UV-responsive polymeric superamphiphile based on a complex of malachite green derivative and a double hydrophilic block copolymer

The influence of arm composition on the self-assembly of low-functionality telechelic star polymers in dilute solutions

We combine synthesis, physical experiments, and computer simulations to investigate self-assembly patterns of low-functionality telechelic star polymers (TSPs) in dilute solutions. In particular, in this work, we focus on the effect of the arm composition and length on the static and dynamic properties of TSPs, whose terminal blocks are subject to worsening solvent quality upon reducing the temperature. We find two populations, single stars and clusters, that emerge upon worsening the solvent quality of the outer block. For both types of populations, their spatial extent decreases with temperature, with the specific details (such as temperature at which the minimal size is reached) depending on the coupling between inter- and intra-molecular associations as well as their strength. The experimental results are in very good qualitative agreement with coarse-grained simulations, which offer insights into the mechanism of thermoresponsive behavior of this class of materials.

A Supramolecular Catalyst Self-Assembled From Polyoxometalates and Cationic Pillar[5]arenes for the Room Temperature Oxidation of Aldehydes

Oxidizing aldehydes to generate carboxylic acids is a crucial reaction in nature and in chemical industry. The aldehyde oxidation, an easily achieved process in liver cells, is inert toward autoxidation in industrial production and difficultly achieved under enzymatic condition (in water, at pH 7, at room temperature). Herein, we prepared a supramolecular catalyst which are nanospheres assembled in aqueous media by chromium centered Anderson polyoxometalates Na₃[CrMo₆O₁₈(OH)₃] (namely, CrMo₆) and cationic pillar[5]arenes (namely, P5A) with 10 positive charges which can be used as the phase transfer catalysts (PTCs). This supramolecular catalyst was exploited on aldehydes oxidation under enzymatic condition with relatively good conversion. Through DLS monitoring, the diameters of nanospheres were variable while changing the charge ratios of the ionic complexes (P5A-CrMo₆), and it is probably because of the closer charge ratios causing the more compact assemblies. Also, the nano-morphologies were monitored by TEM and SEM, and the nanostructures were characterized by zeta potential, the X-ray energy-dispersive spectroscopy (EDS), elemental analysis.

A redox-responsive supramolecular amphiphile fabricated by selenium-containing pillar[5]arene-based host–guest recognition

A novel redox-responsive molecular recognition motif was built between a neutral selenium-containing pillar[5]arene and a pyridinium bromide salt in water. It was further used to construct the first pillararene-based selenium-containing supramolecular amphiphile with application in controlled release.

Carbohydrate-based amphiphilic nano delivery systems for cancer therapy

Nanoparticles (NPs) are novel drug delivery systems that have been attracting more and more attention in recent years, and have been used for the treatment of cancer, infection, inflammation and other diseases. Among the numerous classes of materials employed for constructing NPs, organic polymers are outstanding due to the flexibility of design and synthesis and the ease of modification and functionalization. In particular, NP based amphiphilic polymers make a great contribution to the delivery of poorly-water soluble drugs. For example, natural, biocompatible and biodegradable products like polysaccharides are widely used as building blocks for the preparation of such drug delivery vehicles. This review will detail carbohydrate based amphiphilic polymeric systems for cancer therapy. Specifically, it focuses on the nature of the polymer employed for the preparation of targeted nanocarriers, the synthetic methods, as well as strategies for the application and evaluation of biological activity. Applications of the amphiphilic polymer systems include drug delivery, gene delivery, photosensitizer delivery, diagnostic imaging and specific ligand-assisted cellular uptake. As a result, a thorough understanding of the relationship between chemical structure and biological properties facilitate the optimal design and rational clinical application of the resulting carbohydrate based nano delivery systems for cancer therapy.

