Supramolecular ribbons from amphiphilic trisamides self-assembly

Two amphiphilic C(3)-symmetric OPE-based trisamides have been synthesized and their self-assembling features investigated in solution and on surface. Variable-temperature UV-vis experiments demonstrate the cooperative supramolecular polymerization of these trisamides that self-assemble by the operation of triple C═O···H-N H-bonding arrays between the amide functional groups and π-π stacking between the aromatic units. The helical organization of the aggregates has been demonstrated by circular dichroism at a concentration as low as 1 × 10(-4) M in acetonitrile. In the reported trisamides, the large hydrophobic aromatic core acts as a solvophobic module impeding the interaction between the polar TEG chains and the amide H-bonds. This strategy makes unnecessary the separation of the amide functional groups to the polar tri(ethylene glycol) chains by paraffinic fragments. Achiral trisamide 1 self-assembles into flat ribbon-like structures that experience an amplification of chirality by the addition of a small amount of chiral 2 that generates twisted stripes.     

Template-directed supramolecular self-assembly of coordination dumbbells at surfaces

Scanning tunneling microscopy reveals, at single-molecular resolution, how external parameters--substrate morphology and guest addition--re-direct the assembly of dumbbell-shaped coordination supramolecules towards different surface-confined supramolecular organizations.     

Para-acyl calix[4]arenes: amphiphilic self-assembly from the molecular to the mesoscopic level

Studies of the properties of a series of amphiphilic calixarenes show that they can form stable monolayers, Langmuir-Blodgett layers and solid lipid nanoparticles, the mesostructures were investigated by atomic force microscopy and the crystal structure of one compound shows a partially interdigitated tilted bilayer structure.     

A self-assembly phase diagram from amphiphilic perylene diimides

Supramolecular forces govern self-assembly and further determine the final morphologies of self-assemblies. However, how they control the morphology remains hitherto largely unknown. In this paper, we have discovered that the self-assembled nanostructures of rigid organic semiconductor chromophores can be finely controlled by the secondary forces by fine-tuning the surrounding environments. In particular, we used water/methanol/hydrochloric acid to tune the environment and observed five different phases that resulted from versatile molecular self-assemblies. The representative self-assembled nanostructures were nanotapes, nanoparticles and their 1D assemblies, rigid microplates, soft nanoplates, and hollow nanospheres and their 1D assemblies, respectively. The specific nanostructure formation is governed by the water fraction, R(w) , and the concentration of hydrochloric acid, [HCl]. For instance, nanotapes formed at low [HCl] and R(w) values, whereas hollow nanospheres formed when either the HCl concentration is high, or the water fraction is low, or both. The significance of this paper is that it provides a useful phase diagram by using R(w) and [HCl] as two variables. Such a self-assembly phase diagram maps out the fine control that the secondary forces have on the self-assembled morphology, and thus allows one to guide the formation toward a desired nanostructure self-assembled from rigid organic semiconductor chromophores by simply adjusting the two key parameters of R(w) and [HCl].     

Coarse-grained simulation of amphiphilic self-assembly

The authors present a computer simulation study of amphiphilic self-assembly performed using a computationally efficient single-site model based on Gay-Berne [J. Chem. Phys. 74, 3316 (1981)] and Lennard-Jones particles. Molecular dynamics simulations of these systems show that free self-assembly of micellar, bilayer, and inverse micelle arrangements can be readily achieved for a single model parametrization. This self-assembly is predominantly driven by the anisotropy of the amphiphile-solvent interaction, amphiphile-amphiphile dispersive interactions being found to be of secondary importance. While amphiphile concentration is the main determinant of phase stability, molecular parameters such as head group size and interaction strength also have measurable affects on system properties.     

