Qian Han

Electrochemical enantioselective recognition of tryptophane enantiomers based on chiral ligand exchange

Electrochemical enantioselective recognition of tryptophane (Trp) enantiomers in the presence of Cu(II) using L-cysteine (L-Cys) self-assembled gold electrode is described. The chiral recognition of Trp enantiomers was investigated via cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and quartz crystal microbalance (QCM). Time dependencies of the enantioselective interaction for the L-Cys modified electrodes with Trp enantiomers solutions in the presence of Cu(II) were also studied. The results showed that L-Cys had stronger interaction with D-Trp than L-Trp in the presence of Cu(II), and the discrimination was caused by the selective formation of Cu complexes with L-Cys and Trp enantiomers relying on the principle of chiral ligand exchange. The structure of the Cu complexes was optimized by the hybrid density functional theory (DFT) method. And the enantiomeric composition of L- and D-Trp was monitored by measuring the current responses of the sample.

The application of thionine–graphene nanocomposite in chiral sensing for Tryptophan enantiomers

The thionine-graphene (THi-GR, positively charged) nanocomposite was successfully synthesized as a good biocompatible matrix for ds-DNA which acted as a chiral selector to construct an electrochemical chiral biosensor for Tryptophan (Trp) enantiomers sensing with the assistance of Cu(II). The nano-bionic interface was constructed as follows: Firstly, the nanocomposite was dropped on the surface of glassy carbon electrode (GCE), and then ds-DNA (negatively charged) was immobilized onto the nanocomposite film via the opposite-charged adsorption techniques. This biofunctionalized nanocomposite was characterized with scanning electron microscopy (SEM), ultraviolet-visible (UV-vis) spectrometry and cyclic voltammetry (CV). The chiral biosensor was employed to study the recognition effect between ds-DNA and Trp enantiomers by CV. The results show that larger electrochemical response was obtained from l-Trp when Cu(II) was present, indicating this strategy could be employed to enantioselectively recognize Trp enantiomers. Under optimum conditions, the chiral biosensor exhibited a good linear response to Trp enantiomers in the range of the concentration of [Cu(II)(Trp)2] from 5.0 × 10(-4) to 2.5mM with a low limit of detection of 0.17 μM (S/N=3). The binding constant was calculated to be 2.97 × 10(3)M(-1) for [Cu(II)(l-Trp)2] and 2.50 × 10(2)M(-1) for [Cu(II)(d-Trp)2].

Enantioselective recognition of mandelic acid based on γ-globulin modified glassy carbon electrode.

A new chiral biosensor has been fabricated by immobilizing γ-globulin on gold nanoparticles modified glassy carbon electrodes, which could recognize and detect mandelic acid (MA) enantiomers. Differential pulse voltammetry, quartz crystal microbalance, ultraviolet-visible spectroscopy, and atomic force microscopy were used to characterize the enantioselectivity. The results exhibited that γ-globulin modified electrode could enantioselectively recognize MA enantiomers, and larger response signals were obtained from R-MA. The factors influencing the performance of the resulting biosensor were investigated. The enantiomeric composition of R- and S-MA enantiomer mixtures could be determined by measuring the current responses of the sample. The developed electrodes have the advantages of simple preparation, good stability, and rapid detection.

A reagentless enantioselective sensor for tryptophan enantiomers via nanohybrid matrices

A reagentless method for the selective electrochemical discrimination of tryptophan (Trp) enantiomers has been developed by means of adsorbing human serum albumin (HSA) onto a methylene blue–multi-wall carbon nanotubes nanohybrid (MB–MWNTs) modified glassy carbon electrode (HSA/MB–MWNT/GCE). Cyclic voltammetry (CV) was employed to monitor the immobilization processes and the electrochemical behavior of the Trp enantiomers on the HSA/MB–MWNT/GCE. It was found that the newly developed electrode exhibited different interactions toward the Trp enantiomers, with a stronger binding effect obtained between HSA and L-Trp. The linear range of the biosensor was investigated from 1.0 × 10−1 to 1.0 × 10−8 mol L−1 with a detection limit of 3.3 × 10−9 mol L−1. In addition, the values of the enantioselectivity coefficient (α) and the association constant (k) were calculated. This work appears to provide a reference for the development of a reagentless electrochemical chiral biosensor and improves understanding of the high selectivity between biological molecules and chiral amino acids.

A new chiral electrochemical sensor for the enantioselective recognition of penicillamine enantiomers

A new chiral electrochemical sensor has been successfully prepared through chemical linking l-methotrexate (l-Mtx) onto the gold electrode surface. Cyclic voltammetry and electrochemical impedance spectroscopy were used to investigate the enantioselective interaction between l-Mtx and Pen enantiomers. The results showed that the l-Mtx-modified gold electrode can selectively recognize penicillamine (Pen) enantiomers using Zn(II) as central ion, and larger response signal was observed from d-Pen owing to the selective formation of Zn complexes. The interaction time between the modified electrode and Pen enantiomers containing Zn(II) was considered. And the electrochemical response of the modified electrode to a series of different concentration of Pen in the presence of Zn(II) was also monitored. In addition, the enantiomeric composition of d- and l-Pen enantiomer mixtures was monitored by measuring the current responses of the sample.

