Anilines enzymatic polymerization

Figure 8.1 Two different pathways for aniline enzymatic polymerization. On top, traditional ortho-coupling. Below, template-assisted enzymatic polymerization of aniline. (Reproduced with permission from [15]. Copyright (1998) American Chemical Society).

Enzymes are generally classified into six groups. Table 1 shows typical polymers produced with catalysis by respective enzymes. The target macromolecules for the enzymatic polymerization have been polysaccharides, poly(amino acid)s, polyesters, polycarbonates, phenolic polymers, poly(aniline)s, vinyl polymers, etc. In the standpoint of potential industrial applications, this chapter deals with recent topics on enzymatic synthesis of polyesters and phenolic polymers by using enzymes as catalyst. 

Guo ZW, Ruegger H, Kissner R, Ishikawa T, Willeke M, Walde P (2009) Vesicles as soft templates for the enzymatic polymerization of aniline. Langmuir 25(19) 11390-11405... 

Nagarajan R, Samuelson L, Tripathy S, Liu W, Kumar J, Bruno F (2003) Enzymatic polymerization of aniline or phenols around a template. US Patent 6569651... 

Enzymatic polymerization and oligomerization can be used to make polyesters, polypeptides, polysaccharides, polymers from phenols, polymers from anilines, and many others. This approach could lead to fewer side reactions, higher regio- and stereoselectivity, under milder conditions. Oligomeric polyesters can be prepared from lactones. Caprolactone can be polymerized in bulk with lipases (9.43) to polymers with molecular weights of 7000.305... 

Self-doped PANI are very interesting due to their unique electrochemical behavior unlike PANI, the self-doped polymer remains in its doped state in near neutral or alkaline media [28]. Fully self-doped PANIs are not easy to synthesize due to the lower reactivity of acid-functionalized anilines. Kim et al. [29, 30] introduced an alternative approach in the template-assisted enzymatic polymerization of aniline. Previously, only polyanionic templates had been used for PANI synthesis. However, acid-functionalized anilines bear a net anionic charge in aqueous solution, and attempts to use SPS as template with carboxyl-functionalized aniline resulted in red-brown colored polymers with no polaron transitions, regardless of the synthetic conditions. The use of polycationic templates, such as those shown in Figure 8.2 allowed the synthesis of linear and electrically conductive PANIs with self-doping ability due to the doping effect of the carboxyl groups present in the polymer backbone. 

Figure 8.4 PANI colloids obtained by enzymatic polymerization of aniline in presence of different steric stabilizers, (a) Partially hydrolyzed PVA, (b) fully hydrolyzed PVA, (c) PNIPAM, and...

PANI nanowires are ID nanostructures which are very interesting from the nanotechnology point of view, due to their potential use in sensors and nanoscale electronic devices. DNA can be considered as an anionic polyelectrolyte that can behave as a template for PANI enzymatic polymerization in solution [20]. Double stranded DNA can be attached to aminated surfaces by electrostatic self assembly, providing a linear template for further aniline electrostatic assembly. By using this method followed by enzymatic polymerization of the assembled aniline, Ma et al. [69] and Nickels et al. [70] showed that stretched DNA molecules were able to template the enzymatic synthesis of PANI nanowires, according to the mechanism showed in Figure 8.7. 

Figure 8.8 Schematic representation of a DNA biosensor based on the DNA-templated enzymatic polymerization of aniline (Reproduced with permission from[71]. Copyright (2007) Wiley-VCH Verlag ).

Polythiophenes are another interesting family of conductive polymers that have broad potential applications and technological relevance. However, unlike pyrrole and aniline, the oxidation potential of thiophene is relatively high and is almost insoluble in aqueous media. For this reason, there are only reports dealing with the enzymatic polymerization of (3,4-ethylendioxythiophene) (EDOT), one of the... 

Enzymes may be classified generally into six groups the details of typical polymers produced via catalysis with respective enzymes are listed in Table 23.1. In the past, the target macromolecules for enzymatic polymerization have included polysaccharides, poly(amino acid)s, polyesters, polycarbonates, phenolic polymers, poly(aniline)s, and vinyl polymers. In this chapter, attention is focused on the enzymatic synthesis of phenohc polymers and polyesters, based on the increasing industrial application of these materials. Notably, most such polymers can be obtained from commercially available, inexpensive monomers by using industrially produced enzymes. Another important point is that the enzymatic process must be regarded as an environmentally benign synthetic pathway. Details of the enzymatic synthesis of other polymers are provided in recent pertinent reviews [3-10]. 

Enzymatic polymerization of aniline. The. enzymatic polymerization of aniline was typically carried out at room temperature in a 30 ml, 0.1 M sodium... 

Enzymatic polymerization of a series of aniline derivatives was studied in aqueous and aqueous organic solvents. Phenylenediamines and aminophenols were polymerized in ambient conditions by the catalysis of horseradish peroxidase (HRP) in dioxane without the presence of templates [15,16]. The products were soluble in DME and DMSO. The structures were analyzed by ET-IR and NMR. The larger molar excess of hydrogen peroxide was necessary in reaching a higher polymer yield. Poly(2-aminophenol) and poly(4-aminophenol) resulting from these reactions have been shown to have electroactive properties. 

Scheme 8 Representation of enzymatic polymerization of aniline (at pH 4.3) in the presence of SPS...

Biomacromolecules were exploited as templates in the enzymatic synthesis of electronic and photonic materials for the development of biofunctional complexes and selective biosensors. The aniline was polymerized by the catalysis of HRP on a calf thymus DNA matrix consisting of a synthetic oligonucleotide (poly[dA-dC].poly[dG-dT]) [54]. The complexation of PANI with DNA and the ohgonucleotide was found to induce reversible changes in the secondary structure of the nucleic acid template, leading to the formation of an overwound polymorph. The melting behavior of the PANI/DNA complex demon-... 

Enzymatic polymerization of aniline by using another enzyn , bilirubin oxidase (BOD) has been reported [116]. BOD is a copper-containii oxido-reductase which oxidizes bilirubin to biliverdin and hydrogen peroxide with consumption of dissolved oxygen. The enzymatic polymerization took place on the glass surface of a BOD-adsorbed solid matrix, which was in contact with a buffer solution containing aniline. The enzymatic reaction markedly depended upon the concentration of BOD and aniline imder appropriate conditions, a hlm-like precipitate formed on the glass surface. The enzymatically synthesized polyaniline is considered to contain 1,4- and 1,2-substitution structures, which are partially different form those of chemically or electrochemically prepared polyaniline. 

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