Enzymatic Synthesis of Polyaniline and Other Electrically Conductive Polymers

Abstract

Since their discovery [1] , intrinsically conducting polymer s ( ICP s) have changed our way of thinking about polymers. With properties such as light weight, organic functionality, and distinctive electronic behavior, new applications were soon devised for these materials. Polyaniline ( PANI ) is one of the most interesting ICPs because of its chemical stability, tunable conductivity, and interesting electrochromic behavior [2] . This polymer is usually synthesized by chemical oxidation of the monomer in strong acidic media. Besides PANI, polythiophenes and polypyrrole are other important ICPs that have also been synthesized by oxidative polymerization. These polymers have been extensively used in several applications in the fi elds of organic electronics [3] , sensors [4] , actuators [5] , separation technologies [6] , and energy storage [7] , among others, and new applications for them are found continuously.Enzymatic polymerizations have become an interesting alternative route for polymer synthesis [8] . They are generally carried out under milder conditions than similar synthetic routes. Enzymes are natural catalysts which are non -toxic, biodegradable, energy effi cient and obtained from renewable resources. In this chapter, we review the different strategies that have been used for the enzymatic synthesis of PANI. Xu et al .[9] reviewed published work regarding enzymatic polymerization of aniline derivatives from its beginning until 2004. However, more recently, several groups have developed either new approaches for the enzymatic synthesis of PANI or different methods inspired by it. Indeed, the infl uence of the enzymatic synthesis of PANI can be seen in the development of several biocatalytic and biomimetic synthetic routes not only for the synthesis of PANI, but also for other important conductive polymers, such as polypyrrole ( PPy ) and poly(3,4 -ethylendioxythiophene) ( PEDOT ).

Effect of Template Type on theTrametes versicolorLaccase-Catalyzed Oligomerization of the Aniline Dimerp-Aminodiphenylamine (PADPA)

“…The efficient and environmentally friendly enzymatic synthesis of polyaniline products in their conductive emeraldine salt form (PANI-ES) has been a scientific challenge for many research groups during the last years. − The reasons for this are the many possible applications of conductive polyaniline, − even for biomedical applications (for example, in tissue engineering). , Due to the polymeric nature of PANI-ES products and their insolubility in common solvents, independent of whether they are obtained through electrochemical, chemical, , enzymatic, or enzyme-mimicking , routes, the analysis of the chemical structure of PANI-ES-type products is often difficult or impossible. By using p -aminodiphenylamine (PADPA) instead of aniline, the situation in terms of product analysis is much better. ,− …”

Enzymatic Synthesis of Highly Electroactive Oligoanilines from a p-Aminodiphenylamine/Aniline Mixture with Anionic Vesicles as Templates

“…One of the most intensively investigated enzymatic polymerizations is that of aniline − to yield polyaniline (PANI) in its conductive, half-reduced, and protonated half-oxidized emeraldine salt form (PANI-ES), with delocalized unpaired electrons on every second nitrogen atom and fully aromatic benzene rings, the so-called polaron state. − The chemical structure of a constitutional repeating unit of PANI-ES with bipolarons, separated polarons, or polaron pairs is shown in Scheme . This is a highly idealized representation of the actual PANI-ES chains obtained.…”

“…Polymers or oligomers with characteristic features of polaronic PANI-ES units, with maximal absorption λ max at ≈1000 nm (assigned to the π → polaron transition) and ≈420 nm (polaron → π* transition) , can be obtained from aniline with oxidative enzymes and enzyme-specific oxidants, e.g., a peroxidase and H 2 O 2 or a laccase and O 2 . − Conceptually, there are two conditions that need to be fulfilled for a successful enzymatic polymerization of aniline into PANI-ES products. One is related to the property of the enzyme, the other is related to the property of the reaction medium.…”

“…With respect to the second prerequisite, many previous studies have shown that for obtaining PANI-ES products with an oxidative enzyme, the presence of a “chemical structure-controlling template” is essential. These “templates” are anionic additives containing covalently bound anionic functional groups, which are dispersed in an aggregated state in the reaction medium: anionic polymers, − anionic micelles, − or anionic vesicles. , Among the most effective templates are sulfonated polystyrene, , micelles of sodium dodecylbenzenesulfonate, , or vesicles of sodium bis­(2-ethylhexyl)­sulfosuccinate (known as AOT). , They all represent soft sulfonate-rich interface systems.…”

Application of an enzymatic cascade reaction for the synthesis of the emeraldine salt form of polyaniline

“…Although there are well-established procedures for the chemical (Huang et al 1986;Stejskal and Gilbert 2002;Surwade et al 2009;Stejskal et al 2015) or electrochemical (Huang et al 1986;Okamoto and Kotaka 1998;Stejskal et al 2015) synthesis of the electroconductive polyaniline (PANI), the potential of using oxidative enzymes as biocatalysts is also being explored (Xu et al 2006;Bouldin et al 2010;Cruz-Silva et al 2011;Walde and Guo 2011;Otrokhov et al 2013;Ćirić-Marjanović et al 2017), most often by applying a heme peroxidase with hydrogen peroxide (H 2 O 2 ) as oxidant (Liu et al 1999a, b;Sakharov et al 2003;Caramyshev et al 2005;Rumbau et al 2007;Junker et al 2012Junker et al , 2013 or a high potential laccase in the presence of molecular oxygen (O 2 ) (Karamyshev et al 2003;Shumakovich et al 2012;Junker et al 2014;Zhang et al 2016;Walde et al 2019). The enzymatic approach allows carrying out the synthesis under milder, environmentally friendlier conditions as compared to chemical methods, at least if the acidity of the reaction medium is compared: pH ≈ 3.5-4.5 in the case of the enzymes, pH < 2.5 for the chemical approach (Stejskal et al 2015).…”