Functional supramolecular assemblies derived from dendritic building blocks

Supramolecular Vector/Drug Coassemblies of Polyglycerol Dendrons and Rutin Enhance the pH Response

A coassembly strategy for a supramolecular vector/drug was proposed with a biocompatible ternary dodecyl-bi(third-generation polyglycerol (PG) dendrons) (C₁₂-(G3)₂) amphiphile, dodecyl sulfobetaine (SB3-12) surfactant, and poorly water-soluble drug rutin. C₁₂-(G3)₂ and rutin will mutually enhance their pH response by protonation and deprotonation of dendritic PG and rutin's ionization as the pH changes from the acidic gastric lumen to the weakly alkaline intestine. SB3-12 may increase the payload and bring about sustained release for rutin by intermolecular interactions. Self-assembling behaviors of C₁₂-(G3)₂, SB3-12, sodium dodecyl sulfate (SDS), and dodecyl trimethylammonium bromide (DTAB) and their hybrids with rutin were characterized by UV-vis spectroscopy, a fluorescence probe, and ¹H NMR. UV-vis and ¹H NMR were used to identify the position and orientation of rutin in the vectors. The functions of the vector/drug were confirmed by measuring the solubility and in vitro release of rutin. The ternary coassembling vector/drug easily imparted functions of pH-responsive and sustained release without complex synthetic processes. The nanocaves framed by PG dendrons in the micelles provide pH-responsive compartments for rutin and SB3-12 in the supramolecular vector/drug anchors that accommodate rutin by weak interactions. The finely matched supramolecular vector/drug coassemblies exhibit the pH-responsive function for a potential application in the treatment of inflammatory bowel disease.

Molecular bases for temperature sensitivity in supramolecular assemblies and their applications as thermoresponsive soft materials

Thermoresponsive supramolecular assemblies have been extensively explored in diverse formats, from injectable hydrogels to nanoscale carriers, for a variety of applications including drug delivery, tissue engineering and thermo-controlled catalysis. Understanding the molecular bases behind thermal sensitivity of materials is fundamentally important for the rational design of assemblies with optimal combination of properties and predictable tunability for specific applications. In this review, we summarize the recent advances in this area with a specific focus on the parameters and factors that influence thermoresponsive properties of soft materials. We summarize and analyze the effects of structures and architectures of molecules, hydrophilic and lipophilic balance, concentration, components and external additives upon the thermoresponsiveness of the corresponding molecular assemblies.

Multiple 2D crystal structures in bilayered lamellae from direct self-assembly of 3D systems of soft Janus particles

Numerous crystals and Frank-Kasper phases in two-dimensional (2D) systems of soft particles have been presented by theoretical investigations. How to realize 2D crystals or Frank-kasper phases by direct self-assembly of...

Size-tunable fluorescent dendrimersomes via aggregation-induced emission

Tetraphenylethylene-functionalized amphiphilic Janus dendrimers of up to third generation are synthesized. Their self-assembly has been studied under kinetic and thermodynamic control. By varying the dendrimer generation number and the self-assembly condition, fluorescent dendrimersomes of tunable size (∼60-200 nm) and quantum yield (5.7-17.4%) are obtained in aqueous medium.

Intercluster Exchange-Stabilized Novel Complex Colloidal χc Phase

Designing complex cluster crystals with a specific function using simple colloidal building blocks remains a challenge in materials science. Herein, we propose a conceptually new design strategy for constructing complex cluster crystals via hierarchical self-assembly of simple soft Janus colloids. A novel and previously unreported colloidal cluster-χ (χ_c) phase, which resembles the essential structural features of α-manganese but at a larger length scale, is obtained through molecular dynamics simulations. The formation of the χ_c phase undergoes a remarkable two-step self-assembly process, that is, the self-assembly of clusters with specific size dispersity from Janus colloids, followed by the highly ordered organization of these clusters. More importantly, the dynamic exchange of particles between these clusters plays a critical role in stabilizing the χ_c phase. Such a conceptual design framework based on intercluster exchange has the potential to effectively construct novel complex cluster crystals by hierarchical self-assembly of colloidal building blocks.

