ABSTRACT
Spontaneous self-assembly of macromolecules offers a means to construct a variety of nano-ordered structures. Such nanostructured materials with well-defined shape and size have potential fundamental and practical implications in areas such as materials, supramolecular, and biomimetic chemistries. A typical example for macromolecular self-assembly is provided using block copolymers, wherein different linear homopolymers are linked by covalent bonds [1]. The case of diblock copolymers has been particularly well studied. When diblock copolymers are dissolved in a selective solvent, spontaneous self-assembly into aggregates occurs. Different morphologies will form upon variation of the construction, the quality of the solvent, or the relative length of the two blocks. However, crystalline amylose-lipid complexes have a V-type structure and can be endogenously present in starch granules [2] or formed upon heating of starch suspensions in the presence of either
endogenous or exogenous lipids [3]. The functionality of emulsifiers in starch-containing systems is often related to complex formation with amylose, and thus, explains the importance of the resultant complexes [4-7]. 10.2 Phosphorylase-Catalyzed Synthesis and
Amylosic diblock copolymers were synthesized by phosphorylasecatalyzed polymerization using the polymeric primers having a maltooligosaccharide moiety at the chain end. For example, amylose-block-polystyrenes were produced by covalent attachment of maltoheptaose derivatives to end-functionalized polystyrene and subsequent enzymatic polymerization [8-10]. As one of the methods to produce such block copolymers, maltoheptaose was attached by reductive amination to amine-terminated polystyrene (Fig. 10.1) [9]. The phosphorylase-catalyzed polymerization could be started even though the primer-modified polystyrenes were insoluble in citrate buffer of the polymerization medium. The kinetics of the enzymatic polymerization showed an interesting dependence on the molecular weight of polystyrene owing to the micellar structure of the primer in water. Micellar aggregates of the amylose-block-polystyrenes with various compositions were investigated in water and THF using fluorescence correlation spectroscopy, dynamic light scattering (DLS), and asymmetric flow field-flow fractionation with multiangle light-scattering detection [10]. The analytical data indicated the presence of unimers, oligomers, and large micellar species in THF. Up to four different species were detectable by DLS with hydrodynamic radii ranging from a few nanometers to >10 µm, indicating that the system was not in a thermodynamic equilibrium state. Collapsed aggregates were monitored on a silicon surface by scanning force microscopy and transmission electron microscopy. In water, crew-cut micelles were obtained from the same block copolymers by a single-solvent approach, elevated temperature and pressure. These crew-cut aggregates were much more uniform than the respective star aggregates in THF.
