Self‐Assembly of Achiral Shape Amphiphiles into Multi‐Walled Nanotubes via Helicity‐Selective Nucleation and Growth

Soft nanotubes are normally constructed from chiral amphiphiles through helical self‐assembly. Yet, how to self‐assemble achiral molecules into nanotubes is still a challenge. Here, we report the nanotube construction with achiral shape amphiphiles through helical self‐assembly and also unravel the formation mechanisms. The amphiphiles have a dumbbell shape and are composed by covalently linking three achiral moieties together: two unlike clusters and an organic tether. The difference in polarity between the unlike clusters drives the amphiphiles to self‐assemble into single‐ and multi‐walled nanotubes as well as intermediates. Analysis of the key intermediates unravels the self‐assembly mechanism of helicity‐selective nucleation and growth. Meanwhile, direct visualization of the individual clusters in the ribbons displays a two‐dimensional deformed hexagonal lattice. Thus, we speculate that it is the lattice deformation that creates anisotropic tension along different directions of the ribbon which further results in the formation of helical ribbons towards nanotubes by amphiphiles.     

Self‐assembly of Carbon Particles as a Heat Sink Coating to Promote Radiative Cooling

Novel composite carbon particles are developed that can self‐assemble as a coating on a substrate without a binder. These carbon particles were used as a coating to enhance thermal dissipation and their thermal conductivity, surface emissivity and cooling performance were measured. Carbon particles with both thiol and epoxy functional groups self‐assembled to form a coating on the surface of a heat sink without a binder, which greatly improved the thermal conductivity of the coating. Coating a heat sink with the carbon particles yielded a higher thermal conductivity and emissivity than could be obtained with the addition of binder in the conventional approach, and significantly enhanced the cooling performance. In addition, the cooling performance of the carbon nanotube outperformed all other particles when coated on a substrate, because it had the highest thermal conductivity and good radiation emissivity. We developed an equation to describe the various parameters affecting the cooling performance of the thermally dissipative coating. This equation was confirmed by the experimental data.     

Facile fabrication and self‐assembly of polystyrene–silica asymmetric colloid spheres

This study presents a very simple method to fabricate organic–inorganic asymmetric colloid spheres. In this approach, when silica particles are used as the Pickering emulsifier to stabilize the monomer droplets (styrene) in water via acid–base interaction between silica particles and auxiliary monomer (1‐vinylimidazole), the exposed surfaces of silica particles are very easy to be locally modified with 3‐(trimethoxysilyl)propyl methacrylate. When water‐based initiator is added, polystyrene–silica asymmetric colloid spheres are highly yielded. The sizes of silica and polymer particles can be tunable. These organic–inorganic anisotropic colloid spheres can self‐assemble into an interesting thickness‐dependent film. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Chemically Controlled Spatiotemporal Oscillations of Colloidal Assemblies

We report an autonomous oscillatory micromotor system in which active colloidal particles form clusters, the size of which changes periodically. The system consists of an aqueous suspension of silver orthophosphate microparticles under UV illumination, in the presence of varying concentrations of hydrogen peroxide. The colloid particles first attract each other to form clusters. After a short delay, these clusters abruptly disperse and oscillation begins, alternating between clustering and dispersion of particles. After a cluster oscillation initiates, the oscillatory wave propagates to nearby clusters and eventually all the clusters oscillate in phase‐shifted synchrony. The oscillatory behavior is governed by an electrolytic self‐diffusiophoretic mechanism which involves alternating electric fields generated by the competing reduction and oxidation of silver. The oscillation frequency is tuned by changing the concentration of hydrogen peroxide. The addition of inert silica particles to the system results in hierarchical sorting and packing of clusters. Densely packed Ag₃PO₄ particles form a non‐oscillating core with an oscillating shell composed largely of silica microparticles.     

Multicolour Self‐Assembled Fluorene Co‐Oligomers: From Molecules to the Solid State via White‐Light‐Emitting Organogels

Five fluorene‐based co‐oligomers have been prepared to study their self‐assembly in a wide range of concentrations, from dilute solutions to the solid state. Subtle changes to the chemical structures, introduced to tune the emission colours over the entire visible range, induce strong differences in aggregation behaviour. Only two of the fluorescent co‐oligomer derivatives self‐assemble to form soluble fibrils from which fluorescent organogels emerge at higher concentrations. In contrast, the other compounds form precipitates. Mixed fluorescent co‐oligomer systems exhibit partial energy transfer, which allows the creation of white‐light‐emitting gels. Finally, a mechanism for the hierarchical self‐assembly of this class of materials is proposed based on experimental results and molecular modelling calculations.     

