Shunxing Li

Chromatographic enantioseparations of binaphthyl compounds on an immobilized polysaccharide-based chiral stationary phase.

Seven binaphthyl compounds were enantioseparated by HPLC with an immobilized polysaccharide-based chiral stationary phase, Chiralpak IA. The experiments were performed under normal-phase conditions. Effects of polar modifier and column temperature on the retention time and separation factor were evaluated. All examined compounds obtained complete resolutions. This was the unique one ever reported that 1,1-bi-2-naphthol and its monoether, diether and diester derivatives could all be enantioseparated on a given CSP. Apparent thermodynamic parameters were also deduced from Vant Hoff plots, and some aspects of chiral recognition mechanism were discussed further.

Direct electrochemistry and electrochemical biosensing of glucose oxidase based on CdSe@CdS quantum dots and MWNT-modified electrode

The direct electron transfer of glucose oxidase (GOx) was achieved based on the immobilization of CdSe@CdS quantum dots on glassy carbon electrode by multi-wall carbon nanotubes (MWNTs)-chitosan (Chit) film. The immobilized GOx displayed a pair of well-defined and reversible redox peaks with a formal potential (Eθ’) of −0.459xa0V (versus Ag/AgCl) in 0.1xa0M pHxa07.0 phosphate buffer solution. The apparent heterogeneous electron transfer rate constants (ks) of GOx confined in MWNTs-Chit/CdSe@CdS membrane were evaluated as 1.56xa0s−1 according to Lavirons equation. The surface concentration (Γ*) of the electroactive GOx in the MWNTs-Chit film was estimated to be (6.52u2009±u20090.01)u2009×u200910−11u2009molu2009cm−2. Meanwhile, the catalytic ability of GOx toward the oxidation of glucose was studied. Its apparent Michaelis–Menten constant for glucose was 0.46u2009±u20090.01xa0mM, showing a good affinity. The linear range for glucose determination was from 1.6u2009×u200910−4 to 5.6u2009×u200910−3u2009M with a relatively high sensitivity of 31.13u2009±u20090.02xa0μAu2009mM−1u2009cm−2 and a detection limit of 2.5u2009×u200910−5u2009M (S/N=3).

A novel hybridization indicator for the low-background detection of short DNA fragments based on an electrically neutral cobalt(II) complex.

An electrically neutral cobalt complex, Co(Eim)(4)(NCS)(2) (Eim=1-ethylimidazole, NCS=isothiocyanate) was synthesized and its interaction with double-stranded DNA (dsDNA) was comprehensively studied by electrochemical methods on a glassy carbon electrode (GCE). The experimental results revealed that the cobalt complex could interact with dsDNA via a specific groove-binding mode with an affinity constant of 3.6×10(5)M(-1). The surface-based studies showed that Co(Eim)(4)(NCS)(2) could electrochemically accumulate within the immobilized dsDNA layer rather than single-stranded DNA (ssDNA) layer. Based on this fact, the cobalt complex was utilized as an electrochemical hybridization indicator for the detection of oligonucleotides related to CaMV35S promoter gene. The results showed that the developed biosensor presented very low background interference due to the negligible affinity of the Co(Eim)(4)(NCS)(2) complex with ssDNA. The hybridization specificity experiments further indicated that the biosensor could well discriminate the complementary sequence from the base-mismatched and the non-complementary sequences. The complementary target sequence could be quantified over the range from 5.0×10(-9)M to 2.0×10(-6)M with a detection limit of 2.0×10(-10)M.

Speciation analysis, bioavailability and risk assessment of trace metals in herbal decoctions using a combined technique of in Vitro digestion and biomembrane filtration as sample pretreatment method.

Sample preparation is the first crucial step in the speciation analysis, bioavailability and risk assessment of trace metals in plant samples such as herb and vegetables. Two bionic technologies titled in vitro digestion and extraction with biomembrane were developed for pre-treatment of herbal decoction. The decoctions of Aconiteum carmichaeli and Paeonia lactiflora were digested at body temperature, at the acidity of the stomach or intestine and with inorganic and organic materials (digestive enzymes were included for whole-bionic and excluded for semi-bionic) found in the stomach or intestine. Being similar to the biomembrane between the gastrointestinal tract and blood vessels, monolayer liposome was used as a biomembrane model. Affinity-monolayer liposome metals and water-soluble metals were used for speciation analysis and bioavailability assessment of copper and zinc in herbal decoction. In the decoction of Aconiteum carmichaeli and Paeonia lactiflora, Zn was mainly absorbed in the intestine and Cu was mainly absorbed by both stomach and intestine. The safe dosage for males and females is below 257.1u2009g/day Aconiteum carmichaeli and 529.4u2009g/day Paeonia lactiflora.

Discrimination of a copper complex to single- and double-stranded DNA as determined by electrochemical kinetics and thermodynamics.

Discrimination of a mix-ligand polypyridyl copper complex, [Cu(phendione)(DAP)]SO(4) (phendione=1,10-phenanthroline-5,6-dione, DAP=2,3-diaminophenazine) to single-stranded (ss-) and double-stranded (ds-) DNA is presented in this paper. UV absorption spectra suggested that the copper complex could be a typical metallointercalator for dsDNA. Surface-based electrochemical experiments showed that [Cu(phendione)(DAP)](2+) underwent different electrochemical behaviors at ssDNA and dsDNA modified GCE because of the different affinities of the copper complex with ssDNA and dsDNA, which suggested that the copper complex could be an effective discriminator for ssDNA and dsDNA in sensing analysis. The different binding parameters such as binding constant (K) and binding site size (s), and the kinetic and thermodynamic binding parameters of [Cu(phendione)(DAP)](2+) with ssDNA and dsDNA were also evaluated, further quantificationally proving the discrimination ability.

Use of a chitosan–cadmium polymer as a redox hybridization indicator for CaMV35S promoter gene detection

A water-soluble chitosan-coordinated cadmium polymer was synthesized, and its recognition of single-stranded and double-stranded DNA was investigated. The electrochemical analysis in the homogeneous solutions revealed that the chitosan-coordinated cadmium polymer association with a single stranded DNA was 48 times greater than with double-stranded DNA due to the different interaction with the two kinds of DNA. The surface-based electrochemically absorbed chitosan-coordinated cadmium polymer molecules were easily removed from the double-stranded DNA-modified electrode via rinsing but could not be removed from a single-stranded DNA-modified electrode. Based on this fact, the polymer was utilized as a redox indicator for DNA hybridization detection, as the polymer was able to recognize complementary, noncomplementary, and base-mismatched sequences with a low background interference. The target DNA sequence was quantified from 5.0 × 10-9 to 5.0 × 10-7 M with a detection limit of 4.2 × 10-9 M. The polymerase chain reaction amplification of DNA from the real sample of a kind of transgenically modified soybeans was also detected satisfactorily.