Page 291 - Advances in Textile Biotechnology

272 Advances in textile biotechnology

11.4 Chemo-enzymatic modification of xyloglucans to
functionalize cellulose surfaces
The rich history of studies on the in vivo and in vitro association of XG
with cellulose, including industrially relevant applications, forms a solid
basis for the use of XGs as molecular anchors to attach chemical function-
ality to cellulosic surfaces. Indeed, the realization that the selective modifi -
cation of XG and subsequent aqueous adsorption on cellulosic fi bres could
circumvent some of the aforementioned difficulties associated with direct

chemical derivatization has opened new possibilities to expand fi bre prop-
erties.
As a polymer, XG possesses a number of potentially reactive sites for
functionalization (Fig. 11.1, cf. Fig. 11.4). The most obvious are the numer-
ous primary and secondary hydroxyl groups of the polysaccharide, which
can be derivatized using well-known organic chemical methods with varying
selectivity. Indeed, alkylated, carboxymethylated, sulfated, and oxidized
derivatives of tamarind seed XG have been synthesized (Gerard, 1980;
Lang et al., 1992; Rao and Srivastava, 1973; Takeda et al., 2008), and some
of these have been applied in papermaking (Gerard, 1980; Rao and Srivas-
tava, 1973). In contrast to traditional, ‘chemical’ methods of polysaccharide
modifi cation, enzymes are well-known to offer certain advantages in terms

of specificity and gentle reaction conditions. Although a multitude of
enzymes capable of degrading polysaccharides is known, the number of
enzymes suitable for adding chemical groups onto polysaccharides is cur-
rently limited; however, two alternative, chemo-enzymatic approaches have
been devised to functionalize XG for cellulosic fi bre modifi cation.

11.4.1 Activation of xyloglucans with galactose oxidase

Galactose oxidase catalyzes the regiospecific oxidation of the C-6 hydroxy-

methyl group (a primary alcohol) of galactose and galactosides to the cor-
responding aldehyde (Whittaker, 2003), which can be used as a reactive
chemical handle for further derivatization. XGs are of course replete with
subtending galactosyl residues along their backbones (Fig. 11.1). The
seminal work by Gidley and colleagues on the oxidation of XG in solution
using galactose oxidase formed the basis for the use of this enzyme to make
polysaccharide conjugates (Lang et al., 1992). Subsequently, the catalytic
ability of galactose oxidase was harnessed to activate the galactose branches
of both locust bean galactomannan and tamarind XG for conjugation with
proteins (Berry et al., 2001). In one example, the enzyme glucose oxidase
and a monoclonal antibody were each covalently attached to the polysac-
charides by direct reductive amination. In a complementary approach, a
thiolated recombinant single-chain antibody fragment was coupled with the

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