Chemistry Reference
In-Depth Information
5.2.4
Instrumental Methods
About 1
µ
l of the reaction sample was injected into the GC (Shimadzu GC-2010)
column 0.5
µ
m × 0.25 mm × 15 m SHRX5 capillary column, split injection at 200 °C,
flow rate 30.4 ml min
−1
, FID detector 350 °C, ramp of 75-300 °C over 18 min. The
residual enzyme activity was estimated from the relative peak areas of the product
(octyl laurate) formed by the pure and the recovered lipases. The data were acquired
and processed using the Shimadzu Class-VP software.
5.2.5
Results and Discussion
In the present investigation, CALB was immobilized onto 3-APS surface modified
porous silica gel particles based on the optimal reaction conditions and curing tem-
peratures that were reported in the literature [
11
,
28
]. It was reported that the structure
of 3-APS and its ability to bind on the silica surfaces is highly dependent on the pH
of the treating solution [
11
]. The maximum number of molecules was adsorbed when
the silica was treated with a solution at its natural pH 10.6. Furthermore, the number
of siloxane bonds formed during the preparation of 3-APS modified silica was larg-
est for silica gel samples with the largest amount of water at the silica gel surface
[
28
]. The nuclear magnetic resonance (NMR) studies on a series of samples prepared
by derivatization of silica gel particles with 3-APS under systematically varied sil-
ica pretreatment temperatures, reaction conditions, and post-treatment temperatures
revealed that curing produced an increase in the number of siloxane bonds at the
interface and was optimized in the presence of surface water at curing temperatures
greater than 150 °C. Therefore, these curing conditions for the surface functionaliza-
tion of silica gel particles were chosen in the present investigation. Thus, the surface
functionalized silica gel particles were then used to immobilize the CALB by chemi-
cal crosslinking using glutaraldehyde [
19
], as discussed in the following section.
5.2.6
CALB Immobilization on Surface Modified Porous Silica
Gel Particles
The optical micrographs of the immobilized lipase (CALB) on surface modified
porous silica-gel by 3-APS are presented in Fig.
5.1
(wet silica), and in Fig.
5.2
(dry
silica). There was no marked difference before and after use of the wet silica as well
as the dry silica particles (Scheme
5.1
).
5.2.7
Thermal Stability of the Immobilized CALB
In the present investigations thermal stability of CALB immobilized on 3-APS
modified silica gel particles through chemical crosslinking using glutaraldehyde
was studied and compared with Novozym-435
®
. The normalized relative enzyme
