Self‐Assembly and Structural Evolvement of Polyoxometalate‐Anchored Dendron Complexes

A cationic dendritic molecule that has alkyl chains has been synthesized and employed to encapsulate anionic polyoxometalates through electrostatic interactions. The prepared surfactant‐encapsulated polyoxometalate (SEP) complexes were used as building blocks to fabricate self‐assemblies in solution and the solid state. Monodispersion, lamellar, and columnar assemblies of SEP complexes have been characterized in detail. With increasing the number of peripheral cationic dendrons on inorganic clusters, the SEPs undergo changes from globular assemblies to monodispersions in solution and from lamellar assemblies to hexagonal columnar structures in the solid state, depending on the amounts of cationic dendrons in the complexes. The structural evolvement was simulated through consideration of the size and shape of the cationic dendron and polyanionic clusters, and the experimental results are in good agreement with the interpretation of the simulations. The present research demonstrates a new kind of dendritic complex and provides a route for controlling their assembling states by simply alternating the number of cationic dendrons in the complexes.     

Polyurethanes Containing Indole‐Based Non‐Linear Optical Chromophores: from Linear Chromophore to H‐Type

Two new “H” type of indole‐based chromophores were designed and successfully introduced to the polymeric system, the resultant polymers demonstrated enhanced NLO effects, good processability, thermal stability and nearly excellent transparency, indicating the advantages of “H” type chromophore moieties. And they could be promising candidates for the practical applications as new photonic materials.

     

Novel Water‐Soluble Shape‐Regulatable Luminescent Nanoparticles by Non‐Covalently Bonded Self‐Assembly

Summary: Novel non‐covalently connected water‐soluble nanoparticles that contain poly(fluorene‐co‐phenylene) with hydroxy‐capped alkoxy side chains (PF3BOH) and poly(acrylic acid) (PAA) have been obtained and characterized. With different proportions of PF3BOH and PAA, the shape and size of the nanoparticles can be regulated. The nanoparticles are quite stable in water with no precipitate being observed after weeks. Transmission electron microscopy and dynamic laser light scattering are used to confirm the morphology of the PF3BOH/PAA nanoparticles. Their optical properties have been investigated and show similar optoelectronic properties to a PF3BOH solid film although they do not undergo aggregation.

TEM images of the nanoparticles obtained upon varying the PAA/PF3BOH content.     

Self‐Assembly of Two‐Component Gels: Stoichiometric Control and Component Selection

Two‐component systems capable of self‐assembling into soft gel‐phase materials are of considerable interest due to their tunability and versatility. This paper investigates two‐component gels based on a combination of a L ‐lysine‐based dendron and a rigid diamine spacer (1,4‐diaminobenzene or 1,4‐diaminocyclohexane). The networked gelator was investigated using thermal measurements, circular dichroism, NMR spectroscopy and small angle neutron scattering (SANS) giving insight into the macroscopic properties, nanostructure and molecular‐scale organisation. Surprisingly, all of these techniques confirmed that irrespective of the molar ratio of the components employed, the “solid‐like” gel network always consisted of a 1:1 mixture of dendron/diamine. Additionally, the gel network was able to tolerate a significant excess of diamine in the “liquid‐like” phase before being disrupted. In the light of this observation, we investigated the ability of the gel network structure to evolve from mixtures of different aromatic diamines present in excess. We found that these two‐component gels assembled in a component‐selective manner, with the dendron preferentially recognising 1,4‐diaminobenzene (>70 %), when similar competitor diamines (1,2‐ and 1,3‐diaminobenzene) are present. Furthermore, NMR relaxation measurements demonstrated that the gel based on 1,4‐diaminobenzene was better able to form a selective ternary complex with pyrene than the gel based on 1,4‐diaminocyclohexane, indicative of controlled and selective π–π interactions within a three‐component assembly. As such, the results in this paper demonstrate how component selection processes in two‐component gel systems can control hierarchical self‐assembly.     

Construction of Polycation‐Based Non‐Viral DNA Nanoparticles and Polyanion Multilayers via Layer‐by‐Layer Self‐Assembly

Summary: The multilayers of polycation‐based non‐viral DNA nanoparticles and biodegradable poly(L ‐glutamic acid) (PGA) were constructed by a layer‐by‐layer (LbL) technique. Poly(ethyleneimine) (PEI) was used to condense DNA to develop non‐viral DNA nanoparticles. AFM, UV‐visible spectrometry, and TEM measurements revealed that the PEI‐DNA nanoparticles were successfully incorporated into the multilayers. The well‐structured, easily processed multilayers with the non‐viral DNA nanoparticles may provide a novel approach to precisely control the delivery of DNA, which may have great potential for gene therapy applications in tissue engineering, medical implants, etc.

