Two-dimensional networks of an azobenzene derivative: bi-pyridine mediation and photo regulation

Two-dimensional photosensitive supramolecular assemblies based on an azobenzene derivative and bi-pyridine are built up and investigated using scanning tunneling microscopy (STM). In order to probe the photo-induced self-assembled behavior of these two molecules, irradiation experiments with different wavelengths are designed and performed. Our STM results show that the constructed H-bonded networks can be reversibly regulated under irradiation with UV light and visible light.

Moiré pattern induced by the electronic coupling between 1-octanol self-assembled monolayers and graphite surface

Two-dimensional self-assembly of 1-octanol molecules on a graphite surface is investigated using scanning tunneling microscopy (STM) at the solid/liquid interface. STM images reveal that this molecule self-assembles into a compact hydrogen-bonded herringbone nanoarchitecture. Molecules are preferentially arranged in a head-to-head and tail-to-tail fashion. A Moiré pattern appears in the STM images when the 1-octanol layer is covering the graphite surface. The large Moiré stripes are perpendicular to the 1-octanol lamellae. Interpretation of the STM images suggests that the Moiré periodicity is governed by the electronic properties of the graphite surface and the 1-octanol layer periodicity.

Functionalization of two-component molecular networks: recognition of Fe³⁺

Two-component supramolecular networks have been constructed with a symmetric triphenylene derivative with three carboxyl groups (sym-TTT) and melamine. Two kinds of hydrogen bonds with different strength are involved in the multi-component self-assembly, one is H-bond between carboxyl group of sym-TTT and melamine, the other is intermolecular H-bond between melamine molecules. These interactions drive a structural transformation from close-packed network to hexagonal network with active amino groups inside of the cavity. Scanning tunneling microscopy (STM) measurements reveal that the functionalized network of sym-TTT/melamine could recognise Fe(3+). These results could be helpful for designing functionalized molecular networks by multi-component self-assembling strategy.

Peculiar adsorbed phase behaviour of binary mixtures of oligopyridines and extension to a ternary mixture in a host-guest system

Binary mixtures of bis(terpyridine)s show a U shape behaviour in concentration dependent surface coverage at constant molar ratio. The phase separation can be exploited to create ternary mixtures with exclusive adsorption of the third component in one phase.

Heterogeneous bilayer molecular structure at a liquid-solid interface

Hexaphenylbenzene (HPB) derivatives, HPB-6a and HPB-6pa, can form a supramolecular network which is stabilized by the intermolecular hydrogen bonding between carboxyl group at an octanoic acid/graphite interface. The observation of the heterogeneous bilayer structure formed exclusively by coronene and HPB-6pa at the octanoic acid/graphite interface is reported. Pronounced selectivity of coronene for the supramolecular networks with different sizes is reflected through the formation of bilayer structure for HPB-6pa network with the introduction of coronene as the guest species, indicating stronger interactions between HPB-6pa and coronene.

The role of self-assembling polypeptides in building nanomaterials

Polypeptides are functional biomolecules that play a key role in life science, where they can act as hormones and signaling molecules. They can self-assemble into a variety of nanostructures, including two dimensional (2D) lamellae, one dimensional (1D) nanofibrils and nanotubes, and zero dimensional (0D) nanospheres. The driving force behind these advanced nanomaterials involves weak non-covalent interactions that include hydrogen bonding, and hydrophobic and electrostatic interactions. Here we discuss each of the interactions in relation to self-assembly and provide examples of some novel applications in engineering materials, tissue engineering and nanoelectronics. The overall aim is to provide a comprehensive, yet easily accessible review of the known nanomaterials produced by self-assembling polypeptides, which may lead to the construction of more advanced polypeptide nanostructures for future applications.

Observation of reduced cytotoxicity of aggregated amyloidogenic peptides with chaperone-like molecules

The pathogenesis of many neurodegenerative diseases is associated with different types of aggregates of amyloidogenic peptides, including senile plaques, fibrils, protofibrils, and oligomers. It is therefore valuable to explore diversity of approaches toward reducing the cytotoxicity of amyloidogenic peptides by modulating aggregation behaviors. Herein we report an approach toward reducing the neuronal cytotoxicity of amyloidogenic peptides by accelerating the aggregation process, which is different from prevalent methods via inhibiting the aggregation of peptides. The pyridyl derivatives behave like chaperones to dramatically change the assembling characteristics of the peptides via strong hydrogen bond formation with C-termini of amyloid β (Aβ) peptides, which is revealed by using scanning probe microscopy. The light scattering experiments demonstrated the effect of the chaperone-like molecules on accelerating the aggregation process of Aβ peptides, accompanied by the reduced neuronal cytotoxicity of amyloidogenic peptides. These results would give rise to a complementary approach for modulating biological effects of the aggregates of amyloidogenic peptides.

