Ruiying Gong

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.

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.

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.

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.

Polythiophene with oligopeptide side chain: preparation and nano-structure

This manuscript describes the first example of nanorods formation of an oligopeptide-modified polythiophene (PTh). The oligopeptide-modified monomer was carefully engineered in such a way to keep both high solubility and the ability for self-assembly. A terthiophene with a clickable side chain on the middle thiophene ring and two octyl side chains on the terminal thiophene rings was synthesised to guarantee the solubility; a tetrapeptide (N3-GVGV-OMe) was chosen to provide self-assembly capability. The monomer obtained by click chemistry showed both high solubility and the ability to form organogels. The monomer was easily polymerised either in solution state or in organogel state to give the corresponding PTh with oligopeptide side chain. The size of the nanorods could be controlled by adjusting the reaction conditions. The formation of the nano-structure was attributed to the H-bonding between oligopeptide side chain and its interaction with Fe (II) ion.

Oligopeptide-assisted self-assembly of oligothiophenes: co-assembly and chirality transfer.

The biomolecule-assisted self-assembly of semiconductive molecules has been developed recently for the formation of potential bio-based functional materials. Oligopeptide-assisted self-assembly of oligothiophene through weak intermolecular interactions was investigated; specifically the self-assembly and chirality-transfer behavior of achiral oligothiophenes in the presence of an oligopeptide with a strong tendency to form β-sheets. Two kinds of oligothiophenes without (QT) or with (QTDA) carboxylic groups were selected to explore the effect of the end functional group on self-assembly and chirality transfer. In both cases, organogels were formed. However, the assembly behavior of QT was quite different from that of QTDA. It was found that QT formed an organogel with the oligopeptide and co-assembled into chiral nanostructures. Conversely, although QTDA also formed a gel with the oligopeptide, it has a strong tendency to self-assemble independently. However, during the formation of the xerogel, the chirality of the oligopeptide can also be transferred to the QTDA assemblies. Different assembly models were proposed to explain the assembly behavior.