Hybrid Helical Polymer Nanochannels Constructed by Combining Aromatic Amide and Pyridine-Oxadiazole Structural Sequences.

An effective method is reported to synthesize aromatic helical polymer nanochannels by combining both the well-studied aromatic amide helical codons with pyridine-oxadiazole helical codons into helical structure sequences. With this strategy, a type of helical polymer nanochannel that shows structure-directed transmembrane transport functions is synthesized. Although such nanochannels show relatively weak selectivity for the transportation of alkali metal ions, accessible chemical mutation of helical structure sequences will provide a great chance for the design of desired channel property. The straightforward preparation of well-established pyridine-oxadiazole helical structure will significantly promote the synthesis of this kind of aromatic helical polymer nanochannels. With the development of aromatic amide foldamers, moreover, a number of "monomers" will be available for the preparation of helical polymer nanochannels.

Construction of a smart temperature-responsive GPx mimic based on the self-assembly of supra-amphiphiles.

Glutathione peroxidase (GPx) is a major defense against hydroperoxides as a kind of seleno-enzyme that protects cells from oxidative damage. A supramolecular vesicle with controllable GPx activity and morphology has been successfully constructed by the self-assembly of supra-amphiphiles formed by host-guest recognition between cyclodextrin and adamantane derivatives. By introducing thermosensitive poly(N-isopropylacrylamide) (PNIPAM) scaffolds and the catalytic moiety selenium into adamantane and cyclodextrin, respectively, the complex of catalysis-functionalized cyclodextrin with thermosensitivity-functionalized adamantane directed the formation of a supramolecular vesicle which acted as a GPx mimic at 37 °C. The self-assembled nanoenzyme exhibited an obvious temperature responsive characteristic and high GPx-like catalytic activity promoting the reduction of hydrogen peroxide (H2O2) with glutathione (GSH) as the reducing substrate at 37 °C. However, the vesicle disassembled when the temperature decreased to 25 °C due to the transition of PNIPAM between the coil and the globule. Interestingly, the catalytic activity changed along with the transformation of morphologies. The vesicle structure self-assembled at 37 °C provided the favorable microenvironment for the enzymatic reaction, hence we successfully developed a temperature-responsive nanoenzyme model. Moreover, the catalytic activity of the thermosensitive GPx mimic exhibited excellent reversibility and typical saturation kinetics behaviour similar to a natural enzyme catalyst. It is assumed that the proposed GPx model not only has remarkable advantages such as easy functionalization and facile preparation but also provided a new way to develop intelligent responsive materials.

Temperature-driven switching of the catalytic activity of artificial glutathione peroxidase by the shape transition between the nanotubes and vesicle-like structures.

Smart supramolecular nanoenzymes with temperature-driven switching property have been successfully constructed by the self-assembly of supra-amphiphiles formed by the cyclodextrin-based host-guest chemistry. The self-assembled nanostructures were catalyst-functionalized and thermosensitively-functionalized through conveniently linking the catalytic center of glutathione peroxidase and thermosensitive polymer to the host cyclodextrin molecules.The ON-OFF switches for the peroxidase activity by reversible transformation of nanostructures from tube to sphere have been achieved through changing the temperature. We anticipate that such intelligent enzyme mimics could be developed to use in an antioxidant medicine with controlled catalytic efficiency according to the needs of the human body in the future.

Artificial enzymes based on supramolecular scaffolds.

Enzymes are nanometer-sized molecules with three-dimensional structures created by the folding and self-assembly of polymeric chain-like components through supramolecular interactions. They are capable of performing catalytic functions usually accompanied by a variety of conformational states. The conformational diversities and complexities of natural enzymes exerted in catalysis seriously restrict the detailed understanding of enzymatic mechanisms in molecular terms. A supramolecular viewpoint is undoubtedly helpful in understanding the principle of enzyme catalysis. The emergence of supramolecular artificial enzymes therefore provides an alternative way to approach the structural complexity and thus to unravel the mystery of enzyme catalysis. This critical review covers the recent development of artificial enzymes designed based on supramolecular scaffolds ranging from the synthetic macrocycles to self-assembled nanometer-sized objects. Such findings are anticipated to facilitate the design of supramolecular artificial enzymes as well as their potential uses in important fields, such as manufacturing and food industries, environmental biosensors, pharmaceutics and so on.

Selenium/Tellurium-Containing Hyperbranched Polymers: Effect of Molecular Weight and Degree of Branching on Glutathione Peroxidase-Like Activity.

A series of novel hyperbranched polyselenides and polytellurides with multiple catalytic sites at the branching units has been synthesized via the polycondensation of A2 + B3 monomers. The GPx-like activities of these polymer mimics were assessed and it was found that the polytellurides showed higher GPx-like activities than the corresponding polyselenides. Interestingly, the polymers with higher molecular weights and degree of branching (DB) showed higher GPx-like activities than the analogous lower molecular weight polymer. The enhancement in the catalytical activity of the hyperbranched polymers with increasing molecular weight affirmed the importance of the incorporation of multiple catalytic groups in the macromolecule which increases the local concentration of catalytic sites.

