Shujuan Meng

The construction and application of chiral electrochemical sensors

The review is based on the construction and application of chiral electrochemical sensors in the last three years and presents recent advances in applications of chiral electrochemical sensors based on a three-point interaction and the methods for fabricating chiral surfaces for enantioselective recognition.

The construction of electrochemical chiral interfaces using hydroxypropyl chitosan

A simple chiral electrochemical sensor based on hydroxypropyl chitosan (HPCS) covalently bound to multi-walled carbon nanotubes (MWCNTs) was developed for the recognition of mandelic acid (MA) enantiomers. HPCS preferably combines with (S)-MA over (R)-MA, which was attributed to the favorable host–guest interactions between HPCS and the MA enantiomers. In addition, the recognition efficiency was significantly increased after hydroxypropyl groups were grafted onto chitosan (CS), which may be due to a stereo-hindrance effect. Moreover, the electrochemical recognition of amino acid enantiomers was investigated; the functional groups of the enantiomers play an important role in the enantioselective discrimination.

Electrochemical enantiorecognition of tryptophan enantiomers based on a multi-walled carbon nanotube–hydroxyethyl chitosan composite film

A novel chiral electrochemical sensor based on hydroxyethyl chitosan (HECS) covalently binding with the carboxylic multi-walled carbon nanotubes (MWCNT–COOH) was fabricated for discrimination of tryptophan (Trp) enantiomers. HECS preferably combined with L-Trp than with D-Trp because of the favorability of host–guest interactions between HECS and Trp enantiomers. Thus, the recognition efficiency was remarkably improved after hydroxyethyl groups were grafted onto chitosan (CS); this might be attributed to the formation of hydrogen bonds between Trp enantiomers and HECS. In addition, the small stereo-hindrance effect could play an important role in enantioselective discrimination.

Highly selective tryptophan enantiomers electrochemical chiral sensor based on poly-lysine and functionalized multi-walled carbon nanotubes

A novel electrochemical chiral sensor was reported for recognizing tryptophan enantiomers based on multi-walled carbon nanotubes functionalized by 3,4,9,10-perylenetetracarboxylic acid binding with the l-lysine (MWCNTs-PTCA-PLL) via electropolymerization. The electrochemical behaviors of the proposed sensors were then characterized by cyclic voltammetry (CV). Differential pulse voltammetries (DPVs) were applied to investigate the stereoselective recognition of tryptophan (Trp) enantiomers. d-Trp and l-Trp showed different responses in DPVs, and a larger selectivity was obtained from d-Trp. pH level and the effect of the incubation time on the chiral recognition were also investigated for optimizing experimental parameters. In addition, the results of analyzing percentage composition revealed this sensor was able to determine the enantiomeric mixtures. The novel strategy with high stability, good sensitivity, and selective characteristics had opened up a new avenue to recognize Trp enantiomers.

Amino acid-inspired electrochemical recognition of phenylalanine enantiomers using amphoteric chitosan

Inspired by amino acids with amphoteric groups for electrochemical enantiorecognition, amphoteric chitosan (ACCS) was prepared with chloroacetic acid and CS, and has perfect solubility in alkaline and acid solution, compared with CS. ACCS was linked to the ethylenediamine-functionalized multiwalled carbon nanotubes (MWCNTs–EA) through covalent bonding. Chiral interfaces were fabricated with MWCNTs–EA–ACCS and used for the electrochemical enantiorecognition of phenylalanine (Phe) enantiomers. The ACCS chiral interfaces showed excellent selectivity toward the Phe enantiomers. Also, the optimization of parameters such as pH, temperature and response time was carried out for the electrochemical recognition. Furthermore, the ACCS is capable of determining the percentage of enantiomers in mixed solutions. The electrochemical recognition of amino acid enantiomers with different functional groups was investigated, and it was found that the amphoteric functional groups of ACCS play an important role in the enantioselective discrimination.

Chiral electrochemical recognition of tryptophan enantiomers at a multi-walled carbon nanotube–N-carboxymethyl chitosan composite-modified glassy carbon electrode

A simple chiral electrochemical sensor based on N-carboxymethyl chitosan (NCCS) covalently bound with ethylenediamine-carboxylic multiwalled carbon nanotubes (MWCNTs-EA) was developed for enantioselective recognition of tryptophan (Trp) enantiomers; NCCS preferably combined with L-Trp than with D-Trp. The recognition efficiency prominently increased after the introduction of N-carboxymethyl into chitosan (CS). The carboxymethyl and imino groups of NCCS play an important role in enantioselective discrimination system. Moreover, the parameters of enantioselective recognition such as pH, temperature and response time were investigated. The electrochemical recognition of amino acid enantiomers with different functional groups was carried out. The chiral recognition mechanism was investigated by quantum computing. The results were confirmed by quantum chemical calculations.

Electrochemical recognition for tryptophan enantiomers based on 3, 4, 9, 10-perylenetetracarboxylic acid–chitosan composite film

A novel and simple chiral sensing platform had been successfully fabricated by means of amidation reaction between 3, 4, 9, 10-perylenetetracarboxylic acid (PTCA) and chitosan (CS) to form 3, 4, 9, 10-perylenetetracarboxylic acid–chitosan (PTCA–CS) composite film. Since CS has chiral center and PTCA has excellent electrical conductivity, the PTCA–CS composite modified glassy carbon electrode (PTCA–CS/GCE) could be treated as an effective electrochemical chiral sensor and applied for chiral discrimination of tryptophan (Trp) enantiomers theoretically. PTCA–CS composite was characterized by Fourier transform infrared (FTIR) spectroscopy and cyclic voltammetry (CV). When the prepared chiral sensing interface interacted with tryptophan isomers, a higher selectivity was received from D-Trp by differential pulse voltammetry (DPV). It indicated that the PTCA–CS/GCE can be treated as an electrochemical chiral sensor for the discrimination of Trp enantiomers. Further study demonstrated that the peak currents were linearly increased with the increasing percentage of L-Trp of Trp racemic mixture. Furthermore, the enantioselective interaction of the PTCA–CS/GCE was systematically studied by other experimental factors, such as the incubation time and acidity.

Mechanical Properties of Epoxy Resin/PMMA/SiO 2 Dental Composites

Epoxy resin/ Thermoplastic polymethyl methacrylate (PMMA)/SiO2 dental composites were synthesized successfully at last after the following two steps: polymerization of MMA act as the initiator at this first process. Then the obtained PMMA was incorporated into epoxy resin and SiO2 to prepare the hybrid thermosets. The structural characteristics of epoxy resin/PMMA/SiO2 composites were characterized by Fourier transform infrared spectroscopy (FT–IR), scanning electron microscopy (SEM), and X-ray diffraction (XRD). What is more, the mechanical properties and water solubility of the composites have also been tested. It is found that the stability has been improved after adding SiO2 nanoparticles. In addition, the mechanical properties of composites which were modified by silica indicated that the mechanical properties of materials could be improved after preprocessing of SiO2 nanoparticles in epoxy resin/PMMA composites. Interference of epoxy resin produced magnetic adsorption and chemical reaction with the existence of hydroxyls, ether bonds and epoxy groups. In conclusion, the improvement in surface properties was ascribed to the enrichment of epoxy resin moiety on the surface of the nanostructured thermosets.