Transferases in Polymer Chemistry - Enzymatic Polymerisation - page 33

(e.g., inorganic particles and surfaces, synthetic polymers). For this, a primer
functionality (maltooligosaccharide) can be coupled to a synthetic structure and
subsequently elongated by enzymatic polymerization, resulting in amylose blocks.
Various examples of these types of hybrid materials are outlined in the following
section.
Amylose Hybrids with Short Alkyl Chains
Pfannemüller et al. showed that it is possible to obtain carbohydrate-containing
amphiphiles with various alkyl chains via amide bond formation. For this, mal-
tooligosaccharides were oxidized to the corresponding aldonic acid lactones, which
could subsequently be coupled to alkylamines [ 128 - 136 ] . Such sugar-based sur-
factants are important industrial products with applications in cosmetics, medical
applications etc. [ 137 - 139 ] . The authors were also able to extend the attached mal-
tooligosaccharides by enzymatic polymerization using potato phosphorylase, which
resulted in products with very interesting solution properties [ 140 , 141 ] .
Amylose Brushes on Inorganic Surfaces
Amylose brushes (a layer consisting of polymer chains dangling in a solvent with
one end attached to a surface is frequently referred to as a polymer brush) on spheri-
cal and planar surfaces can have several advantageous uses, such as detoxification of
surfaces etc. The modification of surfaces with thin polymer films is widely used to
tailor surface properties such as wettability, biocompatibility, corrosion resistance,
and friction [ 142 - 144 ] . The advantage of polymer brushes over other surface mod-
ification methods like self-assembled monolayers is their mechanical and chemical
robustness, coupled with a high degree of synthetic flexibility towards the introduc-
tion of a variety of functional groups.
Commonly, brushes are prepared by grafting polymers to surfaces by, e.g., chem-
ical bonding of reactive groups on the surface and reactive end groups of the attached
polymers. This “grafting to” approach has several disadvantages as it is very diffi-
cult to achieve high grafting densities and/or thicker films due to steric crowding of
reactive surface sites by already adsorbed polymers.
The “grafting from” approach (polymers are grown from initiators bound to sur-
faces) is a superior alternative because the functionality, density, and thickness of
the polymer brushes can be controlled with almost molecular precision.
The first surface-initiated enzymatic polymerization reported was the synthe-
sis of amylose brushes on planar and spherical surfaces [ 145 ]. For this, silica
or silicone surfaces were modified with self-assembled monolayers of (3 amino-
propyl)trimethoxysilane or chlorodimethylsilane, respectively. To these functionali-
ties, oligosaccharides were added via (a) reductive amidation of the oligosaccharides
to surface-bound amines, (b) conversion of the oligosaccharide to the according al-
donic acid lactone and reaction with surface bound amines, and (c) incorporation