Hierarchical organization of a robust porphyrin cage self-assembled by hydrogen bonds

Porphyrins appended with four rigid hydrogen bonding motifs on the meso positions were synthesized and self-assembled into a cofacial cage with four complementary bis(decyl)melamine units in dry solvents. The hydrocarbon chains on the melamine mediate the formation of nanofilms on surfaces as the solvent slowly evaporates.

Hierarchical, interface-induced self-assembly of diphenylalanine: formation of peptide nanofibers and microvesicles

To gain insight into the hierarchical self-assembly of peptides and the surface effect on assembly formation, an aromatic peptide of diphenylalanine (FF) was used in this study as the model peptide. We found that the diphenylalanine peptide could self-assemble into a core-branched nanostructure through non-covalent interactions in aqueous solution. The pre-assemblies further assembled into nanofibers and microvesicles on the glass surface and microporous membrane, respectively, showing a significant dependence on surface characteristics. The structural and morphological differences between nanofibers and microvesicles were investigated directly using several spectroscopy and microscopy techniques. Our results revealed a hierarchical and interface-induced assembly behavior of diphenylalanine peptide. The novel strategy based on the surface effect allows one to controllably fabricate various peptide-based nanostructures.

Supramolecular surface-confined architectures created by self-assembly of triangular phenylene-ethynylene macrocycles via van der Waals interaction

At the liquid/graphite interface triangular and rhombic phenylene-ethynylene macrocycles substituted by alkyl chains self-assemble to form porous two-dimensional (2D) molecular networks of honeycomb and Kagomé types, respectively, or close-packed non-porous structures via alkyl chain interdigitation as the directional intermolecular linkages. Factors that affect the formation of the 2D molecular networks, such as alkyl chain length, solvent, solute concentration, and co-adsorption of guest molecules, were elucidated through a systematic study. For the porous networks, various molecules and molecular clusters were adsorbed in the pores reflecting the size and shape complementarity, exploring a new field of 2D host-guest chemistry.

Towards supramolecular engineering of functional nanomaterials: pre-programming multi-component 2D self-assembly at solid-liquid interfaces

Materials with a pre-programmed order at the supramolecular level can be engineered with a sub-nanometer precision making use of reversible non- covalent interactions. The intrinsic ability of supramolecular materials to recognize and exchange their constituents makes them constitutionally dynamic materials. The tailoring of the materials properties relies on the full control over the self-assembly behavior of molecular modules exposing recognition sites and incorporating functional units. In this review we focus on three classes of weak-interactions to form complex 2D architectures starting from properly designed molecular modules: van der Waals, metallo-ligand and hydrogen bonding. Scanning tunneling microscopy studies will provide evidence with a sub-nanometer resolution, on the formation of responsive multicomponent architectures with controlled geometries and properties. Such endeavor enriches the scientist capability of generating more and more complex smart materials featuring controlled functions and unprecedented properties.

Multilevel supramolecular architectures self-assembled on metal surfaces

We report the controllability of the complexity of surface-supported supramolecular assembly on metal surfaces. By introducing mismatch between the molecular packing and the surface atomic periodicity in the systems with comparable strength of intermolecular and molecule-substrate interactions, a homomolecular assembly exhibiting two-dimensional multilevel structures up to quaternary level was observed. In such a multiperiodicity modulated system, neither the intermolecular nor molecule-substrate interactions solely dominate the assembly, resulting in complicated multilevel structures. We further demonstrated that the multilevel assemblies can serve as templates for site-selective adsorption of guest molecules.

Tailoring two-dimensional PTCDA-melamine self-assembled architectures at room temperature by tuning molecular ratio

Engineering and tuning multi-component supramolecular self-assemblies on surfaces is one of the challenges of nanotechnology. We use scanning tunneling microscopy to investigate the influence of molecular ratio on the self-assembly of PTCDA-melamine structures on Au(111)-(22 x complex square root of 3). Our observations reveal that three different chiral supramolecular networks having a PTCDA:melamine ratio of 3:2, 1:2, 1:4 can be selectively created by tuning the ratio of molecules deposited on the surface. The 1:2 ratio network having melamine in excess has been observed previously but the 1:4 network has not yet been reported. In comparison, the multi-component 3:2 network having PTCDA in excess is a completely new structure.

Strong adsorption of aminotriazines on graphene

DFT calculations reveal that aminotriazines have a strong affinity for graphite and suggest that part of the driving force for adsorption is a specific attractive interaction of NR(2) groups with the underlying surface.