Chemistry Reference
In-Depth Information
Fig. 5.4
Relative activ-
ity of free CALB (
A
),
Novozym-435
®
(
B
), CALB
immobilized wet silica (
C
),
dry silica particles (
D
) and
CALB entrapped in bioin-
spired silica (
E
: PAH-silica
and
F
: PEI-silica) under
without and with incubation
at 40 and 90 °C in toluene
for 24 h respectively. The
activities were normal-
ized and accounted for
the amount of free CALB
immobilized
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5.2.8
Support Material Swelling
The apparent high catalytic activity of the Novozym-435
®
, particularly at higher
temperatures, may have come from the fact that a thick lay of CALB was coated
on the surface of the resin particles. It is tentatively attributed to the swelling of the
resin, ~ 350 % by dry weight in toluene, which led to an increased surface area of
the particles that, in turn, improving the access to enzymatic active sites. The swell-
ing of the resin particles may expose new sites, which are otherwise buried deep
inside the thick layer and this has resulted in an enhanced overall catalytic activ-
ity of the Novozym-435
®
. However, CALB immobilized dry-silica and wet-silica
particles predominantly contained a monolayer of enzyme molecules on the surface
of the silica particles. The chemically immobilized CALB onto the surface of the
silica particles have displayed higher catalytic activity compared to Novozym-435
®
when the amount of CALB was taken in to consideration. The relative normalized
activities of free CALB (A), Novozym-435
®
(B), CALB immobilized wet silica
(C), CALB immobilized dry silica particles (D) and CALB entrapped in bioinspired
silica (E: PAH-silica and F: PEI-silica) with incubation (24 h) and without incuba-
tion in toluene are shown in Fig.
5.4
.
However, the Novozym-435
®
particles were found to change in appearance from
opaque to translucent due to partial miscibility which led to swelling of the resin.
Swelling of the resin particles up to approximately 350 % by dry weight in organic
solvents was found [
24
]. This indicated that the resin had undergone significant
morphological changes during the incubation period. For CALB immobilised in
PAH-silica sample, the reduction in the enzymatic activity as a function of incuba-
tion temperature was similar to that observed for silica gel supported CALB sys-
tems. However, interestingly at 40 °C incubation, there was no reduction in enzy-
matic activity for CALB immobilised on PEI-silica. Although the reasons for this
are not clear at this point in time, this observation is consistent with the literature
[
23
] and is very encouraging in developing better biocatalysts in future.
