Zongxia Guo

Induction of Chirality in an Achiral Monolayer at the Liquid/Solid Interface by a Supramolecular Chiral Auxiliary

An achiral oligo(p-phenylene vinylene) derivative with a ureido-triazine hydrogen bonding unit self-assembles into rows of hydrogen bonded dimers at the liquid/solid interface. Scanning tunneling microscopy reveals the formation of chiral domains, but overall, the surface remains racemic. Addition of a chiral auxiliary which is able to interact with the dimers through hydrogen bonding, showed that global organizational chirality could be achieved since a majority of the domains show the same handedness. After removing the chiral auxiliary with a volatile solvent, the global organizational chirality could be trapped, revealing a memory effect. With this straightforward supramolecular approach, we were able to create a chiral surface with preferred handedness composed of achiral molecules at the air/solid interface.

A multi-stimuli responsive organogel based on a tetrapeptide-dithienylcyclopentene conjugate

Multi-stimuli responsive organogels based on low-molecular-weight gelators (LMWGs) have attracted much attention due to their potential applications. Herein, the synthesis and the self-assembly behavior of a novel molecular gelator based on a tetrapeptide–dithienylcyclopentene conjugate is described. This gelator forms stable gels in THF, acetone and acetonitrile, in which the formation of anti-parallel β-sheets of the biomimetic tetrapeptides is the key driving force. Further studies suggest that the organogel is multi-responsive to various external stimuli including temperature, light, chemicals, and mechanical force. Moreover, in the presence of catechol, this gelator forms a more robust organogel, accompanied by a dramatic change of the assembly manner and rheological properties. These prominent features of this conjugate make it an excellent smart soft material with potential applications in areas such as drug encapsulation and release systems.

Surface-Induced Diastereomeric Complex Formation of a Nucleoside at the Liquid/Solid Interface: Stereoselective Recognition and Preferential Adsorption

With the aim of achieving surface-mediated enantioselective adsorption, the self-assembly of chiral oligo(p-phenylenevinylene) (OPV3T) with nucleosides is investigated at the liquid/solid interface by means of scanning tunneling microscopy and molecular modeling. OPV3T enantiomers form mirror related hexameric rosette patterns. The DNA nucleoside, thymidine, does not self-assemble into stable adlayers but coadsorbs with OPV3T on the surface, leading to a pattern transformation of OPV3T from rosettes to dimers, and a change in chiral expression as well. Diastereoselective recognition between OPV3T and thymidine enantiomers can be used to resolve thymidine enantiomers at an achiral surface with an OPV3T enantiomer as the resolving agent. The impact of molar ratio and concentration on the self-assembly and chiral resolution is systematically investigated. Because there is no interaction between OPV3T and thymidine in solution, the liquid/solid interface acts as the platform for the chiral resolution of thymidine enantiomers.

Homochiral and heterochiral assembly preferences at different length scales – conglomerates and racemates in the same assemblies

Length scale dependent formation of conglomerates and racemic compounds has been observed in self-assembled hierarchical supramolecular architectures based on oligo(p-phenylenevinylene)-phenylglycinamide at the liquid-solid interface and in solution.

Oligothiophenes on CVD graphene grown on multi-crystalline copper foil: supramolecular assembly and impact of morphology

On graphene grown on copper foil, oligothiophenes form identical supramolecular assemblies on different copper facets. Most importantly, we found that the graphene ripple structures, even with a height as small as ~0.5 nm, can significantly alter the molecule-substrate interaction, which has never been observed previously.

