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another with diacyldiaminopyridine units. The complementary flavin guest molecule
was incorporated into the
3 mm spherical vesicles. Bis(thymine) functional small
molecules served as noncovalent cross-linkers when mixed with randomly functiona-
lized diacyldiaminopyridine-functionalized polystyrene (Thibault et al. 2003). In
chloroform solutions, mixing of these complementary units led to the formation of
1 mm microgels. Temperature-dependent turbidity measurements at 700 nm
showed that clearing of the solutions was obtained upon heating to 50 8C, which
was due to thermal disruption of hydrogen bonding, and turbidity was reproducibly
obtained upon cooling to room temperature. Sanyal et al. (2004) further demonstrated
reversible attachment of diacyldiaminopyridine containing styrenic copolymers to
thymine modified surfaces using X-ray photoelectron spectroscopy and a quartz
crystal microbalance to measure the adsorption. The adsorbed polymer was easily
removed via washing with hydrogen bond screening solvents such as chloroform/
ethanol mixtures but was retained upon washing with chloroform (Sanyal et al.
2004). Noncovalent attachment of diacyldiaminopyridine-functionalized polyoligo-
silsequioxanes to thymine functionalized polystyrene was also studied (Carroll
et al. 2003). Stubbs and Weck (2003) also examined ROMP homopolymers of dia-
cyldiaminopyridine- and diacyldiaminotriazine-functionalized norbornenes. Because
of the propensity for self-association of these hydrogen bonding units, homopolymers
precipitated from solution during polymerization. The polymers were redissolved
slowly through the addition of 1-butylthymine in chloroform. To avoid precipitation
during polymerization, the authors utilized noncovalent protecting chemistry with the
addition of 1-butylthymine.
Block copolymers containing the diacyldiaminopyridine group were also syn-
thesized. Starting with poly(tert-butyl acrylate-b-hydroxyethylmethacrylate), block
copolymers synthesized from ATRP, Li et al. (2006) carried out postpolymerization
esterification of the hydroxyl groups with a carboxylic acid containing acrylamide-
functionalized diacyldiaminopyridine hydrogen bonding cross-linker. The unreacted
hydroxyl groups were then reacted with methacrylic anhydride to introduce further
cross-linkable groups. The block copolymers hydrogen bonded with alkyl functional
thymines and uracils in nonselective solvents as observed in FTIR spectra. The intro-
duction of a selective solvent (cyclohexane) produced micelles that were then cross-
linked in solution. Extraction of the alkyl functional thymines or uracils through
dialysis led to hollow nanospheres. Binding isotherms of the nanospheres with the
thymine or uracil containing molecules were obtained.
4.3.3. Block Copolymers Containing DNA Oligonucleotides
Conjugates of synthetic polymers with DNA oligonucleotides were also synthesized.
Noro and coworkers (2005) utilized the phosphoramidite route to incorporate nucleo-
tide bases in a stepwise fashion from a hydroxyl containing polymer precursor.
Coupling of thymidine phosphoramidite to polymeric hydroxyl groups was achieved
with benzimidazoleum triflate (Fig. 4.5). Oxidation with tert-butyl hydroperoxide led
to the formation of phosphodiester bonds. The addition of acid allowed deprotection
of the remaining hydroxyl groups of the deoxyribose sugar linkage, enabling