Adaptive soft molecular self-assemblies

Adaptive molecular self-assemblies provide possibility of constructing smart and functional materials in a non-covalent bottom-up manner. Exploiting the intrinsic properties of responsiveness of non-covalent interactions, a great number of fancy self-assemblies have been achieved. In this review, we try to highlight the recent advances in this field. The following contents are focused: (1) environmental adaptiveness, including smart self-assemblies adaptive to pH, temperature, pressure, and moisture; (2) special chemical adaptiveness, including nanostructures adaptive to important chemicals, such as enzymes, CO2, metal ions, redox agents, explosives, biomolecules; (3) field adaptiveness, including self-assembled materials that are capable of adapting to external fields such as magnetic field, electric field, light irradiation, and shear forces.

Polymer nanoparticles self-assembled from photo-, pH- and thermo-responsive azobenzene-functionalized PDMAEMA

Polymer nanoparticles self-assembled from an amphiphilic azobenzene-functionalized PDMAEMA have been constructed, the morphological changes of which under stimulation of UV light, temperature and pH changes are demonstrated.

Polymeric supra-amphiphiles based on terminal group electrostatic interactions: fabrication of micelles with modifiable surfaces

On the basis of terminal group electrostatic interactions (TGEI), a supra-amphiphile is formed between a homopolymer of polylactic acid with carboxyl group at one end (PLA-COOH) and hepta-6-hydrazyl-β-cyclodextrin (HH-CD). The amphiphile can self-assemble into a micellar structure in aqueous solution. The outer surface of the micelle, which is composed of cyclodextrins, can be further modified via host-guest interactions. Considering the biocompatibility of the building blocks, the application of the micelles in a nanocarrier of anticancer drugs is further explored.

Supra-amphiphiles: a new bridge between colloidal science and supramolecular chemistry

In addition to conventional amphiphiles, an emerging research area is supra-amphiphiles, which are constructed on the basis of noncovalent interactions and dynamic covalent bonds. In this feature article, we have provided a general introduction to the concept, design principles, and topologies of supra-amphiphiles, starting from some rationally tailored building blocks. In addition, we highlight some progress in the functional assembly of supra-amphiphiles, such as responsive nanoscale carriers, antibacterial and antitumor agents, fluorescent-based chemical sensors, and enzyme mimics. The supra-amphiphile is a new bridge between colloidal science and supramolecular chemistry, and it is a field where we can make full use of our imaginative power.

Hierarchical molecular self-assemblies: construction and advantages

Hierarchical molecular self-assembly offers many exotic and complicated nanostructures which are of interest in nanotechnology and material science. In the past decade, various strategies leading to hierarchical molecular self-assemblies have been developed. In this review we summarize the recent advances in the creation and application of solution-based self-assembled nanostructures that involve more than one level of arrangement of building blocks. The strategies for construction hierarchical self-assembled structures and the advantages brought up by these assemblies are focused on. The following contents are included: (1) general approaches to fabricate hierarchical self-assembly, including self-assemblies based on supramolecules and specially designed block copolymers; (2) the advantages brought about by the hierarchical self-assembly, including the fabrication of special self-assembled structures, rich responsiveness to external stimuli, and the materials' performance.

Nanoparticle assembly of a photo- and pH-responsive random azobenzene copolymer

Stimuli-responsive polymeric nanoparticles with a core of hydrophobic azobenzene-containing acrylate units and a shell of hydrophilic acrylic acid units were prepared from a novel photo- and pH-responsive amphiphilic random azobenzene copolymer. Upon UV light irradiation, the trans azobenzene changed to the cis form and thus the water contact angle and the absorption of water on the polymer film could be changed, while little effect was exerted on the morphology of the nanoparticles although the polarity of the core of nanoparticles increased. Adjusting pH of the nanoparticle solution could exert a strong effect on the morphology of the nanoparticles. The prime nanoparticles (pH 6) changed to nanoparticle aggregates at pH 3, and to swollen nanoparticles at pH 11. The controlled release of Nile Red from the nanoparticles under the stimuli was demonstrated.

Self-assembly of supramolecularly engineered polymers and their biomedical applications

Self-assembly behavior of supramolecularly engineered polymers and their biomedical applications have been summarized.

