Biomedical subjects
Publications and source records attributed to Yaohua Han.
Aromatic oligoureas are forced into well-defined conformation by incorporated intramolecular hydrogen bonds. Shape-persistent tetraureas macrocycles were obtained in a one-step [2+2] reaction in good yields.
Molecules and assemblies of molecules with well-defined secondary structures have been designed and characterized by controlling noncovalent interactions. By specifying intermolecular interactions, a class of information-storing molecular duplexes have been successfully developed. These H-bonded molecular duplexes demonstrate programmable, sequence-specificity and predictable, tunable stabilities. Based on these highly specific molecular zippers (or glues), a systematic approach to designing self-assembled structures is now feasible. Duplex-directed formation of beta-sheets, block copolymers and templated organic reactions have been realized. By specifying intramolecular noncovalent interactions, a backbone-rigidification strategy has been established, leading to unnatural molecular strands that adopt well-defined, crescent or helical conformations. The generality of this backbone-rigidification strategy has been demonstrated in three different classes of unnatural oligomers: oligoaramides, oligoureas and oligo(phenylene ethynylenes). Large nanosized cavities have been created based on the folding of these helical foldamers. Tuning the size of the nanocavities has been achieved without changing the underlying helical topology. These helical foldamers can serve as novel platforms for the systematic design of nanostructures.
A general strategy for creating nanocavities with tunable sizes based on the folding of unnatural oligomers is presented. The backbones of these oligomers are rigidified by localized, three-center intramolecular hydrogen bonds, which lead to well-defined hollow helical conformations. Changing the curvature of the oligomer backbone leads to the adjustment of the interior cavity size. Helices with interior cavities of 10 A to >30 A across, the largest thus far formed by the folding of unnatural foldamers, are generated. Cavities of these sizes are usually seen at the tertiary and quaternary structural levels of proteins. The ability to tune molecular dimensions without altering the underlying topology is seen in few natural and unnatural foldamer systems.