Chemistry Reference
In-Depth Information
O
O
OO
HRP, H
2
O
2
S
X
O
O
+
n
S
S
X
T=4
C, pH=2, 16 H
O
HC
CH
O
S
n
SO
3
Na
SO
3
Na
Scheme 4
Mechanism of enzymatic polymerization of EDOT. (Reprinted with permission from
2007, American Chemical Society)
1
0,8
a
0,6
0,4
0,2
b
c
0
200
400
600
Wavelength (nm)
800
1000
1200
Fig. 5
UV-Vis spectra for PEDOT complexes synthesized for 16 h at
(
a
)
pH 2,
(
b
)
pH 4, and
(
c
)
pH 6. (Reprinted with permission from Rumbau et al. [
43
].
c
2007, American Chemical Society)
of a bipolaron absorption band at 800 nm, associated with PEDOT polymer, was the
one obtained at pH 2.
The results demonstrate that the high oxidation potential of the monomer may
not be the reason for the lack of polymerization in previous failed attempts. The
choice of appropriate working conditions (pH 2, and a polymerization time as long
as 16 h) allows the biocatalytic synthesis of PEDOT polymer. On the other hand, it
is well known that the activity of HRP decreases abruptly in acidic media (at pH 4,
the HRP activity is around 0 after 1 h [2]) but, surprisingly, even though the en-
zymatic activity should normally be significantly reduced sometime after the first
60 min, the reaction was observed to proceed uninterruptedly throughout the 16 h.
The authors thought that, under these strong acidic conditions, the enzyme could be
deactivated and the polymerization process could be triggered only by the presence
of H
2
O
2
. In a control experiment performed employing the same conditions except
for the absence of HRP, no polymerization was observed. In conclusion, the HRP
was assumed to be the catalyst triggering the polymerization reaction and the en-
hanced enzyme activity due to an excess of EDOT monomer in the media. As the