Helicity of a polyacetylene directed by molecular recognition of biscalixarene and fullerene

The dynamic helix interconversion of the C₆₀-appended polyacetylene was directed by the molecular recognition of a chiral biscalix[5]arene.

Dendrimer-based micelles as cyto-compatible nanocarriers

The aim of the present study is to compare the synthesized dendritic architectures in terms of self-assembly and transport potential for hydrophobic guest molecules.

Nonionic Dendritic and Carbohydrate Based Amphiphiles: Self-Assembly and Transport Behavior

Herein, a new series of non-ionic dendritic and carbohydrate based amphiphiles is synthesized employing biocompatible starting materials and studied for supramolecular aggregate formation in aqueous solution. The dendritic amphiphiles 12 and 13 possessing poly(glycerol) [G2.0] as hydrophilic unit and C-10 and C-18 hydrophobic alkyl chains, respectively, exhibit low critical aggregation concentration (CAC) in the order of 10^-5 m and hydrodynamic diameters in the 8-10 nm range and supplemented by cryogenic transmission electron microscopy. Ultraviolet-visible (UV-Vis) and fluorescence spectroscopy suggests the effective solubilization of hydrophobic guests by the self-assembled architectures, with the nanotransporters 12 and 13 possessing the highest encapsulation efficiency of 80.74 and 98.03% for curcumin. Efficient uptake of encapsulated curcumin in adenocarcinomic human alveolar basal epithelial (A549) cells is observed by confocal laser scanning microscopy. Amphiphiles 12 and 13 are non-cytotoxic at the concentrations studied, however, curcumin encapsulated samples efficiently reduce the viability of A549 cells in vitro. Experimental studies indicate the ability of amphiphile 13 to encapsulate 1-anilinonaphthalene-8-sulfonic acid (ANS) and curcumin with binding constant of 1.16 × 105⁵ m^-1 and 1.43 × 10⁶ m^-1 , respectively. Overall, our findings demonstrate the potential of these dendritic amphiphiles for the development of prospective nanocarriers for the solubilization of hydrophobic drugs.

Amphiphilic carbosilane dendrons as a novel synthetic platform toward micelle formation

A novel family of amphiphilic ionic carbosilane dendrons containing fatty acids at the focal point were synthesized and characterized. They spontaneously self-assembled in aqueous solution into micelles both in the absence and presence of salt, as confirmed by surface tension, conductivity, and DLS measurements. Dendron based micelles have spherical shapes and increase in size on decreasing dendron generation. These dendritic micelles have been demonstrated to be able to form complexes with therapeutic macromolecules such as siRNA and show a high loading capacity for drugs such as procaine, suggesting their potential use as nanocarriers for therapeutics.

Vesicles from Amphiphilic Dumbbells and Janus Dendrimers: Bioinspired Self-Assembled Structures for Biomedical Applications

The current review focuses on vesicles obtained from the self-assembly of two types of dendritic macromolecules, namely amphiphilic Janus dendrimers (forming dendrimersomes) and amphiphilic dumbbells. In the first part, we will present some synthetic strategies and the various building blocks that can be used to obtain dendritic-based macromolecules, thereby showing their structural versatility. We put our focus on amphiphilic Janus dendrimers and amphiphilic dumbbells that form vesicles in water but we also encompass vesicles formed thereof in organic solvents. The second part of this review deals with the production methods of these vesicles at the nanoscale but also at the microscale. Furthermore, the influence of various parameters (intrinsic to the amphiphilic JD and extrinsic-from the environment) on the type of vesicle formed will be discussed. In the third part, we will review the numerous biomedical applications of these vesicles of nano- or micron-size.