Molecular structural transformation regulated dynamic disordering of supramolecular vesicles as pH-responsive drug release systems

The spontaneous release of drug payloads in the whole body always results in the compromised drug bioavailability and ultimate therapeutic efficacy. To achieve enhanced therapeutic efficacy and reduced side effects, pH-responsive targeted drug delivery systems have been studied due to their enhanced tumor accumulation and controllable maximum drug release feature. The present study described a co-assembly constructed by a pH responsive molecule (i.e., malachite green carbinol base (MG)) and liposome for highly efficient doxorubicin (DOX) release in tumor cells (MG-DOX⊂L). The structural transformation of MG effectively regulates the drug release profile in acidic environment. The pH-responsive sensitivity of co-assembly can be fine-tuned by altering the mixing ratios of building blocks with pH responders (i.e., MG molecules). MG-DOX⊂L was beneficial for the DOX release at pH5.0 and showed a higher cytotoxicity in KB cells owing to the pH-responsive drug release in acidic organelles following endocytosis pathway. In vivo tumor targetability and growth inhibition were evaluated in KB cell-xenografted nude mice. We have demonstrated that effective tumor growth inhibition in vivo is attributed to the synergistic contributions from highly efficient cellular entry and responsive intracellular release of DOX from MG-DOX⊂L.

25th anniversary article: reversible and adaptive functional supramolecular materials: "noncovalent interaction" matters

Supramolecular materials held together by noncovalent interactions, such as hydrogen bonding, host-guest interactions, and electrostatic interactions, have great potential in material science. The unique reversibility and adaptivity of noncovalent intreractions have brought about fascinating new functions that are not available by their covalent counterparts and have greatly enriched the realm of functional materials. This review article aims to highlight the very recent and important progresses in the area of functional supramoleuclar materials, focusing on adaptive mechanical materials, smart sensors with enhanced selectivity, soft luminescent and electronic nanomaterials, and biomimetic and biomedical materials with tailored structures and functions. We cannot write a complete account of all the interesting work in this area in one article, but we hope that it can in a way reflect the current situation and future trends in this prosperously developing area of functional supramolecular materials.

Macromolecular self-assembly and nanotechnology in China

Macromolecular self-assembly refers to the assembly of synthetic polymers, biomacromolecules and supra-molecular polymers. Through macromolecular self-assembly, the fabrication of ordered structures at different scales, the control of the dynamic assembly process and the integrations of advanced functions can be realized. Macromolecular self-assembly and nanotechnology research in China has developed rapidly, from the early periods of follow-up at low to high level and progress into a stage of innovation and creation. This review selects some representative progresses achieved recently, aiming to reflect the current status of macromolecular self-assembly and nanotechnology research in China.

Selenium-containing polymers: promising biomaterials for controlled release and enzyme mimics

Although researchers have made great progress in the development of responsive polymeric materials for controlled drug release or diagnostics over the last 10 years, therapeutic results still lag behind expectations. The development of special materials that respond to physiological relevant concentrations, typically within the micromolar or nanomolar concentration regime, remains challenging. Therefore, researchers continue to pursue new biomaterials with unique properties and that respond to mild biochemical signals or biomarkers. Selenium is an essential element in human body with potential antioxidant properties. Because of selenium's electronegativity and atomic radius, selenium-containing compounds exhibit unique bond energy (C-Se bond 244 kJ mol⁻¹; Se-Se bond 172 kJ mol⁻¹). These values give the C-Se or Se-Se covalent bonds dynamic character and make them responsive to mild stimuli. Therefore, selenium-containing polymers can disassemble in response to changes under physiological relevant conditions. This property makes them a promising biomaterial for controlled release of drugs or synthetic enzyme mimics. Until recently, few researchers have looked at selenium-containing polymers as novel biomaterials. In this Account, we summarize our recent research on selenium-containing polymers and show their potential application as mild-responsive drug delivery vehicles and artificial enzymes. We begin by reviewing the current state of the art in the synthesis of selenium-containing main chain block copolymers. We highlight the dual redox and gamma-irradiation behaviors of diselenide-containing block copolymers assemblies, discussing the possibility of their use in a combination of chemotherapy and actinotherapy. We also describe the coordination of platinum with monoselenide containing block copolymers. Such structures offer the possibility of fabricating multidrug systems for cooperative chemotherapy. In addition, we summarize the methods for the covalent and noncovalent preparation of selenium-containing polymers with side chains, which highlight the opportunity to reversibly tune the amphiphilicity of selenium-containing polymers. Finally, we present strategies for the design of highly efficient selenium-containing dendritic polymers that can mimic enzymes. This field is still in its infancy period, and further research can only be limited by our imagination.

