Oxireductases in the Enzymatic Synthesis of Water-Soluble Conducting Polymers - Enzymatic Polymerisation - page 10

solubility of the monomer is very poor in water, the reaction takes place in a biphasic
media, where the HRP is localized more preferentially in the monomer phase. To
prove this statement, a mixture of EDOT, template, and enzyme was prepared in
acidic water (pH 2). This solution was kept under magnetic stirring for 24 h. Then,
a solution of H 2 O 2 was added. The reaction proceeded as usual and a conducting
water-soluble PEDOT was obtained after an additional 16 h. Thus, as a consequence,
the EDOT monomer droplets act as (1) enzyme protectors against deactivation, and
(2) monomer feed to keep a constant EDOT concentration in the reaction media.
The HRP-catalyzed enzymatic polymerization of EDOT was thus successfully per-
formed at the specific synthesis conditions (low pH, protected enzyme). Also, FTIR
spectroscopy confirmed the classical bands of PEDOT at 1698, 1381, 1066, and
940-875 cm − 1 , and of the PSSNa stabilizers at 1009 and 1128 cm − 1 (Fig. 6 ) . Fur-
thermore, the electrical conductivity of the films was verified by the four-points
probe. Typical values for PEDOT of 2 10 − 3 Scm − 1 × were measured, further con-

firming the success of our synthetic route.
The obtained PEDOT polymer showed a very good capacity for film forma-
tion at a macroscopic level, and very low surface roughness also at a microscopic
level, as can be observed in the surface picture of the film obtained by atomic force
microscopy (Fig. 7 ) .
Despite these successful polymerizations, these reactions proceed well only at
low pH and temperatures, which is restrictive for some applications. Therefore, the
most recent work on the biocatalytic polymerization of EDOT reports the use of
terthiophene as a radical mediator to synthesize PEDOT/PSSNa under milder pH
and at ambient conditions using the enzyme soybean peroxidase (SBP) and PSSNa
[ 44 ]. SBP belongs to the family of plant peroxidases that can oxidize a wide vari-
ety of organic and inorganic substrates using hydrogen peroxide. Although SBP has
been reported to have a higher redox potential than HRP, SBP cannot catalyze the
polymerization of EDOT under non-acidic conditions. Therefore, the polymeriza-
tion of EDOT was accomplished in this work by introducing a small amount ( 1%)

of an oligomeric thiophene such as 2,5-di(2-thienyl)thiophene [terthiophene] in the

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Fig. 6 FTIR spectra for enzymatic PEDOT/PSSNa film synthesized at an EDOT to PSSNa ratio
of 1:1. (Reprinted with permission from Rumbau et al. [ 43 ]. c 2007, American Chemical Society)