Yibao Li

Self-Assembled 1-Octadecanethiol Monolayers on Graphene for Mercury Detection

We report studies on surface modification of graphene with 1-octadecanethiol and its application as heavy metal sensors. The alkanethiol molecules can self-assemble into large-scale highly ordered monolayers on single-layer graphene regardless of the roughness of graphene surfaces inherited from the underlying amorphorous silicon oxide (SiO2) dielectric substrates. Atomically resolved scanning tunneling microscopy imaging of modified graphene sheets on SiO2 was conducted to reveal configuration details of the self-assembled structure. Functionalization of graphene field effect transistors (Gra-FETs) with 1-octadecanethiol was realized and successfully explored for mercury(II) (Hg2+) detection at 10 ppm.

Strong aggregation and directional assembly of aromatic oligoamide macrocycles

Aromatic oligoamide macrocycles exhibit strong preference for highly directional association. Aggregation happens in both nonpolar and polar solvents but is weakened as solvent polarity increases. The strong, directional assembly is rationalized by the cooperative action of dipole-dipole and π-π stacking interactions, leading to long nanotubular assemblies that are confirmed by SEM, TEM, AFM, and XRD. The persistent nanotubular assemblies contain non-collapsible hydrophilic internal pores that mediate highly efficient ion transport observed with these macrocycles and serve as cylindrical sites for accommodating guests such as metal ions.

Self-assembly of novel fluorescent silole derivatives into different supramolecular aggregates: fibre, liquid crystal and monolayer

Two novel organogelators based on 2,3,4,5-tetraphenylsilole functionalized with long-chain alkoxydiacylamido platforms (1a and 1b) were synthesized. The silole derivatives induced gelation of only hydrocarbon solvents and showed aggregation-induced emission (AIE) in the gel state, in contrast to very weak emission in solution. The polarized optical microscopic (POM) and field emission scanning electron microscopy (FE-SEM) studies exhibited that the xerogels formed fibrous structures. Hydrogen bonding and π-stacking interactions were the main driving forces for the formation of organogels, based on the FT-IR and absorption investigations. Differential scanning calorimetry (DSC) and POM studies indicated that both compounds 1a and 1b exhibited stable liquid crystalline (LC) phases over a wide temperature range. It is interesting that uniform and well-ordered monolayers were also obtained for both compounds on the HOPG surface. The new silole derivatives are quite unique because they can self-assemble into one-dimensional (fibres), three-dimensional (liquid crystal) and even two-dimensional (molecular monolayer) aggregates.

Star-Shaped Oligofluorenes End-Capped with Carboxylic Groups: Syntheses and Self-Assembly at the Liquid–Solid Interface

A series of star-shaped oligofluorenes end-capped with carboxylic acid groups were synthesized. Different numbers of carboxyl groups that can form hydrogen bonds, and long alkane chains that have stabilizing effects, were intentionally introduced. The resulting molecular architectures of the so-prepared star-shaped oligofluorenes at the liquid-solid interface were investigated by scanning tunneling microscopy. It is found that the number of hydrogen-bonding groups and the symmetry of the target molecules have crucial influences on the structures of the ordered assemblies.

Single-molecule observation of the K+-induced switching of valinomycin within a template network

The K(+)-induced switching of valinomycin has been studied using a molecular template formed by an aromatic oligoamide macrocycle at the liquid/solid interface by scanning tunneling microscopy (STM). Individual valinomycin and its K(+) complex can be identified and resolved in the molecular template, and the high-resolution STM images of valinomycin and its K(+) complex show triangle-like and cyclic structural characteristics, respectively.

Thermodynamic Controlled Hierarchical Assembly of Ternary Supramolecular Networks at the Liquid–Solid Interface

Building and networking: Ternary supramolecular networks have been formed by coadsorption of dissimilar ternary building units at the liquid-solid interface. The structural characteristics of the networks undergo distinctive transformations as the building units change from binary to ternary components (see graphic).

Molecular arrays formed in anisotropically rearranged supramolecular network with molecular substitutional asymmetry

We have designed two molecular building blocks, 2,6,11-tricarboxydecyloxy-3,7,10-triundecyloxy triphenylene (asym-TTT) and 2,6,10-tricarboxydecyloxy-3,7,11-triundecyloxy triphenylene (sym-TTT) with asymmetric and symmetric carboxyl groups, to construct distinct supramolecular networks. The supramolecular network of asym-TTT facilitates the formation of the directional-oriented molecular arrays of zinc phthalocyanines (ZnPc). The high-resolution scanning tunneling microscopic (STM) images as well as the density-functional theory (DFT) calculations reveal the preferential adsorption of ZnPc dimers in the anisotropic rearrangement of an asym-TTT supramolecular network. The self-repairing process of the molecular arrays after sweeping ZnPc dimers further confirms the anisotropic reconstruction of the asym-TTT network. The controlled experiments on the symmetrically substituted compound indicate the impact of the asymmetrically substituted carboxyl groups on the supramolecular networks.

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.

Single Molecule Studies of Cyclic Peptides Using Molecular Matrix at Liquid/Solid Interface by Scanning Tunneling Microscopy†

We report in this work the single molecule studies of cyclic peptide, cyclosporine A (CsA), using a molecular network formed by star-shaped oligofluorene (StOF-COOH(3)) at the liquid/solid interface by scanning tunneling microscopy (STM). Individual cyclosporine A can be identified and resolved in the molecular network, and the high-resolution STM images of CsA show polygon-like characteristics with a diameter of approximately 1.7 nm. Furthermore, the complex of CsA and Mg(2+) has also been observed to adsorb inside of the molecular matrix. The STM results reveal two adsorption characteristics for the CsA-Mg(2+) complex, which is suggestive of asymmetrical configurations of the complex. The difference in binding energy between the two observed adsorption configurations is estimated to be 1.88 kJ·mol(-1). These results help set the stage for studying the fine structures and functions of various cyclic peptides at the liquid/solid interface.

Synergistic Inhibitory Effect of Peptide–Organic Coassemblies on Amyloid Aggregation

Inhibition of amyloid aggregation is important for developing potential therapeutic strategies of amyloid-related diseases. Herein, we report that the inhibition effect of a pristine peptide motif (KLVFF) can be significantly improved by introducing a terminal regulatory moiety (terpyridine). The molecular-level observations by using scanning tunneling microscopy reveal stoichiometry-dependent polymorphism of the coassembly structures, which originates from the terminal interactions of peptide with organic modulator moieties and can be attributed to the secondary structures of peptides and conformations of the organic molecules. Furthermore, the polymorphism of the peptide-organic coassemblies is shown to be correlated to distinctively different inhibition effects on amyloid-β 42 (Aβ42) aggregations and cytotoxicity.