Self-assembly and chemical processing of block copolymers: a roadmap towards a diverse array of block copolymer nanostructures

Block copolymers can yield a diverse array of nanostructures. Their assembly structures are influenced by their inherent structures, and the wide variety of structures that can be prepared especially becomes apparent when one considers the number of routes available to prepare block copolymer assemblies. Some examples include self-assembly, directed assembly, coupling, as well as hierarchical assembly, which can yield assemblies having even higher structural order. These assembly routes can also be complemented by processing techniques such as selective crosslinking and etching, the former technique leading to permanent structures, the latter towards sculpted and the combination of the two towards permanent sculpted structures. The combination of these pathways provides extremely versatile routes towards an exciting variety of architectures. This review will attempt to highlight destinations reached by LIU Guojun and coworkers following these pathways.

Thermo- and light-regulated formation and disintegration of double hydrophilic block copolymer assemblies with tunable fluorescence emissions

We report on thermo- and light-regulated formation and disintegration of double hydrophilic block copolymer (DHBC) micelles associated with tunable fluorescence emissions by employing two types of DHBCs covalently labeled with fluorescence resonance energy transfer (FRET) donor and acceptor moieties, respectively, within the light and temperature dually responsive block. Both DHBCs are molecularly soluble at room temperature in their aqueous mixture, whereas, upon heating to above the critical micellization temperature (CMT, ~31 °C), they coassemble into mixed micelles possessing hydrophilic coronas and mixed cores containing FRET donors and acceptors. Accordingly, the closer spatial proximity between the FRET pair (NBDAE and RhBEA moieties) within micellar cores leads to substantially enhanced FRET efficiency, compared to that in the non-aggregated unimer state. Moreover, upon UV irradiation, the light-reactive moieties undergo light-cleavage reaction and transform into negatively charged carboxylate residues, leading to elevated CMT (∼46 °C). Thus, thermo-induced mixed micelles in the intermediate temperature range (31 °C < T < 46 °C) undergo light-triggered disintegration into unimers, accompanied with the decrease of FRET efficiency. Overall, the coassembly and disassembly occurring in the mixed DHBC solution can be dually regulated by temperature and UV irradiation, and most importantly, these processes can be facilely monitored via changes in FRET efficiency and distinct emission colors.

Association behaviors of dodecyltrimethylammonium bromide with double hydrophilic block co-polymer poly(ethylene glycol)-block-poly(glutamate sodium)

The association behaviors of single-chain surfactant dodecyltrimethylammonium bromide (DTAB) with double hydrophilic block co-polymers poly(ethylene glycol)-b-poly(sodium glutamate) (PEG(113)-PGlu(50) or PEG(113)-PGlu(100)) were investigated using isothermal titration microcalorimetry, cryogenic transmission electron microscopy, circular dichroism, ζ potential, and particle size measurements. The electrostatic interaction between DTAB and the oppositely charged carboxylate groups of PEG-PGlu induces the formation of super-amphiphiles, which further self-assemble into ordered aggregates. Dependent upon the charge ratios between DTAB and the glutamic acid residue of the co-polymer, the mixture solutions can change from transparent to opalescent without precipitation. Dependent upon the chain length of the PGlu block, the mixture of DTAB and PEG-PGlu diblocks can form two different aggregates at their corresponding electroneutral point. Spherical and rod-like aggregates are formed in the PEG(113)-PGlu(50)/DTAB mixture, while the vesicular aggregates are observed in the PEG(113)-PGlu(100)/DTAB mixture solution. Because the PEG(113)-PGlu(100)/DTAB super-amphiphile has more hydrophobic components than that of the PEG(113)-PGlu(50)/DTAB super-amphiphile, the former prefers forming the ordered aggregates with higher curvature, such as spherical and rod aggregates, but the latter prefers forming vesicular aggregates with lower curvature.

