Chemistry Reference
In-Depth Information
Figure 4.4 Formation of cylindrical aggregates via multidirectional self-association bonding
of adenine functional block copolymers. Reprinted from Bazzi and Sleiman (2002). Copyright
2002 American Chemical Society.
Hydrogen bonding in nucleobase-functionalized block copolymers was utilized to
template nanostructured materials in solution for potential drug delivery applications.
Zhou et al. (2002) introduced cross-linkable and hydrogen bonding functionality in
the form of poly(2-cinnamoyloxyethyl methacrylate-co-2-thyminylacetoxyethyl
methacrylate-b-tert-butyl acrylate). Complementary, noncross-linkable poly(2-
hydrocinnamoyloxyethyl methacrylate-co-9-adeninylacetoxyethyl methacrylate)
was also synthesized. These complementary polymers were solution blended in
chloroform/cyclohexane mixtures to produce micelles containing the nucleotide
pairs with soluble tert-butyl acrylate blocks extending into solution (Zhou et al.
2002). Photocross-linking of these micelles and subsequent extraction of the
adenine-functionalized polymers resulted in porous nanospheres, which absorbed
adenine from solution more rapidly than nonextracted or noncross-linked micelles.
Kinetics varying from first order for low molar mass porogens to zero order for
higher molar mass porogens were observed, which suggested potential applications
in drug delivery (Liu and Zhou 2003). In a related study, Hu and Liu produced
mixed micelles from poly(2-cinnamoyloxyethyl methacrylate-co-2-thyminylacetox-
yethyl methacrylate-b-tert-butyl acrylate) and poly(2-cinnamoyloxyethyl methacry-
late-co-9-adeninylacetoxyethyl methacrylate-b-styrene) (Hu and Lui 2005; Yan
et al. 2006). These mixed micelles were photocross-linked and then the tert-butyl
acrylate blocks were hydrolyzed to produce poly(acrylic acid) residues, which
phase separated from the styrene-functionalized block copolymer tails in the micellar
corona, as observed with TEM. The phase separation resulted in either a two-faced
appearance or flowerlike patterns in the corona.
Lehn and Rotello's groups extensively studied diacyldiaminopyridines that form
triple hydrogen bonded associated structures with uracil and thymine groups
(Gulik-Krzywicki et al. 1993; Carroll et al. 2003; Stubbs and Weck 2003; Sanyal
et al. 2004). Ilhan et al. (2000) studied the formation of vesicles from mixtures of
randomly functionalized complementary copolymers containing thymine groups and