Light-responsive vesicles for enantioselective release of chiral drugs prepared from a supra-amphiphilic M-helix.

A kind of light-responsive vesicle was prepared by aqueous self-assembly of α-CD and an azobenzene-containing M-helical foldamer, which displayed dynamic disassembly-reassembly structural transformation when alternately irradiated by UV and visible light. Distinctively, this vesicle also exhibited enantioselective release abilities toward racemic propranolol (a ß-blocker), owing to the M-helical building blocks.

Biomimetic Pulsating Vesicles with Both pH-Tunable Membrane Permeability and Light-Triggered Disassembly-Re-assembly Behaviors Prepared by Supra-Amphiphilic Helices.

The reversible unfolding-refolding transition is considerably important for natural elastomeric proteins (e.g., titin) to fulfill their biological functions. It is of great importance to develop synthetic versions by borrowing their unique stretchable design principles. Herein, we present a novel pulsating vesicle by means of the aqueous self-assembly of supra-amphiphilic helices. Interestingly, this vesicle simultaneously features dynamic swelling and shrinkage movements in response to external proton triggers. Titin-like unfolding-refolding transformation of artificial helices was proved to play a crucial role in this pulsatile motion. Moreover, the vesicular membrane of this vesicle has exhibited tunable permeability during reversible expansion and contraction circulation. Meanwhile, light can also be used as a driving force to further regulate the disassembly-reassembly transformation of the pulsating vesicle. In addition, the drug delivery system was also employed as an investigating model to estimate the permeability variation and disassembly-reassembly behaviors of the pulsating vesicles, which displayed unique dual quick- and sustained-release behaviors toward anti-cancer agents. It is anticipated that this work opens an avenue for fabricating novel stretchable biomimetics by using the exclusive unfolding-refolding nature of artificial foldamers.

Reductive-Responsive, Single-Molecular-Layer Polymer Nanocapsules Prepared by Lateral-Functionalized Pillar[5]arenes for Targeting Anticancer Drug Delivery.

Herein, a new reductive-responsive pillar[5]arene-based, single-molecule-layer polymer nanocapsule is constructed for drug delivery. The functionalized system shows good biocompatibility, efficient internalization into targeted cells and obvious triggered release of entrapped drugs in a reducing environment such as cytoplasm. Besides, this smart vehicle loaded with anticancer drug shows excellent inhibition for tumor cell proliferation and exhibits low side effect on normal cells. This work not only demonstrates the development of a new reductive-responsive single molecular layer polymer nanocapsule for anticancer drug targeting delivery but also extends the design of smart materials for biomedical applications.

Construction of supramolecular polymer by enzyme-triggered covalent condensation of CB[8]-FGG-based supramonomer.

A rapid and effective enzymatic strategy for the fabrication of a supramolecular polymer is presented for the first time, in which a bifunctional ternary host-guest supramonomer is first prepared followed by subsequent enzymatic coupling of supramonomers.

Selenium-containing organic nanoparticles as silent precursors for ultra-sensitive thiol-responsive transmembrane anion transport.

An anion transporter with a selenoxide group was able to form nanoparticles in water, whose activity was fully turned off due to the aggregation effect. The formed nanoparticles have a uniform size and can be readily dispersed in water at high concentrations. Turn-on of the nanoparticles by reducing molecules is proposed to be a combined process, including the reduction of selenoxide to selenide, disassembly of the nanoparticles and location of the transporter to the lipid membrane. Accordingly, a special acceleration phase can be observed in the turn-on kinetic curves. Since turn-on of the nanoparticles is quantitatively related to the amount of reductant, the nanoparticles can be activated in a step-by-step manner. Due to the sensibility of this system to thiols, cysteine can be detected at low nanomolar concentrations. This ultra-sensitive thiol-responsive transmembrane anion transport system is quite promising in biological applications.

Protein-based supramolecular polymers: progress and prospect.

Proteins are naturally evolved macromolecules with highly sophisticated structures and diverse properties. The design and controlled self-assembly of proteins into polymeric architectures via supramolecular interactions offers unique advantages in understanding the spontaneously self-organisational process and fabrication of various bioactive materials. This feature article highlights recent advances and future trends in supramolecular polymers that are directly assembled from the building blocks of proteins. Non-covalent interactions capable of inducing polymerization include aromatic π-π stacking, host-guest interactions, metal coordination, and interprotein interactions combined with site-selective protein modification to explore the dynamic and specific unidirectional aggregation behaviours among protein units. We also discuss some extended supramolecular protein polymers achieved by rational design and fine-tuning the protein-protein interactions, which may help to inspire future design of more complicated polymeric protein assemblies. The protein-based supramolecular polymer system provides a versatile platform for functionalization and thereby shows great potential in the development of novel biomaterials with controlled structures and properties.

Highly efficient dendrimer-based mimic of glutathione peroxidase.

In this communication, we report the synthesis of the three generations of Fréchet-type poly(aryl ether) dendrimers with a diselenide core that demonstrate generation-dependent glutathione peroxidase (GPx) activity with initial reduction rates as high as 2431.20 muM min-1 for the third-generation product, around 1400 times faster than Ebselen. It represents a successful example of using a dendrimer as a model for a GPx mimic.