Enantioselective recognition of penicillamine enantiomers on bovine serum albumin-modified glassy carbon electrode

As a natural chiral selector, bovine serum albumin (BSA) has been used to recognize penicillamine (Pen) enantiomers through electrochemical methods. The recognition and assay rely on the stereoselectivity of BSA embedded in ultrathin Al2O3 sol–gel film coated on the surface of glassy carbon electrode (BSA/GCE). The enantioselective interaction between Pen enantiomers and BSA was monitored by cyclic voltammetry and electrochemical impedance spectroscopy measurements, from which larger response signals were obtained from d-Pen. The factors influencing the performance of the modified biosensor were also investigated. The association constant (K) was calculated to be 1.93 × 104 L mol−1 for d-Pen and 1.20 × 103 L mol−1 for l-Pen. A good linear response was exhibited with the concentration of Pen enantiomers by BSA/GCE over the range of 1 × 10−8–1 × 10−1 mol L−1 with a detection limit of 3.31 × 10−9 mol L−1.

The application of chiral arginine and multi-walled carbon nanotubes as matrices to monitor hydrogen peroxide

The enantioselective interaction between horseradish peroxidase (HRP) and arginine enantiomers was investigated by electrochemical methods through studying the electrocatalytic activity of H2O2 biosensor, which was obtained through l-arginine or d-arginine functionalized multi-walled carbon nanotubes (d-Arg-MWCNTs or l-Arg-MWCNTs) immobilizing horseradish peroxidase (HRP) on glassy carbon electrode. Cyclic voltammetric and chronoamperometry were used to characterize the properties of the biosensor. Under the optimal conditions, LAM-CS@HRP/dpAu/GCE biosensor showed better electrocatalytic activity to H2O2 compared to DAM-CS@HRP/dpAu/GCE and MWCNTs-CS@HRP/dpAu/GCE, implying that the different configurations of nanocomposites have different interactions with HRP. The currents of LAM-CS@HRP/dpAu/GCE biosensor had a linear relationship with the concentration of H2O2 in the range of 2.5×10(-6) to 2.9×10(-3)M with a detection limit of 8.3×10(-7)M (S/N=3). For MWCNTs-CS-HRP/dpAu/GCE electrode, the calibration range of H2O2 was from 6.4×10(-4) to 2.9×10(-2)M and a detection limit of 2×10(-5)M (S/N=3). For the case of DAM-CS@HRP/dpAu/GCE, there has a linear relationship with the concentration of H2O2 from 1.8×10(-5) to 2.6×10(-3)M and the detection limit is 6×10(-5)M (S/N=3).

Chiral recognition of penicillamine enantiomers based on a vancomycin membrane electrode

An enantioselective membrane electrode based on vancomycin (Van) was proposed for the assay of penicillamine enantiomers. Cyclic voltammetry, electrochemical impedance spectroscopy, atomic force microscopy and UV-Vis spectra were employed to investigate the chiral recognition phenomenon. The results exhibited that the binding effect between D-penicillamine (D-Pen) and the proposed Van membrane electrode was obviously stronger than that of L-penicillamine (L-Pen). In addition, the amount of Van, the pH of the supporting electrolyte solution and the concentration of Pen enantiomers were systematically investigated and optimized. The association constant (K) was calculated to be 1.05 × 104 L mol−1 for D-Pen and 1.40 × 102 L mol−1 for L-Pen. The enantioselective concentration range of the proposed membrane electrode is 10−7 to 10−2 mol L−1. The results suggested that the chiral selective membrane has the potential to discriminate and determine chiral drugs in the pharmaceutical application of electrochemical analysis.

Chiral glutamic acid functionalized graphene: preparation and application

Through the amide group of glutamic acid enantiomer and oxygen-containing groups in graphene oxide, chiral functionalized graphene nanosheets were synthesized, which showed good enantioselective recognition of 3,4-dihydroxyphenylalanine enantiomers. These chiral graphene hybrids should be novel promising materials for biological and pharmacological applications.

Stereoselective interaction between hemoglobin and penicillamine enantiomers modified chiral surfaces

Chiral surfaces were obtained based on self-assembled monolayers of penicillamine enantiomers (L- or D-Pen) onto gold electrodes, and the enantioselective behavior was investigated by adsorbing hemoglobin (Hb) on the different chiral surfaces. Electrochemical methods, UV-vis and atomic force microscopy were adopted to monitor the protein adsorption. The properties of Hb adhesion on different chiral surfaces were further demonstrated by electrocatalytic responding to H2O2. The results showed that L-Pen had a higher dense adsorption to Hb than that of D-Pen. The Michaelis–Menten constants of the Hb/L-Pen/Au and Hb/D-Pen/Au sensors were first calculated to appeal to chiral recognition, the results showed that Hb/L-Pen/Au had a stronger catalytic ability, and further certified that Hb could adsorb on L-Pen assembled surfaces more easily. This work provided a promising reference for the investigation of chiral molecules.