Nanotubular self-organization of amide dendrons with focal β-sheet forming peptide units

To develop rational design principles for a self-organized structure using dendron-peptide conjugates, a β-sheet forming short peptide (VVLL) was introduced to the focal point of a second-generation amide dendron (2G-VVLL) and its self-organization characteristics were investigated. 2G-VVLL self-organized into a nanotubular structure in the aqueous phase. The twisted β-sheet structure of the focal peptide unit was essential for the construction of the nanotubular structure. The design principle could be applied to another dendron-peptide conjugate (2G-AAVV). These findings are expected to assist in the construction of novel precisely controlled nanoarchitectures using amide dendrons with focal peptide units.

Supracolloidal helices from soft Janus particles by tuning the particle softness

Because of the unique architectures and promising potential applications of biomimetic helical structures in biotechnology and nanotechnology, the design and fabrication of these structures by experimentally realizable anisotropic colloidal particles remain one of the most challenging tasks in materials science. Here we show how soft Janus particles self-assemble into supracolloidal helices with distinctive structural characteristics, including single helices, double helices, and Bernal spirals, by appropriately tuning the particle softness. We further examine the kinetic mechanisms governing the formation of different helical structures by using particle-based dynamics simulations. Our results provide a new way for experimentally fabricating structure-controllable supracolloidal helices solely from the self-assembly of soft Janus particles.

Self-Assembled Dendron-Cyclodextrin Nanotubes with a Polyethylenimine Surface and Their Gene Delivery Capability

Self-assembled dendron-cyclodextrin nanotubes (Den-CD-NTs) with selected surface functionalities can serve as templates for the formation of complexes with polymers, and the resulting nanotube-polymer complexes can be utilized as gene carriers. The negatively charged surfaces of Den-CD-NTs were covered with a positively charged polyethylenimine (PEI) layer using electrostatic interactions, and the resulting nanotube-PEI complex, having a positively charged surface exhibited intracellular uptake. Furthermore, the nanotube-PEI complex exhibited the capability for DNA complexation with reduced enzymatic degradation, and also showed higher transfection efficiency and lower cytotoxicity than PEI. Therefore, Den-CD-NTs, in simple complexation with a surface PEI layer, are potentially useful gene delivery vectors.

Functional organogelators formed by liquid-crystal carbazole-containing bis-MPA dendrimers

Functional organogels based on carbazole-containing liquid crystal block codendrimers that show an increased fluorescence emission and redox properties.

Reversible polyphenylacetylene helix conversion driven by a thermoresponsive rotaxane switch in the solid state

The reversible helical pitch change of polyphenylacetylenes by a thermoresponsive trichloroacetate-containing rotaxane switch inserted into the side chain was demonstrated through an accompanying clear color change.

Highly functionalized heterogeneous dendrigraft catalysts with peripheral copper moieties for the facile synthesis of 2-substituted benzimidazoles and 2,2-disubstituted benzimidazoles

A highly functionalized heterogeneous copper loaded dendrigraft amidoamine catalyst for the synthesis of 2-substituted and 2,2-disubstituted benzimidazoles is reported.

Effect of Topological Structures on the Self-Assembly Behavior of Supramolecular Amphiphiles

Three types of azobenzene-based telechelic guest polymers, PEG-azo, azo-PEG-azo, and PEG-azo4, were synthesized by a facile method. Subsequently, a series supramolecular amphiphiles with three distinct topological structures (hemitelechelic, ditelechelic, and quadritelechelic) were constructed through coupling with host polymer β-cyclodextrin-poly(l-lactide) (β-CD-PLLA) by combined host-guest complexation. Research on the self-assembly behavior of these amphiphiles demonstrated that the variation in self-assembly was tuned by the synergistic interaction of hydrophilicity and the curvature of the polymer chains, and very importantly, the topological structure of amphiphiles demonstrated effective control of the self-assembly behavior.