A TEM image of the cross section of a (PGA/PEI‐DNA nanoparticle)₂₀ multilayer.     

The Effects of Microenvironment Polarity and Dendritic Branching of Aliphatic Hydrocarbon Dendrons on the Self‐Assembly of 2‐Ureido‐4‐pyrimidinones

Two series of aliphatic hydrocarbon‐based G1–G3 dendritic 2‐ureido‐4‐pyrimidinones (UPy) ( S‐Gn )₂ and ( L‐Gn )₂, differing from one another by the distance between the branching juncture to the urea end, were prepared and characterized. These hydrocarbon dendrons were also appended to a p‐aminonitrobenzene solvatochromic chromophore in order to probe their microenvironment polarity. While positive solvatochromism was observed which indicated the chromophore was solvent accessible, there was no significant difference between the microenvironment polarities on going from the G1 to the G3 dendrons. The self‐assembling behavior and tautomeric preference of the dendritic UPy derviatives were examined by ¹H NMR spectroscopy. The dimerization constants (K_dim*) of the DDAA tautomers were unchanged at 10⁷ M ^?1 in CDCl₃ at both 25 and 50 °C, which were comparable to those of UPy compounds bearing other nonpolar substitutents. Furthermore, the lower limits on the K′_dim* of the DADA tautomeric forms of the ( S‐Gn )₂ and ( L‐Gn )₂ series were determined to be 10⁶ and 10⁵ M ^?1 in CDCl₃, respectively. It was found that a closer proximity of the dendron branching juncture to the UPy unit could lead to a destabilization effect on the dimeric states. Hence, the ( L‐Gn )₂ dimers are more stable than those of ( S‐Gn )₂ in the DDAA form, but the latter are more stable than the former in the tautomeric DADA state. This study showed that both the highly nonpolar microenvironment and the proximity of the dendritic branching juncture to the UPy motif could alter the strength and profile of the hydrogen bond‐mediated self‐assembling process.     

Supramolecular Dendrimers: Convenient Synthesis by Programmed Self‐Assembly and Tunable Thermoresponsivity

We report here the noncovalent synthesis of thermosensitive dendrimers. Short oligoguanosine strands were linked to the focal point of a dendron by using “click chemistry”, and quadruplex formation was used to drive the self‐assembly process in the presence of metal ions. The dynamic nature of these noncovalent assemblies can be exploited to create combinatorial libraries of dendrimers as demonstrated by the co‐assembly of two components. These supramolecular dendrimers showed thermoresponsive behavior that can be tuned by varying the templating cations or the number of guanines in the oligonucleotide strand.     

Coordination‐Driven Self‐Assembly of Carbazole‐Based Metallodendrimers with Generation‐Dependent Aggregation‐Induced Emission Behavior

A new family of 120° carbazole‐based dendritic donors D1 – D3 have been successfully designed and synthesized, from which a series of novel supramolecular carbazole‐based metallodendrimers with well‐defined shapes and sizes were successfully prepared by [2+2] and [3+3] coordination‐driven self‐assembly. The structures of newly designed rhomboidal and hexagonal metallodendrimers were characterized by multinuclear NMR (¹H and ³¹P) spectroscopy, ESI‐TOF mass spectrometry, FTIR spectroscopy, and the PM6 semiempirical molecular orbital method. The fluorescence emission behavior of ligands D1 – D3 , rhomboidal metallodendrimers R1 – R3 , and hexagonal metallodendrimers H1 – H3 in mixtures of dichloromethane and n‐hexane with different n‐hexane fractions were investigated. The results indicated that D1 – D3 featured typical aggregation‐induced emission (AIE) properties. However, different from ligands D1 – D3 , metallodendrimers R1 – R3 and H1 – H3 presented interesting generation‐dependent AIE properties. Furthermore, evidence for the aggregation of these metallodendrimers was confirmed by a detailed investigation of dynamic light‐scattering, Tyndall effect, and SEM. This research not only provides a highly efficient strategy for constructing carbazole‐based dendrimers with well‐defined shapes and sizes, but also presents a new family of carbazole‐based dendritic ligands and rhomboidal and hexagonal metallodendrimers with interesting AIE properties.     