A DNA–Fullerene Conjugate as a Template for Supramolecular Chromophore Assemblies: Towards DNA‐Based Solar Cells

A fullerene was covalently attached to a (dA)₂₀ template that serves as structural scaffold to self‐assemble an ordered and mixed array of ethynyl‐pyrene‐ and ethynyl‐Nile‐red‐nucleoside conjugates. Fluorescence spectroscopy revealed evidence for energy transfer between the two different chromophores. Moreover, fluorescence quenching is significantly enhanced by the attached fullerene in mixed assemblies of different chromophore ratios. This indicates exciton dissociation by electron transfer from the photo‐generated exciton on the chromophore stack to the fullerene. The fullerene–DNA‐conjugate was integrated as a photo‐active layer in solar cells that showed charge‐carrier generation in the spectral regime of all three components of the conjugate. This work clearly demonstrates that DNA is suitable as structural element for chromophore assemblies in future organic optoelectronic devices, such as solar cells.     

Hydrogel Microellipsoids that Form Robust String‐Like Assemblies at the Air/Water Interface

Soft colloidal particles such as hydrogel microspheres assemble at air/water or oil/water interfaces, where the soft colloids are highly deformed and their surface polymer chains are highly entangled with each other. Herein, we report the formation of robust one‐dimensional, string‐like colloidal assemblies through self‐organization of hydrogel microspheres with shape anisotropy at the air/water interface of sessile droplets. Shape‐anisotropic hydrogel microspheres were synthesized via two‐step polymerization, whereby a hydrogel shell was formed onto preformed rigid microellipsoids. The shape anisotropy of the hydrogel microspheres was confirmed by transmission electron microscopy and high‐speed atomic force microscopy as well as by light‐scattering measurements. The present findings are crucial for the understanding of natural self‐organization phenomena, where “softness” influences microscopic assembled structures such as those of Nostoc bacteria.     

Self‐Recognition Between Two Almost Identical Macroions During Their Assembly: The Effects of pH and Temperature

Two Keplerate‐type macroions, [Mo^VI₇₂Fe^III₃₀O₂₅₂‐ (CH₃COO)₁₂{Mo₂O₇(H₂O)}₂{H₂Mo₂O₈(H₂O)}(H₂O)₉₁]?ca. 150 H₂O= {Mo₇₂Fe₃₀} and [{Na(H₂O)₁₂}?{Mo^VI₇₂Cr^III₃₀O₂₅₂(CH₃COO)₁₉‐ (H₂O)₉₄}]?ca. 120 H₂O= {Mo₇₂Cr₃₀} , with identical size and shape but different charge density, can self‐assemble into spherical “blackberry”‐like structures in aqueous solution by means of electrostatic interactions. These two macroanions can self‐recognize each other and self‐assemble into two separate types of homogeneous blackberries in their mixed dilute aqueous solution, in which they carry ?7 and ?5 net charges, respectively. Either adjusting the solution pH or raising temperature is expected to make the self‐recognition more difficult, by making the charge densities of the two clusters closer, or by decreasing the activation energy barrier for the blackberry formation, respectively. Amazingly, the self‐recognition behavior remains, as confirmed by dynamic and static light scattering, TEM, and energy dispersive spectroscopy techniques. The results prove that the self‐recognition behavior of the macroions due to the long‐range electrostatic interaction is universal and can be achieved when only minimum differences exist between two types of macroanions.     

CdSe Nanoplatelets: Living Polymers

Colloidal CdSe nanoplatelets are considered to be excellent candidates for many applications in nanotechnology. One of the current challenges is to self‐assemble these colloidal quantum wells into large ordered structures to control their collective optical properties. We describe a simple and robust procedure to achieve controlled face‐to‐face self‐assembly of CdSe nanoplatelets into micron‐long polymer‐like threads made of up to ～1000 particles. These structures are formed by addition of oleic acid to a stable colloidal dispersion of platelets, followed by slow drying and re‐dispersion. We could control the average length of the CdSe nanoplatelet threads by varying the amount of added oleic acid. These 1‐dimensional structures are flexible and feature a “living polymer” character because threads of a given length can be further grown through the addition of supplementary nanoplatelets at their reactive ends.     

Metabolically Active,Fully Hydrolysable Polymersomes

The synthesis and aqueous self‐assembly of a new class of amphiphilic aliphatic polyesters are presented. These AB block polyesters comprise polycaprolactone (hydrophobe) and an alternating polyester from succinic acid and an ether‐substituted epoxide (hydrophile). They self‐assemble into biodegradable polymersomes capable of entering cells. Their degradation products are bioactive, giving rise to differentiated cellular responses inducing stromal cell proliferation and macrophage apoptosis. Both effects emerge only when the copolymers enter cells as polymersomes and their magnitudes are size dependent.     

