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M. Erdem et al. / Reactive & Functional Polymers 70 (2010) 238–243
Table 3
Comparison of Michaelis–Menten model kinetic parameters for PIBs and NIBs at pH 9.0 and 25 °C.
Polymer
IRRmax ꢀ 103
(l
M minꢁ1
)
a[M] ꢀ 105 (M)
kcat ꢀ 105 (minꢁ1
)
Km (mM)
kcat/Km (minꢁ1 Mꢁ1
)
bRatio of catalytic efficiency
PIB-1
NIB-1
PIB-2
NIB-2
PIB-3
13.71
2.95
9.90
2.16
6.04
1.57
45.8
1.93
3.12
3.64
4.86
5.06
6.33
2.9
71.04
9.46
27.20
4.44
11.94
2.48
158.0
0.25
0.83
0.92
0.96
1.18
1.36
1.28
2.842
0.114
0.296
0.046
0.101
0.018
1.234
25
–
6
–
6
NIB-3
–
–
cCu-MAH
a
b
c
Concentration of metal ions calculated from ICP–OES data.
These values were calculated from the ratio of kcat/Km (PIB)/kcat/Km (NIB).
From Ref. [37].
paraoxon toward to these metals. On the other hand, to get a better
understanding for the catalytic efficiency of PIBs and NIBs, kcat/Km
must be considered and compared each other. In this manner, the
MAH-Co2+ containing PIBs shows the higher catalytic activity for
the hydrolysis of paraoxon than other PIBs (Table 3). When the cat-
alytic efficiencies of PIBs compared to the NIBs by means of the
equation: kcat/Km (PIB)/kcat/Km (NIB), it was seen that the ratio of
catalytic efficiencies were 22 for PIB-1, 6 for PIB-2, and 6 for PIB-3.
tions especially in the catalytic degradation of nerve agents and
organophosphorous pesticides. Although the enzymes are better
choice for detoxification of nerve agents, their low stability and
high production cost prevent their use in large scale. To improve
the stability, decrease the cost and for selective catalysis of a pes-
ticide, we have proposed a new metal-chelating monomer in our
previous work [37]. In this study, we have attempted to find out
the effect of variations of metal species as catalysts for paraoxon
hydrolysis. For this purpose, we have synthesized six catalysts con-
taining MAH-Co2+,-Ni2+, or -Zn2+ named as PIBs or NIBs. Spectro-
scopic and microscopic methods and nitrogen sorption analysis
were used for the characterization of polymers. Due to imprinting
process, surface area values and porosities of PIBs were always
high. The results of kinetic experiments demonstrate that all of
PIBs and NIBs have similar affinity towards paraoxon, except for
PIB-1. Morover, PIB-1 showed higher catalytic efficiency, kcat/Km,
than those of other PIBs, NIBs and previous one (MAH-Cu2+ con-
taining catalyst) for paraoxon hydrolysis. In addition, PIB-1 pro-
vided 356 times rate enhancement relative to the rate of
paraoxon hydrolysis carried out in the absence of catalyst. The
hydrolysis rate also increased with increasing temperature and it
was observed that there is a correlation between activation energy
and catalytic efficiency.
3.4. The effect of temperature on paraoxon hydrolysis
For the investigation of the effect of temperature on the parao-
xon hydrolysis using PIB-1, PIB-2, and PIB-3, some experiments
were carried out under the general hydrolysis conditions. The ef-
fect of temperature was studied for the temperature range from
25 °C to 55 °C. As expected, initial reaction rate constants for the
hydrolysis of paraoxon using PIBs were increased by increasing
the temperature.
Reaction activation energy (Ea) was calculated from each of
these constants at different temperature. The plot of ln kPIB vs. 1/
T was drawn (Fig. 5) using Arrhenius equation to determine Ea.
The activation energies for the hydrolysis of paraoxon using PIB-
1, PIB-2, and PIB-3 were found to be 22.3 kJ molꢁ1, 30.9 kJ molꢁ1
,
34.1 kJ molꢁ1, respectively. Moreover, it was clearly observed that
when the activation energy of the paraoxon hydrolysis using PIB-1,
PIB-2, and PIB-3 increases, the catalytic efficiency of catalyzed
polymers, kcat/Km, decreases.
Acknowledgments
The authors thank Turkish State Planning Agency (DPT) and the
Commission of Scientific Research Projects of Anadolu University
for financial support to carry out this research work.
4. Conclusions
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