Kinetics of lipase-catalysed functionalisation of epsilon-caprolactone monomer and oligomer with methyl-dglucopyranoside / Muhammad Naziz Saat
One-pot synthesis of oligomeric sugar ester was carried out by lipase-catalysed esterification of -caprolactone (ECL) with methyl-D-glucopyranoside (MGP) followed by chain elongation of ECL monomer/oligomer. Functionalisation was performed in a custom-fabricated glass reactor equipped with Rusht...
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| Format: | Thesis |
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2019
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| Online Access: | http://studentsrepo.um.edu.my/11659/ http://studentsrepo.um.edu.my/11659/2/Muhammad_Naziz.pdf http://studentsrepo.um.edu.my/11659/1/Muhammad_Naziz.pdf |
| Summary: | One-pot synthesis of oligomeric sugar ester was carried out by lipase-catalysed
esterification of -caprolactone (ECL) with methyl-D-glucopyranoside (MGP) followed
by chain elongation of ECL monomer/oligomer. Functionalisation was performed in a
custom-fabricated glass reactor equipped with Rushton turbine impeller using tertbutanol
as reaction medium. Two-level half-fractional factorial design was employed to
analyse the effects of selected operating variables namely lipase (1.2-2.8 % w/v), initial
ɛ-caprolactone (3.8-11.5 % w/v), initial methyl-D-glucopyranoside (0.04-0.14 % w/v),
temperature (40-60 °C) and agitation rate (90-180 rpm) as a function of maximum dry
weight (% w/v) of MGP-functionalised ECL oligomer (MGP-6-O-oligo-ECL). It was
found that individual variables viz. lipase (XLip), initial -caprolactone (XECL) and
temperature (XTemp) significantly affect the maximum product formation (p < 0.05). Twoway
interaction effects between variables viz. lipase with initial ECL (XLip XECL), lipase
with temperature (XLip XTemp), initial ECL with initial MGP (XECL XMGP), and initial ECL
with temperature (XECL XTemp) were found to be significant (p < 0.05) on the final dry
weight of functionalised oligomer. Significant two-way interaction between variables
suggested the presence of confounding effect among the variables studied. From
descriptive statistic of the half-fractional factorial model, the percentage of variation (R2)
of the regression model was observed at 99.8 %, which indicated good fitting between
predicted and actual data. The model validation using residual analysis showed the
variation among predicted and experimental data was normally distributed. From the
output of response optimizer program, the best conditions for maximum functionalised
oligomer production are as follows: lipase loading of (2.8 % w/v), initial ECL (11.46 % w/v), initial MGP (0.04 % w/v), temperature (60.0 °C), and agitation rate (90 rpm). The
proposed mechanism for the functionalisation includes MGP esterification of ECL
monomer/oligomer followed by chain elongation with free 6-hydroxyhexanoate
monomer units, and both steps are catalysed by lipase. A ping-pong bi-bi mechanism
without ternary complex was proposed for esterification of ECL with MGP with apparent
values of kinetic constants namely maximal velocity (Vmax), Michaelis constant for MGP
(KmMGP) and Michaelis constant for ECL (KmECL) at 3.848 × 10-3 M h-1, 8.189 × 10-2 M
and 6.050 M, respectively. Chain propagation step of MGP-functionalised ECL oligomer
exhibits the behavior of living polymerization mechanism. The apparent rate constant
(rApp) of chain elongation showed highest value when ECL concentration was increased.
Synthesized functionalised oligomer showed narrow range of molecular weight from
1,400 to 1,600 (g mol-1) with more than 90 % ECL conversion achieved. Spectroscopic
data established the presence of covalent bonding between terminal hydroxyl group in
MGP and terminal carboxyl end group of ECL monomer/oligomer. Thermal analysis
indicated three degradation stages of functionalised oligomer as compared to two stages
of degradation in neat ECL oligomer. The current study highlighted significant potential
for enzyme-mediated, one-pot synthetic process in the production of carbohydratefunctionalised
bio-oligomer with controllable molecular weight as platform chemicals.
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