Enzyme-responsive polymeric supra-amphiphiles formed by the complexation of chitosan and ATP

Chitosan and adenosine-5'-triphosphate (ATP) are employed as building blocks to fabricate polymeric supra-amphiphiles based on electrostatic interactions, which can self-assemble to form spherical aggregates. The spherical aggregates inherit the phosphotase responsiveness of ATP. Compared to our previous work, this enzyme-responsive system can be more biocompatible and block polymers are not needed in preparation, which makes it possible to fabricate the chitosan-based enzyme-responsive assemblies in a large-scale, cheap way. Therefore, the application of the assemblies for nanocontainers and drug delivery is greatly anticipated.

Amphiphilic building blocks for self-assembly: from amphiphiles to supra-amphiphiles

The process of self-assembly spontaneously creates well-defined structures from various chemical building blocks. Self-assembly can include different levels of complexity: it can be as simple as the dimerization of two small building blocks driven by hydrogen bonding or as complicated as a cell membrane, a remarkable supramolecular architecture created by a bilayer of phospholipids embedded with functional proteins. The study of self-assembly in simple systems provides a fundamental understanding of the driving forces and cooperativity behind these processes. Once the rules are understood, these guidelines can facilitate the research of highly complex self-assembly processes. Among the various components for self-assembly, an amphiphilic molecule, which contains both hydrophilic and hydrophobic parts, forms one of the most powerful building blocks. When amphiphiles are dispersed in water, the hydrophilic component of the amphiphile preferentially interacts with the aqueous phase while the hydrophobic portion tends to reside in the air or in the nonpolar solvent. Therefore, the amphiphiles aggregate to form different molecular assemblies based on the repelling and coordinating forces between the hydrophilic and hydrophobic parts of the component molecules and the surrounding medium. In contrast to conventional amphiphiles, supra-amphiphiles are constructed on the basis of noncovalent interactions or dynamic covalent bonds. In supra-amphiphiles, the functional groups can be attached to the amphiphiles by noncovalent synthesis, greatly speeding their construction. The building blocks for supra-amphiphiles can be either small organic molecules or polymers. Advances in the development of supra-amphiphiles will not only enrich the family of conventional amphiphiles that are based on covalent bonds but will also provide a new kind of building block for the preparation of complex self-assemblies. When polymers are used to construct supra-amphiphiles, the resulting molecules are known as superamphiphiles. This Account will focus on the use of amphiphiles and supra-amphiphiles for self-assembly at different levels of complexity. We introduce strategies for the fabrication of robust assemblies through self-assembly of amphiphiles. We describe the supramolecular approach for the molecular design of amphiphiles through the enhancement of intermolecular interaction among the amphiphiles. In addition, we describe polymerization under mild conditions to stabilize the assemblies formed by self-assembly of amphiphiles. Finally, we highlight self-assembly methods driven by noncovalent interactions or dynamic covalent bonds for the fabrication of supra-amphiphiles with various topologies. Further self-assembly of supra-amphiphiles provides new building blocks for complex structures, and the dynamic nature of the supra-amphiphiles endows the assemblies with stimuli-responsive functions.

Acetylcholinesterase responsive polymeric supra-amphiphiles for controlled self-assembly and disassembly

We have fabricated enzyme responsive polymeric supra-amphiphiles by mixing a block copolymer of poly(ethylene glycol)-block-poly(acrylic acid) with myristoylcholine chloride in water. The polymeric supra-amphiphiles self-assemble into spherical aggregates with sizes varying from about 40 to 150 nm. Moreover, the spherical aggregates can be disassembled triggered by acetylcholinesterase, an enzyme which can cut off the ester linkage of myristoylcholine chloride. Nile red can be loaded into the spherical aggregates and released in several hours upon the treatment of acetylcholinesterase. The releasing rate is rather fast considering that it takes more than 150 h for Nile red to diffuse out of the spherical aggregates without addition of acetylcholinesterase. It is anticipated that the new enzyme responsive polymeric supra-amphiphile may be explored as a carrier for drug delivery.