Curvature modulates the self-assembly of amphiphilic molecules

In this work, we used lattice Monte Carlo simulations and theoretical model calculations to show how the self-assembly of adsorbed amphiphilic molecules is affected by the local curvature of solid surfaces. It is found that, beyond a critical curvature value, solid surface geometry governs the spatial ordering of aggregates and may induce the morphological transitions. The simulation results show how the curvature of solid surfaces modulates the distribution of aggregates: the anisotropy in local curvature along and perpendicular to the cylindrical surfaces tends to generate orientationally ordered cylindrical micelles. To account for the morphological transitions induced by the local curvature of solid surfaces, we constructed a theoretical model which includes the Helfrich bending energy, the deformation energy of aggregates induced by solid surfaces, and the adsorption energy. The model calculations indicate that on highly curved solid surfaces the bending energy for bilayer structure sharply increases with surface curvature, which in turn induces the morphological transition from bilayer to cylindrical structure. Our results suggest that the local curvature provides a means of controlling the spatial organization of amphiphilic molecules.     

Surface-based molecular self-assembly: Langmuir-Blodgett films of amphiphilic Ln(III) complexes

The unique photophysical properties of the Ln(III) series has led to significant research efforts being directed towards their application in sensors. However, for “real-life” applications, these sensors should ideally be immobilised onto surfaces without loss of function. The Langmuir-Blodgett (LB) technique offers a promising method in which to achieve such immobilisation. This mini-review focuses on synthetic strategies for film formation, the effect that film formation has on the physical properties of the Ln(III) amphiphile, and concludes with examples of Ln(III) LB films being used as sensors.     

Generation dependent mesophase behavior in extended amphiphilic dendrons in the shape of macromolecular dumbbells

Small angle X-ray scattering studies of 2nd and 3rd generation based extended amphiphilic dendrons in the shape of macromolecular dumbbells with identical hydrophilic volume fractions suggest 2-D hexagonal columnar and Pm3n micellar cubic mesophases, respectively, elucidating the role of shape induced interface curvature in mesophase formation.     

Synthesis and self-assembly of amphiphilic polymeric microparticles

We report the synthesis and self-assembly of amphiphilic, nonspherical, polymeric microparticles. Wedge-shaped particles bearing segregated hydrophilic and hydrophobic sections were synthesized in a microfludic channel by polymerizing across laminar coflowing streams of hydrophilic and hydrophobic polymers using continuous flow lithography (CFL). Particle monodispersity was characterized by measuring both the size of the particles formed and the extent of amphiphilicity. The coefficient of variation (COV) was found to be less than 2.5% in all measured dimensions. Particle structure was further characterized by measuring the curvature of the interface between the sections and the extent of cross-linking using FTIR spectroscopy. The amphiphilic particles were allowed to self-assemble in water or at water-oil interfaces. In water, the geometry of the particles enabled the formation of micelle-like structures, while in emulsions, the particles migrated to the oil-water interface and oriented themselves to minimize their surface energy.     

Synthesis and self-assembly of propeller-shaped amphiphilic molecules

Propeller-shaped aromatic amphiphiles based on a conformationally flexible aromatic segment are shown to self-assemble into well-defined discrete nanostructures with high fluorescence characteristic.     

Fabrication of nanotubules and microspheres from the self-assembly of amphiphilic monochain stearic acid derivatives

A series of amphiphilic monochain derivatives of stearic acid, CH(3)(CH(2))(16)CONH(CH(2))(n)NH(2) (n = 2, 3, 4, 6), CH(3)(CH(2))(16)CONH(CH(2))(2)S(2)(CH(2))(2)NH(2), and [CH(3)(CH(2))(16)CONH](2)(CH(2))(2), are synthesized, and their self-assembly behaviors have been investigated in 1,2-dichloroethane (DCE). In addition to the concentration of the compound in DCE, the number of methylene units in hydrophilic segments play a crucial role in determining the final morphology of self-assembling structures from nanotubules with 20 nm inner diameter to microspheres with an average diameter of 20 μm. The external texture of the microsphere is also influenced by the number of methylene units in the hydrophilic segment. The microspheres formed by highly ordered aggregation of nanobelts show high thermal stability. The particular processes and causations have been expatiated.     