Synthesis and Immunological Evaluation of Self‐Assembling and Self‐Adjuvanting Tricomponent Glycopeptide Cancer‐Vaccine Candidates

Self‐adjuvanting tricomponent vaccines were prepared and assessed for their self‐assembly and immunological activity in mouse models. The vaccines each consisted of a peptide or glycopeptide antigen that corresponds to a complete copy of the variable‐number tandem repeat (VNTR) of the tumor‐associated mucin 1 (MUC1) glycoprotein, the universal T‐cell helper peptide epitope PADRE, and the immunoadjuvant Pam₃CysSer. The vaccines were shown to spontaneously self‐assemble in water to form isotropic particles varying in size from 17 to 25 nm and elicited robust humoral responses in murine models without the addition of an external adjuvant. The serum antibodies could recognize tumor‐associated MUC1 epitopes on the surface of MCF7 breast‐cancer cells and B16 melanoma cells, which overexpress this tumor‐associated glycoprotein.     

Metabolically Active,Fully Hydrolysable Polymersomes

The synthesis and aqueous self‐assembly of a new class of amphiphilic aliphatic polyesters are presented. These AB block polyesters comprise polycaprolactone (hydrophobe) and an alternating polyester from succinic acid and an ether‐substituted epoxide (hydrophile). They self‐assemble into biodegradable polymersomes capable of entering cells. Their degradation products are bioactive, giving rise to differentiated cellular responses inducing stromal cell proliferation and macrophage apoptosis. Both effects emerge only when the copolymers enter cells as polymersomes and their magnitudes are size dependent.     

Inducing Social Self‐Sorting in Organic Cages To Tune The Shape of The Internal Cavity

Many interesting target guest molecules have low symmetry, yet most methods for synthesising hosts result in highly symmetrical capsules. Methods of generating lower symmetry pores are thus required to maximise the binding affinity in host–guest complexes. Herein, we use mixtures of tetraaldehyde building blocks with cyclohexanediamine to access low‐symmetry imine cages. Whether a low‐energy cage is isolated can be correctly predicted from the thermodynamic preference observed in computational models. The stability of the observed structures depends on the geometrical match of the aldehyde building blocks. One bent aldehyde stands out as unable to assemble into high‐symmetry cages‐and the same aldehyde generates low‐symmetry socially self‐sorted cages when combined with a linear aldehyde. We exploit this finding to synthesise a family of low‐symmetry cages containing heteroatoms, illustrating that pores of varying geometries and surface chemistries may be reliably accessed through computational prediction and self‐sorting.     

Electronic Energy Transfer Modulation in a Dynamic Foldaxane: Proof‐of‐Principle of a Lifetime‐Based Conformation Probe

Abiotic aromatic oligoamide foldamers are shown to self‐assemble in solution to form a double helix, which can accommodate a bichromophoric thread in its central void. While in solution reversible electronic energy transfer is instilled between chromophoric termini of the free, flexible thread as evidenced through delayed luminescence, upon rigidification of the rod the chromophores are mutually distanced and effectively decoupled. Consequently, the chromophores display their individual photophysical characteristics. The observed conformation‐dependent changes of dynamic luminescence properties, which are particularly sensitive to distance, offers a new strategy for lifetime‐based detection of geometry on the molecular scale as demonstrated through real‐time luminescence detection of molecular complexation leading to foldaxane formation.     

Amphiphilic Nanoparticles Control the Growth and Stability of Lipid Bilayers with Open Edges

Molecular amphiphiles self‐assemble in polar media to form ordered structures such as micelles and vesicles essential to a broad range of industrial and biological processes. Some of these architectures such as bilayer sheets, helical ribbons, and hollow tubules are potentially useful but inherently unstable owing to the presence of open edges that expose the hydrophobic bilayer core. Here, we describe a strategy to stabilize open bilayer structures using amphiphilic nanoparticle surfactants that present mixtures of hydrophilic and hydrophobic ligands on their surface. We observe that these particles bind selectively to the open edge of bilayer membranes to stabilize otherwise transient amphiphile assemblies. We show how such particles can precisely control the size of lipid tubules, how they can inhibit the formation of undesirable assemblies such as gallstone precursors, and how they can stabilize free‐floating lipid microdiscs.     

