Oxireductases in the Enzymatic Synthesis of Water-Soluble Conducting Polymers - Enzymatic Polymerisation - page 7

for HRP-catalyzed polymerization requires the interaction of the heme-iron active
group of the enzyme with the hydrogen peroxide, generating an oxidized heme-iron
complex [ 42 ] . Then, the oxidized heme-iron complex reacts with the monomer, in a
one-electron transfer reaction to give a monomer radical and a modified iron-heme
complex. The polymer is formed after consecutive reaction of these monomer rad-
icals. This biocatalytic synthesis process has been successfully applied to PANI as
conducting polymer, but rarely to other technologically interesting polymers such
as polythiophenes [ 33 - 36 ] . In a work by Bruno et al. [ 37 ] , this is said to be due to
the higher oxidation potential of monomers such as EDOT and pyrrole compared
to the catalyst HRP, thus proving them to be inappropriate substrates for this enzy-
matic approach. Encouraged by the effectiveness of Fe 2 + as a “green” biomimetic
catalyst, the synthesis of water-soluble PEDOT and polypyrrole was performed by
the same group using PEGylated hematin (PEG-hematin) as catalyst in presence
of PSSNa as template. The EDOT polymerization reaction with PEG-hematin was
spectroscopically monitored in an aqueous solution at pH 1.0. The spectral changes
observed in Fig. 2 indicate that the monomer did not show significant absorption
above 300 nm. However, once H 2 O 2 was added, the polymerization process led to
the appearance of absorption from 600 to 1200 nm, accompanied by the develop-
ment of a dark blue color, with a simultaneous increase in the absorption intensity
of the peaks over time. The broad band at 700 nm, with a large absorption tail at
around 1200 nm, was attributed to the ð − ð ∗ transition in the polymer chain.

The FT-infrared (FTIR) spectrum (Fig. 3 ) of the polymer showed absorptions at
1342, 1218, and 976 cm − 1 , all assigned to doping interactions of SPS. The absence
of bands at 1600-1800 cm − 1 was significant and indicated that no overoxidation
or ring-opening had occurred. This PEDOT was stable over a fairly high range of
temperature (Fig. 3 ) , observing a significant degradation at 110 and 250 ◦ C. The
initial decrease in weight percent is due to evaporation of bound water (Fig. 4 ) .
The electrical conductivity data for the PEDOT (1.10 − 3 Scm − 1 )aresimilartothe
measured conductivity of commercial PEDOT (Baytron).

1.0

SPS/PPYR/PEDOT

0.8

SPS/PEDOT pH1

PYR

SPS/PPYR pH2

0.6

EDOT

0.4

0.2

0.0

200 400 600

Wavelength (nm)

800 1000 1200

Fig. 2 UV-Vis spectra of monomers EDOT and pyrrole, and polymers PEDOT, polypyrrole and
PEDOT- co -polypyrrole. (Reprinted with permission from Bruno et al. [ 37 ]. c 2006, American

Chemical Society)