Tuning multiphase amphiphilic rods to direct self-assembly

New methods to direct the self-assembly of particles are highly sought after for multiple applications, including photonics, electronics, and drug delivery. Most techniques, however, are limited to chemical patterning on spherical particles, limiting the range of possible structures. We developed a lithographic technique for fabrication of chemically anisotropic rod-like particles in which we can specify both the size and shape of particles and implement multiple diverse materials to control interfacial interactions. Multiphase rod-like particles, including amphiphilic diblock, triblock, and multiblock were fabricated in the same template mold having a tunable hydrophilic/hydrophobic ratio. Self-assembly of diblock or triblock rods at a water/oil interface led to the formation of bilayer or ribbon-like structures.     

偶氮苯基两亲性聚合物的自组装行为研究进展

偶氮苯基两亲性聚合物结合了偶氮苯基团的光响应、酶响应、主客体识别特性和两亲性聚合物的自组装特性,能够在选择性溶剂中发生聚合物可控自组装行为,这使得其在药物控释、纳米技术和生物医学材料等领域受到了广泛的关注。本文从结构类型和合成方法出发,综述了新型偶氮苯基两亲性聚合物在溶液中的自组装研究进展,并对该领域的发展前景进行了展望。     

Tuning secondary structure and self-assembly of amphiphilic peptides

Self-assembly is one of nature's mechanisms by which higher order structures are obtained. Two of the main driving forces for self-assembly, hydrophobic interactions and hydrogen bonding, are both present within amphiphilic peptides. Here, it is demonstrated how the intricately interconnected folding and assembly behavior of an N-terminally acylated peptide, with the sequence GANPNAAG, has been tuned by varying its hydrophobic tail and thermal history. The change in interplay between hydrophobic forces and peptide folding allowed the occurrence of different types of aggregation, from soluble peptides with a random coil conformation to aggregated peptides arranged in a beta-sheet assembly, which form helically twisted bilayer ribbons.     

Controlled self-assembly of amphiphilic oligopeptides into shape-specific nanoarchitectures

Here, we report a novel, programmable, molecular self-assembling system to fabricate shape-specific, three-dimensional nanoarchitectures. Three types of simple 16-mer peptides consisting of hydrophobic Leu and hydrophilic Lys, LKL16, KLK16, and LK16, were prepared as building blocks for nanofabrications. A detailed analysis of the conformation and self-assembling mechanism was performed by using circular dichroism (CD), FTIR spectroscopy, and atomic force microscopy (AFM). A wide variety of self-assembled nanoarchitectures, such as beta-sheet-plates, beta-sheet-fibers, alpha-helix-particles, and alpha-helix-plates, could be fabricated by tuning the peptide sequence, reaction time, and solution pH. The ability to control the self-assembled nanostructures should provide a simple and/or essential insight into the mechanism of peptide aggregation, including amyloid formation, and it should be useful for the design of novel bio-related nanomaterials.     

Self-assembly of molecular dumbbells into organized bundles with tunable size

Dumbbell-shaped molecules consisting of three biphenyls connected through vinyl linkages as a conjugated rod segment and aliphatic polyether dendritic wedges with different cross-sections (i.e., dibranch (1), tetrabranch (2) and hexabranch (3)) were synthesized and characterized. The molecular dumbbells self-assemble into discrete bundles that organize into three-dimensional superlattices. Molecule 1, based on a dibranched dendritic wedge, organizes into primitive monoclinic-crystalline and body-centered, tetragonal liquid crystalline structures, while molecules 2 and 3, based on tetra- and hexabranched dendritic wedges, respectively, form only body-centered, tetragonal liquid crystalline structures. X-ray diffraction experiments and density measurements showed that the rod-bundle cross-sectional area decreases with increasing cross-section of the dendritic wedges. The influences of supramolecular structure on the bulk-state optical properties were investigated by measuring the UV/Vis absorption and steady state fluorescence spectroscopies. As the cross-section of the dendritic wedge of the molecule increases, the absorption and emission maxima shift to higher energy. This can be attributed to a quantum size effect of the three-dimensionally confined nanostructure.     

Bioactive molecular sheets from self-assembly of polymerizable peptides

We have demonstrated that polymerizable peptides self-assemble into a unique sheet-like 2D structure in bulk solution that can be covalently fixed to produce 2D molecular objects which were shown to be efficient at delivering cargos into living cells and are nearly nontoxic in contrast to non-polymerized nanostructures.