Amphiphilic Janus Gold Nanoparticles Prepared by Interface‐Directed Self‐Assembly: Synthesis and Self‐Assembly

Materials with Janus structures are attractive for wide applications in materials science. Although extensive efforts in the synthesis of Janus particles have been reported, the synthesis of sub‐10 nm Janus nanoparticles is still challenging. Herein, the synthesis of Janus gold nanoparticles (AuNPs) based on interface‐directed self‐assembly is reported. Polystyrene (PS) colloidal particles with AuNPs on the surface were prepared by interface‐directed self‐assembly, and the colloidal particles were used as templates for the synthesis of Janus AuNPs. To prepare colloidal particles, thiol‐terminated polystyrene (PS‐SH) was dissolved in toluene and citrate‐stabilized AuNPs were dispersed in aqueous solution. Upon mixing the two solutions, PS‐SH chains were grafted to the surface of AuNPs and amphiphilic AuNPs were formed at the liquid–liquid interface. PS colloidal particles decorated with AuNPs on the surfaces were prepared by adding the emulsion to excess methanol. On the surface, AuNPs were partially embedded in the colloidal particles. The outer regions of the AuNPs were exposed to the solution and were functionalized through the grafting of atom‐transfer radical polymerization (ATRP) initiator. Poly[2‐(dimethamino)ethyl methacrylate] (PDMAEMA) on AuNPs were prepared by surface‐initiated ATRP. After centrifugation and dissolving the colloidal particles in tetrahydrofuran (THF), Janus AuNPs with PS and PDMAEMA on two hemispheres were obtained. In acidic pH, Janus AuNPs are amphiphilic and are able to emulsify oil droplets in water; in basic pH, the Janus AuNPs are hydrophobic. In mixtures of THF/methanol at a volume ratio of 1:5, the Janus AuNPs self‐assemble into bilayer structures with collapsed PS in the interiors and solvated PDMAEMA at the exteriors of the structures.     

Anisotropic Self‐Assembly of Citrate‐Coated Gold Nanoparticles on Fluidic Liposomes

The behavior of self‐assembly processes of nanoscale particles on plasma membranes can reveal mechanisms of important biofunctions and/or intractable diseases. Self‐assembly of citrate‐coated gold nanoparticles (cAuNPs) on liposomes was investigated. The adsorbed cAuNPs were initially fixed on the liposome surfaces and did not self‐assemble below the phospholipid phase transition temperature (T_m). In contrast, anisotropic cAuNP self‐assembly was observed upon heating of the composite above the T_m, where the phospholipids became fluid. The number of self‐assembled NPs is conveniently controlled by the initial mixing ratio of cAuNPs and liposomes. Gold nanoparticle protecting agents strongly affected the self‐assembly process on the fluidic membrane.     

The self‐assembled of cyclic D,L‐α‐peptide systems: Insights into the structure and energetics

Cyclic D,L ‐α‐peptides are able to self‐assemble to nanotubes, although the inherent reason of the stability of this kind of nanotube as well as the intrinsic driving force of self‐assembly of the cyclic D ,L ‐α‐peptides still remain elusive. In this work, using several computational approaches, we investigated the structural and energy characteristics of a series of cyclo[(‐L ‐Phe‐D ‐Ala‐)₄] and cyclo[(‐L ‐Ala‐D ‐Ala‐)₄] oligomers. The results reveal that the thermodynamic stability, cooperativity, and self‐assembly patterns of cyclic D ,L ‐α‐peptide nanotubes are mainly determined by the interactions between cross‐strand side chains instead of those between backbones. For cyclo[(‐L ‐Phe‐D ‐Ala‐)₄] oligomers, the steric interaction between cross‐strand side chains, especially the electrostatic repulsion between the phenyls in Phe residues, brings anticooperative effect into parallel stacking mode, which is responsible for the preference of self‐assembling nanotube in antiparallel vs. parallel stacking orientation. Based on our results, a novel self‐assembling mechanism is put forward—it is the L ‐L antiparallel dimer of cyclo[(‐L ‐Phe‐D ‐Ala‐)₄], instead of the commonly presumed monomer, that acts as the basic building block in self assembly. It explains why these cyclic peptides uniquely self‐assemble to form antiparallel nanotubes. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Plank‐Shaped Column‐Forming Mesogens with Substituents on One Side Only

Prolonged glyoxylation of pyrenyl‐1‐glyoxylic acid ethyl ester leads to a mixture of isomers with polar pyrenylene‐1,8‐diglyoxylic acid as the main product, whereas the centrosymmetric 1,6‐isomer is obtained in good yield from the corresponding dibromopyrene. Perkin condensations followed by Pd‐catalyzed cyclizations lead to isomeric dinaphthopyrene‐tetracarboxdiimides that self‐assemble into columnar liquid crystals of hexagonal and rectangular symmetry, of which the rectangular mesophases have unusually elongated unit cells. The cisoid diimides with both alkylimide substituents on the same side of the oblong arene system show a much greater tendency to self‐assemble into fluid stacks of disks than their centrosymmetric isomers. With racemically branched alkyl substituents, uniform vertical surface alignment of the columns in the high‐temperature hexagonal mesophase is resilient to cycling through the lower‐temperature rectangular and crystalline phases.     

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.