Hydrogen-Bonding Recognition Motifs

Rotello and coworkers [30] reported the first PNBE-based random copolymers with nucleobase-functionalized side chains, wherein longer linkers were utilized to achieve solubility. The system relied upon the complementary three-point H-bonding motif between uracil and diacyl DAP pendant groups on two respective polymer chains (figure 4.5a). The resulting side-chain-functionalized supramolecular polymers self-assemble into spherical polymersomes (figure 4.5b). 

Supramolecular copolymers based upon the DAP-THY recognition pair were also utilized to generate hydrogen-bonded aggregates. Rotello and 

Week and Burd [37] also investigated the ability of PNBE-based random and block-copolymers functionalized with two different classes of H-bonding motifs to self-sort. PNBEs containing CA- and THY-functionalized side chains were self-assembled with complementary Hamilton wedge and DAP recognition motifs. 

Binder and Kluger [41, 42] utilized the Hamilton wedge and THY as molecular recognition handles in the construction of side-chain-functionalized poly(oxanorbornene dicarboximides) using a ROMP/click methodology. Monomers functionalized with azido or alkynyl side chains were polymerized to either homopolymers or block copolymers and subsequently subjected to Cu-catalyzed azide-alkyne cycloaddition [72] to install the desired H-bonding motifs. 

Sleiman and coworkers utilized ROMP to prepare triblock copolymers. The triblock copolymers comprised oxanorbornene dicarboxamide monomers containing a DAP moiety or an alkyl chain, as well as an unfunctionalized block 

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Stubbs LP, Week M. Towards a universal polymer backbone design and synthesis of polymeric scaffolds containing terminal hydrogen-bonding recognition motifs at each repeating unit. ChemEur J 2003 9 992-999. 

Figure 1.7 Nucleophilic reaction catalyzed by Kelly s hosts Sn2 reaction in the host with two symmetrical (a) ortwo asymmetrical (b) hydrogen bonding recognition motifs. 

Fig. 5. Protein folding. The unfolded polypeptide chain coUapses and assembles to form simple stmctural motifs such as -sheets and a-hehces by nucleation-condensation mechanisms involving the formation of hydrogen bonds and van der Waal s interactions. Small proteins (eg, chymotrypsin inhibitor 2) attain their final (tertiary) stmcture in this way. Larger proteins and multiple protein assembhes aggregate by recognition and docking of multiple domains (eg, -barrels, a-helix bundles), often displaying positive cooperativity. Many noncovalent interactions, including hydrogen bonding, van der Waal s and electrostatic interactions, and the hydrophobic effect are exploited to create the final, compact protein assembly. Further stmctural...

The previous section described the supramolecular side chain functionalization of polymers based on a single recognition motif. However, biological systems use a wide variety of noncovalent interactions such as hydrogen bonding, metal coordination, and hydrophobic interactions in an orthogonal fashion to introduce function,... 

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