Rujuan Shen

Ferrocenoyl Phenylalanine: A New Strategy Toward Supramolecular Hydrogels with Multistimuli Responsive Properties

In this paper we present a new paradigm for designing hydrogelators that exhibit sharp phase transitions in response to a series of disparate stimuli, including oxidation-reduction reactions (redox), guest-host interactions, and pH changes. We have serendipitously discovered that ferrocenoyl phenylalanine (Fc-F) monomers aggregate in water via a rapid self-assembly mechanism to form stable, multistimuli hydrogels. In comparison to other known mono- and multiresponsive gelators, Fc-F is unique because of its small size, economy of gel-forming components, and exceptionally simple molecular structure. Density functional theory (DFT) ab initio calculations suggest gel formation initially involves an antiparallel, noncovalent dimerization step wherein the ferrocenoyl moiety of one axe-like monomer conjoins with the phenyl group of the second monomer via a π-π stacking interaction to form brick-like dimers. This stacking creates a cavity in which the carboxylic acid groups of each monomer mutually interact via hydrogen bond formation, which affords additional stability to the dimer. On the basis of structural analysis via optical and electrical measurements and additional DFT calculations, we propose a possible stepwise hierachical assembly mechanism for fibril formation. Insights into the self-assembly pathway of Fc-F should prove useful for understanding gelation processes of more complex systems. We expect that Fc-F will serve as a helpful archetypical template for others to use when designing new, stimuli specific hydrogelation agents.

Sensitive immunosensor for tumor necrosis factor α based on dual signal amplification of ferrocene modified self-assembled peptide nanowire and glucose oxidase functionalized gold nanorod.

Sensitive electrochemical immunosensor for the detection of protein biomarker tumor necrosis factor α (TNF-α) was reported that uses ferrocene carboxylic acid (Fc) functionalized self-assembled peptide nanowire (Fc-PNW) as sensor platform and glucose oxidase (GOx) modified gold nanorod (GNR) as label. Greatly enhanced sensitivity is achieved based on a dual signal amplification strategy: first, the synthesized Fc-PNW used as the sensor platform increased the loading of primary anti-TNF-α antibody (Ab(1)) onto electrode surface due to its large surface area. At the same time, the Fc moiety on the nanowire is used as a mediator for GOx to catalyze the glucose reaction. Second, multiple GOx and secondary anti-TNF-α antibody (Ab(2)) molecules are bounded onto each GNR to increase the sensitivity of the immunosensor. After the preparation of the immunosensor based on the traditional sandwich protocol, the response of the immunosensor towards glucose was used as a signal to differentiate various concentrations of TNF-α. The resulting immunosensor has high sensitivity, wide linear range (0.005-10ng/mL) and good selectivity. This immunosensor preparation strategy is a promising platform for clinical screening of protein biomarkers.

From supramolecular hydrogels to functional aerogels: a facile strategy to fabricate Fe3O4/N-doped graphene composites

This manuscript introduces a simple method to fabricate hybrid aerogels with Fe3O4 nanocrystals/nitrogen-doped graphene (Fe3O4/N-GAs) through one-shot self-mineralization of ferrocenoyl phenylalanine/graphene oxide (Fc-F/GO) supramolecular hydrogels. We found that GO could trigger a sol–gel transition of Fc-F gelators below the critical gelation concentration and the electron microscopic results revealed that the self-assembled Fc-F fibrils tightly bound onto graphene sheets. Upon hydrothermal reaction, Fc moieties in these fibrils could be locally oxidized to Fe3O4 nanocrystals by GO, remaining on the top of reduced GO (RGO) sheets and therefore inhibiting the self-aggregation of graphene nanosheets. After drying, the remains of the supramolecular hybrid hydrogels are presented as the three-dimensional (3D) framework of ultra-thin graphene sheets on which Fe3O4 nanoparticles (NPs) are uniformly immobilized as single crystals. Since the new born Fe3O4 nanocrystals are closely anchored on the graphene sheets, the as-prepared Fe3O4/N-GAs complex shows excellent electrocatalytic activity for the oxygen reduction reaction (ORR, compared to commercial Pt/C). Notably, the Fc-F/GO supramolecular hydrogels act as multifunctional reagents, such as capping agents for preventing graphene nanosheets from stacking and Fe and N sources for Fe3O4/N-GAs. We expect that this intriguing strategy can provide a useful archetypical example in designing nonprecious metal oxides/carbon hybrid materials to serve as substitutes for noble metal catalysts.

