Study Of Temperature-responsive Supramolecular Nanotubes

One of the main challenges in supramolecular chemistry is the design of structurallywell-defined architectures with dynamic and stimulus-responsive properties that canbe made to assign functions and provide the capability to control these functions.Continuous efforts have been dedicated to the development of nano-platforms withconditional stimulus, such as electrical, thermal, pH and solvent. Thesestimulus-responsive nanomaterials have attracted growing attention because of theirspecial properties and potential applications in a variety of areas. In thesestimulus-responsive nanomaterials, poly (N-isopropylacrylamide)(PNIPAM) iswidely studied due to not only its polymer advantage of that it can fix and stabilizewell-defined nanostructures and enable further modification, but also its lowercritical solution temperature (LCST) of32.8oC, which is closed to the human bodytemperature. Many reports described the LCST triggers in drug delivery, sensing,and catalysis. However, the construction of the reversibly switchable utilized thetemperature-driven shape transition between the nanotubes and the sphericalvesicle-like structures and the collapse of the PNIPAM chains above the LCST hasnot yet been described.(1)Temperature-Driven Switching of the Catalytic Activity of ArtificialGlutathione PeroxidaseHerein, we report a novel construction of a smart artificial glutathioneperoxidase triggered by directed self-assembly of supra-amphiphiles composed ofcyclodextrin (CD)-based host-guest inclusion. The traditional methods for generatingnanostructures put to use covalent synthesis pathways. In recent years,supramolecular amphiphiles formed through noncovalent driving forces have beendeveloped as a new type of building block for future fabrication of supramolecularstructures through multilevel self-assembly. Our previous work suggested that CDand adamantly hydrophobic moieties proved to be a good scaffold for constructingGPx mimics with high catalytic efficiency. However, the inherent instability of thenanotubes structure significantly limits the study of the enzymatic mechanism and itsfurther application. Recently, we designed and synthesized a smart GPx nanoenzymemodel. The spontaneously formed giant nanotubes were catalyst-functionalized andthermosensitivly functionalized through conveniently linking the catalytic center ofGPx and thermosensitive polymer poly (N-isopropylacrylamide) to the hostmolecule CD. Thus we successfully fabricated a controllable artificial GPxnanoenzyme that could turn on and off enzyme activity by thermol stimuli-divenshape transformation from the nanotube to spherical vesicle-like structures and thelow solvation of the PNIPAM chains above the LCST (Figure1). At25oC, the surface of the nanotube had good solubility, and the catalytic center was exposed inthe solution. At45oC, the surface of the sphere had low solubility, and the catalyticcenter was embedded in the sphere. So the activity of the nanoenzyme could turn onand off by controlling temperature. The switches of peroxidase activity via thereversible transformation of nanostructures from the tube to the sphere have beenobserved clearly. We demonstrate that the strategy of CD-based self-assembly ofsupramolecular amphiphiles has great potential for the construction of functionalnanomaterials and could provide the capability to control these functionsintellectively.(2)The release of the rhodamine B through a reversible tube-to-spheretransitionWe report a novel way to construct responsive nanostructures triggered by directself-assembly of CD-based host-guest superamphiphiles. The giant nanotubes werethermosensitivly functionalized through conveniently linking the thermosensitivepolymer poly (N-isopropylacrylamide) to the host molecule CD. Changing thetemperature, which results in a shape transformation from the nanotube to thespherical vesicle-like structure. The temperature-dependent morphology changeprocesses have been monitored clearly through the optical microscopy.We couldobserve the whole reversible progress clearly. Furthermore, the thermosensitivematerials are used as a trigger for the release of the rhodamine B through a reversibletube-to-sphere transition. Fortunately, we can control the release at differenttemperature through controlling the ratio of hydrophobic grouping to our need.(3)The welding of nanotube used temperature-driven shape transitionbetween the nanotubes and vesicle-like structuresThecopolymerscontainwithhydroxyethylacrylate,CDandrhodamineBweresucceed synthetized. The none-thermo–sensitive nanotube was constructed with thispolymer-CD and adamantly hydrophobic moieties. This nanotube was used as seed.The nanostructures with green fluorescence utilized the temperature-driven shapetransition between the nanotubes and the spherical vesicle-like structures wereconstructed as repaired compose. The seed nanotube could be successful repaired byadding the45℃-repaired compose and then cooling to room temperature.