Photoresponsive carbohydrate-based giant surfactants: automatic vertical alignment of nematic liquid crystal for the remote-controllable optical device

Photoresponsive carbohydrate-based giant surfactants (abbreviated as CELAnD-OH) were specifically designed and synthesized for the automatic vertical alignment (VA) layer of nematic (N) liquid crystal (LC), which can be applied for the fabrication of remote-controllable optical devices. Without the conventional polymer-based LC alignment process, a perfect VA layer was automatically constructed by directly adding the 0.1 wt % CELA1D-OH in the N-LC media. The programmed CELA1D-OH giant surfactants in the N-LC media gradually diffused onto the substrates of LC cell and self-assembled to the expanded monolayer structure, which can provide enough empty spaces for N-LC molecules to crawl into the empty zones for the construction of VA layer. On the other hand, the CELA3D-OH giant surfactants forming the condensed monolayer structure on the substrates exhibited a planar alignment (PA) rather than a VA. Upon tuning the wavelength of light, the N-LC alignments were reversibly switched between VA and PA in the remote-controllable LC optical devices. Based on the experimental results, it was realized that understanding the interactions between N-LC molecules and amphiphilic giant surfactants is critical to design the suitable materials for the automatic LC alignment.

Experimental and theoretical investigations in stimuli responsive dendrimer-based assemblies

Stimuli-responsive macromolecular assemblies are of great interest in drug delivery applications, as it holds the promise to keep the drug molecules sequestered under one set of conditions and release them under another. The former set of conditions could represent circulation, while the latter could represent a disease location. Over the past two decades, sizeable contributions to this field have come from dendrimers, which along with their monodispersity, provide great scope for structural modifications at the molecular level. In this paper, we briefly discuss the various synthetic strategies that have been developed so far to obtain a range of functional dendrimers. We then discuss the design strategies utilized to introduce stimuli responsive elements within the dendritic architecture. The stimuli itself are broadly classified into two categories, viz. extrinsic and intrinsic. Extrinsic stimuli are externally induced such as temperature and light variations, while intrinsic stimuli involve physiological aberrations such as variations in pH, redox conditions, proteins and enzyme concentrations in pathological tissues. Furthermore, the unique support from molecular dynamics (MD) simulations has been highlighted. MD simulations have helped back many of the observations made from assembly formation properties to rationalized the mechanism of drug release and this has been illustrated with discussions on G4 PPI (Poly propylene imine) dendrimers and biaryl facially amphiphilic dendrimers. The synergy that exists between experimental and theoretical studies open new avenues for the use of dendrimers as versatile drug delivery systems.

Towards engineering of self-assembled nanostructures using non-ionic dendritic amphiphiles

We have reported on the formation of different self-assembled nanostructures by subtle changes in the structure of non-ionic dendritic amphiphiles.

Phase transition behaviours of a single dendritic polymer

Dendritic polymers with highly branching structures exhibit many unique properties. In this paper, a computational study using the Wang-Landau sampling technique is carried out to reveal the phase transition behaviours of dendritic homopolymers with various branching structures. Two types of dendritic homopolymers, dendrimers/dendrigrafts (D/D) and hyperbranched (HB) polymers are studied. It is found that with increasing degree of branching in the dendritic polymer, the liquid-solid (LS) transition temperature increases and the coil-globule (CG) transition becomes weak. Additionally, under similar degrees of branching and polymerization, D/D polymers have a higher LS transition temperature than HB polymers. The reason is that the D/D polymers have greater regularity in the radial distribution of the branching units, which facilitates monomer packing during the LS transition. The distinctive internal unit distribution at various temperatures is quantitatively analysed. Our results show the importance of dendritic polymer structure regularity in phase transition behaviours and are valuable in guiding the structural design of dendritic macromolecules for functionalization applications.