A clickable, highly soluble oligopeptide that easily forms organogels

An artificial peptide, N3-GVGV-OMe (G, glycine; V, valine), which mimics the repeating GAGA (A, alanine) sequence in Bombix Mori silk, was synthesised via solution-phase synthesis. Compared with N3-GAGA-OMe sequence, N3-GVGV-OMe showed high solubility in common organic solvents (such as CHCl3, THF and CH2Cl2), and easily formed organogels simply by adding poor solvents (such as toluene or ether) to the peptide solution at room temperature. The hierarchical nanostructure of N3-GVGV-OMe organogel was dependent on the nature of the poor solvents, although in all cases, β-sheets were formed exclusively. Gels formed in ether showed higher level hierarchical assembly, as evidenced by AFM and CD studies. Solution-state FT-IR analysis showed that the pre-organisation of the peptides in solution was not significant, and well-defined antiparallel β-sheets were formed after the addition of the poor solvent. The high solubility and strong tendency for self-assembly of N3-GVGV-OMe, together with its terminal azide group, might facilitate the modification of functional organic molecules even macromolecules for better nanostructure control.

Assessing the role of chirality in the formation of rosette-like supramolecular assemblies on surfaces

Molecular modeling simulations reveal the role of stereogenic centers in the formation of enantiomorphous surface-confined supramolecular rosette-like assemblies in monolayers of oligophenylene vinylene oligomers adsorbed at the graphite/solvent interface.

Assembly of peptide-thiophene conjugates: the influence of peptide content and location

Biomolecule-directed self-assembly of π-conjugated oligomers has attracted great attention in the past decade. In this contribution, two conjugates composed of quaterthiophene and tetrapeptide (Gly-Val-Gly-Val) were synthesised, namely peptide–thiophene–peptide (PTP) and thiophene–peptide–thiophene (TPT), to investigate the influence of peptide content ratio and its location in the molecular structures on the nanostructures and properties of the assemblies. Both conjugates formed organogels consisting of left-handed twisted nanostructures; however, anti-parallel β-sheets were observed in PTP while parallel β-sheets were obtained for TPT, although in both cases oligothiophenes adopted an H-like stacking mode. Obvious solvent-induced supramolecular chirality inversion from the oligothiophene segment was observed for PTP while such phenomenon was not clear for TPT. PTP and TPT gels also showed different stabilities towards temperature increase, as evidenced by variable-temperature circular dichroism study. From the data, it is suggested that the rational design of the location and ratio of peptide plays a key role in constructing materials with determined properties based on peptide–thiophene conjugates. Two peptide–quaterthiophene conjugates with different peptide content and location were designed, and the assemblies of the two conjugates show different packing modes and properties due to the structural difference.

Tuning the self-assembly of oligothiophenes on chemical vapor deposition graphene: effect of functional group, solvent, and substrate.

Tuning and characterizing the interfacial structure of organic semiconductors on graphene is essential for graphene-based devices. Regulation of the supramolecular assembling structure of oligothiophenes on graphene by changing functional groups attached to the backbone of oligothiophenes is described and the assembling behavior is compared with that on the basal plane of highly oriented pyrolytic graphite. It reveals that terminal functional groups attached to the conjugated backbone of oligothiophene can entirely change the assembling structures. Significant solvent and substrate effects have also been confirmed by comparing the assembling structures of oligothiophenes deposited from tetrahydrofuran, 1,2,4-trichlorobenzene, and octanoic acid onto graphene and graphite.

Tetrapeptide–coumarin conjugate 3D networks based on hydrogen-bonded charge transfer complexes: gel formation and dye release

Oligopeptide-based derivatives are important synthons for bio-based functional materials. In this article, a Gly-(L-Val)-Gly-(L-Val)-coumarin (GVGV-Cou) conjugate was synthesized, which forms 3D networks in ethanol. The gel nanostructures were characterized by UV-vis spectroscopy, FT-IR spectroscopy, X-ray diffraction (XRD), SEM and TEM. It is suggested that the formation of charge transfer (CT) complexes between the coumarin moieties is the main driving force for the gel formation. The capability of the gel to encapsulate and release dyes was explored. Both Congo Red (CR) and Methylene Blue (MB) can be trapped in the CT gel matrix and released over time. The present gel might be used as a functional soft material for guest encapsulation and release.