Enzyme Immobilization on Chitosan-Based Supports - Chitosan Based Hydrogels: Functions and Applications - page 354

TAble 8.1
Catalytic System Activities for C. rugosa Lipase on Chitosan in Nonaqueous Media

Activity (mM min − 1 g
Protein − 1 ) References Supports

This work a QSR 0.88

This work a QGAR 2.21

This work a QCER 1.78

Magnin, Dumitriu, Magny, and Chornet (2001) b Chitosan/xanthan 0.0008

Chen and Lin (2003) c Chitosan beads 0.0033-0.0167

Source: Orrego, C. E., et al. 2010. Carbohydr Polym 79: 9-16. With permission.
Note: Cryogel chitosan membranes (QS), Lipase immobilized on QS (QSR), GA cross-linked QS (QGAR), and CE
cross-linked QS (QCER).
a This work: 40°C, n -butanol 0.1 M, and oleic acid 0.1 M/iso-octane.
b Magnin et al.: 37°C, olive oil hydrolysis/iso-octane [55].
c Chen and Lin: 35°C, ethanol 0.25 M, and butyric acid 0.3 M/ n -hexane [54].

at a cathode surface by the mechanism illustrated in Figure 8.6 [57, 58]. When the applied
voltage is sufficient for protons to be reduced at the cathode surface, a localized pH
gradient is generated. If this localized gradient is created in the presence of chitosan
(i.e., if the electrodes are immersed and biased in a slightly acidic chitosan solution),
then chitosan chains that experience the high localized pH at the cathode surface
can deposit as a thin film. This directed assembly can be controlled spatially and tempo-
rally. Once deposited and rinsed, the chitosan film is stable on the electrode in the
absence of an applied potential provided the pH is retained above about 6.3. Until now,
there are no reports of the nano- and microscale morphologies of the electrodeposited
chitosan [58].
Furthermore, chitosan deposition can be used to mediate the assembly of additional
components (e.g., nanoparticles and enzymes). Proteins can be enzymatically assembled
onto the stimuli-responsive backbone ( Section 8.2.3, IV method: electrochemically conju-
gate protein), whereas nucleic acids can be tethered to electrodeposited films to serve as
sites for self-assembly. For example, chitosan-coated wires are an interesting platform that
can be viewed as either conducting fibers or functionalized wires. As illustrated in

1/2 H 2 Low pH

in bulk
(soluble)

H +

+

+

+

+

+

+

+

pH = p K a pH gradient

Figure 8.6
Mechanism for chitosan's directed assembly by electrodeposition. (From Yi, H. et al. 2005. Biomacromolecules
6: 2881-2894. With permission.)