Electron and force microscopy characterization of particle size effects and surface phenomena associated with individual natural organic matter fractions

Natural organic matter (NOM) generically refers to organic substances found in soils, waters, and sediments. It is the brown-to-black, heterogeneous organic material produced through the diagenetic alteration of plant tissue and microbial biomass via a myriad of biotic and abiotic reactions. Since NOM is the primary source of organic carbon in the earth's surficial environment, understanding the processes by which NOM is produced is integral to understanding carbon sequestration, contaminant fate and transport, and other earth surface processes. NOM samples (HA0) consist of nonamphiphilic (HA1), lipid-like (L0 and L1), and strongly amphiphilic (HA2) components. Here we present the structure and morphology of self-assembled NOM components based on scanning electron microscopy (SEM), atomic force microscopy (AFM), and electrostatic force microscopy (EFM) characterizations. Effects of surface charge and hydrophobicity/hydrophilicity of the amphiphile on the interaction and resulting structures were investigated using SEM, AFM, and EFM. Data shows that the component's amphiphilic nature plays a key role in the formation of NOM. SEM data show that aggregates form while AFM/EFM analysis verifies the existence of hydrophobic/hydrophilic moieties in different fractions of HA0. Subsequently, the amphiphilic nature of HA2 will have a substantial effect on interfacial interactions and subsequent self-assembly of HA0's components.

Work function maps and surface topography characterization of nitroaromatic-ended dendron films on graphite

Surface topography and work function maps were simultaneously obtained for carbon surfaces modified by a dendritic molecule: 3,5-Bis (3,5-dinitrobenzoylamino) benzoic acid. The dendrons were spontaneously assembled onto highly ordered pyrolytic graphite samples, exhibiting an increase in the surface potential. This fact is consistent with the incorporation of an electron-acceptor functional group that remains electroactive on the surface.

Synthesis of Anisotropic, Amphiphilic Grafted Multi-Star Polymers and Investigation of their Self-Assembling Characteristics

Herein, we report the synthesis of amphiphilic multi-star architectures consisting of discrete poly(methacrylic acid)-based core cross-linked star polymers joined together by polystyrene-grafted linear connectors by a combination of atom transfer radical polymerisation of protected macroinitiator precursors and a copper-catalysed azide-alkyne cycloaddition grafting-to approach. The anisotropic multi-star architectures, which were obtained as individual di- and tri-star polymers with segregated hydrophobic and hydrophilic domains, undergo aggregation in apolar solvents resulting in the formation of large nanometre-scale vesicles. The self-assembling behaviour of these large amphiphilic multi-star polymers (Mw = 869–1097 kDa) was studied using dynamic light scattering, transmission electron microscopy, and atomic force microscopy.

Dendronized supramolecular polymers

Supramolecular polymers from dendritic motifs combine the dynamic nature of supramolecular construction and inherent features from covalent dendronized polymers.

Dendrimersomes with photodegradable membranes for triggered release of hydrophilic and hydrophobic cargo

Amphiphilic Janus dendrimers with fully photodegradable hydrophobic blocks were synthesized and assembled into dendrimersomes in water. Irradiation with UV light triggered the release of hydrophobic and hydrophilic cargo.

Stimuli Sensitive Amphiphilic Dendrimers

In the past decade, there has been an increasing interest in supramolecular systems that can undergo physical or chemical tranformations upon encountering a specific stimulus. Micelle-forming amphiphilic systems based on polymers and dendrimers are particularly preferred over small molecule amphiphiles, due to their ability to sequester and release a vast library of hydrophobic guest molecules at micromolar polymer or dendrimer concentrations. Here we review a relatively underexplored, yet rapidly advancing, field of amphiphilic systems based on dendritic architechture that exhibit stimuli sensitive behaviour. In particular, we will be focusing on stimuli such as temperature, pH, enzymatic and non-enzymatic proteins. These stimuli-responsive systems offer a unique opportunity in the field of drug delivery and sensing.