Biomimetic chemistry: Folding molecules with protein-like structures and functions
Supramolecular chemistry: Directed association of molecular components and nanopore-based molecular recognition
Biomaterials: Integration of non-covalent and covalent interactions
Nanostructures: Design, synthesis and further assembly
Research in our laboratory involves the creation of bioinspired and biocompatible structures based on the combination of design, synthesis, and extensive further characterization. The major areas of research include: protein-like folding molecules; very large nanorings; functional nanotubes; information-storing molecules and biomaterials.
Protein-Like Folding Molecules
These molecules have backbones adopting crescent and helical shapes based on a strategy of enforced folding established in our group. In addition to their exterior that can be readily modified to suit various media/environments, many of these molecules contain large (nanosized) interior cavities and pores. The specific strategy includes the introduction of intramolecular hydrogen bonding interactions that serve to rigidify the molecules, forcing curved conformations that further fold into helical shapes. Nanosize holes down the center of these molecules are created. Crescents and helices with cavities of adjustable diameters are readily available. These nanoporous molecules are being studied as novel hosts/receptors, as antimicrobial agents, and as catalysts.
Efficient Formation of Very Large (Nanosized) Rings Based on Folding-Assisted Macrocyclization
We recently discovered the formation of macrocycles from one-step reactions in very high (80%-90%) yields based on the enforced folding of non-cyclic precursors. The simplicity and high efficiency of our method are in sharp contrast to many other strategies for preparing large macrocycles, which usually lead to low (a few percent) yields due to the entropically disfavored nature of macrocyclization. The extremely high efficiency of these folding-assisted macrocyclization reactions is very unusual because the corresponding bond-forming reactions are irreversible, i.e., kinetically controlled, which raised many interesting fundamental questions. These readily available macrocycles represent a new series of nanosized structures with persistent shapes and non-collapsible cavities. Using these moacrocyclic molecules as scaffolds, functional nanocavities are being created by placing multiple functional groups in ways that are only associated with much larger biomacromolecules.
Functional Organic Nanotubes
Nanosized building blocks based on the molecular crescents, helices, and macrocycles we created are being assembled into higher-order structures. Current efforts are being focused on the alignment of these porous molecules into organic nanotubes with functional pores of tunable sizes. This project requires the synergistic interplay of non-covalent (supramolecular) and covalent approaches, which require molecular design and synthesis, along with a wide variety of techniques and skills for probing supramolecular architectures.
Projects in this area are on the design of unnatural oligopeptides containing arrays of hydrogen bond donors and acceptors, thus generating self-assembling molecular systems with adjustable stability and sequence-specificity. For example, oligomers containing alpha-amino acid and aromatic gamma-amino acid residues have been designed to assemble into molecular zippers with programmable sequence-specificity and adjustable stability. These information-storing molecular zippers served as association modules to direct the specific formation of natural and unnatural structures such as beta-sheets and non-covalent block copolymers, and as templates for directing chemical reactions. By incorporating reversible covalent interactions into these H-bonded duplexes, sequence-specific formation of covalently linked molecular zippers was recently realized under thermodynamically controlled conditions. This has provided a new, highly efficient method for the preparation of many previously unavailable covalent structures by simply mixing the corresponding molecular components. For example, a current project involves the design and preparation of water-soluble, biocompatible block copolymers aimed for various biological applications.