Supramolecular Self‐Assembly of Cucurbit[6]uil and Ionic Liquid in Non‐aqueous System

A novel [2]pseudorotaxane of cucurbit[6]uril(CB[6]) and 1‐butyl‐3‐methyl‐imidazolium bromide ([C₄mim]Br) was synthesized by directly mixing the host and the guest molecules in non‐aqueous system. Structural characterizations of the [2]pseudorotaxane were carried out by 1D, 2D NMR and X‐ray crystallography techniques both in solution and in crystal structure. The crystal structure demonstrated that CB[6] and [C₄mim]Br formed a complex with the ratio 1:1, in which one guest [C₄mim]Br was included inside the CB[6], while two other [C₄mim]Br molecules were free and surrounded the [2]pseudorotaxane as solvent molecules, which could stabilize the crystal structure through hydrogen bonds. Moreover, parallel solvent channels consisting by free [C₄mim]Br molecules occupied the pores among the frame of the pseudorotaxanes and formed zigzag lines in the crystal structure. [C₄mim]Br can serve as not only the guest reactant but also the solvent in the formation of [2]pseudorotaxane formation.     

A Self‐Assembly Approach to Temperature‐Responsive Polymer Nanocontainers

Summary: Thermosensitive polymer nanocontainers were formed by self‐assembly of diblock copolymers poly(2‐cinnamoylethyl methacrylate)‐block‐poly(N‐isopropylacrylamide) (PCEMA‐block‐PNIPAM) and subsequent photo‐crosslinking of the PCEMA shells. It was found that the diameter of the nanocontainers ranges from tens of nanometers to thousands of nanometers, depending on the self‐assembly conditions. The phase transition of the nanocontainers takes place at 32 °C; the structural changes are reversible in a heating and cooling cycle.

Schematic illustration of the structural transition behavior of the thermosensitive polymer nanocontainers.     

Self‐Assembly and Dispersion of Chromogenic Molecules: A Versatile and General Approach for Self‐Assessing Polymers

Summary: Self‐assessing polymer blends based on poly(ethylene terephthalate glycol) or linear low‐density polyethylene and small amounts (0.5–2% w/w) of chromogenic sensor dyes are prepared and investigated. The cyano‐substituted oligo(p‐phenylene vinylene) dyes employed in the study exhibit pronounced optical absorption changes upon self‐assembly, because of charge‐transfer interactions or conformation changes. The extent of dye aggregation (and therewith the optical absorption characteristics) in these blends is significantly influenced by exposure to external stimuli. Subjecting appropriately processed samples to either temperatures above their glass transition or mechanical deformation can significantly change the extent of aggregation, which in turn leads to a color change.

Mechano‐optical response of a 1.0% w/w LLDPE/C18‐RG blend film. Pristine films are orange due to aggregated dye molecules. Deformation leads to dispersion of the dye and irreversibly changes the color to yellow.     

A Novel and Non‐Cytotoxic Self‐Healing Supramolecular Elastomer Synthesized with Small Molecular Biological Acids

A novel and non‐cytotoxic self‐healing supramolecular elastomer (SE) is synthesized with small‐molecular biological acids by hydrogen‐bonding interactions. The synthesized SEs behave as rubber at room temperature without additional plasticizers or crosslinkers, which is attributed to the phase‐separated structure. The SE material exhibits outstanding self‐healing capability at room temperature and essential non‐cytotoxicity, which makes it a potential candidate for biomedical applications.

     

Self‐Assembly Drug Delivery System Based on Programmable Dendritic Peptide Applied in Multidrug Resistance Tumor Therapy

In recent decades, diverse drug delivery systems (DDS) constructed by self‐assembly of dendritic peptides have shown advantages and improvable potential for cancer treatment. Here, an arginine‐enriched dendritic amphiphilic chimeric peptide CRRK(RRCG(Fmoc))₂ containing multiple thiol groups is programmed to form drug‐loaded nano‐micelles by self‐assembly. With a rational design, the branched hydrophobic groups (Fmoc) of the peptides provide a strong hydrophobic force to prevent the drug from premature release, and the reduction‐sensitive disulfide linkages formed between contiguous peptides can control drug release under reducing stimulation. As expected, specific to multidrug resistance (MDR) tumor cells, the arginine‐enriched peptide/drug (PD) nano‐micelles show accurate nuclear localization ability to prevent the drug being pumped by P‐glycoprotein (P‐gp) in vitro, as well as exhibiting satisfactory efficacy for MDR tumor treatment in vivo. This design successfully realizes stimuli‐responsive drug release aimed at MDR tumor cells via an ingenious sequence arrangement.     

