Chemistry Reference
In-Depth Information
)UHH&$/%
1RYR]\P
&$/%LPPRELOL]HGZHWVLOLFD
&$/%LPPRELOL]HGGU\VLOLFD
7HPSHUDWXUH
R
&
Fig. 5.3
Thermal stability (as represented by plots of the relative activity versus temperature)
for the immobilized lipase B from Candida antarctica (CALB) on surface modified porous silica
gel by (3-aminopropyl)trimethoxysilane compared to free CALB and immobilized CALB on an
acrylic resin (Novozym-435
®
). The samples were incubated in toluene for 24 h at the respective
temperatures and then the enzyme activities were determined using an octyl laurate assay
activities of the free CALB, CALB immobilized wet silica, dry silica and Novo-
zym-435
®
incubated in toluene at different temperatures (in the range 40-100 °C)
after 24 h are plotted in Fig.
5.3
. The maximum activity of free CALB and Novo-
zym-435
®
was found at 40 °C while it was at 50 °C for CALB immobilized dry-
silica and 60 °C for CALB immobilized wet silica. The respective maximum ac-
tivities were considered to be 100 % activity and the data were then normalized
accordingly. The activity of the Novozym-435
®
incubated in toluene was found
to drop from 100 % at 40 °C to 60 % at 100 °C. However, the free CALB showed
no catalytic activity at 90°C. Both CALB immobilized dry-silica and wet-silica
showed similar temperature dependent activities and showed no catalytic activity at
100 °C. Furthermore, the observed drop in the activity with increasing temperature
of the free CALB, CALB immobilized dry-silica and wet-silica was much steeper
compared to that of Novozym-435
®
.
Mei et al. [
29
] have employed an IR microspectroscopy method to determine the
distribution of enzyme in Novozym-435
®
and the structure of the Novozym-435
®
.
The IR imaging showed that the CALB was localized as an external shell of the Le-
watit bead with a surface thickness of 80-100 µm. The SEM analysis showed that
the average pore size in the Novozym-435
®
beads was about 100 nm, more than 10
times larger than the size of the CALB molecule.
