsions and the reaction temperature. As far as γ is concerned, it is found that as γ increases, the microdomain size of the bicontinuous microemulsion as well as the activity of the solubilized HRP decreases significantly, leading to a great decrease of the PANI conductivity. Compared with γ, the change of α has small effect on the PANI conductivity. As the α-dependent microdomain size changes little with increasing α, the small change of the PANI conductivity should be ascribed mainly to the HRP activity. For T, over the range of 20 °C–35 °C, it has a slight effect on the microdomain size of the bicontinuous microemulsion, but it has a marked effect on the enzymatic properties of HRP. As the temperature increases, the activity of HRP increases, but its thermal stability decreases greatly. Therefore, the thermal stability of HRP is the major factor causing that the PANI conductivity decreases significantly with increasing T. The present work deepens the understanding of the template effect of anionic surfactant aggregates in the biosynthesis of conducting PANI. To the best of our knowledge, this work is the first study of the use of bicontinuous microemulsions as reaction media for the enzymatic synthesis of a conducting polymer.

Graphical abstract

The bicontinuous microemulsion plays a template role in the PANI biosynthesis, and the PANI conductivity also depends on the activity and stability of the solubilized HRP, which are determined by the microdomain size of the microemulsions and the reaction temperature.

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Introduction

As a conducting polymer, polyaniline (PANI) has good electronic conductivity as well as chemical stability. PANI could be thus used as metal anti-corrosion coating, electromagnetic shielding material, sensing element and so on [[1], [2], [3], [4], [5]]. PANI is usually obtained by oxidative polymerization of aniline monomers. PANIs prepared under different conditions, have different branching degrees, different oxidation states and doping levels, which results in different electronic and optical properties of PANI. The oxidative polymerization of aniline is a complex process. It involves several highly reactive species and leads to various by-products (formed by branching or intramolecular cyclization reaction) [5]. In the presence of a template, however, the reaction pathways to form by-products can be suppressed to some extent [[5], [6], [7]]. Here the so-called template refers to some additives that have a positive and desired effect on the synthesis of conducting PANI. It is shown that the effect of a template is exerted by its direct interaction with the aniline monomers and the growing polyaniline chains or by keeping the reaction in its spatial confinement (forming a microreactor) [8,9].

The chemical/electrochemical polymerization is a conventional approach for the synthesis of conducting polymers [10,11]. This approach usually requires strong acids and strong oxidants/high oxidation potentials, thereby resulting in formation of by-products during the process [9,12,13]. In contrast, the enzymatic polymerization of aniline could be carried out under mild conditions (low acidity, low oxidation potential of the oxidant) with good selectivity [5,9,12]. Therefore, it is of great potentiality to develop an enzymatic approach for the biosynthesis of PANI. Currently, there have been many reports on the enzymatic biosynthesis of PANI [6,8,9,[14], [15], [16], [17]]. It is shown that, for the enzymatic polymerization, conducting PANI could be obtained without template [5,12]; however, in the presence of a template it is easy to obtain PANI with large molecular weight and good electronic conductivity [[5], [6], [7]]. The positive role of templates in the biosynthesis of conducting PANI has been confirmed [[7], [8], [9],15], especially when a heme-containing mimic enzyme (such as hemoglobin) is used as a catalyst for the biosynthesis (it is reported that without template it is difficult to obtain high-quality PANI [5,18,19]).

The templates used for the synthesis of conducting polymers are divided into two categories: one is a hard template and the other is a soft one. Currently, the mostly used templates are soft ones, which are composed mainly of strongly acidic polyelectrolytes or various aggregates formed via self-assembly by strong acid-based surfactants. The major role of these templates in the synthesis of PANI is manifested in the following three aspects [5,7]: one is to regulate the reaction process to obtain the desired structure and properties of PANI, the second is to provide a dopant for PANI, and the third is to improve the water solubility and processability of PANI. Compared with anionic polyelectrolytes, surfactant aggregates as templates are more favored due to their well-defined microstructure. The surfactant aggregates that have been tried so far as templates are micelles [7,17,[20], [21], [22]] and vesicles [14,15,23,24]. These two templates are formed by aggregation of surfactants in a single aqueous medium and thus have fewer microstructure-tuning parameters when compared with microemulsions composed of oil, water, surfactant and cosurfactant. Microemulsions can be divided into two categories, i.e., droplet microemulsions and bicontinuous microemulsions. Compared with droplet microemulsions [25], bicontinuous microemulsions not only have large interfacial area, low interfacial tension, and low viscosity, but also have the unique property of zero average interfacial curvature [[26], [27], [28], [29]]. If bicontinuous microemulsions could serve as a template, it would be beneficial to the linear growth of polyaniline chains and to the spins hops between polyaniline chains, and the conductivity of the PANI thus obtained would be improved. There has been no report in this respect, so it is worthwhile to try to do so. In order to understand the template effect of bicontinuous microemulsion on the biosynthesis of conducting PANI, it is necessary to study the influence of the microemulsion structure on the conductivity of the PANI obtained by enzymatic polymerization of aniline in anionic surfactant stabilized bicontinuous microemulsions and the underlying mechanism.

