Gyeongwon Yun

Supramolecular Velcro for Reversible Underwater Adhesion

We thus decided to investigate whether a syntheticsystementirelyunrelatedtoDOPAcouldachieveunderwateradhesion and potentially overcome limitations, such as thelack of reversibility at the macroscopic level.Amajorchallengeinadhesioninanaqueousenvironmentis how to repel the water molecules between the adhesive andadherend surfaces. The presence of water prevents directchemical contact between them, and diminishes the surfaceenergy of the adherend that provides the driving force foradhesion.

Highly Stable, Water-Dispersible Metal-Nanoparticle-Decorated Polymer Nanocapsules and Their Catalytic Applications†

A facile synthesis of highly stable, water-dispersible metal-nanoparticle-decorated polymer nanocapsules (M@CB-PNs: M=Pd, Au, and Pt) was achieved by a simple two-step process employing a polymer nanocapsule (CB-PN) made of cucurbit[6]uril (CB[6]) and metal salts. The CB-PN serves as a versatile platform where various metal nanoparticles with a controlled size can be introduced on the surface and stabilized to prepare new water-dispersible nanostructures useful for many applications. The Pd nanoparticles on CB-PN exhibit high stability and dispersibility in water as well as excellent catalytic activity and recyclability in carbon-carbon and carbon-nitrogen bond-forming reactions in aqueous medium suggesting potential applications as a green catalyst.

Hydrolytic Transformation of Microporous Metal–Organic Frameworks to Hierarchical Micro‐ and Mesoporous MOFs

A new approach to the synthesis of hierarchical micro- and mesoporous MOFs from microporous MOFs involves a simple hydrolytic post-synthetic procedure. As a proof of concept, a new microporous MOF, POST-66(Y), was synthesized and its transformation into a hierarchical micro- and mesoporous MOF by water treatment was studied. This method produced mesopores in the range of 3 to 20 nm in the MOF while maintaining the original microporous structure, at least in part. The degree of micro- and mesoporosity can be controlled by adjusting the time and temperature of hydrolysis. The resulting hierarchical porous MOF, POST-66(Y)-wt, can be utilized to encapsulate nanometer-sized guests such as proteins, and the enhanced stability and recyclability of an encapsulated enzyme is demonstrated.

Self-assembled, covalently linked, hollow phthalocyanine nanospheres

A rational design and synthesis of covalently linked Pc nanospheres with a very thin shell and hollow interior, composed of approximately 12 000 Pc units on average, was demonstrated through thiol–ene “click” chemistry without using any templates or emulsifiers. The ZnPc nanospheres allow post-synthetic modification to improve their dispersibility in aqueous solution without altering the morphology of the nanospheres or the properties of ZnPc cores. More importantly, the ZnPc nanospheres showed higher singlet oxygen generation efficiency and in vitro phototoxicity than monomeric Pc molecules, suggesting that ZnPc nanospheres are potentially useful as a PS for PDT. We anticipate that the ZnPc nanospheres would allow other post-synthetic modifications such as the introduction of targeting ligands to deliver the nanospheres to specific target sites and perform a dual chemo- and photodynamic therapy by the encapsulation of therapeutic agents. The easy synthesis of a hollow spherical framework with a high Pc content, coupled with facile post-synthetic modification may allow Pc nanospheres to be a versatile platform for a diverse range of medical and non-medical applications.

Hollow nanotubular toroidal polymer microrings

Despite the remarkable progress made in the self-assembly of nano- and microscale architectures with well-defined sizes and shapes, a self-organization-based synthesis of hollow toroids has, so far, proved to be elusive. Here, we report the synthesis of polymer microrings made from rectangular, flat and rigid-core monomers with anisotropically predisposed alkene groups, which are crosslinked with each other by dithiol linkers using thiol-ene photopolymerization. The resulting hollow toroidal structures are shape-persistent and mechanically robust in solution. In addition, their size can be tuned by controlling the initial monomer concentrations, an observation that is supported by a theoretical analysis. These hollow microrings can encapsulate guest molecules in the intratoroidal nanospace, and their peripheries can act as templates for circular arrays of metal nanoparticles.