Synthesis and structural characterization of dendritic‐linear PMA‐APM‐r‐PS copolymers for a self‐assembled microporous matrix

A set of dendritic‐linear copolymers, poly(maleic anhydride‐grafted‐3,3′‐dimethyl‐(4‐aminophenylazanediyl)bis(2‐methylpropanoate))‐random‐polystyrene (PMA‐APM‐r‐PS), was successfully prepared by copolymerization of the novel dendritic macromonomer, 4‐(4‐(bis(3‐(4‐(bis(3‐methoxy‐2‐methyl‐3‐oxopropyl)amino)phenylamino)‐2‐methyl‐3‐oxopropyl)amino)phenylamino)‐4‐oxobut‐2‐enoic acid (MA‐APM), with styrene monomer. The dendritic MA‐APM macromonomer dendron 3,3′‐dimethyl‐(4‐aminophenylazanediyl)bis(2‐methylpropanoate) (APM) was then grafted by using the divergent growth method. FTIR, ¹H NMR, and ¹³C NMR spectra were used to identify the structures of the dendron, the dendritic macromonomer, and the dendritic‐linear PMA‐APM‐r‐PS copolymer. Furthermore, microporous dendritic‐linear PMA‐APM‐r‐PS copolymer films were prepared by using solvent‐induced phase separation at room temperature. We investigated the phase separation behavior and morphological structures of the dendritic‐linear copolymer film as functions of dendritic GMA‐HPAM segments in the content using SEM. Self‐assembly of the dendritic‐linear PMA‐APM‐r‐PS copolymer in the MG2‐X system, which represented the second generation dendron containing X wt % of the dendritic MA‐APM segment, resulted in submicron phase segregation. Interestingly, the submicron phase segregation morphology of the MG2–43 sample presented a uniform size distribution of ordered‐array structures. The results of this study demonstrate that controlling the appropriate macromonomer content via the grafting of a three‐dimensional structure results in a self‐assembly process that is capable of providing an ordered‐array microporous morphology in a polymer film. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3290–3301, 2010     

Copolymerization of Ethylene and 10‐Undecen‐1‐ol using a Montmorillonite‐Intercalated Metallocene Catalyst: Synthesis of Polyethylene/Montmorillonite Nanocomposites with Enhanced Structural Stability

Summary: Ethylene and 10‐undecen‐1‐ol have been successfully copolymerized by an organically modified montmorillonite (OMMT)‐intercalated metallocene catalyst, Et[Ind]₂ZrCl₂, activated by methylaluminoxane (MAO). The obtained hydroxy‐functionalized polyethylene (PE‐OH)/OMMT nanocomposites exhibit enhanced structural stability as compared with the neat PE‐based ones, with no significant collapse of the nanocomposite structure being detected by WAXD examination after high‐temperature processing. The simultaneous polyolefin functionalization provides an effective and convenient solution to stabilize the PE/MMT nanocomposite structure formed by in‐situ polymerization.

     

Non‐Covalent Polyvalent Ligands by Self‐Assembly of Small Glycodendrimers: A Novel Concept for the Inhibition of Polyvalent Carbohydrate–Protein Interactions In Vitro and In Vivo

Polyvalent carbohydrate–protein interactions occur frequently in biology, particularly in recognition events on cellular membranes. Collectively, they can be much stronger than corresponding monovalent interactions, rendering it difficult to control them with individual small molecules. Artificial macromolecules have been used as polyvalent ligands to inhibit polyvalent processes; however, both reproducible synthesis and appropriate characterization of such complex entities is demanding. Herein, we present an alternative concept avoiding conventional macromolecules. Small glycodendrimers which fulfill single molecule entity criteria self‐assemble to form non‐covalent nanoparticles. These particles—not the individual molecules—function as polyvalent ligands, efficiently inhibiting polyvalent processes both in vitro and in vivo. The synthesis and characterization of these glycodendrimers is described in detail. Furthermore, we report on the characterization of the non‐covalent nanoparticles formed and on their biological evaluation.