Section snippets

Materials

Sodium bis(2-ethylhexyl) sulfosuccinate (NaAOT, ≥97%) was obtained from J&K Scientific Ltd. Decane (C10H22, >99%), sodium dodecylsulfate (SDS, AR) and horseradish peroxidase (HRP, pI ~ 7, >300 U/mg) were obtained from Aladdin Co., Ltd. 2,2′-Azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS, ≥98%) was obtained from Sigma-Aldrich. Aniline (ANI, AR) and hydrogen peroxide (H2O2, AR) were purchased from Sinopharm Chemical Reagent Co., Ltd. All chemical reagents were of

Phase behavior of Na2HPO4/citric acid buffer-decane-AOT/SDS pseudoternary system

AOT is a strong acid-based anionic surfactant, which has been widely used as a building block for constructing an anionic template for enzymatic polymerization of arylamines [5,15]. In the present study, AOT is also used to formulate a bicontinuous microemulsion. According to the literature [33,34], the phase inversion temperature of AOT-stabilized bicontinuous microemulsions is relatively high (40 °C–50 °C), which is not suitable for the enzyme-catalyzed polymerization of aniline (enzymatic

Conclusions

The oxidative polymerization of aniline catalyzed by HRP in the AOT/SDS stabilized bicontinuous microemulsion was studied for the first time. It was observed that there exist significant correlations between the PANI conductivity and the experimental parameters (γ, α and T). A bicontinuous microemulsion with lower γ and α values is better for the enzymatic synthesis of conducting PANI. In order to understand the underlying mechanism, the microstructure of bicontinuous microemulsions and the

CRediT authorship contribution statement

Wei Jin: Investigation, Methodology, Writing - original draft. Rongrong Wang: Validation, Visualization. Xirong Huang: Conceptualization, Writing - review & editing, Funding acquisition.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

We are grateful for the financial supports from the National Natural Science Foundation of China (21773143) and the Key Research & Development Plan of Shandong Province(2019GSF107090).

References (42)

  • D.G. Hayes et al.

    Protein extraction into the bicontinuous microemulsion phase of a water/SDS/pentanol/dodecane winsor-III system: effect on nanostructure and protein conformation

    Colloids Surf. B Biointerfaces

    (2017)
  • R. Wang et al.

    Anionic surfactant-stabilized hydrophobic ionic liquid-based bicontinuous microemulsion: formulation, microstructure and laccase kinetics

    J. Mol. Liq.

    (2019)
  • A.K. Steudle et al.

    Activity of squalene-hopene cyclases in bicontinuous microemulsions

    Colloids Surf. B Biointerfaces

    (2015)
  • J.H. Porada et al.

    Microemulsions with hydrophobic ionic liquids: influence of the structure of the anion

    J. Mol. Liq.

    (2017)
  • Y. Zhang et al.

    The phase behavior and solubilization of isopropyl myristate in microemulsions containing hexadecyl trimethyl ammonium bromide and sodium dodecyl sulfate

    J. Mol. Liq.

    (2017)
  • H. Kunieda et al.

    Solution behavior and hydrophile-lipophile balance temperature in the aerosol OT-isooctane-brine system: correlation between microemulsions and ultralow interfacial tensions

    J. Colloid Interface Sci.

    (1980)
  • S. Luginbühl et al.

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

    Synth. Met.

    (2017)
  • G. Wang et al.

    Nanomaterial-doped conducting polymers for electrochemical sensors and biosensors

    J. Mater. Chem. B

    (2018)
  • C.O. Baker et al.

    Polyaniline nanofibers: broadening applications for conducting polymers

    Chem. Soc. Rev.

    (2017)
  • G. Ćirić-Marjanović et al.

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

    Chem. Pap.

    (2017)
  • L.A. Samuelson et al.

    Biologically derived conducting and water soluble polyaniline

    Macromolecules

    (1998)
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