Reversible Morphological Transformation between Polymer Nanocapsules and Thin Films through Dynamic Covalent Self‐Assembly

A facile method has been developed for synthesizing polymer nanocapsules and thin films using multiple in-plane stitching of monomers by the formation of reversible disulfide linkages. Owing to the reversibility of the disulfide linkages, the nanostructured materials readily transform their structures in response to environmental changes at room temperature. For example, in reducing environments, the polymer nanocapsules release loaded cargo molecules. Moreover, reversible morphological transformations between these structures can be achieved by simple solvent exchanges. This work is a novel approach for the formation of robust nano/microstructured materials that dynamically respond to environmental stimuli.

Covalent Self‐Assembly and One‐Step Photocrosslinking of Tyrosine‐rich Oligopeptides to Form Diverse Nanostructures

We present covalently self-assembled peptide hollow nanocapsule and peptide lamella. These biomimetic dityrosine peptide nanostructures are synthesized by one-step photopolymerization of a tyrosine-rich short peptide without the aid of a template. This simple approach offers direct synthesis of fluorescent peptide nanocages and free-standing thin films. The simple crosslinked peptide lamella films provide robust mechanical properties with an elastic modulus of approximately 30 GPa and a hardness of 740 MPa. These nanostructures also allow for the design of peptidosomes. The approach taken here represents a rare example of covalent self-assembly of short peptides into nano-objects, which may be useful as microcompartments and separation membranes.

Synthesis of Metal Nanoparticles in Metal‐Phenolic Networks: Catalytic and Antimicrobial Applications of Coated Textiles

The synthesis of metal nanoparticle (NP)-coated textiles (nanotextiles) is achieved by a dipping process in water without toxic chemicals or complicated synthetic procedures. By taking advantage of the unique nature of tannic acid, metal-phenolic network-coated textiles serve as reducing and stabilizing sites for the generation of metal nanoparticles of controllable size. The textiles can be decorated with various metal nanoparticles, including palladium, silver, or gold, and exhibit properties derived from the presence of the metal nanoparticles, for example, catalytic activity in water (>96% over five cycles using palladium nanoparticles) and antibacterial activity against Gram-negative bacteria (inhibition of Escherichia coli using silver nanoparticles) that outperforms a commercial bandage. The reported strategy offers opportunities for the development of hybrid nanomaterials that may have application in fields outside of catalysis and antimicrobials, such as sensing and smart clothing.

Cucurbit[6]uril-based polymer nanocapsules as a non-covalent and modular bioimaging platform for multimodal in vivo imaging

Cucurbit[6]uril (CB[6])-based polymer nanocapsules (CB[6]PNs) were used as a multimodal platform for cancer-targeted in vivo bioimaging. By taking advantage of the strong and robust host–guest interaction between CB[6] and spermidine (spmd) under in vivo conditions, the surface of the CB[6]PNs was non-covalently modified with various spmd-conjugated functionalities in a modular manner. The CB[6]PNs modified with imaging probes and targeting ligands showed tumor targeted PET and NIR imaging in mice. This proof of concept demonstrates the potential of non-covalently modified nanomaterials in real world in vivo systems.

Self-Assembled Metal-Phenolic Networks on Emulsions as Low-Fouling and pH-Responsive Particles

Interfacial self-assembly is a powerful organizational force for fabricating functional nanomaterials, including nanocarriers, for imaging and drug delivery. Herein, the interfacial self-assembly of pH-responsive metal-phenolic networks (MPNs) on the liquid-liquid interface of oil-in-water emulsions is reported. Oleic acid emulsions of 100-250 nm in diameter are generated by ultrasonication, to which poly(ethylene glycol) (PEG)-based polyphenolic ligands are assembled with simultaneous crosslinking by metal ions, thus forming an interfacial MPN. PEG provides a protective barrier on the emulsion phase and renders the emulsion low fouling. The MPN-coated emulsions have a similar size and dispersity, but an enhanced stability when compared with the uncoated emulsions, and exhibit a low cell association in vitro, a blood circulation half-life of ≈50 min in vivo, and are nontoxic to healthy mice. Furthermore, a model anticancer drug, doxorubicin, can be encapsulated within the emulsion phase at a high loading capacity (≈5 fg of doxorubicin per emulsion particle). The MPN coating imparts pH-responsiveness to the drug-loaded emulsions, leading to drug release at cell internalization pH and a potent cell cytotoxicity. The results highlight a straightforward strategy for the interfacial nanofabrication of pH-responsive emulsion-MPN systems with potential use in biomedical applications.