Enzyme Immobilization on Chitosan-Based Supports - Chitosan Based Hydrogels: Functions and Applications - page 359

acidic media. LMCCR also exhibits considerable adsorption performances for various
substances such as acetic acid, alanine, bovine serum albumin (BSA), and Zn 2+ . LMCCR is
proved to show preferable applications in enzyme immobilization, while the activity
recovery and the half-life of the immobilized GOx with LMCCR as a solid support are
42.68% and 96 days [70].
8.4.1.4 Succinyl Anhydride-Modified Chitosan as pH-Sensitive Support
The drawbacks with using the insoluble chitosan in bioconversions are slow binding/
catalysis due to diffusion-controlled mass transfer and steric hindrance in an already
biphasic system involving water-insoluble substrates, and low geometrical congruence
with protein surfaces. To overcome these problems, an attempt has been made at immobi-
lization of the biocatalysts to reversibly soluble polymeric carriers by changing the physi-
cal conditions, such as pH, temperature, and addition of certain ions. A variety of natural
and synthetic polymers with reversible solubility including alginic acid, hydroxypropyl
methylcellulose acetate succinate and N -isopropylacrylamide were identified. Enzymes
immobilized on such carriers could be used in biocatalysis in the soluble form and recov-
ered by precipitation for reuse, while the substrate can easily access the active site of the
immobilized enzyme, reducing the interparticle and intraparticle diffusion limitations.
N -Succinyl chitosan (NSC), which was obtained by introducing succinyl groups into chito-
san N-terminal of the glucosamine units, can be made soluble-insoluble by changing the
pH. NSC was initially developed as wound dressing materials. Currently, it is also applied
as cosmetic materials and drug carriers.
Zhou et al. prepared NSC via ring-opening reactions with succinic anhydride in the
dimethyl sulfoxide system. The obtained NSC is soluble at pH above 4.8 and is insoluble at
pH below 4.4. The immobilized alliinase had increased thermal stability and showed a
similar dependence on pH value as NSC. Besides, the affinity of alliinase to its substrate
increased when immobilized on NSC [71].
8.4.1.5 Photopolymerized Chitosan
Photopolymerized injectable chitosans have received a great deal of attention. For chitosan
hydrogels by photopolymerization, their temperature and pH can be similar to body
environment on the polymerization process. Additionally, control of the polymerization
reaction can be accomplished through adjusting the exposure area and the time of light
incidence.
Monier et al. described a versatile strategy for photopolymerized chitosan, which
includes the loading of a-cyano-4-hydroxycinnamic acid onto the chitosan backbone
through the amide bond formation using EDC and NSH via initial carboxyl group activa-
tion followed by reaction with chitosan-bearing amino groups. Significantly, this reaction
does not require the addition of a light-sensitive initiator, which is typically required for
cross-linking reactions based on photosensitive acrylate, acrylamide, or azide moieties. As
a consequence, unanticipated side reactions due to the presence of free radical initiators
are minimized [72].
Lipase from C. rugosa was entrapped in the modified photo-cross-linkable chitosan
membranes and cross-linking was carried out by irradiation in the ultraviolet (UV) region.
The optimum temperature for immobilized lipase was 40°C, which was identical to that of
free enzyme. The optimal pH for immobilized lipase was 8.0, which was slighty higher
than that of the free lipase (pH 7.5). The apparent K m value of immobilized lipase was