Cation Tuning toward the Inference of the Gelation Behavior of Supramolecular Gels.

We serendipitously discovered that the tripeptide Asp–Phe–Phe trifluoroacetic acid salt (hereafter abbreviated as β-AspFF) formed a reversible thermotropic gel in chloroform solution (at temperatures higher than the boiling point of chloroform), and a stable gel in toluene solution (at equal to or lower than the room temperature). Experimental results indicate that doping metal ions into β-AspFF toluene gels can trigger morphological variations in the gel skeleton, thereby increasing gel volume and inducing the collapse of organogels. Investigation on the cation-tuned gelation behavior of β-AspFF can be used to elucidate heating-induced gel collapse (of normal gel) or reverse thermotropic gelation as well as select carbamide and acetamide as activators of β-AspFF gels in chloroform solution at room temperature.

In Situ Fabrication of Defective CoNx Single Clusters on Reduced Graphene Oxide Sheets with Excellent Electrocatalytic Activity for Oxygen Reduction

A facile one-step strategy for anchoring defective CoNx single clusters on partly reduced graphene oxide (RGO) is constructed to significantly improve the catalytic performance of non-noble metal complexes toward oxygen reduction reaction (ORR). Sequent loading with trace amounts of metal-free porphyrin and Co2+ in RGO can dramatically enhance both the half-wave potential and the peak current density. Intriguingly, the RGO/P/2Co single cluster exhibits the best ORR catalytic performance with the half-wave potential of 0.834 V, extremely approaching that of commercial Pt/C (0.836 V). This half-wave potential surpasses most of the reported half-wave potentials of RGO supported non-noble metal ORR catalysts through low-temperature synthesis. Furthermore, the as-prepared RGO/P/2Co delivers a peak current density of 1.3 times higher than that of Pt/C at the same loading, together with a high mass activity of 2.76 A mgCo-1. During the durability test, a cathodic current loss less than 10% is recorded after 8000 continuous potential cycles. Insights into this successful example will be conducive to the development of elegant routes for constructing metal nitrogen (MN)-based ORR catalysts with high efficiency, outstanding stability, and excellent selectivity.

Pb2+-specific metallohydrogel based on tryptophan-derivatives: preparation, characterization, multi-stimuli responsiveness and potential applications in wastewater and soil treatment

A novel Pb2+-specific metallohydrogel HAIP–Pb was synthesized. HAIP–Pb possesses multi-stimuli responsiveness, including to pH, temperature, etc. Various measurements were performed to gain insights into the mechanism of gelation. The HAIP gelator can gel Pb2+ and simultaneously adsorb toxic dyes. Intriguingly, HAIP can cause gelation of soil containing Pb2+ ions.

Designing isometrical gel precursors to identify the gelation pathway for nickel-selective metallohydrogels

Two novel multi-responsive metallohydrogels, namely, 2-PF-Ni and 3-PF-Ni, were successfully constructed from phenylalanine derivatives. The 2-PF gelator shows specific responses to Ni2+; particularly, 2-PF-Ni is lavender colored, which has been rarely reported among hydrogels triggered by Ni2+. 3-PF-Ni is light green and exhibits perfect thixotropy. This paper provides insights into the gelation mechanisms of these two metallogels.

Self-assembly of DNA networks at the air–water interface over time

This paper introduces the first example of two dimensional (2D) DNA networks that were formed through self-assembly at an air–water interface over time. DNA molecules are highly hydrophilic and have never been reported to exhibit surface activity. Our experimental results confirmed an increase of surface pressure resulting from the formation of a DNA film. We found that upon layer-by-layer Langmuir–Blodgett transformation, 2D DNA molecules preferred to stack on the pre-loaded DNA domains rather than occupy the empty areas on the silicon wafers. We also observed that the fluorescence intensity of DNA films continually increased with incubation time, suggesting that DNA molecules may undertake supra-molecular rearrangements to form well-organized networks. We believe that the success in obtaining well-organized and large scaled DNA 2D and 3D templates may greatly simplify the procedure and decrease the cost for DNA nanotechnologies.

Encapsulation of nanocrystals with responsive gels for spatial optical identification

Abstract A tripeptide (β-AspFF) gelator was designed and synthesised using solid-phase peptide synthesis. The as-prepared gelator formed a stable and clear multi-responsive gel in toluene solution. Encapsulating the quantum dots with β-AspFF effectively increased stability and antioxidisation ability which are beneficial for optical identification. Graphical abstract